Laser-assisted method for cutting crystalline materials

Abstract

To provide a laser assist method for cutting and dividing, or removing a relatively thin layer of a crystal (for example, semiconductor) material from a substrate.SOLUTION: A method for processing a crystalline substrate to form multiple patterns of unersurface laser damage facilitates subsequent fracture of the substrate to yield first and second substrate portions of reduced thickness. Multiple groups of parallel lines of multiple undersurface damage patterns may be sequentially interspersed with one another, with at least some lines of different groups not crossing one another. Certain implementations include formation of multiple undersurface laser damage patterns including groups of parallel lines that are non-parallel to one another, but with each line remaining within ±5 degrees of perpendicular to the <11-20> direction of a hexagonal crystal structure of a material of the substrate.SELECTED DRAWING: Figure 11D

Description

Detailed Description of the Invention

[0001] [Related Application Description] This application claims priority to U.S. Patent Application No. 16 / 274,064, filed February 12, 2019, U.S. Provisional Patent Application No. 62 / 803,340, filed February 8, 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.

[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 epitaxial growth of other materials (e.g., AlN and other Group III nitrides). Vicinal wafers can be produced either 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 at an angle away from perpendicular to the ingot sidewalls.

[0005] There are several limitations to wire sawing of semiconductor materials. Kerf loss based on the width of the cut material is unavoidable in saw cutting, which represents a significant loss of semiconductor material. The stresses that wire saw cutting imposes on the wafer are relatively high, resulting in non-zero bow and warp characteristics. The processing time for a single boule (or ingot) is very long, and events such as wire breakage can extend the processing time 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, the resulting wafer must be cleaned of debris.

[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 first perspective crystallographic view showing a 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 epitaxial 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, where a vector 10 (orthogonal to the vicinal plane 9) is tilted away from the

[0001] direction by a tilt angle β, which is (slightly) tilted toward 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 has not been practical until now given the challenges of wire sawing and device fabrication.

[0010] In an attempt to address the limitations associated with wire sawing, alternative techniques have been developed for removing thin layers of semiconductor material from bulk crystals. One technique involving the removal of a layer of SiC 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] Another separation technique involving laser subsurface damage creation is disclosed in U.S. Patent No. 9,925,619 to Disco Corporation. The laser subsurface damage line is created by moving a SiC ingot on a forward stroke, indexing the focal point of the laser, then moving the ingot on a retract stroke, indexing the focal point of the laser, and so on. Laser subsurface damage creation creates an internal crack in the ingot running parallel to the c-plane, and ultrasonic vibration is applied to the ingot to induce spallation.

[0012] A similar separation technique involving laser subsurface damage formation is disclosed in US Patent No. 10,155,323 to Disco Corporation. A pulsed laser beam is delivered to a SiC ingot to form multiple successive modifications, each with a diameter of 17 microns, with 80% overlap in the feed direction, and the laser focus is indexed, alternating between these modification and indexing steps to create a separation layer in which adjacent cracks are connected in the indexing direction. Ultrasonic vibration is then applied to the ingot to induce spallation.

[0013] Another technique for removing a thin layer of semiconductor material from a bulk crystal is disclosed in US Patent Application Publication No. 2018 / 0126484 A1 to Siltectra GmbH. Laser radiation is applied to the solid-state material to create a desorption zone or multiple partial desorption zones, followed by formation of a polymer receiving layer (e.g., PDMS) and cooling (optionally combined with high speed spinning) to induce mechanical stresses that separate the thin layer of solid-state material along the desorption zone from the remainder of the material.

[0014] 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 position and / or the vertical location of the substrate surface as part of an ingot relative to its original growth location.

[0015] 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.

[0016] [Summary of the Invention] The present disclosure relates in various aspects to a method for processing a crystalline material substrate such that a plurality of subsurface laser damage sites are formed within an area of ​​the crystalline material to facilitate subsequent fracturing of the substrate to obtain first and second crystalline material portions. The subsurface laser damage formations are distributed among a plurality of non-overlapping areas of the crystalline material. For example, a first group of subsurface laser damage sites may be formed within the first and second non-overlapping areas of the crystalline material. A second group of subsurface laser damage sites may then be formed within the same first and second non-overlapping areas of the crystalline material, where at least some (or all) of the second group of subsurface laser damage sites do not intersect with the first group of subsurface laser damage sites formed within the non-overlapping areas. Additional groups of subsurface laser damage sites may be distributed among the same first and second non-overlapping areas of the crystalline material until a desired amount of subsurface laser damage is formed. It has been found that by distributing the subsurface laser damage in this manner, greater spacing can be achieved between adjacent subsurface laser damage sites (and greater spacing can be achieved between non-overlapping areas when such areas are spaced apart), resulting in less subsurface laser damage being required to carve out the crystalline material, thereby allowing for increased throughput of the laser tool and reduced kerf loss.

[0017] In certain embodiments, each group of subsurface laser damage sites is in the form of a plurality of parallel lines, each set of parallel lines in a non-overlapping area of ​​the crystalline material forming a subsurface laser damage pattern. In certain implementations, a plurality of (e.g., first and second, first through third, etc.) groups of a plurality of substantially parallel lines of a plurality of (e.g., first and second, first through third, etc.) subsurface laser damage patterns are dispersed. In certain embodiments, at least some lines of the second plurality of substantially parallel lines do not intersect with any lines of the first plurality of substantially parallel lines. Certain embodiments include forming a first subsurface laser damage pattern and a next subsurface laser damage pattern in a substrate of a crystalline material having a hexagonal crystal structure, each of the first and second subsurface laser damage patterns comprising a plurality of substantially parallel lines, each line being within ±5 degrees of a normal to a <11-20> direction of the hexagonal crystal structure, and the lines of the first plurality of substantially parallel lines being non-parallel to the lines of the next plurality of substantially parallel lines. Further embodiments include forming a first plurality of subsurface laser damage regions within each of the plurality of areas of the crystalline material, and forming a second plurality of subsurface laser damage regions within each of the plurality of areas of the crystalline material, where at least some of the first plurality of subsurface damage regions do not intersect with areas of the second plurality of subsurface damage regions. Additional embodiments include forming the first and second plurality of subsurface laser damage regions consecutively across each of the plurality of areas to form a distributed subsurface laser damage region, where at least some of the first plurality of subsurface laser damage regions do not intersect with areas of the second plurality of subsurface laser damage regions. Another further embodiment includes forming a first subsurface laser damage pattern substantially centered at a first depth within a crystalline material of a substrate; and forming a next subsurface laser damage pattern substantially centered at a next depth within the substrate, the next depth being different from the first depth, the next subsurface laser damage pattern being substantially aligned with the first subsurface laser damage pattern, and at least a portion of the vertical extent of the first and next subsurface laser damage patterns overlap.Each of the above methods may facilitate subsequent fracturing of the crystalline material substrate. An additional method is multiple grinding to remove subsurface damage. and edge grinding to impart a chamfered or rounded edge profile, where the order of grinding steps is selected to reduce the likelihood of imparting additional surface damage after edge grinding and to prepare the wafer for chemical mechanical planarization and / or a protective surface coating is employed. The material processing apparatus further includes a laser processing station, a fragmentation station, a plurality of coarse grinding stations arranged in parallel downstream of the fragmentation station, and at least one fine grinding station arranged downstream of the plurality of coarse grinding stations.

[0018] In one aspect, the present disclosure relates to a method of processing a crystalline material comprising providing focused laser radiation within a crystalline material of a substrate and performing lateral relative movement between the laser and the substrate to form a subsurface laser damage having a first subsurface laser damage pattern comprising a first plurality of substantially parallel lines. The method further comprises providing focused laser radiation within the crystalline material and performing lateral relative movement between the laser and the substrate after forming the first subsurface laser damage pattern to form a subsurface laser damage having a second subsurface laser damage pattern comprising a second plurality of substantially parallel lines. The first subsurface laser damage pattern forms within the crystalline material a first plurality of cracks propagating laterally outward from the first plurality of substantially parallel lines, and the second subsurface laser damage pattern forms within the crystalline material a second plurality of cracks propagating laterally outward from the second plurality of substantially parallel lines. According to such a method, the lines of the second plurality of substantially parallel lines are interleaved between the 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.

[0019] In certain embodiments, each line of the second plurality of substantially parallel lines does not intersect with any line of the first plurality of substantially parallel lines.

[0020] In certain embodiments, each line of the second plurality of substantially parallel lines is disposed between different pairs of adjacent lines of the first plurality of substantially parallel lines.

[0021] In certain embodiments, the crystalline material has a hexagonal crystal structure, and 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 perpendicular direction to a <11-20> direction of the hexagonal crystal structure and is substantially parallel to a surface of the substrate.

[0022] In certain embodiments, the spacing between at least some of the first plurality of substantially parallel lines is substantially the same as the spacing between at least some of the second plurality of substantially parallel lines.

[0023] In certain embodiments, each line of the second plurality of substantially parallel lines does not intersect with any line of the first plurality of substantially parallel lines.

[0024] In certain embodiments, the method further includes, after forming the first subsurface laser damage pattern and the second subsurface laser damage pattern, providing focused laser radiation within the crystalline material and performing lateral relative movement between the laser and the substrate to form a subsurface laser damage pattern having a third subsurface laser damage pattern comprising a third plurality of substantially parallel lines, wherein the lines of the third plurality of substantially parallel lines are interspersed or interleaved between the lines of the first plurality of substantially parallel lines and the second plurality of substantially parallel lines.

[0025] In certain embodiments, each line of the third plurality of substantially parallel lines is a line of the first plurality of substantially Disposed between one of the parallel lines and one of the second plurality of substantially parallel lines.

[0026] In certain embodiments, a focused depth of the laser radiation within the substrate differs between at least two of the first, second, and third subsurface laser damage patterns by a distance in a range from about 2 microns to about 5 microns.

[0027] In certain embodiments, the first subsurface laser damage pattern comprises a first plurality of cracks propagating laterally outwardly within the crystalline material from the first plurality of lines of substantially parallel lines, the second subsurface laser damage pattern comprises a second plurality of cracks propagating laterally outwardly within the crystalline material from the second plurality of lines of substantially parallel lines, 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 within the crystalline material from the third plurality of lines 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.

[0028] In certain embodiments, each line of the third plurality of substantially parallel lines is disposed between a corresponding line of the first plurality of substantially parallel lines and a corresponding line of the second plurality of substantially parallel lines to form a tri-line group, wherein the first, second, and third subsurface laser damage patterns combine to form a plurality of tri-line groups, and for one or more tri-line groups of the plurality of tri-line groups, the tri-line group is separated from at least one adjacent tri-line group by an inter-group spacing that is greater than the spacing between any two adjacent lines in the one or more tri-line groups.

[0029] In certain embodiments, the method further includes, after formation of the first, second, and third subsurface laser damage patterns, providing focused laser radiation within the crystalline material and performing lateral relative movement between the laser and the substrate to form a subsurface laser damage pattern having a fourth subsurface laser damage pattern comprising a fourth plurality of substantially parallel lines, the fourth plurality of substantially parallel lines being interspersed or interleaved between the first, second, and third plurality of substantially parallel lines.

[0030] In certain embodiments, the crystalline material has a hexagonal crystal structure, and each line of the first plurality of substantially parallel lines, each line of the second plurality of substantially parallel lines, and each line of the third plurality of substantially parallel lines are offset from normal to a <11-20> direction of the hexagonal crystal structure by an angle in the range of about 1 degree to about 5 degrees, but are substantially parallel to the surface of the substrate.

[0031] In certain embodiments, a focused depth of the laser radiation within the substrate is substantially the same during formation of the first subsurface laser damage pattern and the second subsurface laser damage pattern.

[0032] In certain embodiments, at least some of the first plurality of substantially parallel lines are disposed at substantially the same depth within the crystalline material as at least some of the second plurality of substantially parallel lines.

[0033] In certain embodiments, a method includes detecting a presence of a condition indicative of non-uniform doping of a crystalline material across at least a portion of a surface of a substrate, the non-uniform doping including at least one first doped region and at least one second doped region, and forming a first subsurface laser damage pattern and a second subsurface laser damage pattern in response to detecting the condition indicative of non-uniform doping of the crystalline material. and varying a laser power when forming the subsurface laser damage in the first doped region to provide a laser radiation of a first average power and when forming the subsurface laser damage in the second doped region to provide a laser radiation of a second average power.

[0034] In certain embodiments, the method further includes performing a repeating pass of at least one of the first, second, or third subsurface laser damage patterns, including providing focused laser radiation within the crystalline material to form a repeating subsurface laser damage pattern that is aligned with at least one of the first, second, or third subsurface laser damage patterns, wherein the repeating subsurface damage pattern is centered at a different depth relative to the surface of the crystalline material than the at least one of the first, second, or third subsurface laser damage patterns.

[0035] In certain embodiments, the crystalline material comprises a single crystal semiconductor material.

[0036] In certain embodiments, the lines of the first plurality of substantially parallel lines are non-parallel to the lines of the second plurality of substantially parallel lines, and the angular orientation of the lines in the second plurality of substantially parallel lines differs from the angular orientation of the lines in the first plurality of substantially parallel lines by 10 degrees or less.

[0037] In certain embodiments, the method further includes fracturing the crystalline material substantially along or between at least one of the first subsurface laser damage pattern and the second subsurface laser damage pattern to provide 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.

[0038] In certain embodiments, at least one of the first crystalline material portion or the second crystalline material portion comprises a free-standing wafer configured to have at least one epitaxial layer grown thereon. In certain embodiments, one of the first crystalline material portion or the second crystalline material portion comprises a device wafer including at least one epitaxial layer grown on a surface thereof.

[0039] In another aspect, the present disclosure relates to a method of processing a crystalline material, comprising: providing laser radiation focused within a substrate of the crystalline material and performing lateral relative movement between the laser and the substrate to form subsurface laser damage having a first subsurface laser damage pattern comprising a first plurality of substantially parallel lines; and providing laser radiation focused within the substrate and performing lateral relative movement between the laser and the substrate to form subsurface laser damage having a second subsurface laser damage pattern comprising 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, the difference between an angular orientation of the lines of the second plurality of substantially parallel lines and an angular orientation of the lines of the first plurality of substantially parallel lines is 10 degrees or less, and at least some of the lines of the second plurality of substantially parallel lines do not intersect any of the lines of the first plurality of substantially parallel lines.

[0040] In certain embodiments, each line of the next plurality of substantially parallel lines does not intersect with any line of the first plurality of substantially parallel lines.

[0041] In certain embodiments, each line of the next plurality of substantially parallel lines is disposed between a different pair of adjacent lines of the first plurality of substantially parallel lines.

[0042] In certain embodiments, the crystalline material has a hexagonal crystal structure, and the initial plurality of substantially parallel wires Each line and each line of the next plurality of substantially parallel lines is within ±5 degrees of perpendicular to the <11-20> direction of the hexagonal crystal structure and is substantially parallel to the surface of the substrate.

[0043] In certain embodiments, the lines of the next plurality of substantially parallel lines are interspersed or interleaved between lines of the first plurality of substantially parallel lines, with each line of the next plurality of substantially parallel lines being disposed between a different pair of adjacent lines of the first plurality of substantially parallel lines.

[0044] In certain embodiments, one or more of the next plurality of substantially parallel lines intersect one or more of the first plurality of substantially parallel lines.

[0045] In certain embodiments, the initial subsurface laser damage pattern comprises a first subsurface laser damage pattern including a first plurality of substantially parallel lines and a second subsurface laser damage pattern including a second plurality of substantially parallel lines, and the subsequent laser damage pattern embodies a third subsurface laser damage pattern, the lines of the third plurality of substantially parallel lines being interspersed or interleaved between the lines of the first plurality of substantially parallel lines and the second plurality of substantially parallel lines, and each line of the third plurality of substantially parallel lines being disposed between one line of the first plurality of substantially parallel lines and one line of the second plurality of substantially parallel lines.

[0046] In certain embodiments, each line of the first plurality of substantially parallel lines is separated from the nearest line of the second plurality of substantially parallel lines by at least 100 microns.

[0047] In certain embodiments, a focused depth of the laser radiation within the substrate differs between at least two of the first, second, and third subsurface laser damage patterns by a distance in a range from about 2 microns to about 5 microns.

[0048] In certain embodiments, the first subsurface laser damage pattern comprises a first plurality of cracks propagating laterally outwardly within the crystalline material from the first plurality of lines of substantially parallel lines, the second subsurface laser damage pattern comprises a second plurality of cracks propagating laterally outwardly within the crystalline material from the second plurality of lines of substantially parallel lines, 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 within the crystalline material from the third plurality of lines 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.

[0049] In certain embodiments, a focused depth of the laser radiation within the substrate is substantially the same during formation of the first subsurface laser damage pattern and the next subsurface laser damage pattern.

[0050] In certain embodiments, the method further includes detecting the presence of 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 at least one first doped region and at least one second doped region, and in response to detecting the condition indicative of non-uniform doping of the crystalline material, during formation of the first subsurface laser damage pattern and the next subsurface laser damage pattern, modifying a laser power 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.

[0051] In certain embodiments, the crystalline material comprises a single crystal semiconductor material.

[0052] In certain embodiments, the method further includes fracturing the crystalline material substantially along or between at least one of the first subsurface laser damage pattern and the next subsurface laser damage pattern to provide first and second portions of crystalline material, both of which have a reduced thickness compared to the substrate but substantially the same length and width as the substrate.

[0053] In certain embodiments, at least one of the first crystalline material portion or the second crystalline material portion comprises a free-standing wafer configured to have at least one epitaxial layer grown thereon. In certain embodiments, one of the first crystalline material portion or the second crystalline material portion comprises a device wafer including at least one epitaxial layer grown on a surface thereof.

[0054] In another aspect, the disclosure relates to a method of processing a crystalline material comprising: providing laser radiation focused at a first depth within a crystalline material of a substrate and performing a lateral relative movement between the laser and the substrate to form subsurface laser damage having a first subsurface laser damage pattern substantially centered at the first depth within the crystalline material; and providing laser radiation focused at a next depth within the crystalline material and performing a lateral relative movement between the laser and the substrate to form subsurface laser damage having a next laser damage pattern substantially centered at a next depth within the crystalline material, the next depth being different from the first depth, the next subsurface laser damage pattern being substantially aligned with the first subsurface laser damage pattern, and a vertical extension of at least a portion of the subsurface laser damage of the first subsurface laser damage pattern overlapping with a vertical extension of at least a portion of the subsurface laser damage of the next subsurface laser damage pattern.

[0055] In certain embodiments, the difference between the first depth and the next depth is within a range of about 2 microns to about 5 microns.

[0056] In certain embodiments, the crystalline material comprises a hexagonal crystal structure, the first subsurface laser damage pattern comprises a first plurality of substantially parallel lines, and the second subsurface laser damage pattern comprises a next plurality of substantially parallel lines, each line of the first plurality of substantially parallel lines and each line of the next plurality of substantially parallel lines is within ±5 degrees of normal to a <11-20> direction of the hexagonal crystal structure and is substantially parallel to the surface of the substrate.

[0057] In certain embodiments, the lines of the subsequent plurality of substantially parallel lines do not intersect with the lines of the initial plurality of substantially parallel lines.

[0058] In certain embodiments, one or more of the next plurality of substantially parallel lines intersect one or more of the first plurality of substantially parallel lines.

[0059] In certain embodiments, the first subsurface laser damage pattern and the next subsurface laser damage pattern each comprise a first subsurface laser damage pattern including a first plurality of substantially parallel lines and a second subsurface laser damage pattern including a second plurality of substantially parallel lines, where the lines of the first plurality of substantially parallel lines are non-parallel to the lines of the second plurality of substantially parallel lines.

[0060] In certain embodiments, each line of the first plurality of substantially parallel lines is separated from the nearest line of the second plurality of substantially parallel lines by at least 100 microns.

[0061] In certain embodiments, the method further includes detecting the presence of 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 at least one first doped region and at least one second doped region, and in response to detecting the condition indicative of non-uniform doping of the crystalline material, during formation of the first subsurface laser damage pattern and the next subsurface laser damage pattern, modifying a laser power 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.

[0062] In certain embodiments, the first subsurface laser damage pattern comprises a first plurality of substantially parallel lines and the second subsurface laser damage pattern comprises a next plurality of substantially parallel lines, wherein the lines of the first plurality of substantially parallel lines are non-parallel to the lines of the next plurality of substantially parallel lines, and wherein no line of the next plurality of substantially parallel lines is oriented more than 10 degrees from the lines of the first plurality of substantially parallel lines.

[0063] In certain embodiments, the method further includes fracturing the crystalline material substantially along or between at least one of the first depth and the next depth to obtain first and second portions of crystalline material, both of which have a reduced thickness compared to the substrate but substantially the same length and width as the substrate.

[0064] In certain embodiments, at least one of the first crystalline material portion or the second crystalline material portion comprises a free-standing wafer configured to have at least one epitaxial layer grown thereon. In certain embodiments, one of the first crystalline material portion or the second crystalline material portion comprises a device wafer including at least one epitaxial layer grown on a surface thereof.

[0065] In another aspect, the present disclosure relates to a method for processing a crystalline material comprising a plurality of non-overlapping areas, the method including forming a first plurality of subsurface laser damage regions within each of the plurality of areas of the crystalline material and forming a second plurality of subsurface laser damage regions within each of the plurality of areas of the crystalline material, wherein at least some of the subsurface laser damage regions of the first plurality of subsurface laser damage regions do not intersect with subsurface laser damage regions of the second plurality of subsurface laser damage regions, the first plurality of subsurface laser damage regions comprising a first plurality of substantially parallel lines, and the second plurality of subsurface laser damage regions comprising a second plurality of substantially parallel lines. The method includes performing a repetitive step of forming at least one of the first plurality or the second plurality of subsurface laser damage regions within each of a plurality of areas of the crystalline material, including providing focused laser radiation within the crystalline material to form repetitive subsurface laser damage regions aligned with at least one of the first plurality or the second plurality of subsurface laser damage regions, wherein the repetitive subsurface damage regions are centered at a different depth relative to a surface of the crystalline material than at least one of the first plurality or the second plurality of laser damage regions.

[0066] In certain embodiments, each line of the second plurality of substantially parallel lines does not intersect with any line of the first plurality of substantially parallel lines, hi 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.

[0067] In certain embodiments, the spacing between at least some of the first plurality of substantially parallel lines is less than the spacing between at least some of the second plurality of substantially parallel lines. The distance is substantially the same as the distance.

[0068] In certain embodiments, the crystalline material has a hexagonal crystal structure, and 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 perpendicular direction to a <112-0> direction of the hexagonal crystal structure and is substantially parallel to a planar surface of the crystalline material.

[0069] In certain embodiments, the method further includes forming a third plurality of subsurface laser damage regions within each of the plurality of areas of the crystalline material after forming the first plurality of subsurface laser damage regions and the second subsurface laser damage regions.

[0070] In certain embodiments, the first plurality of subsurface laser damage regions comprises a first plurality of substantially parallel lines, the second plurality of subsurface laser damage regions comprises a second plurality of substantially parallel lines, and the third plurality of subsurface laser damage regions comprises a third plurality of substantially parallel lines, at least some of the third plurality of substantially parallel lines being interspersed between the first plurality of substantially parallel lines and the second plurality of substantially parallel lines.

[0071] In certain embodiments, the method further includes repeating the formation of at least one of the first, second, or third subsurface laser damage regions to form a repetitive subsurface laser damage region that is aligned with at least one of the first, second, or third subsurface laser damage patterns, wherein the repetitive subsurface damage region is centered at a different depth relative to the surface of the crystalline material than the at least one of the first, second, or third subsurface laser damage patterns.

[0072] In certain embodiments, each laser damaged region extends substantially from one lateral boundary of the crystalline material to another lateral boundary of the crystalline material.

[0073] In certain embodiments, the plurality of areas comprises at least three areas.

[0074] In certain embodiments, the crystalline material comprises a single crystal semiconductor material.

[0075] In certain embodiments, the crystalline material comprises a substrate, and the method further includes fracturing the crystalline material substantially along or between at least one of the first plurality of subsurface laser damage regions and the second plurality of subsurface laser damage regions to obtain 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.

[0076] In certain embodiments, at least one of the first crystalline material portion or the second crystalline material portion comprises a free-standing wafer configured to have at least one epitaxial layer grown thereon.

[0077] In certain embodiments, one of the first crystalline material portion or the second crystalline material portion comprises a device wafer including at least one epitaxial layer grown on a surface thereof.

[0078] In another aspect, the present disclosure relates to a method for processing a crystalline material comprising a plurality of non-overlapping areas, the method including forming first and second plurality of subsurface laser damage regions sequentially across each of the plurality of areas to form distributed subsurface laser damage regions, wherein at least some of the subsurface laser damage regions of the first plurality of subsurface laser damage regions do not intersect with subsurface laser damage regions of the second plurality of subsurface laser damage regions. After forming the damage region and the second subsurface laser damage region, forming a third plurality of subsurface laser damage regions within each of the plurality of areas of the crystalline material.

[0079] The third plurality of subsurface laser damaged regions comprises a third plurality of substantially parallel lines, at least some of the third plurality of substantially parallel lines being interspersed between the first plurality of substantially parallel lines and the second plurality of substantially parallel lines. At least some of the lines of the third plurality of substantially parallel lines are interspersed between lines of the first plurality of substantially parallel lines and the second plurality of substantially parallel lines.

[0080] In certain embodiments, the first plurality of subsurface laser damage regions comprises a first plurality of substantially parallel lines and the second plurality of subsurface laser damage regions comprises a second plurality of substantially parallel lines.

[0081] In certain embodiments, each line of the second plurality of substantially parallel lines does not intersect with any of the lines in the first plurality of substantially parallel lines.

[0082] 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.

[0083] In certain embodiments, the spacing between at least some of the first plurality of substantially parallel lines is substantially the same as the spacing between at least some of the second plurality of substantially parallel lines.

[0084] In certain embodiments, the crystalline material has a hexagonal crystal structure, and 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 perpendicular direction to a <112-0> direction of the hexagonal crystal structure and is substantially parallel to a planar surface of the crystalline material.

[0085] In certain embodiments, the method further includes forming a third plurality of subsurface laser damage regions within each of the plurality of areas of the crystalline material after forming the first plurality of subsurface laser damage regions and the second subsurface laser damage regions.

[0086] In certain embodiments, the first plurality of subsurface laser damage regions comprises a first plurality of substantially parallel lines, the second plurality of subsurface laser damage regions comprises a second plurality of substantially parallel lines, and the third plurality of subsurface laser damage regions comprises a third plurality of substantially parallel lines, at least some of the third plurality of substantially parallel lines being interspersed between the first plurality of substantially parallel lines and the second plurality of substantially parallel lines.

[0087] In certain embodiments, the method further includes repeating the formation of at least one of the first, second, or third subsurface laser damage regions to form a repetitive subsurface laser damage region that is aligned with at least one of the first, second, or third subsurface laser damage patterns, wherein the repetitive subsurface damage region is centered at a different depth relative to the surface of the crystalline material than the at least one of the first, second, or third subsurface laser damage patterns.

[0088] In certain embodiments, each laser damaged region extends substantially from one lateral boundary of the crystalline material to another lateral boundary of the crystalline material.

[0089] In certain embodiments, the plurality of areas comprises at least three areas.

[0090] In certain embodiments, the crystalline material comprises a single crystal semiconductor material.

[0091] In certain embodiments, the crystalline material comprises a substrate, and the method further includes fracturing the crystalline material substantially along or between at least one of the first plurality of subsurface laser damage regions and the second plurality of subsurface laser damage regions to obtain 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.

[0092] In certain embodiments, at least one of the first crystalline material portion or the second crystalline material portion comprises a free-standing wafer configured to have at least one epitaxial layer grown thereon.

[0093] In certain embodiments, one of the first crystalline material portion or the second crystalline material portion comprises a device wafer including at least one epitaxial layer grown on a surface thereof.

[0094] In another aspect, the present disclosure relates to a method for processing a crystalline material wafer having a first surface having surface damage, the first surface being bounded by an edge, the method including: grinding the first surface with at least one first grinding device to remove a first portion of the surface damage; after grinding the first surface with the at least one first grinding device, edge grinding the edge to form a chamfered or rounded edge profile; and after edge grinding, grinding the first surface with at least one second grinding device to remove a second portion of the surface damage sufficiently to render the first surface suitable for further processing by chemical mechanical planarization.

[0095] In certain embodiments, the method further includes, after grinding of the first surface with the at least one second grinding device, processing the first surface by chemical mechanical planarization to render the first surface capable of epitaxially growing one or more layers of semiconductor material thereon.

[0096] In certain embodiments, the at least one first grinding device comprises at least one grinding wheel having a grinding surface of less than 5000 grit (e.g., 1000 grit, 1400 grit, 2000 grit, 3000 grit, 4000 grit, etc.) and the at least one second grinding device comprises at least one grinding wheel having a grinding surface of at least 5000 grit (e.g., 5000 grit, 7000 grit, 8000 grit, 10,000 grit, 15,000 grit, 20,000 grit, 25,000 grit, 30,000 grit, etc.).

[0097] In certain embodiments, grinding of the first surface with at least one first grinding device includes removal of crystalline material from 20 microns to 100 microns (e.g., 20 microns to 80 microns, 40 microns to 80 microns, 40 to 60 microns, etc.) thick, and grinding of the second surface with at least one second grinding device includes removal of crystalline material from 3 to 15 microns (e.g., 5 to 10 microns) thick.

[0098] In certain embodiments, the surface damage includes laser damage and spallation damage.

[0099] In a particular embodiment, the crystalline material comprises a silicon carbide material and the first surface comprises a Si-terminated surface of the silicon carbide material.

[0100] In another aspect, the present disclosure provides a method for processing a crystalline material wafer having a first surface with surface damage. and after grinding the first surface with the at least one first grinding device, grinding the first surface with at least one second grinding device to remove a second portion of the surface damage sufficiently to render the first surface suitable for further processing by chemical mechanical planarization; after grinding the first surface with the at least one second grinding device, forming a protective coating on the first surface; after depositing a sacrificial material on the first surface, edge grinding the edge to form a chamfered or rounded edge profile; and after edge grinding, removing the protective coating from the first surface.

[0101] In certain embodiments, the method further includes, after removal of the sacrificial material from the first surface, processing the first surface by chemical mechanical planarization to render the first surface suitable for epitaxial growth of one or more layers of semiconductor material thereon.

[0102] In a particular embodiment, the at least one first grinding device comprises at least one grinding wheel having a grinding surface less than 5000 grit, and the at least one second grinding device comprises at least one grinding wheel having a grinding surface of at least 5000 grit.

[0103] In certain embodiments, grinding of the first surface with at least one first grinding device comprises removal of crystalline material from 20 microns to 100 microns thick, and grinding of the second surface with at least one second grinding device comprises removal of crystalline material from 3 to 15 microns thick.

[0104] In a particular embodiment, the protective coating comprises a photoresist.

[0105] In certain embodiments, the surface damage includes laser damage and spallation damage.

[0106] In a particular embodiment, the crystalline material comprises a silicon carbide material and the first surface comprises a Si-terminated surface of the silicon carbide material.

[0107] In another aspect, the present disclosure relates to a material processing apparatus comprising: a laser processing station configured to form a subsurface laser damage region in a crystalline material substrate fed to the laser processing station; a crushing station arranged to receive the crystalline material substrate processed by the laser processing station and configured to crush the crystalline material substrate along the subsurface laser damage region to form crystalline material portions removed from the crystalline material substrate, each crystalline material portion comprising surface damage; a plurality of rough grinding stations arranged in parallel downstream of the crushing station and configured to remove first sites of surface damage from the crystalline material portions, at least a first and a second rough grinding station of the plurality of rough grinding stations configured to be operated simultaneously to remove first sites of surface damage of different crystalline material portions; and at least one fine grinding station arranged downstream of the plurality of rough grinding stations and configured to remove second sites of surface damage from the crystalline material portions sufficiently to render at least one surface of each crystalline material portion suitable for further processing by chemical mechanical planarization.

[0108] In certain embodiments, the apparatus further comprises at least one chemical mechanical planarization station disposed downstream of the at least one precision grinding station and configured to render at least one surface of each crystalline material portion suitable for further processing by chemical mechanical planarization. It further comprises:

[0109] In certain embodiments, the apparatus further comprises at least one edge grinding station configured to grind an edge of each crystalline material portion to form a chamfered or rounded edge profile.

[0110] In a particular embodiment, each coarse grinding station includes at least one grinding wheel having a grinding surface of less than 5000 grit, and at least one fine grinding station includes at least one grinding wheel having a grinding surface of at least 5000 grit.

[0111] In certain embodiments, each coarse grinding station is configured to remove between 20 microns and 100 microns of crystalline material from each crystalline material portion, and each fine grinding station is configured to remove between 3 and 15 microns of crystalline material from each crystalline material portion.

[0112] In certain embodiments, the laser processing station is configured to simultaneously form subsurface laser damaged regions in multiple crystalline material substrates.

[0113] In other embodiments, 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 with one or more of the other disclosed features and elements.

[0114] Other aspects, features, and embodiments of the present disclosure will become more fully apparent from the ensuing disclosure and the appended claims.

[0115] 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]

[0116] [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 that follows a first subsurface laser damage pattern in two portions of the substrate. [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]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 26] 26 is a 45x magnified SEM image of a portion of the SiC wafer fragment from FIG. 25 taken at a tilt angle of 15 degrees, with superimposed arrows indicating the orientation of the [1-100] and [11-20] crystallographic planes. [Figure 27] FIG. 26 is a 1,300x magnified SEM image of a portion of the SiC wafer fragment from FIG. 25 taken at a tilt angle of 15 degrees. [Figure 28] FIG. 26 is a 350x magnified SEM image of a portion of the SiC wafer fragment of FIG. 25 taken at a tilt angle of 15 degrees. [Figure 29] FIG. 26 is a 100x magnified SEM image of a portion of the SiC wafer fragment of FIG. 25 taken at a tilt angle of 2 degrees. [Diagram 30] FIG. 26 is a 1,000x magnified SEM image of a portion of the SiC wafer fragment from FIG. 25 taken at a 2 degree tilt angle. [Figure 31A] FIG. 26 is a confocal laser scanning microscope image of a small central portion of the SiC wafer of FIG. 25, with superimposed crosshairs marking the location of the “trench” formed by the laser scan. [Figure 31B] 21B is a plot of the surface profile of a portion of the SiC wafer of FIG. 21A. [Figure 32A] FIG. 26 is a confocal laser scanning microscope image of a larger section near the top of the SiC wafer of FIG. 25 (at the time of the image), with the superimposed crosshairs marking the location of the “trenches” 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. 25, 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 sturdy 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 the crystalline material substrate separated from the bonded assembly (on a water-cooled chuck), including the sturdy carrier and the portion of the 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. [Figure 36A] 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. [Figure 36B] 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. [Figure 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. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0117] An embodiment of the present disclosure provides a method for processing a crystalline material substrate such that a plurality of patterns of subsurface laser damage are formed that facilitate 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 in the subsequent plurality of substantially parallel lines differs from the angular orientation of the lines in 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 in 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.

[0118] 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.

[0119] Various embodiments disclosed herein address 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 enabling high throughput of a laser tool and achieving low kerf loss. Certain embodiments disclosed 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 some (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 by not intersecting the laser damage patterns, diffusion of localized stresses may be beneficially avoided. In certain embodiments, the formation of the first and second distributed subsurface laser damage patterns is performed in a manner that prevents propagation of localized subsurface cracks between them, while 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 the entire 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 allows for reliable separation of thin layers of crystalline material from the substrate with fewer laser damage lines per layer to be removed, while achieving low levels of laser damage (enabling low kerf loss). It has been found to beneficially achieve increased tool throughput.

[0120] 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.

[0121] Terms such as first, second, etc. may be used herein to describe various elements, but 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 can be called a second element, and similarly, a second element can be called a first element, without departing from the scope of the present disclosure. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0122] 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.

[0123] 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.

[0124] 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.

[0125] 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. Any term used herein shall not be construed as being inconsistent with its meaning in the context of the present specification and related art. It will be further understood that the terms and expressions should be construed as having a meaning that is not idealized or overly formal, and are not to be construed in an idealized or overly formal sense, unless expressly defined as such herein.

[0126] 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 sufficient thickness (i) to be surface-processed (e.g., lapped and polished) to support epitaxial growth of one or more layers of semiconductor material, and optionally (ii) to 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 may have a thickness approximately equal to at least one or more of the following thicknesses: 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 in association 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 divided 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 in association with one or more metal contacts) may subsequently be formed. In certain embodiments, the substrate may have a diameter of 150 mm or greater, or 200 mm or greater. 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.

[0127] 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.

[0128] 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.

[0129] 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 the laser radiation of the first depth is provided through the end face 16 of the ingot 15 to form the subsurface laser damage, a carrier (not shown) may be bonded to the end face 16, the ingot 15 may be fractured along the subsurface laser damage, and an on-axis wafer may then be formed. Conversely, when the laser radiation of the first depth is provided through the end face 16A of the off-axis ingot 15A to form the subsurface laser damage, a carrier (not shown) may be bonded to the end face 16A, the ingot 15A may be fractured along the subsurface laser damage, and an off-axis wafer may then be formed.

[0130] [Subsurface laser damage formation] 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.

[0131] 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.

[0132] 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.

[0133] 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.

[0134] 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).

[0135] 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.

[0136] 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.

[0137] 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.

[0138] 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.

[0139] 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.

[0140] 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.

[0141] 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.

[0142] 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 the correction of aberrations important to achieve the desired results.

[0143] 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.

[0144] In certain embodiments, the crystalline material substrate may exhibit position-wise (e.g., laterally and / or diametrically) varying doping across a major surface (e.g., face) of the substrate. For example, growth of doped SiC may result in the formation of doped ring regions (as shown in Figures 14A, 14C, and 14D) with increased dopant concentration, resulting in higher laser absorption and slight changes in the refractive index, both of which affect the focusing depth of the laser radiation in the substrate. By increasing the laser power when directing the focused laser radiation within the doped ring regions compared to the power used when directing the focused laser radiation into the material outside the doped ring regions, Various characteristics of the doped ring regions can be compensated for. 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 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 the condition indicative of non-uniform doping of the crystalline material, during formation of the subsurface laser damage pattern, the laser power can be altered 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 each other.

[0145] 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.

[0146] 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 and / or laser focus) can be adjusted in response to such measurements before scanning across the 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 formation of the subsurface laser damage pattern for each substrate layer to be removed in the next fracture).

[0147] 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. acan be achieved. Laser damage can then be applied to one or more desired depths in the crystalline material substrate, with the spacing and direction of the laser damage tracks optionally depending on the crystal orientation of the crystalline material substrate. A first carrier can be bonded to the top surface of the crystalline material substrate. Wafers 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.

[0148] Wire sawing of SiC wafers is typically at least about 250 microns per wafer. However, 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.

[0149] 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.

[0150] [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 sequentially formed first and second, or first through third, or first through fourth, subsurface laser damage patterns, each subsurface laser damage pattern comprising multiple parallel lines. To enhance the ease of spallation of crystalline material along or adjacent to the subsurface laser damage regions, it is believed that forming multiple subsurface laser damage patterns consecutively in a distributed manner (e.g., forming a first subsurface damage pattern, then a second subsurface damage pattern, then any subsequent subsurface damage patterns, with the various lines of each damage pattern distributed among the other damage patterns) is preferable over forming the same tracks without distribution. Without wishing to be bound by any particular theory as to the reasons for the improved spallation results obtained with distributed subsurface laser damage patterns in crystalline materials, it is believed that the formation of consecutive distributed subsurface laser damage patterns increases the degree of preservation of internal stresses within the semiconductor material, which in turn promotes the lateral propagation of cracks emanating from different subsurface laser damage lines.

[0151] In certain embodiments, the 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 (e.g., primarily or substantially along the c-plane) from the first plurality of substantially parallel lines, the cracks emanating from each line not connected to the cracks emanating from each adjacent line. In certain embodiments, after formation of the first subsurface laser damage pattern, a bonding A second subsurface laser damage pattern is formed in the crystalline material comprising a second plurality of parallel lines, the second subsurface laser damage pattern including a second plurality of cracks within the crystalline material propagating laterally outward from the lines of the second plurality of substantially parallel lines, at least some of the cracks of the second plurality of cracks connecting with cracks emanating from two adjacent lines of the first plurality of lines (e.g., resulting in the formation of a continuous crack).

[0152] 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.

[0153] 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-dispersed 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-dispersed) 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, there may be a regular (e.g., regularly repeating) pattern of distributed damage lines in at least one region of the substrate, and an irregular (e.g., non-regularly repeating) pattern of either distributed or non-dispersed damage lines in at least one other region of the substrate.

[0154] FIG. 11A provides a top plan view of a crystalline material substrate 70 including first, second, and third subsurface laser damage patterns defined in accordance with 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 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, the first plurality of parallel lines 71 are aligned parallel to the first plurality of parallel lines 72, and the third plurality of parallel lines 73. A first plurality of parallel wires 71 and / or a second plurality of parallel wires 72 are formed in a second pass, and a third plurality of parallel wires 73 are formed in a third pass. The third pass serves to connect cracks originally emanating from either the first parallel wires 71 and / or the second parallel wires 72.

[0155] 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.

[0156] 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.

[0157] 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.

[0158] 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.

[0159] 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.

[0160] 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.

[0161] 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).

[0162] 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 can be formed with a pitch (i.e., spacing between lines) of 500 microns, and a second plurality of parallel lines 82 can 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 can 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 three-line groups 89 separated from each other three-line group by gaps of 250 microns, with adjacent lines within each three-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.

[0163] 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 .

[0164] 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.

[0165] 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.

[0166] 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.

[0167] 15 is a schematic top plan view of a crystalline material substrate 110 including a substrate flat 118 and including first through third plurality of dispersed subsurface laser damage lines 111-113 forming first through third subsurface laser damage patterns. The first plurality of lines 111 and the second plurality of lines 112 are each parallel to one another and non-perpendicular (e.g., at an angle difference in the range of 1 to 5 degrees) to the primary substrate flat 108, while the third plurality of lines 113 is perpendicular to the primary substrate flat 118, but at least some (or all) of the lines do not intersect with the lines of the first group of lines 111 and the second group of 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 line 111 to the third line 113 form a three-line repeat group 114 .

[0168] 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.

[0169] 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.

[0170] 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.

[0171] 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.

[0172] 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.

[0173] FIG. 20A is a top plan view of a crystalline material substrate 150 showing non-overlapping first, second, and third areas 150A-150C in which laser damage regions may be formed. Shading has been added to the first and third areas 150A-150C for illustrative purposes to highlight the boundaries between the first to third areas 150A-150C, but it will be appreciated that an actual crystalline material substrate 150 will typically be of uniform color. Each area 150A-150C contacts a portion of the primary flat 150' of the 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.

[0174] 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 within the first through third areas 150A through 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. Within each of the first through third areas 150A through 150C, a plurality of laser damage regions 151 are provided. Although not shown in FIG. 20B, other laser damage regions 151 may be formed within the first through third areas 150A through 150C (as shown in FIG. 11B). It will be appreciated that laterally extending cracks may emanate from the laser damage regions 151, but that these may preferably not connect adjacent laser damage regions 151. In certain embodiments, multiple subsurface laser damage regions 151 may be formed in a first area 150A, then in a second area 150B, and finally in a third area 150C.

[0175] 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.

[0176] 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 form a plurality of three-line groups 154 that are spaced apart from one another by inter-group spacings 154' that exceed the spacing between adjacent laser damage regions 151-153 in each three-line group 154. Although not shown in FIG. 20C, it will be appreciated that cracks extending laterally from each laser damage region 151-153 may develop, 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 can be formed in the same order as the first subsurface laser damage regions 151 and the second subsurface laser damage regions 152 (e.g., the subsurface laser damage regions 153 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 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.

[0177] [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.

[0178] 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)).

[0179] 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 relative 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 is repeated to form additional laser damage regions 165''', 165'''' in the first area 164A and the second area 164B, and finally to form a first subsurface laser damage pattern over the 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 throughout the substrate 164 can be formed in half the time that 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 both substrates 166A, 166B according to at least one subsurface laser damage pattern. The first laser damage formation step is performed on the first substrate 16. The holder carrying the substrates 166A, 166B can be indexed laterally (e.g., in the direction opposite to the right-pointing arrow) relative to the laser, and the next laser damage formation step includes applying 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, as well as 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.

[0180] [Formation of overlapping subsurface laser damage of different depths] In certain embodiments, a first subsurface laser damage may be formed within the crystalline material substrate centered at a first depth, and an additional subsurface laser damage may 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 may 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 may be performed in response to a determination (e.g., by optical analysis) prior to spallation that one or more prior subsurface laser damage formation steps are incomplete. The formation of overlapping subsurface laser damage at different depths may be performed in conjunction with any other method steps herein, including (but not limited to) the formation of multiple interspersed subsurface laser damage patterns.

[0181] FIG. 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, where the subsurface damage pattern 173 has been created by focused laser radiation 179. The first subsurface laser damage pattern 173 has a vertical extension 174 that remains within the substrate 170 between the first surface 171 and an opposing second surface 172. FIG. 23B is a schematic cross-sectional view of the substrate of FIG. 23A after formation of a second subsurface laser damage pattern 175 centered at a second depth and aligned with the first subsurface laser damage pattern 173, where 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 crystalline material 170 may be performed along or through damage overlap region 177.

[0182] [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 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 may vary from about 2 microns to about 5 microns between different groups of laser lines (e.g., at least two different groups of first and second groups, first through third groups, first through fourth groups, etc.). They differ by distances in the range of up to a micron (ie, from about 2 μm to about 5 μm).

[0183] [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.

[0184] 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.

[0185] [Wafer image] 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, when attempting to form subsurface laser damage in a SiC wafer, it may be beneficial to increase the laser power in the doped ring 182 compared to the outer annular portion 183. In certain embodiments, the presence of conditions indicative of non-uniform doping of the crystalline material across at least a portion of the surface of the substrate may be detected, for example, by detecting changes in optical reflectivity or absorptivity 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). 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 (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.

[0186] Figure 25 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.

[0187] FIG. 26 is a 45x magnified SEM image of a portion of the SiC wafer fragment of FIG. 25 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. 27 is a 1,300x magnified SEM image of a portion of the SiC wafer fragment of FIG. 25 taken at a tilt angle of 15 degrees. FIG. 28 is a 1,300x magnified SEM image of a portion of the SiC wafer fragment of FIG. 25 taken at a tilt angle of 15 degrees. This is a 350x magnified SEM image of a portion of a SiC wafer fragment. As shown in Figure 28, the off-axis cleavage plane correlates to some degree with the laser spacing, but is not consistent across the wafer surface. This can be attributed, at least in part, to variations in the laser line position relative to the cleavage plane. In this wafer, spallation was initiated at the polycrystalline introduction location.

[0188] Figure 29 is a 100x magnification SEM image of a portion of the SiC wafer fragment from Figure 25 taken at a 2 degree tilt angle. Figure 30 is a 1,000x magnification SEM image of a portion of the SiC wafer fragment from Figure 25 taken at a 2 degree tilt angle. Figures 29 and 30 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 30.

[0189] Figure 31A is a confocal laser scanning microscope image of a small central portion of the SiC wafer of Figure 25, with superimposed crosshairs marking the location of the "trench" formed 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.

[0190] FIG. 32A is a confocal laser scanning microscope image of a larger portion near the top of the SiC wafer of FIG. 35 (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.

[0191] Figure 33A is a confocal laser scanning microscope image of a larger portion near the bottom (at the time of image capture) of the SiC wafer of Figure 25, with superimposed crosshairs marking the location of the "trench" created by the laser scan. Figure 33B is a plot of the surface profile of the portion near the bottom of the SiC wafer of Figure 33A. Figure 33B shows the lateral distance variation between adjacent pairs of laser damage lines, with one pair separated by 334 microns and another pair separated by 196 microns, with a maximum depth variation of 13 microns.

[0192] [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.

[0193] [Cooling spallation of rigid supports with support / substrate CTE mismatch] 34A-34F show 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. 2 is a schematic cross-sectional side view of a rigid carrier 202 having a layer of material 198 and having a second surface 204 opposite a first surface 203.

[0194] 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.

[0195] 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.

[0196] In certain embodiments, the cooled chuck 206 has a diameter smaller than that of the rigid carrier 202. Although the cooled chuck 206 can be supplied with a cooling liquid, 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. Favorable separation results have been obtained for fracturing a single crystal SiC material supported by a single crystal sapphire substrate using a cooled chuck maintained at -70°C. Such a temperature can be maintained using a variety of cooling liquids, for example 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 a temperature can be maintained using a single-phase evaporative cooling system. The ability to use a single-phase evaporative cooling system or a two-phase pumped evaporative cooling system rather than liquid nitrogen significantly reduces operational costs.

[0197] 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.

[0198] 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.).

[0199] 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.

[0200] [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 includes applying ultrasonic energy to the crystalline material while in the bonded state. FIG. 35 is a schematic cross-sectional view of an assembly 188A including a crystalline material 190A with subsurface laser damage 196A bonded to a rigid carrier 202A using an intervening adhesive material 198A, the assembly 188A being disposed within 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 fracture 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 prior to separation (e.g., due to CTE mismatch). Such residual stresses can reduce the amount of ultrasonic energy required to initiate fracture of the crystalline material, thereby reducing the likelihood of material failure.

[0201] [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.

[0202] 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.

[0203] 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 can be affected by the CTE difference between the substrate and the carrier. In certain embodiments, the 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 larger mechanical force may be required to complete the fracturing. Conversely, if the CTE mismatch is large, a smaller mechanical force or no mechanical force may be required to complete the fracturing.

[0204] [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.

[0205] 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.

[0206] 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 can 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.

[0207] FIG. 37H shows the thick wafer 242 of FIG. 37G after one or more epitaxial layers 253 have been grown 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 not present. 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. Traditionally, grinding is performed against the second surface 252 to thin the thick wafer 242 to a thickness appropriate for the resulting device (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 so that they can be surface-finished and used to fabricate another operational semiconductor device.

[0208] 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.

[0209] FIG. 37K illustrates the application of a temporary adhesive material 252 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. 37J after adding a first carrier 258 over the temporary adhesive material 257. 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 that is intended to remove a portion (i.e., a layer) of the thick wafer 242.

[0210] 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.

[0211] 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).

[0212] Exemplary methods involving reuse of carrier wafers FIG. 38 is a flow chart outlining steps of a method according to the present disclosure. Starting at the top left, 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 relating 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, leaving one or more crystalline material portions of the crystalline material 280. can undergo epitaxial growth of multiple layers to form epitaxial device 280', while 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.

[0213] 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.

[0214] [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. Without wishing to be bound by any particular theory as to the reason for this phenomenon, 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 make the surface more susceptible to cracking. For this reason, it has been found to be beneficial to perform at least some surface processing (e.g., grinding and / or polishing) prior to edge grinding.

[0215] It has been found that the rough grinding step (i.e., to remove laser damage and spallation damage along the substrate portion and the fractured 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), but the carrier may be removed prior to edge grinding (or to protect the wafer prior to edge grinding). Preferably, the coating is removed (before coating with a coating).

[0216] 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.

[0217] 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 functions to remove damage remaining after fine grinding, which itself removes damage remaining after 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) from 20 microns to 100 microns thick, and the fine grinding station 312 is configured to remove crystalline material from 3 to 15 microns thick. 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.

[0218] 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.

[0219] 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 created by the edge grinding station 332, but leaves a rounded or chamfered edge profile sufficient to prevent fracture of the wafer edge.

[0220] 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 device can be embodied in a rough grinding station 328A, 328B, edge grinding can be performed by an edge grinding station 332, and the second grinding device can be embodied in a fine grinding station 312. In certain embodiments, a carrier removal step can be performed after grinding of the first surface with at least one first grinding device and before edge grinding the edge to form a chamfered or rounded edge profile.

[0221] 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.

[0222] 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 parallel-arranged rough grinding stations 348A, 348B, and a second robot handler 348 upstream of the fine grinding station 352. The coating station 354 may be a coating station such as spin coating, dip coating, spray coating, or the like. The edge grinding station 365 may be configured to apply a protective coating (e.g., photoresist) by a method similar to that described above. The protective coating should be thick and robust enough to absorb any damage that may be imparted 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.

[0223] 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.

[0224] 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.

[0225] 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 side wall 370, according to one embodiment. The upper end face 366 is positioned horizontally to receive a laser beam 376. A carrier 372 is attached to the lower end face 368, and a chuck 374 (e.g., a vacuum chuck) may hold the carrier 372. A gripping effector 378 having a non-perpendicular surface is provided for gripping the side wall 370 of the ingot 364, and the gripping effector 378 is positioned at a non-perpendicular angle A1, A2 to a horizontal actuation rod 380. Using the gripping device 362 to hold the ingot 364 as shown (e.g., near its bottom), the upper end face 366 and an upper portion of the side wall 370 are available for processing using the methods disclosed herein.

[0226] 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 allows for a self-alignment between the gripping effector 378' and the side wall 370' of the ingot 364'. Dynamic alignment becomes easier.

[0227] 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 remainder of the 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.

[0228] Potential technical benefits provided by one or more embodiments of the present disclosure may include: reduced crystalline material kerf loss compared to wire sawing; reduced processing time and increased throughput of crystalline material wafers and resulting devices compared to wire sawing; reduced laser processing time compared to conventional laser-based methods; reduced force required to cause fracture along the laser damage region; reduced need for post-separation surface smoothing to remove laser damage after separation; reduced bowing and breakage of crystalline material; and / or increased reproducibility of thin layers separated from crystalline material substrates.

[0229] 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. splitting the single laser radiation to form a first split laser radiation and a second split laser radiation; providing the first split laser radiation focused within a first portion of a crystalline material substrate and providing the second split laser radiation focused within a second portion of the crystalline material substrate, and performing lateral relative movement between (i) the laser and (ii) the crystalline material substrate to simultaneously form a first subsurface laser damage in each of the first and second portions of the crystalline material substrate, the first subsurface laser damage having a first subsurface laser damage pattern including a first plurality of first lines, each of the first plurality of first lines being substantially parallel; providing the first split laser radiation focused within the first portion of the crystalline material substrate and providing the second split laser radiation focused within the second portion of the crystalline material substrate; and performing a lateral relative movement between (i) the laser and (ii) the crystalline material substrate to simultaneously form a next subsurface laser damage in each of the first and second portions of the crystalline material substrate, the next subsurface laser damage having a next subsurface laser damage pattern including a next plurality of next lines, each of the next plurality of next lines being substantially parallel; within each of the first portion and the second portion of the crystalline material substrate, at least some of the subsequent lines of the subsequent plurality of subsequent lines do not intersect with any initial lines in the initial plurality of initial lines; Within each of the first and second portions of the crystalline material substrate, subsequent lines of the subsequent plurality of subsequent lines are distributed among initial lines of the initial plurality of initial lines. Crystal material processing method.

2. 2. The crystalline material processing method of claim 1, wherein within each of the first and second portions of the crystalline material substrate, one or more initial lines of the initial plurality of initial lines are substantially parallel to one or more subsequent lines of the subsequent plurality of subsequent lines.

3. 2. The crystalline material processing method of claim 1, wherein within each of the first and second portions of the crystalline material substrate, one or more initial lines of the initial plurality of initial lines are non-parallel to one or more subsequent lines of the subsequent plurality of subsequent lines, and an angular orientation of one or more subsequent lines of the subsequent plurality of subsequent lines differs from an angular orientation of one or more initial lines of the initial plurality of initial lines by 10 degrees or less.

4. 2. The crystalline material processing method of claim 1, wherein within each of the first and second portions of the crystalline material substrate, each subsequent line of the subsequent plurality of subsequent lines does not intersect with any initial line of the initial plurality of initial lines.

5. Within each of the first and second portions of the crystalline material substrate, the initial subsurface laser damage pattern includes a first subsurface laser damage pattern including a first plurality of first lines, the first plurality of first lines being substantially parallel, and a second subsurface laser damage pattern including a second plurality of second lines, the second plurality of second lines being substantially parallel; within each of the first and second portions of the crystalline material substrate, the subsequent subsurface laser damage pattern includes a third subsurface laser damage pattern, the third subsurface laser damage pattern includes a third plurality of third lines, the third plurality of third lines being substantially parallel; 2. The crystalline material processing method of claim 1, wherein within each of the first and second portions of the crystalline material substrate, third lines in the third plurality of third lines are distributed between first lines in the first plurality of first lines and between second lines in the second plurality of second lines, and each third line in the third plurality of third lines is disposed between one first line in the first plurality of first lines and one second line in the second plurality of second lines.

6. 6. The crystalline material processing method of claim 5, wherein within each of the first and second portions of the crystalline material substrate, each first line in the first plurality of first lines is separated from a nearest second line in the second plurality of second lines by at least 100 microns.

7. within each of the first and second portions of the crystalline material substrate, the first subsurface laser damage pattern includes a first plurality of cracks within the crystalline material substrate propagating laterally outward from the first lines in the first plurality of first lines; Within each of the first and second portions of the crystalline material substrate, the second subsurface laser damage pattern includes a second plurality of cracks within the crystalline material substrate propagating laterally outward from the second lines of the second plurality of second lines, the second plurality of cracks being disjoint from the first plurality of cracks; 6. The crystalline material processing method of claim 5, wherein within each of the first and second portions of the crystalline material substrate, the third subsurface laser damage pattern includes a third plurality of cracks propagating laterally outward from the third lines in the third plurality of third lines within the crystalline material substrate, 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 with at least some of the cracks in the second plurality of cracks.

8. the crystalline material substrate comprises a hexagonal crystal structure; 2. The crystalline material processing method of claim 1, wherein for each of the first and second portions of the crystalline material substrate, each first line in the first plurality of first lines and each next line in the next plurality of next lines is within ±5 degrees of a perpendicular direction to a <11-20> direction of the hexagonal crystal structure and is substantially parallel to a planar surface of the crystalline material substrate.

9. 2. The crystalline material processing method of claim 1, further comprising fracturing the crystalline material substrate substantially along or between at least one of the first subsurface laser damage pattern and the second subsurface laser damage pattern to obtain a first crystalline material portion and a second crystalline material portion of the crystalline material substrate, each of the first and second portions of the crystalline material substrate having a reduced thickness compared to the crystalline material substrate but having substantially the same length and width as the crystalline material substrate.

10. 10. The method of claim 9, wherein at least one of the first crystalline material portion or the second crystalline material portion comprises a free-standing wafer configured to have at least one epitaxial layer grown thereon.

11. 10. The method of claim 9, wherein one of the first crystalline material portion or the second crystalline material portion comprises a device wafer including at least one epitaxial layer grown thereon.

12. splitting the single laser radiation to form a first split laser radiation and a second split laser radiation; providing the first split laser radiation focused within a first substrate of crystalline material and providing the second split laser radiation focused within a second substrate of crystalline material; and performing lateral relative movement between (i) the laser and (ii) the first substrate and the second substrate to simultaneously form first subsurface laser damage in each of the first substrate and the second substrate, the subsurface laser damage having a first subsurface laser damage pattern including a first plurality of first lines, the first plurality of first lines being substantially parallel; providing the first split laser radiation focused within the first substrate and providing the second split laser radiation focused within the second substrate; and performing lateral relative movement between (i) the laser and (ii) the first substrate and the second substrate to simultaneously form next subsurface laser damage in each of the first substrate and the second substrate, the next subsurface laser damage having a next subsurface laser damage pattern including a next plurality of next lines, the next plurality of next lines being substantially parallel; Within each of the first substrate and the second substrate, at least some of the subsequent lines in the subsequent plurality of subsequent lines do not intersect with any initial lines in the initial plurality of initial lines; Within each of the first substrate and the second substrate, subsequent lines of the subsequent plurality of subsequent lines are distributed among initial lines of the initial plurality of initial lines. Crystal material processing method.

13. 13. The crystalline material processing method of claim 12, wherein within each of the first substrate and the second substrate, each subsequent line of the subsequent plurality of subsequent lines does not intersect with any initial line of the initial plurality of initial lines.

14. Within each of the first substrate and the second substrate, the initial subsurface laser damage pattern includes a first subsurface laser damage pattern including a first plurality of first lines, the first plurality of first lines being substantially parallel, and a second subsurface laser damage pattern including a second plurality of second lines, the second plurality of second lines being substantially parallel; within each of the first substrate and the second substrate, the subsequent subsurface laser damage pattern includes a third subsurface laser damage pattern, the third subsurface laser damage pattern includes a third plurality of third lines, the third plurality of third lines being substantially parallel; 13. The crystalline material processing method of claim 12, wherein within each of the first substrate and the second substrate, the third lines in the third plurality of third lines are distributed between the first lines in the first plurality of first lines and the second plurality of second lines, and each third line in the third plurality of third lines is disposed between one first line in the first plurality of first lines and one second line in the second plurality of second lines.

15. 15. The crystalline material processing method of claim 14, wherein within each of said first substrate and said second substrate, each first line in said first plurality of first lines is separated from a nearest second line in said second plurality of second lines by at least 100 microns.

16. within each of the first substrate and the second substrate, the first subsurface laser damage pattern includes a first plurality of cracks within the crystalline material propagating laterally outward from the first lines in the first plurality of first lines; Within each of the first substrate and the second substrate, the second subsurface laser damage pattern includes a second plurality of cracks within the crystalline material propagating laterally outward from the second lines in the second plurality of second lines, the second plurality of cracks being disjoint from the first plurality of cracks; 15. The crystalline material processing method of claim 14, wherein within each of the first and second substrates, the third subsurface laser damage pattern comprises a third plurality of cracks propagating laterally outward from the third lines in the third plurality of third lines within the crystalline material substrate, at least some of the cracks of the third plurality of cracks connecting with at least some of the cracks of the first plurality of cracks and with at least some of the cracks of the second plurality of cracks.

17. Attaching a first substrate and a second substrate of crystalline material to a holder, the first substrate including a first plurality of regions that do not overlap one another and the second substrate including a second plurality of regions that do not overlap one another; splitting the single laser radiation to form a first split laser radiation and a second split laser radiation; providing the first split laser radiation to the first substrate and the second split laser radiation to the second substrate to form a first plurality of subsurface laser damage regions in each of the first plurality of regions and the second plurality of regions; providing the first split laser radiation to the first substrate and the second split laser radiation to the second substrate to form a second plurality of subsurface laser damage regions in each of the first plurality of regions and the second plurality of regions, wherein within each of the first substrate and the second substrate, subsurface laser damage regions of at least some of the first plurality of subsurface laser damage regions do not intersect with subsurface laser damage regions of the second plurality of subsurface laser damage regions; subsequent to forming the first plurality of subsurface laser damage regions and the second plurality of subsurface laser damage regions, (i) forming a third plurality of subsurface laser damage regions in each region of the first plurality of regions and (ii) in each region of the second plurality of regions; For each of the first substrate and the second substrate, the first plurality of subsurface laser damage regions includes a first plurality of first lines; For each of the first substrate and the second substrate, the second plurality of subsurface laser damage regions includes a second plurality of second lines; For each of the first substrate and the second substrate, the third plurality of subsurface laser damage regions includes a third plurality of third lines; For each of the first substrate and the second substrate, at least some of the third lines of the third plurality of third lines are distributed between first lines of the first plurality of first lines and second lines of the second plurality of first lines. Crystal material processing method.

18. 20. The crystalline material processing method of claim 17, wherein within each of the first and second substrates, the first plurality of subsurface laser damage regions comprises a first plurality of first lines, the first plurality of first lines being substantially parallel, and the second plurality of subsurface laser damage regions comprises a second plurality of second lines, the second plurality of second lines being substantially parallel.

19. 20. The crystalline material processing method of claim 18, wherein within each of said first substrate and said second substrate, each first line in said first plurality of first lines is separated from a nearest second line in said second plurality of second lines by at least 100 microns.

20. 20. The crystalline material processing method of claim 18, wherein within each of the first substrate and the second substrate, each second line in the second plurality of second lines does not intersect with any first line in the first plurality of first lines.

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