Laser-assisted method for parting crystalline material

Abstract

To provide improved laser-assisted methods and devices for parting or removing relatively thin layers of crystalline material from a substrate, such as a boule or a wafer.SOLUTION: A crystalline material processing method includes forming subsurface laser damage at a first average depth position to form cracks in a substrate interior propagating outward from at least one subsurface laser damage pattern, followed by imaging the substrate top surface, analyzing the image to identify a condition indicative of presence of uncracked regions within the substrate, and taking one or more actions responsive to the analysis. One potential action includes changing an instruction set for producing subsequent laser damage formation (at second or subsequent average depth positions), without necessarily forming additional damage at the first depth position. Another potential action includes forming additional subsurface laser damage at the first depth position.SELECTED DRAWING: Figure 49A

Description

Detailed Description of the Invention

[0001] [Related Application Description] This application claims priority to U.S. Patent Application No. 16 / 410,487, filed May 13, 2019, U.S. Provisional Patent Application No. 62 / 803,340, filed February 8, 2019, U.S. Patent Application No. 16 / 274,064, filed February 12, 2019, and U.S. Provisional Patent Application No. 62 / 786,333, filed December 29, 2018, the disclosures of which are hereby incorporated by reference in their entireties. This application also incorporates by reference the disclosure of U.S. Patent Application No. 16 / 274,045, filed February 12, 2019, in its entirety.

[0002] [Technical field] The present disclosure relates to methods for processing crystalline materials, and more particularly, to laser-assisted methods for cutting or removing relatively thin layers of crystalline materials from a substrate, such as a boule or wafer.

[0003] [background] In various applications in microelectronics, optoelectronics, and micromachining, thin layers of crystalline materials are needed as starting structures for fabricating various useful systems. The traditional method for cutting thin layers (e.g., wafers) from larger diameter crystalline ingots of crystalline materials involves the use of wire saws. Wire sawing techniques have been applied to various crystalline materials such as silicon, sapphire, and silicon carbide. A wire saw tool contains a very thin steel wire (typically 0.2 mm in diameter or less) that is threaded through the grooves of one or many guide rollers. Two slicing methods exist, namely, loose abrasive slicing and fixed abrasive slicing. Loose abrasive slicing involves applying a slurry (typically abrasive grains suspended in oil) to a rapidly moving steel wire, and the rolling of the abrasive grains between the wire and the workpiece results in the cutting of the ingot. Unfortunately, the environmental impact of the slurry cannot be ignored. To reduce such effects, fixed abrasive slicing techniques may use diamond-laden wires, which require only an aqueous coolant (not a slurry). Highly efficient parallel slicing allows the production of multiple wafers in a single slicing step. FIG. 1 shows a conventional wire saw tool 1 including parallel wire sections 3 extending between rollers 4A-4C and positioned to simultaneously saw an ingot 2 into multiple thin sections (e.g., wafers 8A-8G), each having a surface generally parallel to an edge surface 6 of the ingot 2. During the sawing process, the wire sections 3 supported by the rollers 4A-4C may be pushed in a downward direction 5 toward a holder 7 below the ingot 2. If the edge surface 6 is parallel to the crystallographic c-plane of the ingot 2 and the wire section 3 saws the ingot 2 parallel to the edge surface 6, then each of the resulting wafers 8A-8G will have an "on-axis" edge surface 6' parallel to the crystallographic c-plane.

[0004] It is also possible to produce vicinal (also known as off-cut or "off-axis") wafers, which have edge faces that are not parallel to the crystallographic c-plane. Vicinal wafers (e.g., of SiC) with a 4 degree off-cut are often employed as growth substrates for high-quality physical vapor transport and epitaxial growth of other materials (e.g., AlN and other Group III nitrides). Vicinal wafers are produced by growing an ingot away from the c-axis (e.g., growing on a vicinal seed material) and sawing the ingot perpendicular to the ingot sidewalls, or by growing an ingot starting from an on-axis seed material and sawing the ingot perpendicular to the ingot sidewalls. This can be done either by sawing at an angle away from the straight line.

[0005] Wire sawing of semiconductor materials has several limitations. Kerf loss, based on the width of material removed per cut, is inevitable in saw cutting and represents a significant loss of semiconductor material. Wire saw cutting imposes relatively high stresses on the wafer, resulting in non-zero bow and warp characteristics. Processing times for a single boule (or ingot) are very long and events such as wire breakage can extend processing times and lead to unwanted material loss. Chipping and cracking on the cut surface of the wafer can reduce the wafer strength. At the end of the wire sawing process, debris must be removed from the resulting wafer.

[0006] For silicon carbide (SiC), which has high wear resistance (and hardness comparable to diamond and boron nitride), wire sawing can require significant time and resources, which can result in significant manufacturing costs. SiC substrates enable the fabrication of desirable power electronics, radio frequency, and optoelectronic devices. SiC appears in many different crystal structures, called polytypes, and certain polytypes (e.g., 4H-SiC and 6H-SIC) have a hexagonal crystal structure.

[0007] Figure 2 is a perspective crystallographic view showing the coordinate system for a hexagonal crystal such as 4H-SiC, where the c-plane (the (0001) plane, which corresponds to the

[0001] (vertical) direction of crystal growth) is perpendicular to both the m-plane (the (1-100) plane) and the a-plane (the (11-20) plane), the (1-100) plane being perpendicular to the [1-100] direction, and the (11-20) plane being perpendicular to the [11-20] direction. Figure 3 is a second perspective crystallographic view of a hexagonal crystal showing a vicinal plane 9 that is non-parallel to the c-plane, with vector 10 (orthogonal to vicinal plane 9) tilted away from the

[0001] direction by a tilt angle β, which is (slightly) tilted towards the [11-20] direction. FIG. 4A is a perspective wafer orientation diagram showing the orientation of the vicinal wafer 11A with respect to the c-plane ((0001) plane), where the vector 10A (orthogonal to the wafer face 9A) is tilted away from the 0001 direction by a tilt angle β. This tilt angle β is equal to the orthogonal tilt (or misorientation angle) β that spans between the (0001) plane and the projection 12A of the wafer face 9A. FIG. 4B is a simplified cross-sectional view of the vicinal wafer 11A superimposed on a portion of the ingot 14A from which the vicinal wafer 11A was defined (e.g., an on-axis ingot having an edge 6A parallel to the (0001) plane). FIG. 4B shows that the wafer face 9A of the vicinal wafer 11A is misaligned from the (0001) plane by the tilt angle β.

[0008] FIG. 5 illustrates a lattice structure including a top surface 26 (e.g., parallel to the (0001) plane (c-plane) and perpendicular to the

[0001] direction), a lattice structure perpendicular to the (11-20) plane and parallel to the [11-20] direction (length L F FIG. 2 is a top plan view of an exemplary SiC wafer 25 that is laterally bounded by a generally circular edge 27 (having a diameter D) that includes a primary flat 28 (having a diameter D). The SiC wafer may include an outer surface that is misaligned from the c-plane (e.g., off-axis at an oblique angle to the c-plane).

[0009] Due to the difficulties associated with fabricating and processing SiC, the cost of SiC device wafers is high compared to various other semiconductor material wafers. Typical kerf loss resulting from wire sawing of SiC can be about 250 microns or more per wafer, which is not negligible at all considering that the wafer thickness resulting from the wire sawing process is roughly 350 microns, which is subsequently thinned (by grinding) to a final thickness of about 100 to 180 microns depending on the end application. Slicing wafers thinner than about 350 microns is costly considering the wire sawing and device fabrication issues. This has not been realistic until now.

[0010] In an attempt to address the limitations associated with wire sawing, alternative techniques have been developed to remove thin layers of semiconductor material from bulk crystals. One technique involving the removal of a layer of silicon carbide from a larger crystal is described by Kim et al., "4H-SiC wafer slicing by using femtosecond laser double pulses," Optical Materials Express, p. 2450, vol. 7, no. 7 (2017). Such a technique involves bombarding silicon carbide with laser pulses to induce subsurface damage, followed by bonding the crystal to a locking fixture and applying a pulling force to induce spalling along the subsurface damage zones, forming laser-written tracks. By using the laser to weaken specific areas of the material and then inducing spalling between these areas, the laser scan time is reduced.

[0011] Additional separation techniques involving the creation of laser subsurface damage in a SiC ingot using a pulsed laser beam and subsequent application of ultrasonic vibration to induce spallation are disclosed in U.S. Patent Nos. 9,925,619 and 10,155,323 to Disco Corporation. Additional techniques for removing thin layers of semiconductor material from bulk crystals are disclosed in U.S. Patent Application Publication No. 2018 / 0126484 A1 to Siltectra GmbH.

[0012] Tools for creating laser subsurface damage in semiconductor materials are known in the art and are commercially available from various suppliers, such as Disco Corporation (Tokyo, Japan). Such tools allow for focusing of laser radiation inside a crystalline substrate and lateral movement of the laser relative to the substrate. A typical laser damage pattern involves the creation of parallel lines that are laterally spaced apart relative to one another at a depth within the crystalline material substrate. Parameters such as focus depth, laser power, translation speed, etc. can be adjusted to create the laser damage, although adjustment of certain factors involves trade-offs. Increasing the laser power tends to create larger subsurface damage, which may increase the ease of fracture (e.g., by reducing the stress required to complete the fracture), but larger subsurface damage also leads to greater surface irregularities along the surface exposed by the fracture, which may require additional processing to make such surfaces sufficiently smooth for further processing (e.g., for incorporation into an electronic device). The ease of spallation can be increased by decreasing the lateral spacing between subsurface laser damage lines, but decreasing the spacing between the laser damage lines increases the number of translational steps between the substrate and the laser, which reduces the throughput of the tool. Additionally, the results obtained from laser processing may vary within a substrate depending on the lateral or radial location at a particular vertical depth and / or the vertical location of the substrate surface as part of an ingot relative to its original growth location.

[0013] Due to variations in material and / or optical properties within thick substrates such as SiC ingots and also between different ingots of the same composition, it is difficult to easily produce wafers of reproducible uniform thickness by laser processing and subsequent fragmentation while avoiding unnecessary material loss.

[0014] Thus, the art continues to seek improved laser-assisted methods for cutting or removing relatively thin layers of crystalline (e.g., semiconductor) material from a substrate to address problems associated with conventional methods.

[0015] [Summary of the Invention] The present disclosure relates to a method and material processing apparatus for processing a crystalline material substrate, in various aspects. Imaging and analysis of the crack-free area after forming the subsurface laser damage in the substrate is used as an indicator to determine when to change the instruction set for forming the subsurface laser damage at the next depth location and / or to address variations in laser damage formation requirements (e.g., laser power, laser focus depth, number of damage formation passes) from substrate to substrate and at different depth locations within a single substrate. A crystalline material processing method includes generating a subsurface laser damage site in an area at a first average depth location in the crystalline material to promote formation of cracks within the substrate propagating outward from the subsurface laser damage pattern, imaging the substrate top surface, analyzing the image to identify conditions indicative of the presence of a crack-free area in the substrate, and performing one or more actions in response to the analyzing (e.g., upon achievement of a suitable condition). One possible action includes forming a supplemental subsurface laser damage at the first average depth location to promote formation of additional cracks in the crack-free area to form a first thickness reduction portion of the substrate (e.g., a first wafer). Another possible procedure includes modifying the instruction set to cause subsequent subsurface laser damage formation (at a second or subsequent average depth location to form a second and any thickness reduced portions of the substrate) without necessarily forming additional damage at the first average depth location. The laser damage facilitates subsequent spalling of the substrate to produce a plurality of substrate portions with reduced thickness. The material processing apparatus includes a laser processing station having a laser, at least one translation stage, a scattering light source arranged to be positioned on a first lateral side of the substrate, and an imaging device positioned on an opposite second lateral side of the substrate. The light source may be positioned substantially perpendicular to the primary flat of the substrate and / or within ±5 degrees of perpendicular to the <11-20> direction of the hexagonal crystal structure of the substrate to enhance visibility of crack-free regions through the top surface of the substrate.

[0016] In one aspect, the disclosure provides a method for forming a subsurface laser damage pattern, the method comprising: providing laser radiation focused along a first average depth location within a crystalline material of a substrate and executing a lateral relative movement between the laser and the substrate to form a subsurface laser damage pattern having at least one subsurface laser damage pattern, the at least one subsurface laser damage pattern being configured to promote formation of at least one group of a plurality of cracks within the substrate, the cracks propagating substantially outwardly from the at least one subsurface laser damage pattern; generating at least one image of a top surface of the substrate after formation of the at least one subsurface laser damage pattern; and analyzing the at least one image to identify conditions indicative of a presence of crack free regions within the substrate; and in response to the analyzing, performing the steps of: and (ii) performing at least one of the following steps: (i) performing relative movement between the laser and the substrate while providing laser radiation focused into the interior of the substrate at least in crack-free regions to form auxiliary subsurface laser damage to assist the at least one subsurface laser damage pattern to form a first thickness reduction in the substrate, and to promote formation of additional cracks in the crack-free regions along or adjacent to the first average depth location; or (ii) modifying an instruction set associated with the substrate for forming subsurface laser damage when creating a subsurface laser damage pattern at a second average depth location and any subsequent average depth locations in the substrate to form at least one additional thickness reduction in the substrate.

[0017] In certain embodiments, the analyzing includes quantifying a top area characteristic of one or more crack-free regions within the substrate and comparing the top area characteristic to at least one predetermined threshold area characteristic.

[0018] In certain embodiments, the at least one predetermined threshold area characteristic is a first predetermined threshold area characteristic. and a second predetermined threshold area characteristic, the second predetermined threshold area characteristic being greater than the first predetermined threshold area characteristic, and the method includes performing step (ii) if the apex area characteristic is at least as great as the first predetermined threshold area characteristic, and performing step (i) if the apex area characteristic is at least as great as the second predetermined threshold area characteristic.

[0019] In certain embodiments, the method includes performing both steps (i) and (ii) in response to analyzing.

[0020] In certain embodiments, step (ii) includes adjusting at least one of: (a) average laser power; (b) laser focusing depth relative to the exposed surface of the substrate; or (c) number of laser damage creation passes when creating the subsurface laser damage pattern at the second average depth position and any subsequent average depth positions in the substrate.

[0021] In certain embodiments, modifying the instruction set in accordance with step (ii) comprises increasing the average laser power by a value in the range of from 0.15 to 0.35 Watts.

[0022] In certain embodiments, step (i) includes adjusting at least one of (a) average laser power, or (b) laser focus depth relative to the exposed surface of the substrate when creating auxiliary subsurface laser damage to assist the at least one subsurface laser damage pattern and promote formation of additional cracks in crack-free areas along or adjacent to the first average depth location.

[0023] In certain embodiments, the substrate has a generally circular edge having a primary flat, and generating at least one image includes (a) illuminating the top surface with scattered light generated by a scattered light source disposed on a first lateral side of the substrate and positioned substantially perpendicular to the primary flat, and (b) capturing at least one image with an imaging device disposed on an opposite second lateral side of the substrate.

[0024] In certain embodiments, the crystalline material has a hexagonal crystal structure, and generating the at least one image includes (a) illuminating the top surface with scattered light generated by a scattered light source disposed on a first lateral side of the substrate and positioned within ±5 degrees of a perpendicular direction to a <112-0> direction of the hexagonal crystal structure, and (b) capturing the at least one image with an imaging device disposed on a second lateral side of the substrate opposite the first lateral side.

[0025] In certain embodiments, the at least one subsurface laser damage pattern includes a first subsurface laser damage pattern and a second subsurface laser damage pattern formed after the first subsurface laser damage pattern, the first subsurface laser damage pattern includes a first plurality of substantially parallel lines and a second subsurface laser damage pattern, the lines of the second plurality of substantially parallel lines are interspersed between lines of the first plurality of substantially parallel lines, and at least some of the lines of the second plurality of substantially parallel lines do not intersect with any of the lines of the first plurality of substantially parallel lines.

[0026] In certain embodiments, each line of the second plurality of substantially parallel lines is disposed between a different pair of adjacent lines of the first plurality of substantially parallel lines.

[0027] In certain embodiments, each line of the first plurality of substantially parallel lines and each line of the second plurality of substantially parallel lines are within ±5 degrees of a perpendicular direction to a <11-20> direction of a hexagonal crystal structure of the crystalline material and are substantially parallel to a surface of the substrate.

[0028] In a specific embodiment, the at least one subsurface laser damage pattern includes a first subsurface laser damage pattern and a second subsurface laser damage pattern formed after the first subsurface laser damage pattern, and the at least one group of the plurality of substantially parallel lines includes a first plurality of substantially parallel lines and a second plurality of substantially parallel lines, wherein the lines of the first plurality of substantially parallel lines are non-parallel to the lines of the second plurality of substantially parallel lines, an angular orientation of the lines of the second plurality of substantially parallel lines differs from an angular orientation of the lines of the first plurality of substantially parallel lines by 10 degrees or less, and at least some of the lines of the second plurality of substantially parallel lines do not intersect with any of the lines of the first plurality of substantially parallel lines.

[0029] In certain embodiments, the at least one subsurface laser damage pattern further comprises a third subsurface laser damage pattern formed after the second subsurface laser damage pattern, the at least one group of the plurality of substantially parallel lines further comprises a third plurality of substantially parallel lines, the at least one group of the plurality of cracks comprises a first, second, and third plurality of cracks, the first subsurface laser damage pattern forms a first plurality of cracks within the substrate propagating laterally outward from the first plurality of substantially parallel lines, and the second subsurface laser damage pattern forms a first plurality of cracks within the substrate propagating laterally outward from the first plurality of substantially parallel lines. The pattern forms a second plurality of cracks within the substrate propagating laterally outward from the line of the second plurality of substantially parallel lines, the second plurality of cracks not connecting with the cracks of the first plurality, and the third subsurface laser damage pattern forms a third plurality of cracks within the substrate propagating laterally outward from the line of the third plurality of substantially parallel lines, at least some of the third plurality of cracks connecting with at least some of the first plurality of cracks and with at least some of the second plurality of cracks.

[0030] In certain embodiments, the method further includes detecting a condition indicative of non-uniform doping of the crystalline material across at least a portion of a surface of the substrate, the non-uniform doping including a first doped region and a second doped region, and, in response to detecting the condition indicative of non-uniform doping of the crystalline material, performing at least one of the following steps (A) or (B): (A) modifying a laser power during formation of the at least one subsurface laser damage pattern to provide a first power level of laser radiation when forming the subsurface laser damage in the first doped region and to provide a second power level of laser radiation when forming the subsurface laser damage in the second doped region; or (B) altering an average depth of formation of subsurface laser damage in the substrate when forming the subsurface laser damage in one of the first doped region or the second doped region.

[0031] In certain embodiments, the method further includes fracturing the crystalline material substantially along the at least one subsurface laser damage pattern to produce first and second crystalline material portions, both of which have a reduced thickness compared to the substrate but substantially the same length and width as the substrate.

[0032] In certain embodiments, the substrate comprises silicon carbide, hi certain embodiments, the substrate comprises an ingot having a diameter of at least 150 mm.

[0033] In another aspect, the present disclosure relates to a material processing apparatus including a laser processing station configured to process a substrate of a crystalline material, the laser processing station including a laser configured to form a subsurface laser damage region within the substrate, at least one translation stage configured to effect relative motion between the laser and the substrate, a scattering light source configured to illuminate a top surface of the substrate, the scattering light source positioned to be positioned on a first lateral side of the substrate, and at least one translation stage configured to illuminate a top surface of the substrate. and an imaging device configured to generate an image of the substrate, the imaging device configured to be positioned on a second lateral side of the substrate opposite the first lateral side.

[0034] In a particular embodiment, the substrate comprises a generally circular edge having a primary flat, and the scattered light source is disposed on a first lateral side of the substrate such that the scattered light source is positioned substantially perpendicular to the primary flat.

[0035] In a particular embodiment, the crystalline material has a hexagonal crystal structure, and the scattering light source is positioned on a first lateral side of the substrate such that it is positioned within ±5 degrees of a direction perpendicular to a <11-20> direction of the hexagonal crystal structure.

[0036] In certain embodiments, the material processing apparatus further comprises a computing device configured to analyze the at least one image to identify conditions indicative of the presence of crack free regions within the substrate.

[0037] In certain embodiments, the computing device is further configured to perform at least one of the following steps (i) or (ii) in response to analyzing by the computing device: (i) performing relative movement between the laser and the substrate while providing laser radiation focused into the interior of the substrate at least in crack-free regions to form auxiliary subsurface laser damage in the substrate and promote formation of additional cracks in the crack-free regions along or adjacent to the first average depth location to form a first thickness reduction in the substrate; or (ii) modifying an instruction set associated with the substrate for forming subsurface laser damage when creating a subsurface laser damage pattern at a second average depth location and any subsequent average depth locations in the substrate to form second and any subsequent thickness reductions in the substrate.

[0038] In certain embodiments, the analyzing performed by the computing device includes quantifying a top area characteristic of one or more crack-free regions within the substrate and comparing the top area characteristic to at least one predetermined threshold area characteristic.

[0039] In certain embodiments, the at least one predetermined threshold area characteristic includes a first predetermined threshold area characteristic and a second predetermined threshold area characteristic, the second predetermined threshold area characteristic being greater than the first predetermined threshold area characteristic, and the computing device is configured to control the material processing apparatus to perform step (ii) if the top area characteristic is at least as great as the first predetermined threshold area characteristic, and the computing device is configured to control the material processing apparatus to perform step (i) if the top area characteristic is at least as great as the second predetermined threshold area characteristic.

[0040] In certain embodiments, the material processing apparatus further comprises a memory configured to store a set of instructions associated with the substrate for forming subsurface laser damage in the substrate, the memory accessible by the computing device.

[0041] In certain embodiments, the material processing apparatus further comprises a fragmentation station configured to receive the substrate from the laser processing station.

[0042] In another embodiment, any of the above-mentioned embodiments and / or various separate embodiments and features described herein may be combined to provide additional advantages. Unless otherwise indicated herein, any of the various features and elements disclosed herein may be combined in any combination to provide additional advantages. may be combined with one or more of the other disclosed features and elements.

[0043] Other aspects, features, and embodiments of the present disclosure will become more fully apparent from the ensuing disclosure and the appended claims.

[0044] The accompanying drawings, which are incorporated in and form a part of this specification, illustrate several aspects of the present disclosure and, together with the description, serve to explain the principles of the disclosure. [Brief description of the drawings]

[0045] [Figure 1] FIG. 1 includes a first frame providing a perspective view of an ingot being received in a conventional wire saw tool and undergoing a wire sawing process, and a second frame providing a perspective view of a number of wafers obtained by the wire sawing process. [Diagram 2] FIG. 1 is a first perspective crystallographic diagram showing a coordinate system for a hexagonal crystal such as 4H—SiC. [Diagram 3] FIG. 2 is a second perspective crystallographic view for hexagonal crystals, showing vicinal planes non-parallel to the c-plane. [Figure 4A] FIG. 2 is a perspective wafer orientation diagram showing the orientation of a vicinal wafer relative to the c-plane. [Figure 4B] FIG. 4B is a simplified cross-sectional view of the vicinal wafer of FIG. 4A superimposed on a portion of an ingot. [Diagram 5] 1 is a top plan view of an example SiC wafer with superimposed arrows indicating crystal orientation directions. [Figure 6A] FIG. 1 is a schematic side elevation view of an on-axis ingot of crystalline material. [Figure 6B] FIG. 6B is a schematic side elevation view of the ingot of FIG. 6A rotated 4 degrees with a superimposed pattern for cutting the ends of the ingot. [Figure 6C] FIG. 2 is a schematic side elevation view of an ingot after an end has been removed to provide an end face non-perpendicular to the c direction. [Figure 7] FIG. 1 is a schematic perspective view of a moveable laser tool that is configured to focus laser radiation inside a crystalline material to form subsurface damage. [Figure 8A] FIG. 13 provides an example laser tool movement path relative to a crystalline material to form subsurface damage within the crystalline material. [Figure 8B]Includes superimposed arrows indicating the orientation of the subsurface damage lines relative to the [11-20] direction of the hexagonal structure of the crystalline material. [Figure 9] FIG. 2 is a schematic perspective view of the surface structure of an off-axis or vicinal (with respect to the c-axis) 4H—SiC crystal after fracture but before smoothing, where the fractured surface exhibits plateaus and steps. [Figure 10A-10D] 1A-1D are schematic cross-sectional views of the formation of subsurface laser damage in a substrate of a crystalline material by focusing laser radiation respectively into a bare substrate, through a surface of a substrate supported by a carrier, through the carrier and adhesive layer into the substrate, and through the carrier into the substrate. [Figure 11A] FIG. 1 provides a top plan view of a crystalline material substrate including first, second, and third distributed subsurface laser damage patterns defined in accordance with one embodiment, each damage pattern including a plurality of substantially parallel lines perpendicular to the [11-20] direction (and substantially perpendicular to the primary substrate flat), the laser damage patterns combining to form a plurality of three-line groups separated from each other by inter-group spacing that exceeds the spacing between adjacent lines in each three-line group. [Figure 11B] FIG. 11B is a schematic top plan view of the in-process crystalline material substrate of FIG. 11A after formation of a first subsurface laser damage pattern illustrating a first plurality of cracks within the substrate propagating laterally outward from the first plurality of substantially parallel lines. [Figure 11C] FIG. 11C is a top plan view of the crystalline material substrate of FIG. 11B upon formation of a second subsurface laser damage pattern after the first subsurface laser damage pattern, illustrating a second plurality of cracks within the substrate propagating laterally outward from the second plurality of substantially parallel lines but not contacting the first plurality of cracks. [Figure 11D]FIG. 11D is a top plan view of the crystalline material substrate of FIG. 11C upon formation of a third subsurface laser damage pattern after the first and second subsurface laser damage patterns, illustrating a third plurality of cracks within the substrate propagating laterally outward from the third plurality of substantially parallel lines and connecting the first plurality of cracks and the second plurality of cracks. [Figure 12] FIG. 11B is a schematic top plan view of a crystalline material substrate including first, second, and third distributed subsurface laser damage patterns defined according to an embodiment similar to that shown in FIG. 11A, where each damage pattern includes a plurality of substantially parallel lines deflected 3 degrees relative to a normal to a [11-20] direction along the substrate surface (and substantially perpendicular to the primary substrate flat), the laser damage patterns combining to form a plurality of three-line groups separated from each other by inter-group spacing that exceeds the spacing between adjacent lines in each three-line group. [Figure 13] FIG. 1 is a schematic top plan view of a crystalline material substrate containing first through fourth laser damage patterns distributed over it, with all lines parallel to each other and perpendicular to the [11-20] direction along the substrate surface (and substantially perpendicular to the primary substrate flat). [Figure 14] FIG. 1 is a schematic top plan view of a crystalline material substrate including first, second, and third distributed subsurface laser damage patterns defined in accordance with one embodiment, where the first and second groups of lines are each parallel to each other and perpendicular to a [11-20] direction along the substrate surface (and substantially perpendicular to the primary substrate flat), and the third group of lines is non-parallel to the first and second groups of lines but does not intersect with lines of the first and second groups of lines within the substrate. [Figure 15]FIG. 1 is a schematic top plan view of a crystalline material substrate including first, second, and third distributed subsurface laser damage patterns defined in accordance with one embodiment, where the first and second groups of lines are each parallel to one another and offset by 3 degrees from perpendicular to a [11-20] direction along the substrate surface (and are substantially perpendicular to the primary substrate flat), and the third group of lines is perpendicular to the primary substrate flat but does not intersect the lines of the first and second groups of lines within the substrate. [Figure 16] FIG. 1 is a schematic top plan view of a crystalline material substrate including first, second, and third dispersed subsurface laser damage patterns defined in accordance with one embodiment, where all of the laser damage lines are parallel to one another and the spacing between groups of laser damage lines is not uniform across at least a portion of the substrate. [Figure 17] FIG. 1 is a schematic top plan view of a crystalline material substrate including first, second, and third distributed subsurface laser damage patterns defined in accordance with one embodiment, where all of the laser damage lines are parallel to one another and the laser damage lines exhibit variations in intra-group spacing, inter-group spacing, and group composition. [Figure 18] FIG. 1 is a schematic top plan view of a crystalline material substrate including first, second, and third successively formed subsurface laser damage patterns defined in accordance with one embodiment, where the first and second groups of laser damage lines are parallel to one another while the third group of laser damage lines is non-parallel to and intersects the first and second groups of laser damage lines. [Figure 19] FIG. 1 is a schematic top plan view of a crystalline material substrate including first, second, and third subsurface laser damage patterns formed in succession, where each group of laser damage lines includes parallel lines and where each group of laser damage lines is non-parallel to each other group of laser damage lines. [Figure 20A] 1 is a top plan view of a crystalline material substrate showing first, second, and third non-overlapping areas in which laser damage regions may be formed. [Figure 20B]FIG. 20B is a top plan view of the crystalline material substrate of FIG. 20A after forming a first plurality of subsurface laser damage regions in the first area through the third area. [Figure 20C] FIG. 20C is a top plan view of the crystalline material substrate of FIG. 20B after forming a second plurality of subsurface laser damage regions within the first area to the third area. [Figure 20D] FIG. 20D is a top plan view of the crystalline material substrate of FIG. 20C after forming a third plurality of subsurface laser damage regions within the first area to a third area. [Figure 21] FIG. 1 is a schematic top plan view of a holder in a laser processing apparatus arranged to hold four substrates on which subsurface laser damage can be created using one or more lasers. [Figure 22A] FIG. 1 is a schematic top plan view of a single substrate being processed with a split laser beam to simultaneously create subsurface laser damage in two portions of the substrate that follow a first subsurface laser damage pattern. [Figure 22B] FIG. 13 is a schematic top plan view of two substrates being processed with a split laser beam to simultaneously create subsurface laser damage in both substrates that follows the first subsurface laser damage pattern. [Figure 23A] 1 is a schematic cross-sectional view of a crystalline material substrate including a first subsurface laser damage pattern centered at a first depth. [Figure 23B] FIG. 23B is a schematic cross-sectional view of the substrate of FIG. 23A after formation of a second subsurface laser damage pattern centered at a second depth and aligned with the first subsurface laser damage pattern, where the vertical extensions of the first and second damage patterns overlap. [Figure 24A] 1 is a perspective photograph of a SiC wafer after separation from a thermoplastic adhesive bonded sapphire carrier according to the methods described herein. [Figure 24B] FIG. 24B is a perspective photograph of a sapphire carrier from which the SiC wafer of FIG. 24A has been separated. [Figure 24C]FIG. 24B is a partially inverted version of the SiC wafer photograph of FIG. 24A to emphasize the contrast between the central doping ring and the outer annular portion of the wafer. [Figure 24D] FIG. 24D is an image of FIG. 24C annotated with a dotted oval to indicate the boundary between the central doping ring and the outer annular portion of the wafer. [Diagram 25] FIG. 2 is a schematic cross-sectional side view of a SiC ingot grown on a seed crystal, showing a cylindrically shaped doped region extending upward from the seed crystal along the central portion of the ingot through its entire thickness. [Figure 26] 26 is a schematic top view of a SiC wafer obtained from the SiC ingot of FIG. 25 along the indicated thin cross-sectional portion thereof. [Figure 27] FIG. 2 is a schematic cross-sectional side view of a SiC ingot grown on a seed crystal, showing a frustum-shaped doped region extending upward from the seed crystal along the central portion of the ingot through its entire thickness. [Figure 28] FIG. 1 is a schematic cross-sectional side view of a SiC ingot grown on a vicinal (e.g., off-cut) seed crystal, showing a frusto-conical shaped doped region extending upward from the seed crystal at a point offset from the center of the seed crystal through the entire thickness of the ingot. [Figure 29] Oblique photograph of the Si face of a SiC wafer that has been separated from an ingot by a process involving subsurface laser damage formation and subsequent separation; the inset (top right) depicts a fragment of the SiC wafer, with the edge depicted in a subsequent scanning electron microscope (SEM) image. [Figure 30A] FIG. 45× magnification SEM image of a portion of the SiC wafer fragment of FIG. 29 taken at a tilt angle of 15 degrees, with superimposed arrows indicating the orientation of the [1-100] and [11-20] crystallographic planes. [Figure 30B] FIG. 29 is a 1,300x magnified SEM image of a portion of the SiC wafer fragment from FIG. 29 taken at a tilt angle of 15 degrees. [Figure 30C] FIG. 350X magnified SEM image of a portion of the SiC wafer fragment of FIG. 29 taken at a tilt angle of 15 degrees. [Figure 30D] FIG. 30 is a 100x magnified SEM image of a portion of the SiC wafer fragment of FIG. 29 taken at a tilt angle of 2 degrees. [Figure 30E] FIG. 29 is a 1,000x magnified SEM image of a portion of the SiC wafer fragment from FIG. 29 taken at a tilt angle of 2 degrees. [Figure 31A] FIG. 29 is a confocal laser scanning microscope image of a small central portion of the SiC wafer of FIG. 29, with superimposed crosshairs marking the location of the “trench” formed by the laser scan. [Figure 31B] 31B is a plot of the surface profile of a portion of the SiC wafer of FIG. 31A. [Figure 32A] FIG. 29 is a confocal laser scanning microscope image of a larger section near the top of the SiC wafer (at the time of the image capture), with the superimposed crosshairs marking the location of the “trench” formed by the laser scan. [Figure 32B] FIG. 32B is a plot of the surface profile of a portion of the SiC wafer near the top of FIG. 32A. [Figure 33A] Confocal laser scanning microscope image of a larger section near the bottom (at the time of image capture) of the SiC wafer of FIG. 29, with the superimposed crosshairs marking the location of the “trench” formed by the laser scan. [Figure 33B] FIG. 33B is a plot of the surface profile of a portion of the SiC wafer near the bottom of FIG. 33A. [Figure 34A] 1 is a schematic cross-sectional side view of a sturdy carrier having an adhesive material bonded to a surface thereof. [Figure 34B] FIG. 34B is a schematic cross-sectional view of an assembly including the tough carrier and adhesive material of FIG. 34A bonded to a crystalline material substrate having a subsurface laser damage region proximate to the adhesive material lip. [Figure 34C] FIG. 34C is a schematic cross-sectional view of the assembly of FIG. 34B, in which a surface of the sturdy carrier is positioned on a cooling device in the form of a water-cooled chuck. [Fig. 34D]Schematic cross-sectional view of a large portion of a crystalline material substrate separated from its bonded assembly (on a water-cooled chuck), including the sturdy carrier and the portion of crystalline material removed from the substrate, following spalling of the crystalline material along the subsurface laser damage region. [Figure 34E] FIG. 34D is a schematic cross-sectional view of the bonded assembly of FIG. 34D after removal from the water-cooled chuck, with residual laser damage along the top-facing surfaces. [Fig. 34F] FIG. 1 is a schematic cross-sectional view of a portion of crystalline material supported by a heated vacuum chuck, in which the tough carrier and adhesive material have been laterally translated away from the crystalline material portion following thermal softening and release of the adhesive material. [Diagram 35] Schematic cross-section of a crystalline material with subsurface laser damage bonded to a rigid carrier, where the crystalline material and carrier are placed in a liquid bath of an ultrasonic generator. [Fig. 36A-36C] FIG. 11 is a schematic cross-sectional view illustrating a step for fracturing a crystalline material with subsurface laser damage, comprising applying a mechanical force proximate one edge of the carrier to impart a bending moment to at least a portion of the carrier. [Fig. 37A-37O] FIG. 1 is a schematic cross-sectional view illustrating steps of a device wafer separation process according to which a thick wafer is fractured from a crystalline material, at least one epitaxial layer is grown on the thick wafer, the thick wafer is fractured to form first and second bonded assemblies each including a carrier and a thin wafer separated from the thick wafer, the first bonded assembly including at least one epitaxial layer as part of an operational semiconductor-based device. [Figure 38] FIG. 1 is a flow chart outlining generally the steps for creating subsurface laser damage, bonding a rigid carrier to an ingot of crystalline (e.g., SiC) material, followed by laser cutting of the bonded assembly including the carrier and a portion of the crystalline material, followed by further processing of the bonded assembly to form an epitaxial layer on a device wafer, and returning the ingot and rigid carrier to the beginning of the process. [Figure 39]FIG. 39 is a schematic cross-sectional view of a portion of the crystalline material substrate of FIG. 38 showing subsurface laser damage, with superimposed dotted lines identifying areas of expected kerf loss material that can result from laser damage and subsequent surface processing (e.g., grinding and planarization). [Diagram 40] FIG. 1 is a schematic diagram of a material processing apparatus according to one embodiment, including a laser processing station, a material breaking station, a plurality of parallel-arranged rough grinding stations, a fine grinding station, and a CMP station. [Diagram 41] FIG. 41 is a schematic diagram of a material processing apparatus according to an embodiment similar to the embodiment of FIG. 40, but in which an edge grinding station is located between the fine grinding station and the coarse grinding station. [Diagram 42] FIG. 1 is a schematic diagram of a material processing apparatus according to one embodiment, including a laser processing station, a material breaking station, multiple parallel arranged rough grinding stations, a fine grinding station, a surface coating station, an edge grinding station, a coating removal station, and a CMP station. [Figure 43A] FIG. 2 is a schematic cross-sectional side view of a first apparatus for holding an ingot having an end face that is non-perpendicular to a sidewall, according to one embodiment. [Figure 43B] FIG. 2 is a schematic cross-sectional side view of a second apparatus for holding an ingot having an end face that is non-perpendicular to a sidewall, according to one embodiment. [Diagram 44] FIG. 1 is a schematic cross-sectional side view of a conventional laser focusing device in which an incoming horizontal beam is focused with a lens to form an output beam having a beam waist pattern with a minimum width at a downstream position corresponding to the focal length of the lens. [Diagram 45] FIG. 1 is a schematic cross-sectional side view of a vertically oriented focused laser beam exhibiting a beam waist in a crystalline material, illustrating the resolving threshold points at different perpendicular positions relative to the beam waist. [Figure 46A] 1 is a plot of laser power versus successive wafer identification numbers for wafers derived from a SiC ingot, showing an increase in laser power along with the wafer identification number. [Figure 46B] 1 is a plot of laser power versus successive wafer identification numbers for wafers derived from a SiC ingot, showing an increase in laser power along with the wafer identification number. [Figure 46C] 1 is a plot of laser power versus successive wafer identification numbers for wafers derived from a SiC ingot, showing an increase in laser power along with the wafer identification number. [Figure 47] FIG. 1 is a plot of resistivity (Ohm-cm) versus slice number for 50 wafers produced from a SiC ingot; a superimposed polynomial fit shows that resistivity decreases with slice number, with higher slice numbers representing closer to the seed crystal from which the ingot was grown (e.g., via a physical vapor transport (PVT) process). [Figure 48] FIG. 48 is a plot of laser power (watts) versus resistivity for wafers produced from the SiC ingot of FIG. 47 with a superimposed polynomial fit showing that higher resistivity values ​​require less laser power to achieve. [Figure 49A] 1 is a schematic cross-sectional side view of a scattering light source and an imaging device positioned proximate to a substrate in a laser processing station; [Figure 49B] FIG. 2 is a top plan view of a scattered light source and an imaging device positioned proximate to a substrate in a laser processing station. [Figure 50A] Image of the top surface of a crystalline SiC substrate with subsurface laser damage showing areas of different color and irregularly shaped dark areas that correspond to crack-free areas in the substrate. [Figure 50B] FIG. 50B is a schematic diagram of a representation of a substrate showing the irregularly shaped dark regions of FIG. 50A within the dotted areas that substantially correspond to the boundaries between the different colored regions of the top surface of the substrate of FIG. 50A. [Figure 50C] FIG. 50C is a close-up of the irregularly shaped dark regions of FIGS. 50A-B, with rectangular boxes added around each region. [Figure 51]FIG. 1 is a schematic diagram of a material processing apparatus according to one embodiment, including a laser processing station including a laser, at least one translation stage, a scattering light source configured to irradiate a top surface of a substrate, and an imaging device configured to generate at least one image of the top surface of the substrate. [Figure 52] 1 is a flowchart illustrating steps of a first crystalline materials processing method, the method including generating an image of a top surface of a substrate having subsurface laser damage, analyzing the image to identify the presence of conditions indicative of one or more crack-free regions, comparing one or more characteristics of the crack-free regions to first and second thresholds, and taking action in response to the comparison to increase reliability of producing a substrate portion (e.g., a wafer) from the substrate (i.e., (A) performing additional laser passes at substantially the same depth location, optionally adjusting one or more laser parameters to form auxiliary laser damage, and / or (B) adjusting one or more laser parameters to form subsurface laser damage at second and subsequent depth locations). [Diagram 53] A flowchart illustrating steps of a second crystalline material processing method, the method including generating an image of a top surface of a substrate having subsurface laser damage, analyzing the image to quantify a top area characteristic of one or more crack-free regions, comparing the top area characteristic to first and second threshold area characteristics, and taking action in response to the comparison (i.e., performing an additional laser pass at the same depth location and / or adjusting power for the subsurface laser damage at the next depth location) to increase reliability of producing a substrate portion (e.g., a wafer) from the substrate. [Figure 54] A schematic diagram of a generalized representation of a computer system that may be included in any component of the systems or methods disclosed herein. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0046] The present disclosure relates to a method and material processing apparatus for processing a crystalline material substrate, in various embodiments. The crystalline material processing method includes creating a subsurface laser damage site in an area at a first average depth of the crystalline material to promote the formation of cracks within the substrate propagating outward from the subsurface laser damage pattern, imaging the substrate top surface, analyzing the image to identify conditions indicative of the presence of crack-free regions in the substrate, and performing one or more actions in response to the analyzing (e.g., upon achievement of the appropriate conditions). One possible action includes forming a supplemental subsurface laser damage at the first average depth to promote the formation of additional cracks in the crack-free regions to form a first thickness reduction portion of the substrate (e.g., a first wafer). Another possible action includes modifying the instruction set to perform a subsequent laser damage formation (at a second or subsequent average depth to form a second and any thickness reduction portions of the substrate) without necessarily forming additional damage at the first average depth. The laser damage facilitates subsequent spalling of the substrate to produce a plurality of substrate portions with reduced thickness.

[0047] In certain embodiments, the analyzing includes quantifying a top area characteristic of one or more crack-free regions within the substrate and comparing the top area characteristic to at least one predetermined threshold area characteristic. In certain embodiments, if the first threshold area characteristic is exceeded, the average laser power is incrementally increased in a subsequent laser damage formation step (i.e., at a second or subsequent average depth position to form a substrate portion of a second and subsequent reduced thickness), not necessarily involving formation of additional damage at the first average depth position. Instead of or in addition to increasing the laser power, the set of instructions for performing the subsequent second laser damage formation step may change the laser focus depth relative to the top surface and / or change some of the laser damage formation steps. If a larger second threshold area characteristic is exceeded (indicating that the crack-free area may be large enough to prevent spalling), a supplemental subsurface laser damage is formed at the first average depth location to supplement the at least one subsurface laser damage pattern and promote the formation of additional cracks in the crack-free area along or adjacent to the first average depth location to form a thickness reduction portion of the substrate. The damage can be formed before the substrate is removed from the laser processing station, thereby avoiding an extra step of unloading and remounting the substrate, increasing the throughput of the laser processing station.

[0048] In an additional aspect, the present disclosure relates to a material processing apparatus comprising a laser processing station configured to process a substrate of a crystalline material, the laser processing station comprising a laser configured to form a subsurface laser damage region within the substrate, at least one translation stage configured to perform relative movement between the laser and the substrate, a scattering light source configured to illuminate a top surface of the substrate, the scattering light source arranged to be positioned on a first lateral side of the substrate, and an imaging device configured to generate at least one image of the top surface of the substrate, the imaging device arranged to be positioned on a second lateral side of the substrate opposite the first lateral side. Such an apparatus makes crack-free regions within the substrate adjacent to the subsurface laser damage visible at its surface as dark (e.g., black or nearly black) spots on the top surface of the substrate. Such an apparatus also makes regions of different degrees of cracking between the subsurface laser damage areas appear different colors at the top surface of the substrate. The dark spots typically appear first in facet areas (corresponding to doping rings), so that in certain embodiments, facet areas can be distinguished.

[0049] As already mentioned, variations in material and / or optical properties within a thick substrate such as a SiC ingot and also between different ingots of the same composition make it difficult to easily and reproducibly produce wafers of uniform thickness by laser processing while avoiding unnecessary material loss. Applicant has found that when wafers are successively formed from a SiC ingot by subsurface laser damage formation and subsequent spallation, it is necessary to increase the laser power as the damage formation progresses at depth to enable successful spallation. (Again, when forming multiple wafers from a SiC ingot, the initial wafers distal to the seed can be successfully sliced ​​after laser damage formation created at lower average laser powers, but as the growth position of the sliced ​​wafers moves closer to the seed, the laser damage used to slice the next wafer requires progressively higher laser power levels.) This behavior is believed to be driven primarily by changes in bulk optical absorption, but may also be influenced by other changes in the crystal lattice. One theoretical solution to this problem would be to simply use higher laser power at each successive depth when creating the subsurface damage, but this would result in unnecessary material loss when the damage is created "early" in the ingot (e.g., at the first few depths distal to the seed) and would also result in significantly larger wafer-to-wafer thickness variations due to variability in both damage depth and the point of decomposition relative to the laser beam waist (as a result of the focal length of the beam focusing optics). Continuous adjustment of wafer thickness is not only impractical, but also imprecise due to measurement inaccuracies introduced by the rough surface created by the laser separation process, and due to the relationship between laser depth and required laser power.

[0050] Before detailing the detailed features of the above-mentioned methods and apparatus (specific embodiments of which are described in connection with Figures 45 to 51), an apparatus and method for processing crystalline material substrates will be introduced.

[0051] [Terminology and definitions] Although terms such as first, second, etc. may be used herein to describe various elements, it will be understood that these elements are not limited by these terms. These terms are used only to distinguish one element from another. For example, a first element could be termed a second element, and similarly, a second element could be termed a first element, without departing from the scope of the disclosure. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0052] When an element, e.g., a layer, region, or substrate, is referred to as being "on" or extending "onto" another element, it will be understood that the element may be directly on or extending directly onto the other element, or intervening elements may be present. In contrast, when an element is referred to as being "directly on" or extending "directly onto" another element, there are no intervening elements. Again, when an element, e.g., a layer, region, or substrate, is referred to as being "on" or extending "onto" another element, it will be understood that the element may be directly on or extending directly onto the other element, or intervening elements may be present. In contrast, when an element is referred to as being "directly on" or extending "directly onto" another element, there are no intervening elements. Also, when an element is referred to as being "connected" or "coupled" to another element, it will be understood that the element may be directly connected or coupled to the other element, or intervening elements may be present. In contrast, when an element is referred to as being "directly connected" or "directly coupled" to another element, there are no intervening elements present.

[0053] Relative terms such as "lower" or "upper" or "upper" or "lower" or "horizontal" or "vertical" may be used herein to describe the relationship of one element, layer, or region to another element, layer, or region as shown in the figures. It will be understood that these terms, and those discussed above, are intended to encompass various orientations of the device in addition to the orientation depicted in the figures.

[0054] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms unless the context clearly indicates otherwise. It will be further understood that the terms "comprise", "comprising", "include" and / or "including" as used herein specify the presence of referenced features, integers, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or groups thereof.

[0055] Unless otherwise defined, all terms (including technical and / or scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. It will be further understood that terms used herein should be interpreted as having a meaning consistent with their meaning in the context of the present specification and related art, and are not to be interpreted in an idealized or overly formal sense unless expressly defined otherwise herein.

[0056] As used herein, "substrate" refers to a crystalline material, such as a single crystal semiconductor material, that is divisible into at least two thinner portions having substantially the same lateral dimensions (e.g., diameter, or length and width) as the substrate, and that has a thickness sufficient to (i) allow surface processing (e.g., lapping and polishing) to support epitaxial growth of one or more layers of semiconductor material, and optionally (ii) be self-supporting when separated from a rigid carrier, optionally including an ingot or wafer. In certain embodiments, the substrate may have a generally cylindrical shape and / or have a thickness of approximately at least one or more of the following thicknesses: The thickness of the substrate may be approximately the same as the thickness of the substrate, for example, 300 μm, 350 μm, 500 μm, 750 μm, 1 mm, 2 mm, 3 mm, 5 mm, 1 cm, 2 cm, 5 cm, 10 cm, 20 cm, 30 cm, or more. In certain embodiments, the substrate may include a thicker wafer that is divisible into two thinner wafers. In certain embodiments, the substrate may be part of a thicker wafer having one or more epitaxial layers (optionally associated with one or more metal contacts) disposed thereon as part of a device wafer having a plurality of electrically operative devices. The device wafer may be divisible according to aspects of the present disclosure to provide a thinner device wafer and a second thinner wafer onto which one or more epitaxial layers (optionally associated with one or more metal contacts) may subsequently be formed. In certain embodiments, the substrate may have a diameter of 150 mm or more, or 200 mm or more. In certain embodiments, the substrate may comprise 4H—SiC having a diameter of 150 mm, 200 mm, or greater, and a thickness within the range of 100 to 1000 microns, or within the range of 100 to 800 microns, or within the range of 100 to 600 microns, or within the range of 150 to 500 microns, or within the range of 150 to 400 microns, or within the range of 200 to 500 microns, or any other thickness range, or any other thickness value specified herein.

[0057] The terms "first average depth position", "second average depth position", and "next average depth position", as used herein, refer to a depth position (e.g., horizontal plane) within a substrate measured from an initial top surface of the substrate for forming a thickness reduction portion of the substrate. For example, the first average depth position may correspond to a subsurface laser damage position for forming a first wafer from the ingot, the second average depth position may correspond to a subsurface laser damage position for forming a second wafer from the ingot, and so on. In certain embodiments, each thickness reduction portion obtained from the substrate has the same or substantially the same thickness. The term "average depth position" is used instead of depth position in recognition of the fact that in certain embodiments, small differences in laser focus depth may occur between runs or even within a single run for forming a laser damage pattern for forming a single thickness reduction portion of a substrate (e.g., a wafer), and such small differences are preferably within the range of 1 to 10 microns, or 2 to 8 microns, or 2 to 6 microns. This should be distinguished from a much larger difference between the first and second average depth positions, typically within a range of at least 100 microns (or at least 150 microns, 200 microns, 300 microns, 400 microns, 500 microns, or more).

[0058] The embodiments described below represent the necessary information to enable those skilled in the art to practice the embodiments and show the best mode for practicing the embodiments. Upon reading the following description in light of the accompanying drawings, those skilled in the art will understand the concepts of the present disclosure and recognize applications of these concepts not specifically addressed herein. These concepts and applications should be understood to be within the scope of the present disclosure and the appended claims.

[0059] [material] The methods disclosed herein can be applied to substrates of a variety of crystalline materials, both single crystal and polycrystalline. In certain embodiments, the methods disclosed herein can utilize cubic, hexagonal, and other crystalline structures and can be directed to crystalline materials with on-axis and off-axis crystal orientations. In certain embodiments, the methods disclosed herein can be applied to semiconductor materials and / or wide band gap materials. Exemplary materials include, but are not limited to, Si, GaAs, and diamond. In certain embodiments, such methods can utilize single crystal semiconductor materials with hexagonal crystal structures, such as 4H-SiC, 6H-SIC, or Group III nitride materials (e.g., GaN, AlN, InN, InGaN, AlGaN, or AlInGaN). In the various exemplary embodiments described below, we will generally refer to SiC or specifically to 4H-SiC, but it will be appreciated that any suitable crystalline material may be used. Among the various SiC polytypes, the 4H-SiC polytype is particularly attractive for power electronic devices due to its high thermal conductivity, wide band gap, and isotropic electron mobility. Bulk SiC growth can be performed on-axis (i.e., with no intentional angular deviation from its c-plane, suitable for forming undoped or semi-insulating materials) or off-axis (with a non-zero angle away from a growth axis, such as the c-axis, typically within the range of 0.5 to 10 degrees (or a subrange thereof, such as 2 to 6 degrees, or another subrange), which may be suitable for forming N-doped or highly conductive materials). The embodiments disclosed herein are applicable to on-axis and off-axis crystalline materials, as well as doped and unintentionally doped crystalline semiconductor materials. Doped semiconductor materials (e.g., N-doped SiC) exhibit some infrared absorption and therefore require the use of higher laser powers than undoped materials to impart subsurface laser damage. In certain embodiments, the crystalline material may include single crystal materials and may further include single crystal semiconductor materials. Certain embodiments disclosed herein may utilize on-axis 4H-SiC or vicinal (off-axis) 4H-SiC having an offcut in the range of 1 to 10 degrees, or 2 to 6 degrees, or about 4 degrees.

[0060] Certain embodiments herein may use substrates of doped or undoped SiC, such as SiC ingots (also known as boules), which may be grown by physical vapor transport (PVT) or other conventional ingot fabrication methods. When doped SiC is used, such doping renders the SiC N-type or semi-insulating in character. In certain embodiments, the N-type SiC ingot is intentionally doped with nitrogen. In certain embodiments, the N-type SiC ingot comprises a resistivity value in the range of 0.015 to 0.028 Ohm-cm. In certain embodiments, the SiC ingot may have a resistivity value that varies with vertical position, where different substrate portions (e.g., wafers) have different resistivity values, which may be due to variations in bulk doping levels during ingot growth. In certain embodiments, the SiC ingot may have a doping level that varies laterally, from a higher doping region adjacent the center of the ingot to a lower doping level adjacent its lateral edges. Due to variations in ingot doping and resistivity with respect to horizontal and vertical position, it may be necessary to adjust the laser damage formation parameters to form various thickness reductions (e.g., wafers) of a substrate (e.g., an ingot) and / or during the formation of a single thickness reduction of a substrate. In certain embodiments, resistivity is greatest adjacent the exposed surface of the ingot and lowest adjacent the growing seed. The decrease in resistivity corresponds to increased doping and increased laser absorption.

[0061] 6A and 6C are schematic side elevational views of on-axis and off-axis crystalline substrates in the form of ingots that may be used with the methods disclosed herein. FIG. 6A is a schematic side elevational view of an on-axis ingot 15 of crystalline material having a first end face 16 and a second end face 17 perpendicular to the c-direction (i.e., the <0001> direction for hexagonal crystal structure materials such as 4H-SiC). FIG. 6B is a schematic side elevational view of the ingot 15 of FIG. 6A rotated 4 degrees with a superimposed pattern 18 (shown in dotted lines) for cutting and removing ends of the ingot 15 proximate the end faces 16, 17. FIG. 6C is a schematic side elevational view of an off-axis ingot 15A formed from the ingot 15 of FIG. 6B after the ends have been removed to provide new end faces 16A, 17A that are non-perpendicular to the c-direction. When laser radiation at a first depth is delivered through an end face 16 of the ingot 15 to form a subsurface laser damage, a carrier (not shown) is bonded to the end face 16 and the ingot 15 is fractured along the subsurface laser damage, after which an on-axis wafer may be formed. Conversely, if laser radiation at a first depth is delivered through end face 16A of off-axis ingot 15A to form the subsurface laser damage, a carrier (not shown) may be bonded to end face 16A and ingot 15A may be fractured along the subsurface laser damage, after which an off-axis wafer may be formed.

[0062] [Subsurface laser damage formation] Processing a crystalline material substrate to form a plurality of patterns of subsurface laser damage facilitates subsequent fracturing of the substrate to produce first and second crystalline material portions of the substrate having reduced thickness. A particular method includes dispersing a plurality of successively formed groups of a plurality of substantially parallel lines of a plurality of subsurface laser damage patterns, where at least some lines of the second (e.g., subsequently formed) plurality of lines do not intersect with lines of the first plurality of lines. A particular method includes forming first and subsequent subsurface laser damage patterns each including another plurality of substantially parallel lines in a crystalline material substrate, where the lines of the first and subsequent plurality of substantially parallel lines are non-parallel to each other, the angular orientation of the lines of the subsequent plurality of substantially parallel lines differs from the angular orientation of the lines of the first plurality of substantially parallel lines by 10 degrees or less, and at least some lines of the subsequent plurality of substantially parallel lines do not intersect with any of the lines of the first plurality of substantially parallel lines. Certain methods include forming a first subsurface laser damage pattern substantially centered at a first depth within a crystalline material of a substrate, and forming a second subsurface laser damage pattern substantially centered at a second depth within the substrate (different from the first depth), where the second subsurface laser damage pattern is substantially aligned with the first subsurface laser damage pattern and where at least a portion of the vertical extension of the first and subsurface laser damage patterns overlap.

[0063] The continuous formation of distributed, interspersed, or interleaved subsurface laser damage patterns across the crystalline material is believed to beneficially maintain sufficient stress within the crystalline material to promote subsequent material spallation using the methods herein while allowing for high throughput of the laser tool associated with modest material damage and correspondingly low kerf loss. In principle, it would be simple to use high laser power to scan nearly the entire crystalline material to promote spallation along the laser damage lines. While such an approach can reliably separate thin layers of crystalline material from bulk substrates (e.g., ingots), high laser powers tend to increase material damage and require significant surface processing (e.g., grinding and planarization) to remove the damage. Close spacing between the laser damage lines would aid in promoting spallation, but at the expense of significantly reducing the throughput of the laser processing tool. Conventional techniques for creating subsurface laser damage include creating a subsurface laser damage line in the forward direction across a crystalline material, then performing lateral relative indexing between the material and the laser, then creating a subsurface laser damage line in the backward direction, then performing lateral indexing in the same lateral direction, etc. Such techniques generally require higher laser power or closer spacing between successively created laser damage lines, which tend to reduce throughput or impart more extensive damage, which in turn increases kerf loss due to the need to remove additional material from the surface being laser machined to remove the laser damage. This conventional approach does not involve forming a first distributed subsurface laser damage pattern (e.g., including forming a first plurality of laser damage regions across a plurality of non-overlapping areas of the substrate) followed by forming a second distributed subsurface laser damage pattern (e.g., including forming a second plurality of laser damage regions across the same plurality of non-overlapping areas of the substrate), where the second subsurface laser damage pattern is interleaved or interspersed among the first subsurface laser damage patterns.

[0064] Various embodiments disclosed herein enable high throughput of laser tools. Addressing the concern of facilitating reliable separation of a thin layer (e.g., wafer) of crystalline material from a substrate without excessively high laser power while achieving low kerf loss. Certain embodiments herein include forming a first distributed subsurface laser damage pattern in a crystalline material substrate (e.g., across each of a plurality of non-overlapping areas of the substrate) and then forming at least one subsequent distributed subsurface laser damage pattern in the same substrate (e.g., across each of the same plurality of non-overlapping areas), where at least a portion (e.g., lines) of the at least one subsequent laser damage pattern are disposed within gaps between the laser damage lines of the first laser damage pattern, thereby providing a dispersed or interleaved subsurface laser damage pattern. In certain embodiments, at least some (or all) of the laser damage lines of the at least one subsequent formed laser damage pattern do not intersect with the laser damage lines of the first subsurface laser damage pattern. It is believed that the non-intersecting laser damage patterns may beneficially avoid diffusion of localized stresses. In certain embodiments, the formation of the first and second distributed subsurface laser damage patterns is performed in a manner that prevents the propagation of localized subsurface cracks between them, while the application of the third (or subsequent) distributed subsurface laser damage pattern causes the localized subsurface cracks to propagate and merge in a substantially continuous manner across an interior plane of the crystalline material substrate, thereby facilitating subsequent spallation along the laser damage region using the techniques disclosed herein. The formation of distributed subsurface laser damage according to the methods described herein has been found to beneficially provide increased throughput of the laser tool while enabling reliable separation of thin layers of crystalline material from a substrate with fewer laser damage lines per layer to be removed, while providing lower levels of laser damage (allowing for low kerf loss).

[0065] Various embodiments refer to laser subsurface damage including lines oriented relative to the crystal structure of the substrate. In certain embodiments, the substrate includes a crystalline material having a hexagonal crystal structure, and the laser damage lines are oriented perpendicular to or within ±5 degrees of perpendicular to the <11-20> direction of the hexagonal crystal structure, and parallel or substantially parallel to the surface of the substrate (e.g., within ±5 degrees, ±3 degrees, or ±1 degree therefrom). Although primary flats on conventional 4H-SiC wafers are intended to be oriented parallel to the <11-20> direction of the hexagonal crystal structure, the primary flats may not be truly parallel to such direction due to variations in manufacturing. Various SiC wafer manufacturers provide published specifications for primary flat orientations that are ±5 degrees from parallel to the <11-20> direction of the hexagonal crystal structure. Thus, it is preferable to use X-ray diffraction (XRD) data rather than wafer flat alignment to determine the appropriate laser orientation for the formation of subsurface laser damage.

[0066] Tools for creating laser subsurface damage in crystalline materials are known in the art and are commercially available from various suppliers, such as Disco Corporation (Tokyo, Japan). Such tools allow for focusing of laser radiation inside a crystalline material substrate and lateral movement of the laser relative to the substrate. A typical laser damage pattern in the art involves the creation of parallel lines that are laterally spaced apart relative to one another at some depth within the crystalline substrate. Parameters such as focusing depth, laser power, translation speed, and subsurface damage line spacing can be adjusted to impart laser damage, although adjustment of certain factors involves trade-offs. Increasing laser power tends to impart larger subsurface damage, which may improve the ease of fracture (e.g., by reducing the stress required to complete the fracture), but larger subsurface damage leads to greater surface irregularities along the surface exposed by the fracture, which may require additional processing to make such surfaces sufficiently smooth for subsequent processing (e.g., for incorporation into an electronic device), which additional processing results in additional kerf loss. Subsurface Laser The ease of spallation can be improved by decreasing the lateral spacing between the damage lines, but decreasing the spacing between the laser damage lines increases the number of translation steps between the substrate and the laser, which reduces the throughput of the tool.

[0067] FIG. 7 is a schematic perspective view of an example of a laser tool 29 configured to focus laser radiation within a crystalline material 30 to form subsurface damage 40. The crystalline material 30 includes an upper surface 32 and an opposing lower surface 34, and the subsurface damage 40 is formed within the crystalline material 30 between the upper surface 32 and the lower surface 34. Laser radiation 36 is focused using a lens assembly 35 into a focused beam 38, the focal point of which is within the crystalline material 30. Such laser radiation 36 can be pulsed at any suitable frequency (typically in the nanosecond, picosecond, or femtosecond range) and beam intensity, and has a wavelength less than the bandgap of the crystalline material 30 such that the laser radiation 36 can be focused at a target depth below the surface of the crystalline material 30. At the focal point, the beam size and short pulse width result in an energy density high enough to result in highly localized absorption that forms the subsurface damage. One or more characteristics of the lens assembly 35 can be altered to adjust the focus of the focused beam 38 to a desired depth within the crystalline material 30. Lateral relative movement (e.g., lateral translation) between the lens assembly 35 and the crystalline material 30 can be effected to propagate the subsurface damage 40 in a desired direction, as shown diagrammatically by dotted line 44. Such lateral movement can be repeated in a variety of patterns, including those described below.

[0068] 8A and 8B provide exemplary laser tool translation paths relative to a crystalline material for forming subsurface damage therein. In certain embodiments, the laser tool portion (including, for example, the lens assembly) can be configured to move and the crystalline material does not move, while in other embodiments, the laser tool portion can be held stationary and the crystalline material is moved relative to the tool portion. FIG. 8A illustrates a reversing y-direction linear scanning motion 46 suitable for forming a pattern of laterally spaced parallel lines of subsurface damage in a first crystalline material 45A. FIG. 8B illustrates a y-direction linear scanning motion 48 (advancing slightly in the x-direction for each y-direction reversal) across (and beyond) the surface of crystalline material 45B sufficient to form parallel subsurface laser damage lines distributed across crystalline material 45B. As shown, the laser damage lines are perpendicular to the [11-20] direction of the hexagonal crystal structure of crystalline material 45B along the surface of crystalline material 45B and are substantially parallel to the surface of crystalline material 45B.

[0069] Covering the entire surface of the crystalline material with a laser line formed in the y-direction while stepping in one direction in the x-direction with each reversal in the y-direction may be referred to as a single pass of laser damage formation. In certain embodiments, the laser processing of the crystalline material to form subsurface damage may be performed in two, three, four, five, six, seven, or eight passes, or any other suitable number of passes. By increasing the number of passes at lower laser power, kerf loss can be reduced. To achieve a desired balance of material loss versus process speed, a desirable number of laser subsurface damage formation passes has been found to be two to five passes, or three to four passes, before performing the spallation step.

[0070] In certain embodiments, the lateral spacing between adjacent laser subsurface damage lines (whether formed in a single pass or multiple passes) can be in the range of 80 to 400 microns, or 100 to 300 microns, or 125 to 250 microns. The lateral spacing between adjacent laser subsurface damage lines affects the laser processing time, ease of spallation, and effective laser damage depth (depending on c-plane orientation or misorientation).

[0071] It has been observed that the formation of subsurface laser damage lines in crystalline materials results in the formation of small cracks within the material that propagate outward (e.g., laterally outward) from the laser damage line. Such cracks appear to extend substantially or primarily along the C-plane. The length of such cracks appears to be a function of the laser power level (which can be calculated as the product of the energy per pulse times the pulse frequency). For adjacent laser subsurface damage lines spaced a certain distance apart, it has been observed that increasing the laser power when forming such laser subsurface damage lines tends to increase the ability of the cracks to connect or merge between the laser subsurface damage lines, which is desirable for facilitating easy spallation.

[0072] If the crystalline material undergoing laser damage formation contains an off-axis (i.e., non-c-plane) orientation (e.g., within a range of 0.5-10 degrees, 1-5 degrees, or another misorientation), such misorientation can affect the desired laser damage line spacing.

[0073] A SiC substrate may include a surface that is misaligned with the c-plane (e.g., off-axis at an oblique angle to the c-plane). An off-axis substrate may also be referred to as a vicinal substrate. After fracture of such a substrate, the as-fractured surface may include plateaus and steps (which may then be smoothed by surface treatments such as grinding and polishing). FIG. 9 is a schematic perspective view of the surface structure of an off-axis 4H-SiC crystal 50 (having an angle A with respect to the c-axis basal plane) after fracture but before smoothing. The fractured surface exhibits steps 52 and plateaus 54 relative to the c-axis basal plane 56. For a 4 degree off-axis surface, the steps theoretically have a height of about 17 microns for a plateau width of 250 microns. For a 4H-SiC crystal with subsurface laser damage, the 250 micron spacing between the laser lines creates a plateau that is 250 microns wide. After fracturing, the stepped surface is ground smooth, planarized, and polished in preparation for epitaxially growing one or more layers thereon.

[0074] When subsurface laser damage is created in a crystalline material (e.g., SiC) and the subsurface laser damage line is oriented away from the normal to the substrate flat (i.e., non-perpendicular to the [11-20] direction), such laser damage line extends through multiple steps and plateaus in a manner comparable to off-axis semiconductor materials. For the purposes of the following discussion, we will use the term "off-axis laser subsurface damage line" to refer to laser subsurface damage lines that are non-perpendicular to the [11-20] direction.

[0075] Making the spacing between adjacent subsurface laser damage lines too large will prevent the spalling of the crystalline material. Making the spacing between adjacent subsurface laser damage lines too small will tend to reduce the step height but increase the number of vertical steps, and increasing the number of vertical steps typically requires a greater separation force to complete the spallation.

[0076] Narrowing the spacing between adjacent laser damage lines to too small a distance results in yield reduction and substantially increases process time and cost. A minimum laser energy threshold is required for SiC decomposition. If this minimum energy level produces a connected crack between two laser lines spaced approximately 100 microns apart, there is little benefit in terms of reducing kerf loss by narrowing the laser line spacing below this threshold.

[0077] The surface roughness of the crystalline material exposed by spalling can affect subsequent handling such as robot vacuums, as well as wear on the grinding wheels, which are a major consumable expense. Roughness is affected by both the spacing of the subsurface laser damage lines and the orientation of such subsurface damage lines with respect to the crystalline structure of the semiconductor material. By reducing the spacing between the subsurface damage lines, the possible step height is simply reduced. Providing a cleavage plane that is parallel to the laser line along the C-plane will tend to break long parallel steps that would otherwise be present in the laser damage region, which also helps to mitigate at least some of the effects from tilt or curvature of the C-plane. When the laser line is perpendicular to the substrate flat, the cleave plane parallel to the laser line along the C-plane will extend approximately 150 mm from the flat to the opposite curved edge of the wafer. A slight deviation in the tilt or curvature of the C-plane, which is typical for SiC substrates, will cause the plane to jump as the fracture propagates. jumping), which can result in significant variability in the spalled surface. A drawback of providing off-axis laser subsurface damage lines is that such subsurface damage lines generally require increased laser power to form connected cracks between adjacent laser lines. Thus, in certain embodiments, providing a combination of on-axis (perpendicular to the primary flat) and off-axis laser subsurface damage lines provides a good balance between avoiding excessive variability in the spalled surface without the need to excessively increase laser power to form connected cracks between adjacent laser lines.

[0078] In certain embodiments, a laser having a wavelength of 1064 nm may be used to carry out the methods disclosed herein, and the inventors have gained experience processing 4H-SiC. In certain embodiments, a wide range of pulse frequencies may be used, but pulse frequencies from 120 kHz to 150 kHz have been successfully utilized. A translation stage speed of 936 mm / s between the laser and the substrate being processed has been successfully utilized, although in certain embodiments, higher or lower translation stage speeds may be used with appropriate adjustments to the laser frequency to maintain the desired laser pulse overlap. The average laser power range for forming subsurface laser damage in doped SiC materials is in the range of 3 W to 8 W, and 1 W to 4 W for undoped SiC materials. The energy of the laser pulse can be calculated by dividing the power by the frequency. A laser pulse width of 3 ns to 4 ns may be used, although other pulse widths may be used in other embodiments. In certain embodiments, a numerical aperture (NA) of the laser lens in the range of 0.3 to 0.8 may be used. In embodiments directed to processing SiC, considering the refractive index change from air (~1) to SiC (~2.6), a large change in the refraction angle occurs inside the SiC material to be processed, making the NA of the laser lens and correction of aberrations important to achieve the desired results.

[0079] One of the major contributors to kerf loss is subsurface laser damage, which is located below the main spallation area on the ingot face. In general, kerf loss increases with increasing subsurface laser damage. One possible cause of increased subsurface laser damage is the inability to adequately compensate the optical properties of the crystalline material. In certain embodiments, optical parameter optimization can be performed periodically (e.g., every time a crystalline material substrate (e.g., an ingot) is fed into the laser tool) prior to the formation of subsurface laser damage on the substrate. Such optimization can utilize variable height adjustment to achieve an initial condition where the best focal point of the laser beam is formed on the upper surface of the crystalline material substrate, and then adjust the aperture and / or correction collar adjustment ring of the laser tool to correspond to the desired depth of the formation of subsurface laser damage in the crystalline material depending on the next condition.

[0080] In certain embodiments, the crystalline material substrate may exhibit doping that varies positionally (e.g., laterally and / or diametrically) across a major surface (e.g., face) of the substrate. The dopant concentration is typically higher in the central region of a SiC{0001} wafer, observable by the darker color of such regions. This increased dopant concentration is due to increased impurity incorporation that occurs during facet growth. During growth of a SiC{0001} ingot, the {0001} facet appears near the center of the ingot. Rapid spiral growth occurs on the {0001} facet, but <0001> The crystal growth rate along the {0001} facet region is relatively slow. The dopant concentration in the center (i.e., facet region) of the SiC wafer may be 20% to 50% higher than the dopant concentration outside this region. The formation of doped ring regions of increased dopant concentration in SiC is shown in Figures 14A, 14C, and 14D. Such regions have higher laser absorptance and slightly altered refractive index, both of which affect the focusing depth of the laser radiation in the substrate. By increasing the laser power when the focused laser radiation is directed into the doped ring region compared to the power used when the focused laser radiation is directed into the material outside the doped ring region, the different characteristics of the doped ring region can be compensated for. In certain embodiments, the presence of conditions indicative of non-uniform doping of the crystalline material over at least a portion of the surface of the substrate can be detected to determine the presence of at least one first doped region and at least one second doped region. (Methods for detecting various doping states include, but are not limited to, interferometry, resistivity measurements, absorptivity or reflectivity measurements, and other techniques known to those skilled in the art.) Thereafter, in response to detecting a condition indicative of non-uniform doping of the crystalline material, the laser power can be varied during formation of the subsurface laser damage pattern to provide a first average power of laser radiation when forming the subsurface laser damage in the first doped region, and to provide a second average power of laser radiation when forming the subsurface laser damage in the second doped region, the first and second average power levels being different from one another. Alternatively or additionally, the depth of formation of the subsurface laser damage in the substrate (i.e., relative to the exposed surface of the substrate) when forming the subsurface laser damage in one of the first doped region or the second doped region can be varied. In certain embodiments, the difference in laser focus depth between the first and second doped regions to form a single reduced thickness portion of a substrate (e.g., one wafer) may be in the range of 1 to 15 microns, or 1 to 10 microns, or 2 to 8 microns, or 4 to 6 microns.

[0081] In certain embodiments, crystalline material substrates may exhibit different laser absorption levels versus vertical position in the substrate (e.g., within an ingot), especially in the case of intentionally doped materials. Laser absorption levels may also vary from substrate to substrate (e.g., from ingot to ingot). It is believed that such variations may be due to doping variations. In certain embodiments, lower average laser powers (e.g., 3 W) may be used to form subsurface laser damage in substrate regions distal to the growth seeds, and higher average laser powers (e.g., 5.5 W) may be used to form subsurface laser damage in substrate regions proximal to the growth seeds.

[0082] In certain embodiments, optical measurements of the depth of the laser focus in the semiconductor material can be performed (e.g., taking into account semiconductor material / air refractive index changes) to initially set the laser subsurface damage to the correct depth relative to the surface of the crystalline material substrate, and the laser damage settings (e.g., laser power, laser focus, and / or number of laser damage creation passes) can be adjusted in response to such measurements before scanning the entire surface of the substrate. In certain embodiments, optical measurements of the depth of the laser focus can be performed once per ingot, or once each time after a portion of the ingot is fractured and removed (i.e., before the creation of the subsurface laser damage pattern for each substrate layer that will be removed in the next fracture).

[0083] In certain embodiments, the semiconductor material processing methods disclosed herein may include some or all of the following items and / or steps: A second carrier wafer may be attached to a bottom surface of a crystalline material substrate (e.g., an ingot). The top surface of the crystalline material substrate may then be ground or polished to an average surface roughness R of less than about 5 nanometers, e.g., in preparation for the surface to transmit laser energy. a Laser damage can then be applied to one or more desired depths within the crystalline material substrate. The spacing and direction of the laser damage tracks optionally depend on the crystal orientation of the crystalline material substrate. A first carrier can be bonded to the top surface of the crystalline material substrate. The wafer resulting from the crystalline material substrate can be associated with an identification code or other information linked to the first carrier. Alternatively, laser markings can be applied to the wafer (rather than the carrier) prior to separation to facilitate tracking of the wafer during and after fabrication. The crystalline material substrate is then fractured (using one or more methods disclosed herein) along the subsurface laser damage region to obtain a portion of the semiconductor material substrate bonded to the first carrier and a remaining portion of the crystalline material substrate bonded to the second carrier. Both the removed portion of the semiconductor material substrate and the remaining portion of the semiconductor material substrate are ground smooth and cleaned as necessary to remove residual subsurface laser damage. The removed portion of the semiconductor material substrate can be separated from the carrier. The process can then be repeated using the remaining portion of the semiconductor material substrate.

[0084] While wire sawing of SiC wafers typically involves a kerf loss of at least about 250 microns per wafer, the laser-assisted and carrier-assisted separation methods applied to SiC disclosed herein can achieve kerf losses in the range of 80 to 140 microns per wafer.

[0085] In certain embodiments, laser subsurface damage may be formed in the crystalline material substrate prior to bonding the substrate to the rigid carrier. In certain embodiments, a rigid carrier transparent to the desired wavelength of laser radiation may be bonded to the crystalline material substrate prior to subsurface laser damage formation. In such embodiments, the laser radiation may be optionally transmitted through the rigid carrier into the interior of the crystalline material substrate. Different carrier-substrate subsurface laser formation configurations are illustrated in FIGS. 10A-10D. FIG. 10A is a schematic diagram of laser radiation 61 being focused through the surface of a bare substrate 62 to form subsurface laser damage 63 in the substrate 62, to which the rigid carrier may be attached after the formation of the subsurface laser damage. FIG. 10B is a schematic diagram of laser radiation 61 being focused through the surface of a substrate 62 to form subsurface laser damage 63 in the substrate 62, which has previously been bonded to a rigid carrier 66 using an adhesive material 64. 10C is a schematic diagram of laser radiation 61 being focused through rigid carrier 66 and adhesive 64 to form subsurface laser damage 63 in substrate 62 that is pre-bonded to rigid carrier 66. In certain embodiments, the surface of substrate 62 distal from rigid carrier 66 may include one or more epitaxial and / or metallization layers, with substrate 62 embodying an operational electrical device prior to formation of subsurface laser damage 63. FIG. 10D is a schematic diagram of laser radiation 61 being focused through rigid carrier 66 into substrate 62 (without intervening layers) to form subsurface laser damage 63 in substrate 62 that is pre-bonded (e.g., via anodic bonding or other adhesive-free means) to rigid carrier 66.

[0086] [Distributed subsurface laser damage] In certain embodiments, subsurface laser damage can be formed in a crystalline material by the sequential formation of multiple distributed laser damage patterns, each subsurface laser damage pattern comprising multiple substantially parallel lines. In certain embodiments, each subsurface laser damage pattern can extend substantially the entire length (e.g., perpendicular to the substrate flat) of the crystalline material substrate and can comprise spaced apart lines distributed across substantially the entire width. In certain embodiments, the distributed damage pattern can comprise first and second, or first through third, or first through fourth, subsurface laser damage patterns formed in succession, each subsurface laser damage pattern comprising multiple parallel lines. To enhance the ease of spalling of the crystalline material along or adjacent to the subsurface laser damage region, multiple subsurface laser damage patterns can be sequentially formed in a distributed manner (e.g., forming a first subsurface damage pattern and then It is believed that forming a second subsurface damage pattern, and then forming any subsequent subsurface damage patterns (distributing the various lines of each damage pattern among the other damage patterns) is preferable to forming the same tracks without dispersion. Without wishing to be bound by any particular theory as to the reason for the improved spallation results obtained with dispersed subsurface laser damage patterns in crystalline materials, it is believed that the successive formation of dispersed subsurface laser damage patterns results in a greater degree of preservation of internal stresses within the semiconductor material, which in turn promotes the lateral propagation of cracks emanating from the different subsurface laser damage lines.

[0087] In certain embodiments, a first subsurface laser damage pattern in the crystalline material includes a first plurality of parallel lines within the crystalline material and a first plurality of cracks propagating laterally outward from the first plurality of substantially parallel lines (e.g., primarily or substantially along the c-plane), where the cracks emanating from each line are not connected to cracks emanating from each adjacent line. In certain embodiments, after formation of the first subsurface laser damage pattern, a second subsurface laser damage pattern is formed in the crystalline material including a second plurality of parallel lines, where the second subsurface laser damage pattern includes a second plurality of cracks within the crystalline material propagating laterally outward from the second plurality of substantially parallel lines, where at least some of the cracks in the second plurality of cracks connect with cracks emanating from two adjacent lines of the first plurality of lines (e.g., resulting in a continuous crack).

[0088] In certain embodiments, first, second, and third subsurface laser damage patterns are sequentially formed in the crystalline material, each subsurface laser damage pattern comprising a plurality of parallel lines, the lines of each subsurface laser damage pattern being distributed among the lines of each of the other subsurface laser damage patterns. In certain embodiments, the first subsurface laser damage pattern comprises a first plurality of cracks propagating laterally outwardly from the first plurality of substantially parallel lines within the crystalline material, the second subsurface laser damage pattern comprises a second plurality of cracks propagating laterally outwardly from the second plurality of substantially parallel lines within the crystalline material, the second plurality of cracks not connecting with the first plurality of cracks, and the third subsurface laser damage pattern comprises a third plurality of cracks propagating laterally outwardly from the third plurality of substantially parallel lines within the crystalline material. In such embodiments, at least some of the cracks in the third plurality of cracks connect (e.g., resulting in a continuous crack) with (i) at least some of the cracks in the first plurality of cracks and (ii) at least some of the cracks in the second plurality of cracks. In certain embodiments, a fourth subsurface laser damage pattern can be formed after the first through third subsurface laser damage, the fourth subsurface laser damage pattern serving to further connect cracks emanating from any two or more of the first, second, or third lines. In certain embodiments, three, four, five, or more interspersed patterns of subsurface laser damage can be provided.

[0089] In certain embodiments, one or more portions of a substrate may include a distributed subsurface laser damage pattern, while other portions of the substrate may include a non-distributed laser damage pattern. In certain embodiments, different distributed patterns of subsurface laser damage may be provided on the same substrate. For example, a distributed pattern of subsurface laser damage on a single substrate may include five damage lines in a first region, four damage lines in a second region, three damage lines in a third region, two damage lines in a fourth region, one damage line (i.e., non-distributed) in a fifth region, zero damage lines in a sixth region, or any combination of two or three of the above, optionally each of the above regions having substantially the same unit area. In certain embodiments, a regular (e.g., regularly repeating) pattern of distributed damage lines may be provided on at least one region of the substrate. In one embodiment, a pattern of scattered or non-scattered damage lines may be present in at least one other region of the substrate, and an irregular (e.g., non-regularly repeating) pattern of scattered or non-scattered damage lines may be present in at least one other region of the substrate.

[0090] FIG. 11A provides a top plan view of a crystalline material substrate 70 including first, second, and third distributed subsurface laser damage patterns defined according to one embodiment. The first, second, and third subsurface damage patterns each individually include a first plurality of parallel lines 71, a second plurality of parallel lines 72, and a third plurality of parallel lines 73 that extend perpendicular to a primary substrate flat 78 (and perpendicular to the [11-20] direction). The three laser damage patterns combine to form a plurality of three-line groups 74 that are separated from one another by inter-group spacings 75 that exceed the spacings 76, 77 between adjacent lines in each three-line group 74. For clarity, cracks formed by the first plurality of parallel lines 71, the second plurality of parallel lines 72, and the third plurality of parallel lines 73 are not shown in FIG. 11A. In a particular embodiment, a first plurality of parallel lines 71 are formed in a first pass, a second plurality of parallel lines 72 are formed in a second pass, and a third plurality of parallel lines 73 are formed in a third pass. The third pass serves to connect cracks originally emanating from either the first parallel lines 71 and / or the second parallel lines 72.

[0091] 11A, in one embodiment, a first plurality of parallel lines 71 may be formed with a pitch (i.e., spacing between lines) of 500 microns, and a second plurality of parallel lines 72 may be formed with a pitch of 500 microns and offset by 250 microns relative to the first plurality of parallel lines 71. Then, a third plurality of parallel lines 73 may be formed with a pitch of 500 microns and offset by 125 microns relative to the first plurality of parallel lines 71. This configuration creates a plurality of tri-line groups 74 separated from each other tri-line group by gaps of 250 microns, with adjacent lines within each tri-line group separated from one another by gaps of 125 microns.

[0092] The inventors have found that the order of the three-pass laser damage formation process described in connection with FIG. 11A is important. If the order of the passes is changed to form the first, third, and second plurality of subsurface laser damage lines in a sequential manner, a higher laser power is required to complete the crack initiation across the 250 micron intergroup spacing 75. It is believed that this may be due to crack initiation occurring between the 125 micron spacing lines in the second pass when using the original (first, second, third pass) sequential order, where the crack formed in the third pass is of sufficient size to simply connect with the crack emanating from the second subsurface damage line across the second 125 micron gap 77. When the pass order is first, third, second, crack initiation across the intergroup spacing 75 is not observed unless the laser power is increased, but increasing the laser power typically increases kerf loss. Thus, according to certain embodiments in which the order of steps is first, second, third, it may be desirable for the cracks formed in the first and second steps to not connect to each other, and then for the cracks formed in the third step to create connected cracks that traverse both the 125 micron gaps 76, 77 and the 250 micron inter-group spacing 75.

[0093] In certain embodiments, the boundaries of each tri-line group 74 may be considered to bound a damage-bearing area of ​​the substrate 70, with the damage-bearing area of ​​each tri-line group 74 being spaced apart (i.e., by inter-group spacing 75) from the damage-bearing area of ​​each other tri-line group. Notably, as shown in FIG. 11D below, cracks formed by subsurface laser damage may propagate across inter-group spacing 75 between adjacent tri-line groups 74.

[0094] Figures 11B-11D illustrate the fabrication of the crystalline material substrate 70 of Figure 11A. Figure 11B illustrates the substrate 70 after the formation of a first plurality of subsurface laser damage lines 71 (perpendicular to a flat 78 of the substrate 70) having a pitch (or line-to-line spacing) 71B forming a first subsurface laser damage pattern 71A. Cracks 71C propagate laterally outward from the first plurality of subsurface laser damage lines 71, but cracks originating from different subsurface laser damage lines 71 do not connect to one another.

[0095] 11B shows substrate 70 after formation of a second plurality of subsurface laser damage lines 72 (perpendicular to flat 78 of substrate 70) having a pitch (or inter-line spacing) 72B forming a second subsurface laser damage pattern 72A. Cracks 72C propagate laterally outward from the second plurality of subsurface laser damage lines 71, but cracks originating from different subsurface laser damage lines 71 do not connect to each other.

[0096] 11C illustrates substrate 70 after formation of a third plurality of subsurface laser damage lines 73 (perpendicular to flat 78 of substrate 70) having a pitch (or inter-line spacing) 73B forming a third subsurface laser damage pattern 73A. Cracks 73C propagate laterally outward from third plurality of subsurface laser damage lines 73, such cracks 73C being sufficient to connect cracks 71C, 72C formed by first subsurface laser damage lines 71 and second subsurface laser damage lines 72. As shown, the crack connections between the first, second, and third plurality of subsurface damage lines are also sufficient to allow cracks to propagate further and connect across inter-group spacing 75.

[0097] In a particular embodiment, the third laser pass forming the third subsurface damage pattern is performed at a higher laser power level than the first two passes to help extend the crack to connect across the inter-group spacing 75, which is wider than the spacing 76, 77 between the lines in each three-line group 74. The inventors have found that increasing the laser power during the third pass is sufficient to connect the cracks not only between laser subsurface damage lines spaced 125 um apart (as shown in FIG. 11D), but also between laser subsurface damage lines positioned 250 um apart. This results in roughly a 25% increase in tool throughput with a small penalty in kerf loss (e.g., about 110 um kerf loss instead of 100 um).

[0098] In certain embodiments, all of the laser subsurface damage lines may be non-perpendicular to the primary substrate flat (and to the [11-20] direction) within a range of about 1 degree to 5 degrees from perpendicular. For example, FIG. 12 is a schematic top plan view of a crystalline material substrate 80 including a substrate flat 88 and first, second, and third plurality of substantially parallel subsurface laser damage lines 81-83 that are dispersed or interspersed with each other to form first to third subsurface laser damage patterns. Each of the plurality of substantially parallel subsurface laser damage lines 81-83 is offset by 3 degrees from perpendicular to the primary substrate flat (and to the [11-20] direction), and the laser damage patterns combine to form a plurality of three-line groups 89 that are separated from each other by inter-group spacings 85 that are greater than the spacings (or gaps) 86, 87 between adjacent lines in each three-line group 89. In one embodiment, a first plurality of parallel lines 81 may be formed with a pitch (i.e., spacing between lines) of 500 microns, and a second plurality of parallel lines 82 may be formed with a pitch of 500 microns and offset by 250 microns relative to the first plurality of parallel lines 81. Then, a third plurality of parallel lines 83 may be formed with a pitch of 500 microns and offset by 125 microns relative to the first plurality of parallel lines 81. This configuration creates a plurality of tri-line groups 89 separated from each other tri-line group by gaps of 250 microns, with adjacent lines within each tri-line group being separated from each other by gaps of 125 microns. As shown, the parallel subsurface laser damage lines 81-83 in each group are parallel to each other.

[0099] 13 is a schematic top plan view of a crystalline material substrate 90 including a substrate flat 98 and first through fourth plurality of substantially parallel subsurface laser damage lines 91-94 interspersed or interleaved with one another to form first through fourth subsurface laser damage patterns, all parallel to one another and perpendicular to the substrate flat 98 (and to the [11-20] direction). In a particular embodiment, the first through fourth plurality of subsurface laser damage lines 91-94 may each include lines having a pitch of 500 nm, with the second plurality of lines 92 being offset from the first plurality of lines 91 by 250 microns, the third plurality of lines being offset from the first plurality of lines 91 by 125 microns, and the fourth plurality of lines being offset from the first plurality of lines 91 by 375 microns. Ultimately, there will be a gap of 125 microns between each of the first through fourth plurality of lines 91-94. The first line 91 to the fourth line 94 form a four-line repeat group 95 .

[0100] An alternative method for forming a crystalline material substrate similar to substrate 90 shown in Figure 13 includes using four passes of laser subsurface damage formation, each pass forming lines having a pitch of 500 microns. After the first pass, the lines formed by the second pass are offset 125 microns from the lines of the first pass, then the lines of the third pass are offset 250 microns from the lines of the first pass, then the lines of the fourth pass are offset 375 microns from the lines of the first pass.

[0101] 14 is a schematic top plan view of a crystalline material substrate 100 including a substrate flat 108 and including first to third plurality of dispersed subsurface laser damage lines 101 to 103 forming first, second and third subsurface laser damage patterns. The first and second plurality of lines 101 and 102 are each parallel to each other and perpendicular to the primary substrate flat 108 (and to the [11-20] direction), with the third plurality of lines 103 being non-parallel to the first and second plurality of lines 101 and 102 (e.g., at an angle difference in the range of 1 to 5 degrees), but not intersecting either the first or second lines 101 and 102 within the substrate 100. In a particular embodiment, the first and second plurality of parallel lines 101 and 102 are formed first, and then the third plurality of parallel lines 103 is formed thereafter. In a particular embodiment, the first plurality of parallel lines 101 and the second plurality of parallel lines 102 each have a pitch of 500 microns, and the second plurality of parallel lines 102 are offset by 250 microns relative to the first plurality of parallel lines 101. The first lines 101 through the third lines 103 form a multi-line repeating group 104.

[0102] 14, the subsurface laser damage lines do not intersect, in certain embodiments, one or more subsurface laser damage lines (e.g., formed in a subsequent laser damage step) may intersect with one or more other subsurface damage lines (e.g., formed in a prior or initial laser damage step). In certain embodiments, the relative angle between intersecting subsurface laser damage lines may be within a range of 4 to 30 degrees, or 5 to 20 degrees, or 5 to 15 degrees, or 5 to 10 degrees.

[0103] 15 is a schematic top plan view of a crystalline material substrate 110 including a substrate flat 118 and including first through third pluralities of dispersed subsurface laser damage lines 111-113 forming first through third subsurface laser damage patterns. The first and second pluralities of lines 111 and 112 are each parallel to one another and non-perpendicular to the primary substrate flat 108 (e.g., at an angle difference in the range of 1 to 5 degrees), while the third plurality of lines 113 is perpendicular to the primary substrate flat 118 but at least some (or all) of the lines are perpendicular to the first group of lines 111 and lines 112 in the substrate 110. In a particular embodiment, the first plurality of parallel lines 111 and the second plurality of parallel lines 112 each have a pitch of 510 microns, and the second plurality of parallel lines 112 are offset by 250 microns with respect to the first plurality of parallel lines 111. The first lines 111 through the third lines 113 form a three-line repeat group 114.

[0104] FIG. 16 is a schematic top plan view of a crystalline material substrate including dispersed first, second, and third subsurface laser damage patterns defined in accordance with one embodiment, where all of the laser damage lines are parallel to one another and the spacing between groups of laser damage lines is not uniform across at least a portion of the substrate.

[0105] FIG. 17 is a schematic top plan view of a crystalline material substrate including dispersed first, second, and third subsurface laser damage patterns defined in accordance with one embodiment, where all of the laser damage lines are parallel to one another and the laser damage lines exhibit variations in intra-group spacing, inter-group spacing, and group composition.

[0106] FIG. 18 is a schematic top plan view of a crystalline material substrate including first, second, and third successively formed subsurface laser damage patterns defined in accordance with one embodiment, where the first and second groups of laser damage lines are parallel to one another while the third group of laser damage lines is non-parallel to and intersects the first and second groups of laser damage lines.

[0107] FIG. 19 is a schematic top plan view of a crystalline material substrate including first, second, and third subsurface laser damage patterns formed in succession, where each group of laser damage lines includes parallel lines, and each group of laser damage lines is non-parallel to each other group of laser damage lines. Although FIGS. 11A-19 show an embodiment including three or four groups of a plurality of subsurface laser damage lines, it will be appreciated that any suitable number of groups of subsurface laser damage lines can be provided. For example, in certain embodiments, the first and second plurality of subsurface laser damage lines can be interspersed without the third and / or fourth plurality of subsurface laser damage lines. In certain embodiments, the first and second plurality of subsurface laser damage lines can be formed in the first and second passes, respectively, where each plurality of laser damage lines has a pitch of 250 microns, and the second plurality of laser damage lines is offset by 125 microns relative to the first plurality of laser damage lines.

[0108] In certain embodiments, the subsurface laser damage is distributed among a plurality of non-overlapping areas of the crystalline material by forming a first group of subsurface laser damage sites within the first and second non-overlapping areas of the crystalline material, followed by forming a second group of subsurface laser damage sites within the first and second areas, where at least some (or all) of the sites of the second group of subsurface laser damage sites do not intersect with the sites of the first group of subsurface laser damage sites formed within the non-overlapping areas. One or more additional groups of subsurface laser damage sites may then be formed and distributed among the same first and second non-overlapping areas of the crystalline material. Although first and second areas are described, it will be appreciated that any suitable number of non-overlapping areas may be defined (e.g., three, four, five, six, or more areas). In certain embodiments, such areas may not only be completely non-overlapping, but may also be spaced (e.g., laterally spaced) from one another in a non-contacting relationship.

[0109] 20A is a top plan view of a crystalline material substrate 150 showing first, second, and third non-overlapping areas 150A-150C in which laser damage regions may form. The first area 150A is highlighted to highlight the boundaries between the first to third areas 150A-150C. and third area 150C are shaded for illustrative purposes, it will be appreciated that an actual crystalline material substrate 150 will typically be a uniform color. Each area 150A-150C contacts a portion of the primary flat 150' of substrate 150. Although three areas 150A-150C are shown in FIGS. 20A-20D, any suitable number of areas is contemplated, such as two, three, four, five, six, or more, and such areas may be arranged in any suitable configuration, e.g., in a one-dimensional array, in a two-dimensional array, as multiple sectors (e.g., wedge-shaped sectors) extending from a central point, etc.

[0110] FIG. 20B is a top plan view of the crystalline material substrate 150 of FIG. 20A after forming a first plurality of subsurface laser damage regions 151 in the first area 150A through the third area 150C. As shown, the laser damage regions 151 are provided as substantially parallel lines that are substantially perpendicular to the primary flat 150′ of the substrate 150. A plurality of laser damage regions 151 are provided in each of the first through third areas 150A through 150C. Although not shown in FIG. 20B, it will be appreciated that laterally extending cracks (as shown in FIG. 11B) may emanate from the laser damage regions 151, but that these may preferably not connect adjacent laser damage regions 151. In certain embodiments, the subsurface laser damage regions 151 of the plurality of subsurface laser damage regions 151 may be formed in the first area 150A, then in the second area 150B, and finally in the third area 150C.

[0111] FIG. 20C is a schematic top plan view of the crystalline material substrate 150 of FIG. 20B after forming the second plurality of subsurface laser damage regions 152 within the first through third areas 150A through 150C. As shown, the laser damage regions 152 of the second plurality of subsurface laser damage regions 152 are provided as substantially parallel lines that are substantially perpendicular to the primary flat 150′, providing a plurality of laser damage regions 152 within each of the first through third areas 150A through 150C. Additionally, each laser damage region 152 of the second plurality of subsurface laser damage regions 152 is substantially parallel to the first plurality of subsurface laser damage regions 151. Although not shown in FIG. 20C, it will be appreciated that cracks may occur extending laterally from each laser damage region 151, 152, although such cracks preferably do not connect adjacent laser damage regions 151, 152. In certain embodiments, the subsurface laser damage regions 152 of the plurality of subsurface laser damage regions 152 can be formed in the same order as the first subsurface laser damage regions 151 (e.g., the subsurface laser damage regions 152 can be formed in the first area 150A, then in the second area 150B, and finally in the third area 150C). In this manner, the laser damage regions 152 of the second plurality of subsurface laser damage regions 152 are distributed among the laser damage regions 151 of the first plurality of subsurface laser damage regions 151.

[0112] 20D is a top plan view of the crystalline material substrate of FIG. 20C after forming a third plurality of subsurface laser damage regions 153 within the first area 150A to the third area 150C. As shown, the laser damage regions 153 of the third plurality of subsurface laser damage regions 153 are provided as substantially parallel lines substantially perpendicular to the primary flat 150′, and a plurality of laser damage regions 153 of the third plurality of subsurface laser damage regions 153 are provided within each of the first to third areas 150A to 150C. Each laser damage region 153 of the third plurality of subsurface laser damage regions 153 may be substantially parallel to the first plurality of subsurface laser damage regions 151 and the second plurality of subsurface laser damage regions 152. The subsurface laser damage pattern provided by the first through third subsurface laser damage regions 151-153 defines a plurality of three-line groups 154, which are spaced apart by an inter-group spacing 154' that exceeds the spacing between adjacent laser damage regions 151-153 in each of the three-line groups 154. 20C, it will be appreciated that laterally extending cracks may develop from each of the laser damage regions 151-153, which may extend laterally between all of the laser damage regions 151-153 (as shown in FIG. 11D) and facilitate subsequent spalling of the upper portion of the substrate 150 from the remainder of the substrate 150. In certain embodiments, the subsurface laser damage regions 153 of the plurality of subsurface laser damage regions 152 may be formed in the same order as the first subsurface laser damage region 151 and the second subsurface laser damage region 152 (e.g., the subsurface laser damage regions 153 may be formed in the first area 150A, then in the second area 150B, and finally in the third area 150C). In this manner, the laser damage regions 153 of the third plurality of subsurface laser damage regions 153 are distributed between the laser damage regions 151, 152 of the first plurality of subsurface laser damage regions 151 and the second plurality of subsurface laser damage regions 152.

[0113] [Parallel processing and / or laser beam splitting] In certain embodiments, multiple regions of a substrate can be processed simultaneously to form subsurface laser damage in multiple substrate regions for the purpose of increasing tool throughput, and / or multiple substrates can be placed in a single tool for simultaneous or substantially simultaneous laser processing. In certain embodiments, the output beam of a single laser can be split into multiple beams using one or more beam splitters, and individual beams of these beams can be delivered to either different substrates or different areas of a single substrate to form subsurface laser damage therein using the methods disclosed herein. In certain embodiments, multiple lasers can be used to simultaneously deliver beams to multiple substrates or multiple areas of a single substrate to form subsurface laser damage therein using the methods disclosed herein.

[0114] 21 is a schematic top plan view of a holder 163 of a laser processing apparatus arranged to hold four substrates 155A-155D on which subsurface laser damage may be formed using one or more lasers. As shown, each substrate 155A-155D includes a subsurface laser damage pattern defined thereon, such pattern including a first, second, and third plurality of substantially parallel lines 156-158. The three laser damage patterns combine to form a plurality of three-line groups 156 that are separated from one another by inter-group spacings 160 that exceed spacings 161, 162 between adjacent lines in each three-line group 159. In certain embodiments, the first substrate 155A and the third substrate 155C may have a laser damage pattern formed thereon by a first laser or a first split laser beam portion, and the second substrate 155B and the fourth substrate 155D may have a laser damage pattern formed thereon by a second laser or a second split laser beam portion. In certain embodiments, the holder 163 carrying the substrates 155A-155D is configured to move (e.g., in two (x, y) lateral directions), while one or more lasers and / or their focusing optics are constrained from moving in the lateral directions (but may move vertically (z)).

[0115] FIG. 22A is a schematic top plan view of a single substrate 164 being processed with a laser beam split into multiple portions to simultaneously form subsurface laser damage regions in multiple areas of the substrate 164 according to a first subsurface laser damage pattern. As shown, the substrate 164 includes multiple areas 164A-164C (e.g., similar to areas 150A-150C depicted in FIGS. 20A-20C). A first laser damage formation step includes applying two split laser beam portions to simultaneously form laser damage regions 165' in the first area 164A and the second area 164B. The substrate 164 can be indexed laterally with respect to the laser (e.g., in the direction opposite to the right-pointing arrow) and a next laser damage formation step includes applying two split laser beam portions to simultaneously form laser damage regions 165' in the first area 164A and the second area 164B. The process includes applying two split laser beam portions to simultaneously form laser damage regions 165'' in first area 164A and second area 164B. The process is repeated to form additional laser damage regions 165''', 165'''' in first area 164A and second area 164B, and ultimately to form a first subsurface laser damage pattern over first, second, and third areas 164A-164C. The process may then be repeated to form second and third subsurface laser damage patterns, respectively, interspersed with the first subsurface laser damage pattern. Using the first and second split laser beam portions, a subsurface laser damage pattern distributed across substrate 164 can be formed in half the time it would take to form the pattern with a single, unsplit laser beam. FIG. 22B is a schematic top plan view of two substrates 166A, 166B supported by a holder 168 being processed with a laser beam split into two portions to simultaneously form subsurface laser damage in accordance with at least one subsurface laser damage pattern in both substrates 166A, 166B. A first laser damage formation step includes applying the two split laser beam portions to simultaneously form laser damage regions 167' in the first substrate 166A and the second substrate 166B. The holder carrying the substrates 166A, 166B can be indexed laterally relative to the laser (e.g., in the direction opposite to the right-pointing arrow) and a next laser damage formation step includes applying the two split laser beam portions to simultaneously form laser damage regions 167'' in the first substrate 166A and the second substrate 166B. This process is repeated to form additional laser damage regions 167'', 167'''' in the first substrate 166A and the second substrate 166B, and ultimately to form a first subsurface laser damage pattern over the first substrate 164A and the second substrate 166B.The process may then be repeated to form second and third subsurface laser damage patterns in substrates 166A, 166B, respectively, interspersed with the first subsurface laser damage pattern.

[0116] [Formation of overlapping subsurface laser damage of different depths] In certain embodiments, a first subsurface laser damage can be formed within the crystalline material substrate, centered at a first depth, and an additional subsurface laser damage can be formed within the substrate, centered at a second depth, where the additional subsurface laser damage is substantially aligned with the first subsurface laser damage and where a vertical extension of at least a portion of the additional subsurface laser damage overlaps a vertical extension of at least a portion of the first laser damage. Again, one or more subsequent passes configured to impart laser damage of different depths can be added on top of one or more prior passes to provide subsurface laser damage with overlapping vertical extensions. In certain embodiments, the addition of overlapping subsurface damage can be in response to a determination (e.g., by optical analysis) prior to fracturing that one or more prior subsurface laser damage formation steps are incomplete. In certain embodiments, the difference in laser focus depth between the first and second laser damage patterns for forming a single thickness reduction portion of the substrate (e.g., one wafer) can be in the range of 1 to 10 microns, or 2 to 8 microns, or 2 to 6 microns. The formation of overlapping subsurface laser damage at different depths may be performed in conjunction with any other method step herein, including (but not limited to) the formation of multiple, dispersed subsurface laser damage patterns.

[0117] 23A is a schematic cross-sectional view of a crystalline material substrate 170 including a first subsurface laser damage pattern 173 centered at a first depth relative to a first surface 171 of the substrate 1770, the subsurface damage pattern 173 being created by focused laser radiation 179. The first subsurface laser damage pattern 173 is located opposite the first surface 171. 23A after formation of a second subsurface laser damage pattern 175 centered at the second depth and aligned with the first subsurface laser damage pattern 173, such that the vertical extension 176 of the second damage pattern 175 overlaps the vertical extension 174 of the first damage pattern 173 at a damage overlap region 177. In certain embodiments, subsequent fracture of the crystalline material 170 can be performed along or through the damage overlap region 177.

[0118] [Formation of non-overlapping subsurface laser damage of different depths] In certain embodiments, subsurface laser damage lines may be formed at various depths in the substrate without being aligned with other (e.g., previously formed) subsurface laser damage lines and / or without overlapping vertical extension features of the first and subsequent laser damage. In certain embodiments, the distributed pattern of subsurface laser damage may include groups of laser lines, different groups being focused at different depths relative to the surface of the substrate. In certain embodiments, the focused depth of the laser radiation within the substrate differs between different groups of laser lines (e.g., at least two different groups of the first and second groups, the first through third groups, the first through fourth groups, etc.) by a distance in the range of about 2 microns to about 5 microns (i.e., about 2 μm to about 5 μm).

[0119] [Laser tool calibration] One of the major contributors to kerf loss is subsurface laser damage, which is located below the main spallation area on the ingot face. In general, increasing subsurface laser damage increases kerf loss. One possible cause of increased subsurface laser damage is the inability to fully compensate the optical properties of the crystalline material.

[0120] In certain embodiments, a laser calibration may be performed each time a crystalline material substrate (e.g., an ingot) is fed into the laser tool prior to the formation of subsurface laser damage in the crystalline material substrate. Such a calibration may utilize a variable height adjustment to achieve an initial condition where the best focus point of the laser beam is formed on the upper surface of the crystalline material substrate, and then the aperture or correction collar of the laser tool may be adjusted to correspond to the desired depth of the formation of subsurface laser damage in the crystalline material depending on the next condition.

[0121] [Wafer photo showing the doping regions (also known as doping rings)] FIG. 24A is a perspective photograph of a SiC wafer 180 after separation from a carrier (i.e., a thermoplastic adhesive bonded sapphire carrier 181 shown in FIG. 24B) using the thermally induced fracturing method described herein. Both the wafer 180 and carrier 181 have a diameter of 150 mm. No wafer breakage was observed after thermally induced fracturing. FIG. 24C is a partially inverted version of the SiC wafer photograph of FIG. 24A to highlight the contrast between the central doping ring 182 and the outer annular portion 183 of the SiC wafer 180. FIG. 24D shows the image of FIG. 24C annotated with a dotted oval to indicate the boundary between the central doping ring 182 and the outer annular portion 183 of the SiC wafer 180. The doping ring 182 represents a region of high doping concentration relative to the outer annular portion 183 of the SiC wafer. Since doped semiconductor materials such as SiC exhibit enhanced absorptivity of IR wavelengths, it may be beneficial to increase the laser power in the doped ring 182 compared to the outer annular portion 183 when attempting to form subsurface laser damage in a SiC wafer. In certain embodiments, the presence of a condition indicative of non-uniform doping of the crystalline material across at least a portion of the surface of the substrate can be detected, for example, by detecting a change in optical reflectance or absorptance by optical means to determine the presence of at least one first doped region and at least one second doped region (e.g., the doped ring 182 and the outer annular portion 183). The non-uniform doping of the crystalline material across at least a portion of the surface of the substrate can then be detected. In response to detecting a condition indicative of a first average power of laser radiation during formation of the subsurface laser damage pattern, the laser power can be varied to provide a first average power of laser radiation when forming the subsurface laser damage in the first doped region (e.g., doping ring 182) and to provide a second average power of laser radiation when forming the subsurface laser damage in the second doped region (e.g., outer annular portion 183), the first and second average power levels being different from one another.

[0122] [Schematic of an ingot with doping ring] 25 is a schematic cross-sectional side view of a SiC ingot 184 grown on a seed crystal 185, showing a generally cylindrical doped region 187 extending upward from the seed crystal 185 (at a first or bottom surface 185' of the ingot 184) along a central portion of the ingot 184 through its entire thickness, with the doped region 187 residing at a second or top surface 186' of the ingot 184. The doped region 187 is laterally surrounded by an undoped (e.g., lightly doped or unintentionally doped) region 186 that is generally annular in shape. A thin cross-sectional portion 189 of the ingot 184 taken between the first surface 185' and the second surface 186' may define a wafer 189A as shown in FIG. Wafer 189A includes a central doped region 187 and a generally annular shaped undoped region 186 bounded in part by a primary flat 189'. In certain embodiments, wafer 189A can be produced from ingot 184 using a laser assisted dicing method as described herein.

[0123] 26 depicts the size (e.g., width or diameter) of the doped regions 187 as being substantially constant throughout the thickness of the ingot 184, the inventors have determined that the size of the doped regions may vary with vertical position in the ingot (e.g., typically with a larger width or diameter closer to the seed and smaller the distance away from the seed). It has also been determined that the amount of doping within the doped regions may vary with vertical position in the ingot.

[0124] FIG. 27 is a schematic cross-sectional side view of a SiC ingot 184A grown on a seed crystal 185A, showing a frustoconical doped region 187A extending upward from the seed crystal 185A (at a first or bottom surface 185A' of the ingot 184A) along a central portion of the ingot 184A through its entire thickness. As shown, the doped region 187A is present at a second or top surface 186A' of the ingot 184A, but the width or diameter of the doped region 187A is smaller at the second surface 186A' than at the first surface 185A'. The doped region 187A is laterally surrounded by an undoped (e.g., lightly doped or unintentionally doped) region 186A that is generally annular in shape. In certain embodiments, the doped region 187A may have a width and doping level that varies with vertical position relative to the seed crystal 185A.

[0125] The inventors have also determined that when a vicinal (e.g., offcut at a non-parallel angle to the c-plane) seed is used for growing the SiC ingot, the lateral location and shape of the doped regions may be different compared to the configuration shown in Figure 27. For example, when a vicinal seed is used, the doped regions may be oval in shape rather than circular and / or may be laterally offset relative to the center of the ingot.

[0126] 28 is a schematic cross-sectional side view of a SiC ingot 184B grown on a vicinal (e.g., off-cut) seed crystal 185B, showing a frustoconical shaped doped region 187B extending upwardly from the seed crystal 185B at a point offset from the center of the seed crystal 185B through the entire thickness of the ingot 184B. As shown, doped region 187B resides on a second or top surface 186B′ of the ingot 184B, but is not shown in FIG. The width or diameter of doped region 187B is smaller at second surface 186B' than at first surface 185B'. Doped region 187B may have a generally oval shape when viewed from above. Doped region 187B is laterally surrounded by undoped (e.g., lightly doped or unintentionally doped) regions 186B. In certain embodiments, doped region 187B may have a shape, width, and / or doping level that varies with vertical position relative to seed crystal 185B.

[0127] [Enlarged wafer photo] FIG. 29 is a perspective photograph of the Si face of a SiC wafer that has been separated from an ingot by a process involving subsurface laser damage formation and subsequent separation, with the inset (top right) depicting the intentionally separated fragment of the SiC wafer, with the edge depicted in a subsequent scanning electron microscope (SEM) image.

[0128] FIG. 30A is a 45× magnified SEM image of a portion of the SiC wafer fragment of FIG. 29 taken at a tilt angle of 15 degrees, with superimposed arrows indicating the orientation of the [1-100] and [11-20] crystal planes. The laser lines are perpendicular to the [11-20] direction and are spaced approximately 250 microns apart. FIG. 30B is a 1,300× magnified SEM image of a portion of the SiC wafer fragment of FIG. 29 taken at a tilt angle of 15 degrees. FIG. 30C is a 350× magnified SEM image of a portion of the SiC wafer fragment of FIG. 29 taken at a tilt angle of 15 degrees. As shown in FIG. 30C, the off-axis cleavage planes correlate somewhat with the laser spacing, but are not consistent across the wafer surface. This may be at least partially due to variations in the laser line position relative to the cleavage planes. In this wafer, spallation was initiated at the polycrystalline introductory location.

[0129] Figure 30D is a 100x magnification SEM image of a portion of the SiC wafer fragment from Figure 29 taken at a 2 degree tilt angle. Figure 30E is a 1,000x magnification SEM image of a portion of the SiC wafer fragment from Figure 29 taken at a 2 degree tilt angle. Figures 30D and 30E show that the laser damage is fairly shallow compared to the surface features along the spallation region. The variability of the resulting spallation damage can be seen, especially in the central portion of Figure 30E.

[0130] Figure 31A is a confocal laser scanning microscope image of a small central portion of the SiC wafer of Figure 29, with superimposed crosshairs marking the location of the "trench" created by the laser scan. Figure 31B is a plot of the surface profile of a portion of the SiC wafer of Figure 31A. With reference to Figure 31B, the variability of the laser line position relative to the SiC cleaved plane can be observed.

[0131] FIG. 32A is a confocal laser scanning microscope image of a larger portion near the top of the SiC wafer of FIG. 29 (at the time of image capture), with superimposed crosshairs marking the location of the "trenches" or lines formed by the laser scan. FIG. 32B is a plot of the surface profile of a portion near the top of the SiC wafer of FIG. 32A. In FIG. 32B, a first pair of lines corresponding to laser damage (represented as crosshairs in oval 200) are separated by a depth of more than 30 microns, and a second pair of lines corresponding to laser damage (represented as crosshairs in oval 201) are separated by a depth of more than 20 microns. FIGS. 32A and 32B show irregular spacing between the laser lines, with the individual lines in the first pair of lines (in oval 200) being closer to each other and the individual lines in the second pair of lines (in oval 201) being closer to each other, compared to the other laser damage lines depicted.

[0132] FIG. 33A is a confocal laser scanning microscope image of a larger section near the bottom (at the time of image capture) of the SiC wafer of FIG. 29, with the superimposed crosshairs marking the location of the "trench" created by the laser scan. FIG. 33B is a confocal laser scanning microscope image of the SiC wafer of FIG. Figure 33B is a plot of the surface profile near the bottom of the wafer showing the lateral distance variation between adjacent pairs of laser damage lines, one pair separated by 334 microns and another pair separated by 196 microns, with a maximum depth variation of 13 microns.

[0133] [Substrate fracture after subsurface laser damage formation] As previously discussed herein, subsurface laser damage may be created in a crystalline material substrate to prepare the substrate for fracture to remove at least one thin layer (e.g., a wafer) of crystalline material from the substrate. Examples of specific fracture techniques (e.g., cooling a CTE-mismatched carrier bonded to the substrate, subjecting the substrate to ultrasound, or applying a bending moment to a carrier attached to the substrate) are described herein below, but it will be appreciated that the various subsurface laser damage creation techniques described herein may be used in any suitable fracture technique, including fracture techniques already known to those of skill in the art.

[0134] [Cooling spallation of rigid supports with support / substrate CTE mismatch] 34A-34F illustrate steps of a carrier-assisted method for fracturing a crystalline material according to one embodiment of the present disclosure that utilizes a rigid carrier having a larger CTE than the crystalline material bonded to the crystalline material. FIG. 34A is a schematic cross-sectional side view of a rigid carrier 202 having a layer of adhesive material 198 bonded to a first surface 203 of the rigid carrier 202, and having a second surface 204 opposite the first surface 203.

[0135] FIG. 34B is a schematic cross-sectional view of an assembly 188 including the rigid carrier 202 and adhesive material 198 of FIG. 34A bonded to a crystalline material substrate 190 having a subsurface laser damage region 196 therein. The rigid carrier 202 has a larger diameter or lateral extension than the substrate 190. The substrate 190 includes a first surface 192 proximate to the adhesive material 198 and an opposing second surface 194, with the subsurface laser damage 196 being closer to the first surface 192 than to the second surface 194. The adhesive material 198 extends between the first surface 192 of the crystalline substrate 190 and the first surface 203 of the rigid carrier 202. The adhesive material 198 can be cured according to the requirements of the selected bonding method (e.g., thermal compression adhesive bonding, compression UV bonding, chemically reactive bonding, etc.). In certain embodiments, a second carrier (not shown) may be bonded to the second surface 194 of the substrate 190, where the second carrier is no wider than the substrate 190 and / or has a CTE match with the substrate 190, although these are optional.

[0136] 34C is a schematic cross-sectional view of the assembly of FIG. 34B after positioning the second surface 204 of the rigid carrier 202 on a support surface 208 of a cooling device in the form of a cooled chuck 206 configured to receive a cooling fluid. Contact between the rigid carrier 202 and the cooled chuck 206 transfers heat from the rigid carrier 202 to the cooled chuck 206. During the cooling process, the rigid carrier 202 will contract laterally more than the crystalline material substrate 190 due to the carrier 202 having a larger CTE than the substrate 190, which results in the carrier 202 exerting a shear stress on the substrate 190. Due to the presence of a subsurface laser damage 196 near the adhesive layer 198 bonding the rigid carrier 202 to the substrate 190, the exertion of the shear stress on the substrate 190 will cause the crystalline material to fracture along or adjacent the subsurface laser damage region 196.

[0137] In certain embodiments, the cooled chuck 206 has a diameter smaller than the diameter of the rigid carrier 202. The cooled chuck 206 may be supplied with a cooling liquid, but it is not necessary for the rigid carrier 202 to reach liquid nitrogen temperatures (-160°C) to successfully complete the thermally induced fracturing of the crystalline material substrate 190. A preferred separation for fracturing a single crystal SiC material supported by a single crystal sapphire substrate is performed using a cooled chuck maintained at -70°C. Results have been obtained. Such temperatures can be maintained using a variety of cooling fluids, such as liquid methanol (which remains fluid above its freezing point of -97°C) received from a two-phase pumped evaporative cooling system. Favorable separation results have also been obtained by cooling the carrier, adhesive, and substrate in a freezer maintained at -20°C, in which case such temperatures can be maintained using a single-phase evaporative cooling system. The ability to use a single-phase or two-phase pumped evaporative cooling system rather than liquid nitrogen greatly reduces operating costs.

[0138] 34D is a schematic cross-sectional view of the remaining portion of the crystalline material substrate 190A separated from the bonded assembly including the rigid carrier 202, the adhesive material 198, and the portion 210 of the crystalline material removed from the substrate 190A after fracturing of the crystalline material along the subsurface laser damage region. The remaining portion of the crystalline material substrate 190A is bounded by a new first surface 193 (with residual laser damage 196A) opposite the second surface 194. Correspondingly, the removed portion 210 of the crystalline material is bounded by a new second surface 212 (with residual laser damage 196B) opposite the first surface 192. The bonded assembly 215 including the rigid carrier 202, the adhesive material 198, and the removed portion 160 of the crystalline material can then be retrieved from the cooled chuck 206.

[0139] FIG. 34E is a schematic cross-sectional view of the bonded assembly 215 of FIG. 34D after retrieval from the water-cooled chuck 206. Maintaining the removed portion of crystalline material 210 attached to the rigid carrier 202 provides mechanical support for the removed portion of crystalline material 210, which advantageously enables one or more surface processing steps (e.g., grinding, polishing, etc.) to be performed on the new surface 212 to remove residual laser damage 196B and achieve a desired thickness of the crystalline material 210 (e.g., via grinding and optional subsequent chemical mechanical planarization and / or polishing steps). In certain embodiments, the laser damage removal and thinning may include successive grinding / polishing steps, as well as any suitable polishing and cleaning steps to prepare the new surface 212 for subsequent steps (e.g., surface implantation, laser marking (e.g., along the wafer flat), formation of an epitaxial layer, metallization, etc.).

[0140] 34F is a schematic cross-sectional view of the removed portion 210 of crystalline material supported by the upper surface 218 of a heated vacuum chuck 216, with the rigid carrier 202 and adhesive material 198 having been translated laterally away from the removed portion 212 of crystalline material following high temperature softening and release of the adhesive material 198. That is, the heated vacuum chuck 216 may be heated to a temperature sufficient to soften and / or flow the adhesive material 198 such that application of an external shear stress to the second surface 204 of the rigid carrier 202 can cause the rigid carrier 202 to translate laterally away from the removed portion 212 of crystalline material, which is temporarily held in place by the heated vacuum chuck 216. Thereafter, operation of the heated vacuum chuck 216 may be discontinued, and the removed portion 212 of crystalline material will embody a self-supporting material. If desired, the first surface 203 of the rigid carrier 202 can be cleaned to remove any residue of adhesive 198, and the rigid carrier 202 can optionally be reused for another fracturing step. The removed crystalline material can then be used as a growth substrate for growing one or more epitaxial layers and conductive metal layers to form a device wafer, which is singulated to form individual semiconductor devices.

[0141] [Fracture induced by ultrasonic energy] Another method for inducing spallation along the laser-induced subsurface damage zone of a crystalline material bonded to a rigid carrier involves applying ultrasonic energy to the crystalline material while in the bonded state. FIG. 35 shows a crystalline material bonded to a rigid carrier 20 with an intervening adhesive material 198A. 2A, the assembly 188A is disposed in a liquid bath 225 of an ultrasonic generator device 220. The device 220 further includes a container 222 disposed in contact with an ultrasonic generating element 224, the container 222 containing the liquid bath 225. The presence of the rigid carrier 202A can reduce or eliminate breakage of the crystalline material 190A when subjected to ultrasonic energy, especially if residual stresses remain between the rigid carrier 202A and the crystalline material 190A (e.g., due to CTE mismatch) prior to separation. Such residual stresses can reduce the amount of ultrasonic energy required to initiate fracture of the crystalline material, thereby reducing the likelihood of material breakage.

[0142] [Mechanical force-induced fracture] In certain embodiments, fracture of a crystalline material bonded to a rigid carrier may be facilitated by (i) application of a mechanical force (e.g., optionally localized at one or more locations) proximate at least one edge of the carrier. Such force may impart a bending moment to at least a portion of the carrier, which bending moment may be transferred to the subsurface laser damage region to initiate fracture. Exemplary embodiments are shown in Figures 36A-36C.

[0143] 36A-36C are schematic cross-sectional views illustrating steps for fracturing a crystalline material substrate 236 with subsurface laser damage 233 by applying a mechanical force proximate to one edge of a carrier 238 to which the substrate 236 is bonded. The bonded assembly includes a crystalline material substrate 236 with a subsurface laser damage region 233 bonded between rigid carriers 238, 238'. Each rigid carrier 238, 238' includes a laterally projecting tab portion 239, 239' aligned with a flat 235 of the substrate 236 to provide a locally enlarged border area defining a recess 231 into which a tool 219 can be inserted. FIG. 36A shows the condition prior to insertion of the tool 219 into the recess 191. FIG. 36B shows the state after insertion of the tool 219 into the recess, with the tool 216 tilted upward, which exerts a prying force in a direction that tends to promote separation between the rigid carriers 238, 238', which exerts a bending moment M on at least one of the carriers 238. In a particular embodiment, the substrate 236 comprises a material having a hexagonal crystal structure (e.g., 4H-SiC), and the bending moment M is oriented within ±5 degrees of perpendicular to the [11-20] direction (or equivalently, within ±5 degrees of parallel to the [1-100] direction). FIG. 36C shows the state after initial fracture of the crystalline substrate 236 along the subsurface laser damage region 233, where an upper portion 236 of the crystalline material remains bonded to the upper carrier 238 and a lower portion 236B of the crystalline material remains bonded to the lower carrier 238', with the upper carrier 238 tilted upward relative to the lower carrier 238'. Such fracturing results in a first bonded assembly 229A (including upper carrier 238 and upper portion of crystalline material 236A) separated from a second bonded assembly 229B (including lower carrier 238' and lower portion of crystalline material 236B). In certain embodiments, a mechanical force can be applied proximate both edges of the rigid carrier to which the substrate is bonded to promote fracturing of the subsurface laser damaged crystalline material bonded to the carrier.

[0144] It is noted that combining two or more fracturing techniques (e.g., CTE mismatch and ultrasonically induced fracturing, or CTE mismatch and mechanical action induced fracturing, or ultrasonically induced and mechanical action induced fracturing) is specifically contemplated. In certain embodiments, the liquid in the ultrasonic bath can be cooled before or during application of ultrasonic energy. The amount of mechanical force required to complete the fracturing may be affected by the CTE difference between the substrate and the carrier. In certain embodiments, CTE difference and mechanical force can be combined. If the CTE difference between the carrier and the substrate is small or nonexistent (i.e., the CTEs are matched), a greater mechanical force may be required to complete the fracturing. Conversely, if the CTE mismatch is small or nonexistent, a greater mechanical force may be required to complete the fracturing. If the gap is large, less or no mechanical force may be required to complete the fragmentation.

[0145] [Device wafer division process] In certain embodiments, the crystalline material may be subjected to laser-assisted and carrier-assisted separation methods after the crystalline material has been formed with at least one epitaxial layer (and optionally at least one metal layer) as part of an operational semiconductor-based device. Such device wafer separation processes are particularly advantageous because they can increase the yield of crystalline material (and reduce waste) by significantly reducing the need to grind away substrate material after device formation.

[0146] 37A-37O are schematic cross-sectional views illustrating steps of a device wafer separation process according to which a thick wafer is fractured from a crystalline material, at least one epitaxial layer is grown on the thick wafer, the thick wafer is fractured to form first and second bonded assemblies each including a carrier and a thin wafer separated from the thick wafer, the first bonded assembly including at least one epitaxial layer as part of an operational semiconductor-based device.

[0147] FIG. 37A illustrates a crystalline material substrate 240 having a first surface 241 and a subsurface laser damage 243 disposed at a depth relative to the first surface. FIG. 37B illustrates the substrate 240 of FIG. 37A after adding an adhesive material 244 to cover the first surface 241. FIG. 37C illustrates the items depicted in FIG. 37B after bonding a rigid carrier 246 to the substrate 240 using the adhesive material 244. FIG. 37D illustrates the items of FIG. 37D after fracturing the substrate 240 (e.g., using one or more methods disclosed herein) along the subsurface laser damage 243, resulting in a remaining portion of the substrate 240 separated from the bonded assembly, including the carrier 246, the adhesive material 244, and the crystalline material portion (e.g., thick wafer) 242 removed from the substrate 240. In certain embodiments, the thick wafer 242 may have a thickness in the range of approximately 350 to 750 microns. The exposed surface 243A of the thick wafer 242 and the exposed surface 243B of the remaining portion of the substrate 240 may exhibit surface irregularities, which can be reduced by surface processing steps such as grinding, CMP, polishing, etc. FIG. 37E shows the thick wafer 242 after debonding and removal from the carrier 246, where the thick wafer 242 includes a vertical edge profile. The vertical edges of the wafer easily fracture during wafer handling, resulting in unacceptable edge chips and particles. To reduce the risk of breakage, the wafer edge can be edge ground to create a non-vertical wafer edge with a chamfered or rounded edge. FIG. 37F shows the thick wafer 242 supported between opposing upper and lower gripping portions 248A and 248B of a rotating stage adjacent to a rotating profile grinding tool 249 having a concave cutting surface 249A (e.g., impregnated with diamond particles) configured to impart a rounded edge profile 247 to the thick wafer 242. FIG. 37G shows the thick wafer 242 after edge grinding (also known as edge profiling), where the thick wafer includes a rounded edge 247 that provides an interface between the first wafer surface 251 and the second wafer surface 252.

[0148] FIG. 37H shows the thick wafer 242 of FIG. 37G after growing one or more epitaxial layers 253 on or over the first surface 251 of the thick wafer 251. Due to the incompatibility of adhesives with the high temperatures inherent in epitaxy, the carrier shown in FIG. 37D is absent. FIG. 37I shows the structure 37H after forming conductive (e.g., metal) contacts 254 on the epitaxial layers 253 to form at least one operational semiconductor device, with the thick wafer 242 still having rounded edges 247. Conventionally, grinding is performed against the second surface 252 to remove the thick wafer 242 from the second surface 252 until it is suitable for the resulting device. This is typically done to thin the wafer to an appropriate thickness (e.g., 100 to 200 microns for a Schottky diode or MOSFET). The techniques disclosed herein reduce the need for wafer grinding and instead utilize laser-assisted and carrier-assisted separation to remove portions of the thick wafer and provide a surface finish that can be used to fabricate another operational semiconductor device.

[0149] The inventors have found that the presence of rounded edges 247 on the thick wafer 242 inhibits control of the formation of subsurface laser damage proximate the edges 247 because the rounded profile adversely affects laser focus and depth control. To address this issue, the rounded edges 247 of the thick wafer 242 can be removed prior to further laser processing. FIG. 37J shows the structure of FIG. 37I having been ground with an edge grinder 256 to grind away the rounded edges 247 and provide a substantially vertical edge 255 extending between the first surface 251 and the second surface 252 of the thick wafer 242, with the epitaxial layer 253 and contacts 254 disposed on the first surface 251.

[0150] FIG. 37K shows the structure of FIG. 37J after adding a temporary adhesive material 257 covering the first surface 251, epitaxial layer 253, and contacts 254 of the thick wafer 242 in preparation for receiving and bonding a first carrier. FIG. 37L shows the structure of FIG. 37K after adding a first carrier 258 over the temporary adhesive material 257 and after forming subsurface laser damage 259 in the thick wafer 242 by directing focused laser radiation through the second surface 252 of the thick wafer 242. FIG. 37M shows the structure of FIG. 37L after bonding a second rigid carrier 260 to the second surface 252 of the thick wafer 242 in proximity to the subsurface laser damage 259. For separation purposes, the second rigid carrier 260 serves as a front carrier intended to remove a portion (i.e., a layer) of the thick wafer 242.

[0151] In certain embodiments, laser radiation can be applied to a freestanding thick device wafer and the first and second carriers can be bonded to the front and back surfaces of the thick wafer substantially simultaneously, in certain embodiments, an adhesive material can be applied onto one or both of the front and back surfaces of the carrier or wafer.

[0152] 37N illustrates the items of FIG. 37M after applying at least one fracturing process disclosed herein to fractur e the thick wafer 242 along the subsurface laser damage 259 to obtain a first bonded subassembly 262A and a second bonded subassembly 262B. The first bonded subassembly 262A includes the first thin wafer portion 242A (separated from the thick wafer 242 of FIG. 37M), the epitaxial layer 253, the contacts 254, the temporary adhesive material, and the first carrier 258. The second bonded subassembly 262B includes the second thin wafer portion 242B (separated from the thick wafer 242 of FIG. 37M) and the second carrier 260. The exposed surfaces 259A and 259B of the thin wafer portions 242A and 242B may exhibit surface irregularities due to laser damage and / or spallation, which can be reduced by conventional surface preparation steps (e.g., grinding, CMP, and / or polishing). FIG. 37O illustrates an operational semiconductor device 264 obtained from the first bonded subassembly 262A by removing the temporary adhesive 257 and the first carrier 258. Such figure also illustrates the second thin wafer portion 242B after removal of the second carrier 260 to prepare the second thin wafer portion 242B for further processing (e.g., epitaxial growth).

[0153] Exemplary methods involving reuse of carrier wafers FIG. 38 is a flow chart that generally illustrates steps of a method according to the present disclosure. Starting from the top, a laser 266 can focus laser radiation below a first surface 272 of a thick crystalline material substrate 270 (e.g., a SiC ingot) to create a subsurface laser damage region 268. A carrier wafer 224 can then be bonded to the first surface 272 of the crystalline material substrate 270, the carrier wafer 274 including a first surface 276 (proximal to the first surface 272 of the substrate 270) and a second surface 278 of the carrier wafer 274 opposite the first surface 276. Such bonding between the carrier wafer 278 and the crystalline material substrate 270 can be performed by any method disclosed herein, such as adhesive bonding or anodic bonding. Details related to anodic bonding between a crystalline material substrate and a carrier are disclosed in U.S. Patent Application Publication No. 2016 / 0189954, the contents of which are hereby incorporated by reference herein for all purposes. A fracture process as disclosed herein (e.g., cooling the CTE-mismatched carrier, applying ultrasonic energy, and / or applying mechanical forces) is then applied to fracture the crystalline material 270 along the subsurface laser damage region 218, separating the crystalline material portion 280 attached to the carrier wafer 278 from the remainder of the crystalline material substrate 270A. The newly exposed surface 282A of the remaining portion of the crystalline material substrate 270A with the residual laser damage is ground smooth, cleaned, and returned to the beginning of the process (top left in FIG. 38 ). Additionally, the newly exposed surface 284 of the removed crystalline material 280 is ground smooth while still attached to the carrier 274. The carrier wafer 274 can then be separated from the removed portion of crystalline material 280 and one or more layers can be epitaxially grown on the crystalline material 280 to form epitaxial device 280', while the carrier wafer 274 is cleaned and returned to the beginning of the process (top left of Figure 38) to allow for the removal of another relatively thin slice of crystalline material substrate 270.

[0154] FIG. 39 is a schematic cross-sectional view of a portion of the crystalline material substrate (e.g., SiC ingot) 270 of FIG. 38 showing the subsurface laser damage 268 with the expected kerf loss material region identified by the superimposed dotted line. The expected kerf loss material region 290 includes the laser damage 268 and also material 284 to be mechanically removed (e.g., by grinding and polishing) from a bottom surface 288 (e.g., Si-terminated surface) of the crystalline material portion 280 (e.g., SiC wafer) that will be separated from the substrate 270 and also material 286 to be mechanically removed (e.g., by grinding and polishing) from a top surface 282A (e.g., C-terminated) surface of the remaining portion 270A of the substrate 270. The bottom surface 288 of the crystalline material portion 280 is opposite its top surface 272. In certain embodiments, the entire kerf loss material region may have a thickness in the range of 80-120 microns such that the SiC provides sufficient substrate top surface 282A and wafer bottom surface 288 for further processing.

[0155] [Material processing using multiple grinding stations / steps] In certain embodiments, the crystalline material subjected to laser processing and spallation can be further processed with multiple surface grinding steps to remove subsurface damage and edge grinding to impart a chamfered or rounded edge profile, where the grinding steps are ordered to reduce the likelihood of imparting additional surface damage and to prepare the crystalline material wafer for chemical mechanical planarization and / or a protective surface coating is employed. Such steps can be performed, for example, using a material processing apparatus according to embodiments disclosed herein, where an exemplary apparatus includes a laser processing station, a spallation station, multiple coarse grinding stations arranged in parallel downstream of the spallation station, and at least one fine grinding station arranged downstream of the coarse grinding station. When processing wafers cut by wire sawing, it is common to perform edge grinding before surface grinding or polishing to remove wire sawing surface damage. However, it has been found by the inventors that combining edge grinding of a substrate portion (e.g., a wafer) having laser damage with spallation damage increases the likelihood of cracking the substrate portion. While we do not wish to be bound by any particular theory as to the reasons for this phenomenon, at least It is believed that if edge grinding is performed prior to any surface processing (grinding and / or polishing), the exposed cleavage planes resulting from surface fracture will make the surface more susceptible to cracking. For this reason, it has been found beneficial to perform at least some surface processing (e.g., grinding and / or polishing) prior to edge grinding.

[0156] It has been found that the rough grinding step (i.e., to remove laser damage and spallation damage along the substrate portion and the spallation surface of the bulk substrate) tends to take significantly longer to complete than the preceding laser processing and spallation steps, and significantly longer than the subsequent fine grinding step. For this reason, multiple rough grinding stations are provided in parallel to eliminate bottlenecks in the fabrication of multiple wafers from bulk crystalline material (e.g., ingots). In certain embodiments, robotic handlers may be located upstream and downstream of the multiple rough grinding stations to control the loading and unloading of substrate portions. In certain embodiments, a carrier attachment station may be provided between the laser processing station and the spallation station, and a carrier removal station may be provided upstream (either directly or indirectly) of the edge grinding station. The carrier may desirably remain attached to the substrate portion during at least some of the surface grinding steps to reduce the possibility of breakage, especially for thin substrate portions (e.g., wafers), although the carrier is preferably removed prior to edge grinding (or prior to coating the wafer with a protective coating prior to edge grinding).

[0157] In certain embodiments, the carrier bonding station can use a carrier pre-coated with a temporary bonding medium, align and press the carrier with the substrate surface, and expose the bonding medium to the necessary conditions (e.g., heat and pressure) to effect bonding between the carrier and the substrate. Alternatively, the carrier bonding station can include a coating station that can be used to coat the carrier or the substrate on demand.

[0158] FIG. 40 is a schematic diagram of a material processing apparatus 300 according to an embodiment, including a laser processing station 302, a carrier bonding station 303, a material breaking station 304, a plurality of parallel-arranged rough grinding stations 308A, 308B, a fine grinding station 312, a carrier removal station 313, and a CMP station 314. The laser processing station 302 includes at least one laser and a holder for at least one substrate arranged to receive at least one laser beam for forming subsurface laser damage in a crystalline material (e.g., an ingot). The carrier bonding station 303 is configured to bond the crystalline material (having subsurface laser damage) to at least one rigid carrier. The breaking station 304 is arranged to receive one or more assemblies (each including a substrate bonded to a rigid carrier) from the carrier bonding station 303 and to break at least one substrate along a subsurface laser damage region to remove a substrate portion (which may be similar to a wafer bonded to the carrier). Downstream of the breaking station 304, a first rough grinding station 308A and a second rough grinding station 308B are arranged in parallel, and a first robot handler 306 is provided for alternately transferring the substrate parts received from the breaking station 304 (as part of the bonded assembly) to either the first rough grinding station 308A or the second rough grinding station 308B. Downstream of the first rough grinding station 308A and the second rough grinding station 308B, a second robot handler 310 is provided for transferring the roughly ground substrate parts (as part of the bonded assembly) to a fine grinding station 312. Downstream of the fine grinding station 312, a carrier removal station 313 is provided, which serves to separate the ground substrate parts from the carrier. Downstream of the carrier removal station 313, a chemical mechanical planarization (CMP) station 314 is arranged for cleaning and preparing the substrate parts for further processing, such as epitaxial growth. The CMP station 314 is used to remove the damage remaining after precision grinding. While the fine grinding itself serves to remove damage remaining after the coarse grinding, the fine grinding itself removes damage remaining after the coarse grinding. In certain embodiments, each coarse grinding station 308A, 308B includes at least one grinding wheel having a grinding surface of less than 5000 grit, and the fine grinding station 312 includes at least one grinding wheel having a grinding surface of at least 5000 grit. In certain embodiments, each coarse grinding station 308A, 308B is configured to remove crystalline material from the crystalline material portion (e.g., wafer) at a thickness of 20 microns to 100 microns, and the fine grinding station 312 is configured to remove crystalline material from the crystalline material portion (e.g., wafer) at a thickness of 3 to 15 microns. In certain embodiments, each coarse grinding station 308A, 308B and / or the fine grinding station 312 can include multiple grinding sub-stations, with different sub-stations including grinding wheels of different grits.

[0159] The apparatus according to the embodiment of Figure 40 can be modified to accommodate edge grinding to impart a rounded or chamfered edge profile to a crystalline substrate portion, such as a wafer. Such an edge profile would reduce the risk of wafer edge breakage. Edge grinding may not be performed if the substrate portion is bonded to a carrier, and thus a carrier removal station may be located upstream (either directly or indirectly) of the edge grinding station.

[0160] FIG. 41 illustrates a material processing apparatus 320 according to an embodiment similar to that of FIG. 40 but incorporating an edge grinding station 332. The material processing apparatus 320 includes a laser processing station 322, a carrier bonding station 323, a material breaking station 324, a first robot handler 326, a plurality of parallel-arranged rough grinding stations 328A, 328B, a second robot handler 328, a carrier removal station 331, an edge grinding station 332, a fine grinding station 334, and a CMP station 336. The exemplary edge grinding station 332 may be positioned to grip the wafer between upper and lower gripping portions of a rotating stage that is positioned adjacent to a rotary grinding tool having a concave Dühring surface (e.g., as shown in FIG. 37G). Gripping the wafer in this manner may cause undesirable damage to the wafer surface (e.g., the Si-terminated surface of a SiC wafer). For this reason, the edge grinding station 332 shown in Figure 41 is positioned upstream of the precision grinding station 334 so that any surface damage imparted by the edge grinding station 332 can be removed at the precision grinding station 334. The precision grinding station 334 removes a small thickness of the wafer which may alter the rounded or chamfered edge profile produced by the edge grinding station 332, but leaves a rounded or chamfered edge profile sufficient to prevent fracture of the wafer edge.

[0161] The apparatus 320 according to FIG. 41 can be used to perform a method for processing a crystalline material wafer with a first surface having surface damage, the first surface being bounded by an edge. The method includes grinding the first surface with at least one first grinding device to remove a first portion of the surface damage, edge grinding the edge to form a chamfered or rounded edge profile after grinding the first surface with the at least one first grinding device, and grinding the first surface with at least one second grinding device to remove a second portion of the surface damage sufficiently to make the first surface suitable for further processing by chemical mechanical planarization. In a particular embodiment, the first grinding devices can be embodied in the rough grinding stations 328A, 328B, the edge grinding can be performed by the edge grinding station 332, and the second grinding device can be embodied in the fine grinding station 312. In a particular embodiment, grinding the first surface with the at least one first grinding device can be performed by the edge grinding station 332, and the second grinding device can be embodied in the fine grinding station 312. After grinding and before edge grinding the edges to form a chamfered or rounded edge profile, a carrier removal step can be performed.

[0162] In certain embodiments, a protective surface coating may be employed to reduce the likelihood of imparting additional surface damage during edge grinding and to prepare the crystalline material wafer for chemical mechanical planarization. Such a surface coating may include photoresist or any other suitable coating material and may be applied prior to edge grinding and removed after edge grinding.

[0163] FIG. 42 is a schematic diagram of an embodiment of a material processing apparatus 340 similar to the embodiment of FIG. 40 but incorporating a surface coating station 354 between the fine grinding station 352 and the edge grinding station 356, and a coating removal station 358 between the edge grinding station 356 and the CMP station 360. The material processing apparatus 340 further includes a laser processing station 342, a material breaking station 344, a first robot handler 346, a plurality of rough grinding stations 348A, 348B arranged in parallel, and a second robot handler 348 upstream of the fine grinding station 352. The coating station 354 may be configured to apply a protective coating (e.g., photoresist) by methods such as spin coating, dip coating, spray coating, or the like. The protective coating should be of sufficient thickness and robustness to absorb any damage that may be inflicted by the edge grinding station 365. In the case of SiC wafers, the Si-terminated surface may be coated with a protective coating since this is the surface on which epitaxial growth typically occurs. The coating removal station 358 may be configured to strip the coating by chemical, thermal, and / or mechanical means.

[0164] The apparatus 340 according to Fig. 42 can be used to carry out a method for processing a crystalline material wafer with a first surface having surface damage, the first surface being bounded by an edge. The method includes grinding the first surface with at least one first grinding device (e.g., rough grinding station 348A, 348B) to remove a first portion of the surface damage, thereafter grinding the first surface with at least one second grinding device (e.g., fine grinding station 352) to remove a second portion of the surface damage sufficiently to make the first surface suitable for further processing by chemical mechanical planarization, thereafter forming a protective coating on the first surface (e.g., using a surface coating station 354), thereafter edge grinding the edge (e.g., using an edge grinding station 356) to form a chamfered or rounded edge profile, and thereafter removing the protective coating from the first surface (e.g., using a coating removal station). The first surface may then be processed by chemical mechanical planarization (e.g., by CMP station 360), which prepares the first surface (e.g., the Si-terminated surface of the wafer) for surface cleaning and further processing, such as epitaxial growth.

[0165] In certain embodiments, the gripping device may be configured to hold an ingot having an end face that is non-perpendicular to the side wall to enable machining of the end face by the laser to form subsurface damage. In certain embodiments, the gripping effector may be configured to follow a sloped side wall that has a circular cross section when viewed from above. In certain embodiments, the gripping effector may include a joint to enable the gripping effector to follow the sloped side wall.

[0166] FIG. 43A is a schematic cross-sectional side view of a first gripping device 362 for holding an ingot 364 having end faces 366, 368 that are non-perpendicular to a sidewall 370, according to one embodiment. The upper end surface 366 is positioned horizontally to receive the laser beam 376. A carrier 372 is attached to the lower end surface 368, and a chuck 374 (e.g., a vacuum chuck) may hold the carrier 372. A gripping effector 378 having a non-vertical surface is provided for gripping the sidewall 370 of the ingot 364, and the gripping effector 378 is positioned at a non-perpendicular angle A1, A2 relative to the horizontal actuation rod 380. Using the gripping device 362 to hold the ingot 364 as shown (e.g., near its bottom), the upper end surface 366 and an upper portion of the sidewall 370 are available for processing using the methods disclosed herein.

[0167] FIG. 43B is a schematic cross-sectional side view of a second gripping device 362' for holding an ingot 364' having end faces 366', 368' that are non-perpendicular to a side wall 370', according to one embodiment. The upper end face 366' is arranged horizontally to receive a laser beam 376, while the lower end face 368' may have a carrier 372' attached thereto and held by a chuck 374'. To grip the side wall 370' of the ingot 364', a gripping effector 378' having a non-perpendicular face is provided, which is arranged at a non-perpendicular angle A1, A2 to a horizontal actuation rod 380'. A pivot joint 382' is provided between the actuation rod 380' and the gripping effector 378', which facilitates automatic alignment between the gripping effector 378' and the side wall 370' of the ingot 364'.

[0168] In one example, a 150 mm diameter single crystal SiC substrate (ingot) with a thickness of more than 10 mm is used as the starting material to produce a SiC wafer with a thickness of 355 microns. Laser radiation is applied through the C-terminated top surface of the SiC substrate to form subsurface laser damage. A sapphire carrier is bonded to the top surface of the SiC substrate using a thermoplastic adhesive material disclosed herein, and thermally induced spallation is performed to separate the top (wafer) portion of the SiC from the remainder of the ingot. Both the Si-terminated surface of the separated wafer portion and the C-terminated surface of the remaining ingot are coarse ground using a 2000 grit grinding wheel (e.g., metal, glassy, ​​or resin-bonded grinding wheel) to remove all visible laser and spallation damage. Both the Si-terminated surface of the separated wafer portion and the C-terminated surface of the remainder of the ingot are then precision ground (e.g., using a vitreous grinding surface) to a grit of 7000 or higher (e.g., up to 30,000 grit or higher) to obtain a smoother surface, preferably with an average roughness (Ra) of less than 4 nm, and more preferably in the range of 1-2 nmRa. A smooth surface is required for the remainder of the ingot to avoid any influence on the subsequent laser processing. The wafer shall be ready for CMP and shall be smooth enough to minimize the amount of CMP removal required, since CMP is generally the more costly process. Typical material removal during the precision grinding process to remove all residual subsurface damage from the rough grinding and any remaining laser damage (both visible and invisible to the naked eye) may be in the 5 to 10 micron thickness range. The remainder of the ingot is then returned to the laser for further processing, and the wafer is edge ground and chemical mechanical planarized (CMP) to prepare it for epitaxial growth. To avoid any risk of scratching the precision ground Si surface, an edge grinding can be performed between the rough and fine surface grinding. Material removal during CMP can be in the thickness range of about 2 microns. Total material consumed from the substrate (ingot) can be less than 475 microns. If the final wafer thickness is 355 microns, the kerf loss is less than 120 microns.

[0169] [Wafer-to-wafer thickness variability affected by laser power and crystal variations] As noted earlier in this specification, increasingly higher laser power levels are required to create sufficient laser damage to separate the crystal material such that spallation results in wafers with cross-section locations starting distal to the seed and moving progressively closer to the seed. It is possible. Using higher laser power at each successive depth when creating subsurface damage would result in unnecessary material loss and would also result in significantly larger wafer-to-wafer thickness variations due to variability in both damage depth and decomposition location relative to the laser beam waist. Such concepts can be understood with reference to Figures 44 and 45.

[0170] FIG. 44 illustrates the focusing of an incoming horizontal beam 400 in the direction of propagation by a lens 404 to a minimum width W at a downstream location 406 corresponding to the focal length f of the lens 404. f FIG. 45 is a schematic side cross-sectional view of a conventional laser focusing device forming an output beam 402 with a beam waist pattern having a minimum width at position 406 corresponding to the focal length of the lens (not shown) which then widens into a wider region 408. When the focused laser beam 402 is directed into a crystalline material (e.g., a substrate such as a SiC ingot), the crystalline material will be thermally decomposed at different threshold points (i.e., depths) depending on factors such as the laser power, the degree of absorption of the radiation by the crystalline material (which may be affected by the presence or absence of dopants and / or crystalline defects which may vary with depth (and width) position within the substrate), and the degree of focusing as a function of vertical position. Three different decomposition threshold points 410A-C are shown in FIG.

[0171] The methods and apparatus disclosed herein address the above problems by imaging a top surface of a crystalline material substrate having subsurface laser damage to detect crack-free regions within the substrate, analyzing one or more images to identify conditions indicative of the presence of crack-free regions within the substrate, and taking one or more actions in response to the analysis (e.g., upon attainment of appropriate conditions). Such actions may include performing additional laser passes at the same depth location and / or modifying the instruction set to create subsurface laser damage at the next depth location. Such methods and apparatus facilitate the production of substrate portions of uniform thickness without unnecessary material loss.

[0172] Figures 46A-C each provide plots of laser power versus sequential wafer identification (i.e., sequential wafer identification (ID) numbers from 1 to 55) obtained from three SiC ingots, with the increasing wafer ID numbers indicating greater proximity to the seed crystal in each case (i.e., slice 1 is furthest from the seed crystal). FIG. 46A shows the results for a first SiC ingot, where a first group of wafers 411A were spalled after forming subsurface laser damage at a laser power level of about 3.75 W, a second group of wafers 412A were spalled after forming subsurface laser damage at a laser power level of about 4 W, a third group of wafers 413A were spalled after forming subsurface laser damage at a laser power level of about 4.25 W, a fourth group of wafers 414A were spalled after forming subsurface laser damage at a laser power level of about 4.5 W, and a fifth group of wafers 415A were spalled after forming subsurface laser damage at a laser power level of about 4.6 W. FIG. 46B shows the results for a second SiC ingot, where the first wafer group 411B was spalled after forming subsurface laser damage at a laser power level less than 3.2 W, the second wafer group 412B was spalled after forming subsurface laser damage at a laser power level of about 3.4 W, and the third through fifth wafer groups 413B-415B were spalled after forming subsurface laser damage at higher laser power levels, each about 0.25 W greater than the previous. FIG. 46C shows that laser power levels ranging from about 4 W to about 5.5 W were used among the different wafer groups 411C-420C to successfully form 55 wafers that were subsequently cut (by forming subsurface laser damage and subsequent spalling) from a single SiC ingot. 46A-46C thus show the large variation in laser power requirements from ingot to ingot and within each ingot for laser assisted dicing to form multiple wafers of substantially the same thickness.

[0173] FIG. 47 is a plot of resistivity (Ohm-cm) versus slice number for 50 wafers per ingot produced from approximately fifty (50) SiC ingots, with a superimposed polynomial fit showing that resistivity decreases with slice number. In each case, increasing slice number represents increasing proximity to the seed from which the ingot was epitaxially grown, with slice 1 representing the top of the ingot furthest from the seed. The resistivity range varies from ingot to ingot, but each ingot consistently decreases in resistivity throughout as the proximity to the seed increases. The range of resistivity values ​​on the y-axis of FIG. 47 is consistent with N-type SiC. The decrease in resistivity corresponds to increased doping and increased laser absorption.

[0174] Figure 48 is a plot of laser power (Watts) versus resistivity for wafers produced from approximately fifty (50) SiC ingots with a polynomial fit superimposed, representing the laser power required for successful laser-assisted dicing (with spallation after subsurface laser damage formation) by the methods described herein. Figure 48 shows that while laser power requirements vary significantly from ingot to ingot, the laser power levels required to achieve successful dicing decrease with increasing ingot resistivity levels.

[0175] [Apparatus including a scattered light source and an imaging device] In certain embodiments, a material processing apparatus includes a laser processing station configured to process a substrate of crystalline material to form subsurface laser damage therein, the laser processing station including an illumination device and an imaging device configured to enable detection of a condition indicative of the presence of a crack-free region within the crystalline material. The crack-free region can be used as a visual indicator to determine when additional laser substrate damage is required at a first average depth (to form a first thickness reduction of the substrate, such as a first wafer derived from the ingot) and / or when additional laser power is required to form laser damage at a next average depth (to form a next thickness reduction of the substrate, such as a next wafer derived from the ingot) to provide a stable and repeatable laser cutting process for wafer thickness distribution while avoiding unwanted kerf loss. The term “average depth position” is used in this context because small variations in laser focus depth position (e.g., typically less than 10 microns) may be used between subsurface laser damage runs to produce the same thickness reduction in the substrate and / or within a single laser damage run (e.g., to account for the presence of heavily doped regions such as doped rings).

[0176] Preferably, the illumination device and imaging device are positioned to allow imaging of the substrate surface while the substrate is held by the laser processing chuck. Such capability allows the substrate to be inspected (e.g., imaged and analyzed in an automated fashion) without having to remove and replace the substrate in the laser processing chuck to quickly assess whether additional laser processing may be required prior to spalling. This in-situ inspection of the substrate while in the laser processing station avoids downtime and increases utilization of the laser processing tool, thereby increasing throughput of the laser cutting process. In certain embodiments, the laser is moved away from the substrate held by the laser processing chuck so that imaging can be performed without the laser interfering with illumination or imaging of the substrate surface. obtain.

[0177] 49A and 49B provide schematic cross-sectional side and top plan views, respectively, of a scattering light source 438 and an imaging device 442 disposed proximate to a crystalline material substrate 430 within a laser processing station 425. Referring to FIG. 49A, the crystalline material substrate 430 includes a top surface 433 and subsurface laser damage 434 disposed within the substrate 430 below the top surface 433. The subsurface laser damage 434 generally resembles an irregular sawtooth pattern oriented parallel to the <11-20> direction when the substrate has a hexagonal crystal structure. The substrate 430 includes a central axis 436. The scattering light source 438 is laterally displaced in a first direction 437A relative to the central axis 436, and the imaging device 442 is laterally displaced in an opposite second direction 437B relative to the central axis 436. Both the scattered light source 438 and the imaging device 442 may be displaced upwards relative to the top surface 433 of the substrate 430. Additionally, the scattered light source 438 may be disposed on a first lateral side 431 of the substrate 430, and the imaging device 442 may be disposed on an opposite second lateral side 432 of the substrate 430. In certain embodiments, a definable angle between a light emitting surface of the scattered light source 438 and a light receiving surface of the imaging device 442 (optionally expressible as an angle between a beam 440 emanating from the scattered light source 438 and an incident light ray 444 received by the imaging device 442) may be within a range between about 100 degrees and about 170 degrees. In certain embodiments, the scattered light source 438 may include any suitable light emitting device or devices (e.g., light emitting diodes), with a diffuser disposed between the light emitting device and the light ray 440 emanating from the scattered light source 438. In particular embodiments, imaging device 442 may include one or more charge-coupled device (CCD) or complementary metal-oxide semiconductor (CMOS) image sensors, optionally arranged in an array.

[0178] FIG. 49B provides a top plan view of the same elements depicted in FIG. 49A. The substrate 430 may include a primary flat 435 (shown in FIG. 49B) that is substantially parallel to the <11-20> direction (shown in FIG. 49A). The inventors have found that the orientation of the scattered light source 438 and imaging device 442 relative to the substrate 430 is important to aid in imaging of subsurface laser damage. In certain embodiments, the light source may be positioned substantially perpendicular to the primary flat 435 of the substrate 430 and / or within ±5 degrees of perpendicular to the <11-20> direction of the hexagonal crystal structure of the substrate 430, which enhances visibility of crack-free areas through the top surface 433 of the substrate 430.

[0179] FIG. 50A is an image of the top surface of a crystalline SiC substrate 450 with subsurface laser damage, imaged using an apparatus similar to that shown in FIGS. 49A-B. The substrate 450 in FIG. 50A includes three regions 451-453 of different colors (in the original image) and an irregularly shaped dark region 456 that corresponds to a crack-free region in the substrate 450. In the original image, the outermost substantially annular region 451 (including the primary flat 455) is primarily green, the middle substantially annular region 452 is primarily red, and the central substantially circular region 453 is primarily gold. Within the central region 453, an irregularly shaped black region 456 is visible. The black region 456 corresponds to the presence of a crack-free region along the subsurface laser damage below the top surface of the substrate 450. The different colors (green, red, and gold) of the different regions 451-453 are believed to correspond to the extent of the crack damage. In certain embodiments, the methods disclosed herein include analyzing at least one characteristic of the image to identify areas of differing degrees of crack damage and adjusting one or more laser damage formation parameters (e.g., laser power, laser power, laser power, laser damage intensity, laser damage time, laser damage depth) to form a secondary subsurface laser damage at the same (e.g., first) average depth location (to form a first thickness reduction portion of the substrate, e.g., a first wafer) and / or to form a subsequent subsurface laser damage at a different (e.g., second or subsequent) average depth location (to form a second and subsequent thickness reduction portion of the substrate, e.g., a second and subsequent wafer) to account for differences in substrate characteristics that may vary with vertical (depth) and / or horizontal location within the substrate. and adjusting the laser focusing depth, the laser pulse duration, and / or the number of laser damage formation steps.

[0180] 49-49B show the use of scattered light sources 438 and imaging devices 442 positioned along both lateral sides of the substrate, other configurations and / or types of light sources and imaging devices may be used in certain embodiments. In certain embodiments, at least one microscope, such as an optical microscope, a confocal microscope, a scanning electron microscope, and / or a transmission electron microscope, may be used to scan one or more portions (or the entirety) of the top surface of the substrate with relative translation between the substrate and the microscope.

[0181] Figure 50B is a schematic diagram of substrate representation 450A showing irregularly shaped dark region 456 of Figure 50A within dotted regions 451A-453A (with outermost region 453A encompassing primary flat 455A) that substantially correspond to the boundaries between different colored regions 451-453 of the top surface of substrate 450 of Figure 50A. In certain embodiments, all areas except dark region 456 may be removed from the captured image to facilitate analysis of one or more area characteristics of dark region 456.

[0182] FIG. 50C is an expanded view of the irregularly shaped dark region 456 shown in FIGS. 50A-B, but with the contiguous dark regions individually numbered as 456A-456D, and with the addition of rectangular boxes around each of the regions 456A-456D. Each dark region 456A-456D has a maximum length corresponding to L11-L4 and a maximum width corresponding to W1-W4, respectively. In certain embodiments, analysis of the image obtained from the substrate includes identifying conditions indicative of the presence of crack-free regions within the crystalline material (e.g., dark and / or black regions in certain embodiments) and quantifying a top area characteristic (or at least one top area characteristic) of one or more crack-free regions therein. In certain embodiments, the quantified top area characteristic includes a total top area of ​​all crack-free regions. In certain embodiments, the quantified top area characteristics include individually identifying any contiguous crack-free regions and quantifying the top area of ​​each contiguous crack-free region, and / or quantifying the maximum length and width dimensions of the contiguous crack-free region, and / or determining the length / width aspect ratio of the contiguous crack-free region. In certain embodiments, the length and width may be established with reference to a crystal orientation and / or a primary flat of the substrate (e.g., the length is perpendicular to the primary flat and the width is parallel to the primary flat). The inventors have found that the presence of a large contiguous crack-free region of a given top area may inhibit spalling more easily than the presence of multiple discontinuous crack-free regions of the same total top area. Furthermore, the inventors have found that the orientation and / or aspect ratio of the contiguous crack-free region may affect inhibition of spalling. Small localized black regions, representing crack-free areas, generally do not prevent separation by spallation, but as the size of the black regions increases (especially in the width direction generally parallel to the primary flat and / or generally perpendicular to the laser damage line), such regions may require the addition of another laser damage pass at the same average depth and / or the need to increase the laser power when creating a laser damage region at the next average depth.A crack-free area with a large length (e.g., perpendicular to the primary flat) may be more effective at preventing spalling than a crack-free area with a large width.

[0183] 51 is a schematic diagram of a material processing apparatus 458 according to one embodiment, including a laser processing station 459 including a laser 465, at least one translation stage 466 (e.g., preferably an xyz translation stage) configured to facilitate relative movement between the laser 465 and the substrate 460, a scattered light source 468 configured to illuminate the top surface 463 of the substrate 460, and an imaging device 472 configured to generate at least one image of the top surface 463 of the substrate 460. The substrate 460 may include a laser tool chuck. The material processing apparatus 458 is disposed on a support 464 that supports the substrate 456. The various items within the material processing apparatus 458 are in electrical communication with at least one computing device 474 having an associated memory 476. The computing device 474 may control the operation of the scattering light source 468, the imaging device 472, the laser 465, and the translation stage 466. The memory 476 may further store a substrate-specific instruction set (e.g., a fabrication recipe) that can be used and modified on an individual substrate basis. In certain embodiments, the computing device 474 and memory 476 may be used in performing various steps of the methods disclosed herein, including, but not limited to, analyzing the substrate image to identify conditions indicative of the presence of crack-free regions within the substrate, quantifying one or more top area characteristics of the crack-free regions, and comparing the top area characteristics to one or more predetermined threshold area characteristics. In certain embodiments, the computing device 474 may be further used to analyze the image and detect the presence of regions of different color (e.g., other than the presence of black or dark spots) and adjust operation of the laser 465 to compensate for contamination of the laser facet in response to such analysis. In certain embodiments, the computing device 474 may be further used to detect the presence of different doping conditions in different regions of the substrate and modify the laser power delivery accordingly. In certain embodiments, in response to detecting a condition indicative of non-uniform doping of the crystalline material, the laser power may be modified during formation of the subsurface laser damage pattern to provide a first average power level of laser radiation when forming the subsurface laser damage in the first doped region and to provide a second average power level of laser radiation when forming the subsurface laser damage in the second doped region, the first and second average power levels being different from one another.

[0184] [Methods include imaging, comparison, and laser treatment / power adjustment] 52 is a flow chart 480 illustrating steps of a first crystalline material processing method, which generally includes generating an image of a top surface of a substrate having subsurface laser damage, analyzing the image to identify the presence of conditions indicative of one or more crack-free regions, comparing one or more characteristics of the crack-free regions to first and second thresholds, and taking an action in response to the comparison (i.e., (A) performing additional laser passes at substantially the same depth location, optionally adjusting one or more laser parameters to form auxiliary laser damage, and / or (B) adjusting one or more laser parameters to form subsurface laser damage at second and subsequent depth locations). The method begins at block 482. Proceeding to block 484, a first step includes forming a subsurface laser damage in a crystalline material substrate having at least one subsurface laser damage pattern (optionally including at least one plurality of substantially parallel lines as disclosed herein) along a first (or new) depth location below a top surface of the substrate, the at least one subsurface laser damage pattern configured to promote formation of at least one plurality of cracks in the interior of the crystalline material propagating outwardly from the at least one subsurface laser damage pattern. Proceeding to block 486, a second step includes generating at least one image of a top surface of the substrate. In a particular embodiment, the image generating step includes illuminating the top surface with a scattering light source disposed on a first lateral side of the substrate (preferably disposed substantially perpendicular to a primary flat of the substrate and / or within ±5 degrees of a perpendicular to a <11-20> direction of the hexagonal crystal structure) and capturing at least one image with an imaging device disposed on a second lateral side of the substrate opposite the first lateral side. In certain embodiments, one or more of the alternative or additional imaging methods disclosed herein may be used.

[0185] Proceeding to block 488, a further step is to identify conditions (e.g., dark and / or black areas in certain embodiments) that indicate the presence of crack-free regions within the crystalline material. and analyzing at least one image to determine whether the crack-free region is crack-free. Optionally, at least one top area characteristic of one or more crack-free regions therein may be quantified, and the quantified top area characteristic may optionally include a total top area of ​​all crack-free regions. In certain embodiments, the quantified top area characteristic includes identifying any contiguous crack-free region individually, and quantifying the top area of ​​each contiguous crack-free region, and / or quantifying the maximum length and width dimensions of the contiguous crack-free region, and / or determining the length / width aspect ratio of the contiguous crack-free region. In certain embodiments, the length and width may be established with reference to a crystal direction and / or a primary flat of the substrate (e.g., the length is perpendicular to the primary flat and the width is parallel to the primary flat). The inventors have found that the presence of a large contiguous crack-free region of a given top area may more easily inhibit spalling than the presence of a large number of discontinuous crack-free regions of the same total top area. Additionally, the inventors have found that the orientation and / or aspect ratio of the continuous crack-free regions can affect spallation prevention. Small localized black regions representing crack-free regions generally do not prevent spallation separation, but as the size of the black regions increases (especially in the width direction generally parallel to the primary flat and / or generally perpendicular to the laser damage line), such regions may recognize the need to add another laser damage step at the same average depth and / or increase the laser power when creating a laser damage region at the next average depth. Crack-free regions with a larger length (e.g., perpendicular to the primary flat) may be more problematic for spallation prevention than crack-free regions with a larger width.

[0186] Proceeding to decision block 490, one or more characteristics of the crack-free region (optionally including at least one quantified top area characteristic) are compared to at least one first predetermined threshold. The first threshold may include, but is not limited to, any one or more of the following: a contiguous crack-free region top area threshold, a crack-free total top area threshold, a crack-free maximum width threshold, a maximum length / width aspect ratio threshold, or the like. If the at least one characteristic of the crack-free region does not exceed the at least one first predetermined threshold, the method proceeds to block 498, whereby the substrate is transferred to a fracture station to create a first thickness-reduced portion of the substrate (e.g., a first wafer from the ingot) having a thickness that generally corresponds to a first average depth position. Conversely, if at least one characteristic of the crack-free region is above at least one first predetermined threshold, the method proceeds to block 492, where an instruction set (e.g., fabrication recipe) associated with the substrate is modified by incrementally adjusting at least one laser parameter for forming the subsurface laser damage when creating a subsurface laser damage pattern at a second average depth location and any subsequent average depth locations of the substrate (e.g., to form at least one additional thickness reduction portion of the substrate, e.g., second and subsequent wafers from the ingot). Adjustable laser parameters include any one or more of laser power, laser focal depth, number of laser strokes, laser stroke spacing, laser pulse width, and the like. In certain embodiments including altering the laser power, the instruction set is modified to increase the average laser power by a value within a range of 0.10 to 0.50 watts, or 0.15 to 0.35 watts, or 0.20 to 0.30 watts, or by a value of about 0.25 watts. Adjusting one or more laser parameters to form subsequent laser damage at second and subsequent average depth locations does not necessarily result in the formation of additional damage at the previously established first average depth location.A determination is made at decision block 494 whether additional laser damage at the first average depth location may be necessary to promote fragmentation.

[0187] Decision block 494 determines one or more characteristics (optionally less than one) of the crack-free region. The method includes comparing at least one quantified top area characteristic of the crack-free region to at least one second predetermined threshold. In certain embodiments, the second predetermined threshold is greater than the first predetermined threshold. The second threshold may include, but is not limited to, any one or more of the following: a continuous crack-free region top area threshold, a crack-free total top area threshold, a crack-free maximum width threshold, a maximum length / width aspect ratio threshold, or the like. If the at least one characteristic of the crack-free region does not exceed the at least one second predetermined threshold, the method proceeds to block 498, whereby additional laser damage is not determined to be necessary to support fracturing the substrate along the first average depth location, and the substrate is transferred to a fracturing station. Conversely, if the at least one characteristic of the crack-free region does exceed the at least one second predetermined threshold, the method proceeds to block 496, whereby additional subsurface laser damage is formed along the first average depth location. In certain embodiments, this involves forming auxiliary subsurface laser damage to supplement the at least one subsurface laser damage pattern at or proximate to the first average depth location, and performing relative motion between the laser and the substrate while providing laser radiation that is focused into the interior of the substrate at least in crack-free regions, but optionally throughout the substrate, to promote the formation of additional cracks within the crystalline material propagating outwardly from the auxiliary at least one subsurface laser damage pattern. After forming the auxiliary subsurface laser damage, the method proceeds to block 498, whereby the substrate is transferred to a spallation station.

[0188] Proceeding to block 500, in certain embodiments, the carrier may be bonded to the substrate at the fracture station to form a bonded assembly. Thereafter, according to block 502, the crystalline material is fractured along a first depth location to separate the bonded assembly (including the carrier and the removed portion of the substrate) from the remaining portion of the substrate, such step serving to expose a new top surface of the substrate. Thereafter, according to block 504, the substrate may be returned to the laser processing station (optionally after surface preparation such as grinding and / or polishing of the newly exposed substrate surface) so that another subsurface laser damage step according to block 484 can be performed. If the instruction set associated with the substrate is modified to increase the average laser power according to block 492, the modified instruction set will be used to perform the steps described in block 484 to form the subsurface damage. This modified instruction set is preferably stored in memory and associated with the particular substrate (e.g., in a relational database record including the substrate identifier and parameters for forming the subsurface laser damage in the substrate). In this way, a substrate-specific recipe for creating subsurface laser damage is maintained, which can be dynamically updated.

[0189] After the bonded assembly is fractured from the substrate in block 502, the bonded assembly may be transferred (per block 506) to one or more surface processing stations for modifying the substrate portion attached to the carrier. Examples of surface processing steps that may be performed may include rough grinding, edge grinding, fine grinding, and cleaning, per blocks 508, 510, 512, and 514, respectively. At this point, the processed substrate portion may be ready for epitaxial growth.

[0190] FIG. 53 is a flowchart 520 illustrating steps of a second crystalline material processing method, which generally includes generating an image of a top surface of a substrate having subsurface laser damage, analyzing the image to quantify a top area characteristic of one or more crack-free regions, comparing the top area characteristic to first and second threshold area characteristics, and taking action (i.e., performing an additional laser pass at the same depth location and / or performing a second laser pass at a next depth location) in response to the comparison to increase reliability in producing a substrate portion (e.g., a wafer) from the substrate. and adjusting power for the subsurface laser damage. Proceeding to block 524, a first step includes forming subsurface laser damage in a crystalline material substrate having at least one subsurface laser damage pattern (optionally including at least one set of a plurality of substantially parallel lines) along a (new) first depth location below a top surface of the substrate, the at least one subsurface laser damage pattern configured to promote formation of at least one set of a plurality of cracks in the crystalline material, substantially propagating outward from the at least one subsurface laser damage pattern. Proceeding to block 526, a second step includes generating at least one image of the top surface of the substrate. In certain embodiments, the imaging step includes illuminating the top surface with a scattering light source disposed on a first lateral side of the substrate (preferably disposed substantially perpendicular to the primary flat of the substrate and / or within ±5 degrees of perpendicular to the <11-20> direction of the hexagonal crystal structure) and capturing at least one image with an imaging device disposed on a second lateral side of the substrate opposite the first lateral side. In certain embodiments, one or more alternative or additional imaging methods disclosed herein may be used.

[0191] Proceeding to block 528, further steps include analyzing at least one image to identify conditions indicative of the presence of crack-free regions within the crystalline material (e.g., dark and / or black regions in certain embodiments) and quantifying a top area characteristic (or at least one top area characteristic) of one or more crack-free regions within. In certain embodiments, the quantified top area characteristic includes a total top area of ​​all crack-free regions. In certain embodiments, the quantified top area characteristic includes identifying any contiguous crack-free regions individually and quantifying the top area of ​​each contiguous crack-free region, and / or quantifying the maximum length and width dimensions of the contiguous crack-free regions, and / or determining the length / width aspect ratio of the contiguous crack-free regions. In certain embodiments, the length and width may be established with respect to a crystal direction and / or a primary flat of the substrate (e.g., the length is perpendicular to the primary flat and the width is parallel to the primary flat).

[0192] Proceeding to decision block 530, the at least one quantified top area characteristic is compared to at least one first predetermined area (or area characteristic) threshold. The first threshold may include any one or more of the following: a contiguous crack-free region top area threshold, a crack-free total top area threshold, a crack-free maximum width threshold, a maximum length / width aspect ratio threshold, or the like. If the at least one quantified top area characteristic does not exceed the at least one first predetermined threshold area characteristic, the method proceeds to block 538, whereby the substrate is transferred to a fracture station. Conversely, if the at least one quantified top area characteristic exceeds the at least one first predetermined threshold area characteristic, the method proceeds to block 532, whereby an instruction set (e.g., fabrication recipe) associated with the substrate is modified by incrementally increasing an average laser power for forming subsurface laser damage when creating a subsurface laser damage pattern at a second average depth location and any subsequent average depth locations of the substrate. (The adjustable laser parameters may additionally or alternatively include any one or more of laser focal depth, number of laser strokes, laser stroke spacing, laser pulse width, etc.). In certain embodiments, the instruction set is modified to increase the average laser power by a value within the range of 0.10 to 0.50 watts, or 0.15 to 0.35 watts, or 0.20 to 0.30 watts, or by a value of about 0.25 watts. After gradually increasing the laser power to form subsequent laser damage at the second and subsequent average depth locations, formation of additional damage at the previously established first average depth location is not necessarily performed. A determination is made at decision block 534 whether additional laser damage may be necessary to promote spallation.

[0193] Decision block 534 includes comparing the at least one quantified top area characteristic to at least one second predetermined threshold area characteristic. In certain embodiments, the second predetermined threshold area characteristic is greater than the first predetermined threshold area characteristic. The second threshold area characteristic may include any one or more of the following: a continuous crack-free region top area threshold, a crack-free total top area threshold, a crack-free maximum width threshold, a maximum length / width aspect ratio threshold, or the like. If the at least one quantified top area characteristic does not exceed the at least one second predetermined threshold area characteristic, the method proceeds to block 538, according to which additional laser damage is not determined to be necessary to support the fracturing of the substrate along the first average depth location, and the substrate is transferred to a fracturing station. Conversely, if the at least one quantified top area characteristic exceeds the at least one second predetermined threshold area characteristic, the method proceeds to block 536, according to which supplemental subsurface laser damage is formed along the first average depth location. In certain embodiments, this involves forming auxiliary subsurface laser damage to supplement the at least one subsurface laser damage pattern at or proximate to the first average depth location, and performing relative motion between the laser and the substrate while providing focused laser radiation within the substrate to promote formation of additional cracks within the crystalline material propagating outwardly from the auxiliary at least one subsurface laser damage pattern. After forming the auxiliary subsurface laser damage, the method proceeds to block 538, whereby the substrate is transferred to a spallation station.

[0194] Proceeding to block 540, in certain embodiments, the carrier may be bonded to the substrate at the fracture station to form a bonded assembly. Thereafter, according to block 542, the crystalline material is fractured along a first depth location to separate the bonded assembly (including the removed portion of the carrier and substrate) and the remaining portion of the substrate, with such step serving to expose a new top surface of the substrate. Thereafter, according to block 544, the substrate may be returned to the laser processing station (optionally after surface preparation such as grinding and / or polishing of the newly exposed substrate surface) to enable another subsurface laser damage step according to block 524 to be performed. If the instruction set associated with the substrate is modified to increase the average laser power according to block 532, the modified instruction set will be used to perform the steps described in block 524 to form the subsurface damage. This modified instruction set is preferably stored in memory and associated with the particular substrate, such as in a relational database record including the substrate identifier and parameters for forming the subsurface laser damage in the substrate.

[0195] After the bonded assembly is fractured from the substrate at block 542, the bonded assembly may be transferred (per block 546) to one or more surface processing stations for modifying the substrate portion attached to the carrier. Examples of surface processing steps that may be performed may include rough grinding, edge grinding, fine grinding, and cleaning, per blocks 548, 550, 552, and 554, respectively. At this point, the processed substrate portion may be ready for epitaxial growth.

[0196] Representative Computer Systems That Can Be Used With the Systems and Methods FIG. 54 is a schematic diagram of a generalized representation of a computer system 600 (optionally embodied in a computing device) that may be included in any component of the systems or methods disclosed herein. In this regard, the computer system 600 is adapted to execute instructions from a computer-readable medium to perform these and / or any functions or processes described herein. In this regard, the computer system 600 of FIG. 54 may be adapted to perform the functions of the supported communication services. The computer system 600 may include a set of instructions executable to program and configure a programmable digital signal processing circuit to support scaling. The computer system 600 may be connected (e.g., networked) to other machines in a LAN, an intranet, an extranet, or the Internet. Although only a single device is shown, the term "device" may be construed to include any collection of devices that individually or in conjunction execute a set (or sets) of instructions to perform any one or more of the methodologies discussed herein. The computer system 600 may represent, for example, a server or a user's computer, such as a printed circuit board (PCB) or other electrical circuit card, a server, a personal computer, a desktop computer, a laptop computer, a personal digital assistant (PDA), a computing pad, a mobile device, or any other device.

[0197] The computer system 600, in this embodiment, includes a processing device or processor 602, a main memory 604 (e.g., read only memory (ROM), flash memory, dynamic random access memory (DRAM) such as synchronous DRAM (SDRAM), etc.), and a static memory 606 (e.g., flash memory, static random access memory (SRAM), etc.), which may communicate with each other via a data bus 608. Alternatively, the processing device 602 may be connected to the main memory 604 and / or the static memory 606 directly or via some other connection means. The processing device 602 may be a controller, and the main memory 604 or the static memory 606 may be any type of memory.

[0198] Processing device 602 represents one or more general-purpose processing devices, such as a microprocessor, central processing unit, or the like. More specifically, processing device 602 may be a complex instruction set computing (CISC) microprocessor, a reduced instruction set computing (RISC) microprocessor, a very long instruction word (VLIW) microprocessor, a processor implementing other instruction sets, or other processors implementing combinations of instruction sets. Processing device 602 is configured to execute processing logic in instructions to perform the operations and steps discussed herein.

[0199] Computer system 600 may further include a network interface device 610. Computer system 600 may or may not also include an input 612 configured to receive inputs and selections to be communicated to computer system 600 during instruction execution. Computer system 600 may or may not also include an output 614 including, but not limited to, a display, a video display unit (e.g., a liquid crystal display (LCD) or a cathode ray tube (CRT)), an alphanumeric input device (e.g., a keyboard), and / or a cursor control device (e.g., a mouse).

[0200] Computer system 600 may or may not include a data storage device containing instructions 616 stored on a computer-readable medium 618. The instructions 616 may also reside, in whole or in part, within main memory 604 and / or within processing device 602 during execution thereof by computer system 600, with main memory 604 and processing device 602 also constituting computer-readable media. The instructions 616 may further be transmitted or received via network interface device 610 over network 620.

[0201] The computer readable medium 618 is shown in one embodiment as being a single medium. Although the term "computer-readable medium" is used herein, it should be construed to include a single medium or multiple media (e.g., a centralized or distributed database and / or associated caches and servers) that store one or more sets of instructions. The term "computer-readable medium" should also be construed to include any medium capable of storing, encoding, or carrying a set of instructions for execution by a processing device, causing the processing device to perform any one or more of the methodologies of the embodiments disclosed herein. The term "computer-readable medium" should therefore be construed to include, but is not limited to, solid-state memory, optical media, and magnetic media.

[0202] The embodiments disclosed herein include various steps. The steps of the embodiments disclosed herein may be implemented or performed by hardware components or may be embodied as machine-executable instructions, which may be used to cause a general-purpose or special-purpose processor programmed with the instructions to perform the steps. Alternatively, the steps may be performed by a combination of hardware and software.

[0203] The embodiments disclosed herein may be provided as a computer program product or software, which may include a machine-readable medium (or computer-readable medium) storing instructions that can be used to program a computer system (or other electronic device) to perform the steps of the embodiments disclosed herein. A machine-readable medium includes any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computer). For example, machine-readable media include machine-readable storage media (e.g., ROM, random access memory ("RAM"), magnetic disk storage media, optical storage media, flash memory devices, etc.), and the like.

[0204] Unless expressly stated otherwise, and as is apparent from the above discussion, throughout the description, discussions utilizing terms such as "analyzing," "processing," "computing," "determining," "displaying," and the like, will be understood to refer to the operation and processing of a computer system or similar electronic computing device that manipulates and converts data and memory represented as physical (electronic) quantities in the registers of the computer system into other data similarly represented as physical quantities in the memory or registers of the computer system or other such information storage, transmission, or display device.

[0205] The algorithms and displays presented herein are not inherently related to any particular computer or other apparatus. Various systems may be used with programs in accordance with the teachings herein, or it may be convenient to construct a more specialized apparatus to perform the required method steps. The required structure for a variety of these systems is disclosed in the above description. Further, the embodiments described herein are not described with reference to any particular programming language. It will be appreciated that a variety of program languages ​​can be used to implement the teachings of the embodiments as described herein.

[0206] Those skilled in the art will further appreciate that the various example logic blocks, modules, circuits, and algorithms described in connection with the embodiments disclosed herein may be implemented as electronic hardware, instructions stored in a memory or another computer-readable medium and executed by a processor or other processing device, or a combination of both. The components of the systems described herein may be utilized in any circuit, hardware component, integrated circuit (IC), or IC chip, by way of example. The memories disclosed herein may be any type and size of memory and may be configured to store any type of information desired. To clearly illustrate this interchangeability, the various examples are provided with a number of different configurations. The illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. How such functionality is implemented depends on the particular application, design choices, and / or design constraints imposed on the overall system. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the embodiments herein.

[0207] The various example logic blocks, modules, and circuits described in connection with the embodiments disclosed herein may be implemented or performed using a processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. Furthermore, the controller may be a processor. The processor may be a microprocessor, but alternatively, the processor may be any conventional processor, controller, microcontroller, or state machine. The processor may also be implemented as a combination of computing devices (e.g., a combination of a DSP and a microprocessor, multiple microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration).

[0208] The embodiments disclosed herein may be embodied in hardware and as instructions stored in the hardware and may reside in, for example, a RAM, a flash memory, a ROM, an Electrically Programmable ROM (EPROM), an Electrically Erasable Programmable ROM (EEPROM), a register, a hard disk, a removable disk, a CD-ROM, or any other form of computer readable medium known in the art. The storage medium is coupled to the processor such that information can be read from and written to the storage medium. Alternatively, the storage medium may be integral to the processor. The processor and the storage medium may reside in an ASIC. The ASIC may reside in a remote station. Alternatively, the processor and the storage medium may reside as separate components in a remote station, a base station, or a server.

[0209] It is also noted that the operational steps described in any embodiment herein are described to provide examples and discussion. The described operations can be performed in a different order than the many illustrated orders. Furthermore, an operation described as a single operational step can actually be performed as several different steps. Furthermore, one or more operational steps discussed in the embodiments can be combined. Those skilled in the art will also understand that information and signals can be represented using various technologies and techniques. For example, data, instructions, commands, information, signals, bits, symbols, and chips that may be referred to throughout the above description can be represented as voltages, currents, electromagnetic waves, magnetic fields, particles, optical fields, or any combination thereof.

[0210] Unless expressly stated to the contrary, it is in no way intended that any method described herein be construed as requiring that its steps be performed in a specified order, and thus, unless a method claim actually specifies the order in which its steps are to be followed or the claims or description are otherwise expressly stated to be limited to a particular order, no particular order is intended to be inferred in any way.

[0211] Unless expressly indicated otherwise herein, all of the compounds disclosed herein are It is contemplated that any or more features or characteristics of any one or more of the embodiments described herein can be combined with any or more features or characteristics of the other embodiments.

[0212] Potential technical benefits provided by one or more embodiments of the present disclosure may include: improved repeatability in producing uniform thickness wafers from crystalline material substrates (e.g., ingots) by laser machining and subsequent fracturing while avoiding unnecessary material loss; addressing variability in laser power requirements from substrate to substrate and at different depth locations within a single substrate during laser assisted dicing methods; improved detection of crack-free regions in crystalline material substrates with subsurface laser damage; reduced crystalline material kerf loss compared to wire sawing; reduced processing time and increased throughput of crystalline material wafers and resultant devices compared to wire sawing; reduced laser processing time compared to conventional laser-based methods; reduced force required to cause fracturing along the laser damaged region; reduced need for post-separation surface smoothing to remove laser damage after separation; and / or reduced bowing and breakage of the crystalline material.

[0213] Those skilled in the art will recognize improvements and modifications to the preferred embodiments of the present disclosure, and all such improvements and modifications are deemed to be within the scope of the concepts disclosed herein and in the claims that follow.

Claims

1. providing laser radiation focused along a first average depth location within a crystalline material of a substrate and performing lateral relative movement between the laser and the substrate to form subsurface laser damage having at least one subsurface laser damage pattern, the at least one subsurface laser damage pattern configured to promote formation of at least one group of a plurality of cracks in the substrate propagating outwardly from the at least one subsurface laser damage pattern; generating at least one image of a top surface of the substrate after forming the at least one subsurface laser damage pattern; analyzing the at least one image to identify conditions indicative of the presence of crack free regions within the interior of the substrate, the analyzing including quantifying a top area characteristic of one or more crack free regions within the interior of the substrate and comparing the top area characteristic to at least one predetermined threshold area characteristic; In response to said analyzing, the method comprises the steps of: (i) performing relative motion between the laser and the substrate while providing radiation of the laser focused into the interior of the substrate at least in crack-free regions to form auxiliary subsurface laser damage to complement the at least one subsurface laser damage pattern to form a first thickness reduction in the substrate and to promote formation of additional cracks in the crack-free regions along or adjacent to the first average depth location; (ii) modifying an instruction set associated with the substrate for forming subsurface laser damage when creating a subsurface laser damage pattern at a second average depth location and any subsequent average depth locations in the substrate for the purpose of forming at least one additional thickness reduced portion of the substrate; A method for processing a crystalline material comprising:

2. the at least one predetermined threshold area characteristic includes a first predetermined threshold area characteristic and a second predetermined threshold area characteristic, the second predetermined threshold area characteristic being greater than the first predetermined threshold area characteristic; performing step (i) if the top area characteristic is at least as great as the first predetermined threshold area characteristic, and thereafter performing step (ii); and performing step (i) if said top area characteristic is at least as great as said second predetermined threshold area characteristic.

3. The method of claim 1 , comprising performing both steps (i) and (ii) in response to said analyzing.

4. 4. The crystalline material processing method of claim 1, wherein step (ii) comprises adjusting at least one of: (a) average laser power; (b) laser focusing depth relative to the exposed surface of the substrate; or (c) number of laser damage formation strokes when creating a subsurface laser damage pattern at the second average depth position and any subsequent average depth positions in the substrate.

5. 5. The method of claim 4, wherein said modifying said instruction set in accordance with step (ii) comprises increasing average laser power by a value in the range of 0.15 to 0.35 Watts.

6. 6. The crystalline material processing method of claim 1 , wherein step (i) comprises adjusting at least one of: (a) average laser power; or (b) laser focus depth relative to the exposed surface of the substrate when creating the auxiliary subsurface laser damage to assist the at least one subsurface laser damage pattern and promote the formation of additional cracks in the crack-free regions along or adjacent to the first average depth location.

7. 7. A crystalline material processing method according to claim 1, wherein the substrate has a generally circular edge having a primary flat, and wherein generating the at least one image comprises: (a) illuminating the top surface with scattered light generated by a scattered light source disposed on a first lateral side of the substrate and disposed substantially perpendicular to the primary flat; and (b) capturing the at least one image using an imaging device disposed on an opposite second lateral side of the substrate.

8. the crystalline material has a hexagonal crystal structure; generating the at least one image includes: (a) illuminating the top surface with scattered light generated by a scattered light source disposed on a first lateral side of the substrate and disposed within ±5 degrees of a normal to a <11-20> direction of the hexagonal crystal structure; and (b) capturing the at least one image with an imaging device disposed on a second lateral side of the substrate opposite the first lateral side. A method for processing a crystal material according to any one of claims 1 to 6.

9. the at least one subsurface laser damage pattern includes a first subsurface laser damage pattern and a second subsurface laser damage pattern formed after the first subsurface laser damage pattern; the first subsurface laser damage pattern includes a first plurality of substantially parallel lines, and the second subsurface laser damage pattern includes a second plurality of substantially parallel lines; the lines of the second plurality of substantially parallel lines being interspersed among the lines of the first plurality of substantially parallel lines; At least some of the second plurality of substantially parallel lines do not intersect with any of the first plurality of substantially parallel lines. A method for processing a crystal material according to any one of claims 1 to 8.

10. each line of the second plurality of substantially parallel lines is disposed between a different pair of adjacent lines of the first plurality of substantially parallel lines; The method for processing a crystal material according to claim 9.

11. the crystalline material has a hexagonal crystal structure; each line of the first plurality of substantially parallel lines and each line of the second plurality of substantially parallel lines is within ±5 degrees of a normal to a <11-20> direction of the hexagonal crystal structure and is substantially parallel to a surface of the substrate; The method for processing a crystal material according to claim 9.

12. the at least one subsurface laser damage pattern includes a first subsurface laser damage pattern and a second subsurface laser damage pattern formed after the first subsurface laser damage pattern; the at least one group of substantially parallel lines includes a first plurality of substantially parallel lines and a second plurality of substantially parallel lines; The lines of the first plurality of substantially parallel lines are non-linear with the lines of the second plurality of substantially parallel lines. are parallel, a line angular orientation of the second plurality of substantially parallel lines differs from a line angular orientation of the first plurality of substantially parallel lines by 10 degrees or less; At least some of the second plurality of substantially parallel lines do not intersect with any of the first plurality of substantially parallel lines. A method for processing a crystal material according to any one of claims 1 to 7.

13. the at least one subsurface laser damage pattern further includes a third subsurface laser damage pattern formed after the second subsurface laser damage pattern; the at least one group of substantially parallel lines further comprises a third plurality of substantially parallel lines; the at least one group of cracks includes a first, a second, and a third plurality of cracks; the first subsurface laser damage pattern forms the first plurality of cracks in the interior of the substrate, the first plurality of cracks propagating laterally outward from the first plurality of substantially parallel lines; the second subsurface laser damage pattern forms a second plurality of cracks in the interior of the substrate propagating laterally outward from the second plurality of substantially parallel lines, the second plurality of cracks not connecting with the first plurality of cracks; the third subsurface laser damage pattern forms a third plurality of cracks in the interior of the substrate propagating laterally outward from the third plurality of substantially parallel lines, at least some of the cracks in the third plurality of cracks connecting with at least some of the cracks in the first plurality of cracks and at least some of the cracks in the second plurality of cracks. The method for processing a crystalline material according to claim 12.

14. detecting a condition indicative of non-uniform doping of the crystalline material across at least a portion of a surface of the substrate, the non-uniform doping including a first doped region and a second doped region; In response to detecting the condition indicative of non-uniform doping of the crystalline material, the following steps are performed: (A) modifying a laser power during formation of the at least one subsurface laser damage pattern to provide a first power level of laser radiation when forming subsurface laser damage in the first doped region and to provide a second power level of laser radiation when forming subsurface laser damage in the second doped region; or (B) performing at least one of the steps of: changing an average depth of formation of subsurface laser damage in the substrate when forming subsurface laser damage in one of the first doped region or the second doped region; A method for processing a crystalline material according to any one of claims 1 to 13, further comprising:

15. 15. The method of claim 1, further comprising fracturing the crystalline material substantially along the at least one subsurface laser damage pattern to produce first and second crystalline material portions, both of which have a reduced thickness compared to the substrate but substantially the same length and width as the substrate.

16. 16. A method for processing crystalline materials according to any one of claims 1 to 15, wherein the substrate comprises silicon carbide.

17. 17. A method according to any one of claims 1 to 16, wherein the substrate comprises an ingot having a diameter of at least 150mm.

18. 1. A laser processing station configured to process a substrate of crystalline material, comprising: a laser configured to create a subsurface laser damage region within the substrate; at least one translation stage configured to effect relative movement between the laser and the substrate; a scattered light source configured to illuminate a top surface of the substrate, the scattered light source being positioned to be located on a first lateral side of the substrate; an imaging device configured to generate at least one image of the top surface of the substrate, the imaging device configured to be positioned on a second lateral side of the substrate opposite the first lateral side. A material processing apparatus comprising:

19. the substrate has a substantially circular edge having a primary flat; the scattered light source is disposed on a first lateral side of the substrate such that the scattered light source is positioned substantially perpendicular to the primary flat; 20. The material processing apparatus of claim 18.

20. the crystalline material has a hexagonal crystal structure; the scattering light source is positioned on a first lateral side of the substrate such that the scattering light source is positioned within ±5 degrees of a direction perpendicular to a <11-20> direction of the hexagonal crystal structure; 20. A material processing apparatus according to claim 18 or 19.

21. 20. A material processing apparatus according to claim 18 or 19, further comprising a computing device configured to analyze the at least one image to identify conditions indicative of the presence of crack free regions in the interior of the substrate.

22. The computing device, in response to the analyzing by the computing device, performs the following steps (i) or (ii): (i) performing relative motion between the laser and the substrate while providing radiation of the laser focused into the interior of the substrate at least in crack-free regions to form auxiliary subsurface laser damage to supplement at least one subsurface laser damage pattern in the substrate to form a first thickness reduction in the substrate and promote formation of additional cracks in the crack-free regions along or adjacent to the first average depth location; or 22. The material processing apparatus of claim 21, further configured to perform at least one of the steps of: (ii) modifying an instruction set associated with the substrate for forming subsurface laser damage when creating a subsurface laser damage pattern at a second average depth location and any subsequent average depth locations in the substrate for the purpose of forming at least one additional thickness reduced portion of the substrate.

23. 23. The material processing apparatus of claim 22, wherein the analyzing performed by the computing device includes quantifying a top area characteristic of the one or more crack-free regions in the interior of the substrate and comparing the top area characteristic to at least one predetermined threshold area characteristic.

24. The at least one predetermined threshold area characteristic includes a first predetermined threshold area characteristic and a second predetermined threshold area characteristic, the second predetermined threshold area characteristic being greater than or equal to the first predetermined threshold area characteristic. Bigger than sex, the computing device is configured to control the material processing apparatus to perform step (ii) if the top area characteristic is at least as great as the first predetermined threshold area characteristic; the computing device is configured to control the material processing apparatus to perform step (i) if the top area characteristic is at least as great as the second predetermined threshold area characteristic.

24. The material processing apparatus of claim 23.

25. 25. A material processing apparatus as claimed in any one of claims 22 to 24, further comprising a memory configured to store the set of instructions associated with the substrate for forming subsurface laser damage in the substrate, the memory being accessible by the computing device.

26. 26. A material processing apparatus according to any one of claims 18 to 25, further comprising a fragmentation station configured to receive the substrate from the laser processing station.

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