Carrier-assisted method for parting crystalline material along laser damage region

Abstract

To provide a carrier-assisted method for parting or removing relatively thin layers of crystalline material from a substrate, such as a wafer, having subsurface laser damage.SOLUTION: The method includes joining a surface of a crystalline material substrate 172 to a rigid carrier 176, with a subsurface laser damage region provided within the substrate at a depth relative to the surface. The crystalline material is fractured along the subsurface laser damage region to produce a bonded assembly 178 including the carrier 174 and a portion of the crystalline material substrate. The fracture of the crystalline material having the subsurface damage bonded to the rigid carrier is promoted by: applying a mechanical force proximate to at least one carrier edge to impart a bending moment to the carrier; cooling the carrier when the carrier has a greater coefficient of thermal expansion than the crystalline material; and / or applying ultrasonic energy to the crystalline material.SELECTED DRAWING: Figure 16B

Description

Detailed Description of the Invention

[0001] [Related Application Description] This application claims priority to U.S. Patent Application No. 16 / 274,045, filed March 5, 2019, U.S. Provisional Patent Application No. 62 / 803,333, filed February 8, 2019, and U.S. Provisional Patent Application No. 62 / 786,335, 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 a carrier-assisted method for isolating or removing relatively thin layers of crystalline material from a substrate, such as a boule or wafer, that has subsurface laser damage.

[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] Wire sawing of crystalline materials has several limitations. Kerf loss, based on the width of material removed per cut, is inevitable in saw cutting and represents a significant loss of crystalline 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 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), with the (1-100) plane perpendicular to the [1-100] direction and the (11-20) plane perpendicular to the [11-20] direction. Figure 3 is a second perspective crystallographic view of a hexagonal crystal showing a vicinal plane 9 that is non-parallel to the c-plane, with vector 10 (orthogonal to vicinal plane 9) tilted away from the

[0001] direction by a tilt angle β, which is (slightly) tilted 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 2 is a top plan view of an example SiC wafer 25 laterally bounded by a generally circular edge 27 (having a diameter D) that includes a primary flat 28 (having a diameter D).

[0009] Due to the difficulties associated with fabricating and processing SiC, the cost of SiC device wafers is high compared to various other crystalline 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 in the past 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 crystalline material from bulk crystals. One technique, called controlled spalling, The technique works by growing a tensile stressor layer (e.g., nickel) on the surface of the substrate (e.g., Ge(001)), introducing a crack near the edge of the substrate, and mechanically guiding the crack (e.g., using a flexible handle layer such as tape) as a single fracture front along the surface (see Bedell et al., J. Phys. D: Appl. Phys. 46 (2013)). However, such techniques can result in the application of very high stresses and excessive bowing of the layer being removed. Another technique involving the removal of a layer of silicon carbide from a larger crystal is described in Kim et al., "4H-SiC wafer slicing by using femtosecond laser double pulses," Optical Materials Express, p. 2450, vol. 7, no. 7 (2017). Such techniques include impinging a laser pulse on silicon carbide 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 zone, forming a laser written track. Using a laser to weaken specific areas of the material and then spalling between these areas reduces the laser scanning time. However, it is questionable whether the spallation techniques described above can be applied to reliably remove thin wafers from ingots without breakage and / or be scalable to industrial volumes. Another technique known in the art for inducing spallation along the laser-induced subsurface damage zone of crystalline materials involves applying ultrasonic energy to the crystalline material, but the reliability of such methods to obtain thin (e.g., 350 micron or less) wafers has been questioned, as ultrasonic spallation requires a higher degree of laser damage and may result in higher wafer breakage rates when applied to thin wafers.

[0011] Another technique disclosed in US 2010 / 0289189A1 involves applying a polymer layer (e.g., polydimethylsiloxane (PDMS)) over a solid-state material and exposing the solid-state material (initially at a temperature of 300°C or less) and the polymer layer to a temperature below room temperature (or below about -20°C). Such cooling causes the polymer layer to contract, which induces mechanical stress in the solid-state material, which causes the material to fracture along a plane at a depth of the material. PDMS is a cross-linked polymer, and its stiffness can be controlled by varying the cross-link density (e.g., by changing the weight ratio of curing agent to prepolymer and by changing the curing conditions). The Young's modulus value of PDMS has been reported to be in the range of less than about 4 MPa, even when efforts have been made to improve its mechanical properties. See, for example, Kim et al., J. Micromech. Microeng. 23 (2013) 095024.

[0012] A further technique for removing a thin layer of crystalline material from a bulk crystal is disclosed in US Patent Application Publication No. 2018 / 0126484 A1: 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.

[0013] One drawback of these techniques that utilize polymer layer interface fracture is that the resulting wafers may exhibit undesirably high levels of bowing. Another drawback of techniques that utilize polymer layer interface fracture is that it takes a significant amount of time (e.g., 30 minutes or more) to apply and cure the polymer layer on the solid state material, and additional time to remove the polymer material from the resulting wafer. Another limitation of techniques that require a polymer layer is that such a polymer layer may not be suitable to withstand subsequent wafer processing steps where precise dimensional measurements may be required.

[0014] Yet another technique for removing a thin layer of crystalline material from a bulk crystal is disclosed in US Patent Application Publication No. 2018 / 0243944A1. A donor substrate is irradiated with laser radiation to reveal a crack path, a carrier substrate (i.e., having a thickness of less than 800 microns) is bonded to the donor substrate via a bonding layer, a stress-producing layer (e.g., a PDMS layer) is provided on the carrier substrate, and when the stress-producing layer is thermally loaded (i.e., cooled with a coolant, in particular liquid nitrogen), stress is transferred through the carrier substrate and the bonding layer to generate stress in the donor substrate, which results in a crack propagating along the crack path to remove the solid layer (and the carrier substrate bonded thereto) from the donor substrate. The donor substrate and the carrier substrate are preferably made of the same material, but may be made of different materials. It appears necessary that the maximum thickness of the carrier substrate be limited in order to be able to transmit stress from the stress-producing layer to the donor substrate. One limitation of the above technique is the need to provide at least three layers to cover the donor substrate. Another limitation is that the technique appears to be limited to thermally induced cooling at very low (e.g. liquid nitrogen) temperatures. Yet another limitation is that the maximum thickness of the carrier substrate cannot exceed 800 microns, which may limit the stiffness of the bonded assembly after separation from the donor substrate. Yet another limitation is that to reuse the carrier substrate, it is necessary to remove residual materials of different composition from both sides of it (i.e. the materials of the bonding layer and the materials of the stress-generating layers).

[0015] Thus, the art continues to seek improved methods for dicing or removing relatively thin layers of crystalline material from a substrate that address the problems associated with conventional methods.

[0016] [Summary of the invention] The present disclosure relates to a method of processing a crystalline material in various aspects, including bonding a carrier (e.g., a rigid carrier) to a surface of a crystalline material having subsurface laser damage at a non-zero depth relative to the surface, and then fracturing the crystalline material along the subsurface laser damage region. Such fracturing results in a bonded assembly including the carrier and a portion of the crystalline material removed from the substrate. This fracturing occurs without the need for a separate stress-producing layer disposed over the carrier. The steps described above can be repeated to remove successive thin layers of crystalline material from the ingot to form a wafer. In certain embodiments, the carrier can have crystal-like properties. In certain embodiments, the rigid carrier can be bonded to the surface of the crystalline material by adhesive bonding, the rigid carrier can have a thickness greater than 800 microns, and the rigid carrier can have an elastic modulus of at least 20 GPa (or another threshold value as disclosed herein). In certain embodiments, the adhesive material has a glass transition temperature T greater than 25° C. (or another threshold value as specified herein). g The portion of the crystalline material removed from the substrate may embody a wafer, ready to undergo further processing steps while the portion is part of the bonded assembly. In certain embodiments, first and second rigid carriers may be bonded to opposite sides of the substrate prior to fracturing. In certain examples, fracturing of the crystalline material may be facilitated by (i) applying a mechanical force (e.g., optionally localized at one or more locations) proximate at least one edge of the carrier to impart a bending moment to at least a portion of the carrier, (ii) cooling the carrier if the carrier has a larger coefficient of thermal expansion than the crystalline material, and / or (iii) applying ultrasonic energy to the crystalline material.

[0017] In one aspect, the present disclosure provides a method for temporarily bonding a rigid carrier to a surface of a crystalline material with an intervening adhesive material, the crystalline material comprising a substrate having a subsurface laser damaged region at a depth relative to a first surface, the adhesive material having a glass transition temperature T greater than 25° C. (or another threshold value as specified herein). gThe present invention relates to a method of processing a crystalline material, comprising temporarily bonding a rigid carrier, an adhesive material, and a portion of the crystalline material removed from a substrate. and fracturing the crystalline material along or adjacent the subsurface laser damage region to yield a bonded assembly comprising:

[0018] In a particular embodiment, the rigid carrier has a thickness greater than 800 microns, the rigid carrier has an elastic modulus of at least 20 GPa, and in the bonded assembly, the portion of the crystalline material removed from the substrate has a thickness of at least 160 μm.

[0019] In certain embodiments, the adhesive material comprises a thermoplastic material. In certain embodiments, the adhesive material has a glass transition temperature T of at least 35° C., at least 50° C., at least 60° C., or another threshold value as specified herein. g has.

[0020] In certain embodiments, the adhesive material has a Shore D durometer of at least about 70 when the adhesive material is at 25° C. In certain embodiments, the adhesive material has a modulus of elasticity of at least about 7 MPa when the adhesive material is at 25° C.

[0021] In certain embodiments, the rigid carrier has a thickness greater than 800 microns. In certain embodiments, the rigid carrier has an elastic modulus of at least 20 GPa, at least 100 GPa, or another threshold value as specified herein. In certain embodiments, the rigid carrier comprises a crystalline material.

[0022] In certain embodiments, the rigid carrier comprises a first side and a second side opposite the first side, the adhesive material is disposed in contact with the first side, and the second side is free of the adhesive material and free of the stress-producing material.

[0023] In certain embodiments, the coefficient of thermal expansion (CTE) of the rigid carrier is greater than the CTE of the substrate at 25° C. In certain embodiments, spalling includes cooling at least the rigid carrier to promote spalling of the crystalline material along or adjacent to the subsurface laser damage region.

[0024] In certain embodiments, the disrupting comprises applying ultrasonic energy to at least one of the rigid carrier or the substrate.

[0025] In certain embodiments, at least one of a maximum length or width of at least a portion of the rigid support exceeds a corresponding maximum length or width of the substrate. In certain embodiments, the substrate comprises a notch or flat along at least one edge of the substrate, and at least a portion of the at least one edge of the rigid support extends laterally beyond the notch or flat. In certain embodiments, the fracturing comprises applying a mechanical force proximate to at least one edge of the rigid support, the mechanical force configured to impart a bending moment to at least a portion of the rigid support.

[0026] In certain embodiments, the crystalline material comprises a hexagonal crystal structure and the bending moment is oriented within ±5 degrees of perpendicular to the <11-20> direction of the hexagonal crystal structure.

[0027] In certain embodiments, the method further includes performing at least one additional processing step on the portion of the crystalline material while the portion of the crystalline material remains part of the joined assembly.

[0028] In certain embodiments, the method further comprises bonding an additional rigid support to a second surface of the crystalline material opposite the first surface prior to said fracturing.

[0029] In certain embodiments, the subsurface laser damage region comprises a plurality of substantially parallel subsurface laser damage lines.

[0030] In certain embodiments, the method further includes removing a portion of the crystalline material from the bonded assembly.

[0031] In a particular embodiment, the crystalline material includes SiC.

[0032] In certain embodiments, the method further comprises roughening, texturing, and / or etching at least one of (i) the first surface of the crystalline material, or (ii) an adjacent surface of the rigid carrier, prior to temporary bonding of the rigid carrier to the first surface of the crystalline material with the adhesive material.

[0033] In certain embodiments, the crystalline material comprises a thickness of at least 500 microns prior to spalling the crystalline material along or adjacent the subsurface laser damage region.

[0034] In certain embodiments, the portion of the crystalline material removed from the substrate comprises a free-standing wafer configured to have at least one epitaxial layer grown thereon. In certain embodiments, the portion of the crystalline material removed from the substrate comprises a device wafer including at least one epitaxial layer grown thereon.

[0035] In another aspect, the present disclosure relates to a method for processing a crystalline material, comprising: bonding a first crystal carrier to a first surface of a crystalline material, the crystalline material comprising a substrate having a subsurface laser damage region at a depth relative to the first surface; bonding a second crystal carrier to a second surface of the crystalline material; and fracturing the crystalline material along or adjacent to the subsurface laser damage region to obtain a bonded assembly after the bonding step, the bonded assembly comprising the first crystal carrier and a portion of the crystalline material removed from the substrate.

[0036] In certain embodiments, at least one of the first crystal support or the second crystal support has an elastic modulus of at least 100 GPa. In certain embodiments, at least one of the first crystal support or the second crystal support has a thickness greater than 800 microns.

[0037] In certain embodiments, at 25° C., a coefficient of thermal expansion (CTE) of the first crystalline material carrier is greater than a CTE of the substrate, and the spalling includes cooling at least the first crystalline material carrier to promote spalling of the crystalline material along or adjacent to the subsurface laser damage region.

[0038] In certain embodiments, spalling the crystalline material along or adjacent to the subsurface laser damage region includes applying ultrasonic energy to at least one of the first crystalline carrier or the substrate.

[0039] In certain embodiments, at least one of a maximum length or a maximum width of at least a portion of the first crystal support is greater than a corresponding maximum length or width of the substrate.

[0040] In certain embodiments, the substrate includes a notch or flat along at least one edge of the substrate, and at least a portion of at least one edge of the first crystal support extends laterally beyond the notch or flat.

[0041] In certain embodiments, fracturing the crystalline material along or adjacent to the subsurface laser damage region comprises applying a mechanical force adjacent to at least one edge of the first crystalline carrier. and the mechanical force is configured to impart a bending moment to at least a portion of the first crystalline support. In certain embodiments, the crystalline material comprises a hexagonal crystal structure, and the bending moment is oriented within ±5 degrees of a perpendicular to a <11-20> direction of the hexagonal crystal structure parallel to a surface of the substrate.

[0042] In certain embodiments, at least one of bonding the first crystal carrier to the first surface of the crystalline material or bonding the second crystal carrier to the second surface of the crystalline material comprises anodic bonding.

[0043] In certain embodiments, at least one of bonding the first crystal carrier to the first surface of the crystal material or bonding the second crystal carrier to the second surface of the crystal carrier comprises adhesive bonding utilizing an adhesive material.

[0044] In certain embodiments, the adhesive material has a glass transition temperature T g has.

[0045] In certain embodiments, the first crystal carrier comprises a first surface and a second surface opposite the first surface, the adhesive material is disposed in contact with the first surface, and the second surface is free of the adhesive material and free of the stress-producing material.

[0046] In certain embodiments, the adhesive material comprises a thermoplastic material.

[0047] In certain embodiments, the adhesive material has a Shore D durometer of at least about 70 when the adhesive material is at 25°C.

[0048] In certain embodiments, the adhesive material has a modulus of elasticity of at least about 7 MPa when the adhesive material is at 25°C.

[0049] In certain embodiments, the method further includes performing at least one additional processing step on the portion of the crystalline material while the portion of the crystalline material remains part of the joined assembly.

[0050] In certain embodiments, the subsurface laser damage region comprises a plurality of substantially parallel subsurface laser damage lines.

[0051] In certain embodiments, the method further includes removing a portion of the crystalline material from the bonded assembly.

[0052] In a particular embodiment, the crystalline material includes SiC.

[0053] In certain embodiments, the portion of crystalline material removed from the substrate comprises a free-standing wafer configured to have at least one epitaxial layer grown thereon. In certain embodiments, the portion of crystalline material removed from the substrate comprises a device wafer including at least one epitaxial layer grown thereon.

[0054] In another aspect, the disclosure relates to a method of processing a crystalline material, comprising bonding a rigid carrier to a first surface of a crystalline material, the crystalline material comprising a substrate having a subsurface laser damaged region at a depth relative to the first surface, at least a portion of at least one edge of the rigid carrier extending laterally beyond a corresponding at least one edge of the substrate. The method includes applying a bending moment to at least a portion of the rigid carrier to remove the subsurface laser damage region from the substrate to obtain a bonded assembly including the rigid carrier and a portion of the crystalline material removed from the substrate. The method further includes applying a mechanical force adjacent to at least one edge of the rigid carrier to fracture the crystalline material along or adjacent the damage region.

[0055] In certain embodiments, applying a mechanical force proximate to at least one edge of the rigid support comprises locally applying the mechanical force at a single location proximate to at least one edge of the rigid support.

[0056] In certain embodiments, applying a mechanical force proximate at least one edge of the rigid support comprises locally applying the mechanical force at a plurality of spatially isolated locations proximate at least one edge of the rigid support and exerting an opposing mechanical force at a central location of the rigid support.

[0057] In certain embodiments, at least a portion of at least one edge of the rigid carrier extends laterally beyond at least one edge of the corresponding substrate by at least about 100 microns, or at least about 500 microns (or another distance threshold as disclosed herein).

[0058] In certain embodiments, the substrate includes a notch or flat along at least one edge of the substrate, and at least a portion of at least one edge of the rigid carrier extends laterally beyond the notch or flat.

[0059] In a particular embodiment, the crystalline material comprises a hexagonal crystal structure and the bending moment is oriented within ±5 degrees of perpendicular to a <11-20> direction of the hexagonal crystal structure parallel to the surface of the substrate.

[0060] In certain embodiments, bonding the rigid carrier to the surface of the crystalline material comprises adhesive bonding, utilizing an adhesive material disposed between the rigid carrier and the surface of the crystalline material.

[0061] In certain embodiments, the method further comprises bonding an additional rigid support to a second surface of the crystalline material opposite the first surface prior to the application of the mechanical force, hi certain embodiments, the application of the mechanical force comprises exerting a localized prying force between the first rigid support and the additional rigid support to increase a separation between the first rigid support and the additional rigid support.

[0062] In certain embodiments, the portion of crystalline material removed from the substrate comprises a free-standing wafer configured to have at least one epitaxial layer grown thereon. In certain embodiments, the portion of crystalline material removed from the substrate comprises a device wafer including at least one epitaxial layer grown thereon.

[0063] In another aspect, the disclosure relates to a method of processing a crystalline material comprising: bonding a rigid carrier to a first surface of a crystalline material, the crystalline material comprising a substrate having a subsurface laser damage region at a depth relative to the first surface, the rigid carrier having a thickness greater than 850 microns and comprising at least one of the following characteristics (i) or (ii): the substrate comprises a crystalline substrate, or (ii) the substrate has an elastic modulus of at least 20 GPa; and fracturing the crystalline material along or adjacent to the subsurface laser damage region to obtain a bonded assembly comprising the rigid carrier and a portion of the crystalline material removed from the substrate.

[0064] In certain embodiments, the rigid carrier comprises a crystalline carrier. In certain embodiments, the carrier has an elastic modulus of at least 20 GPa, at least 100 GPa, or another threshold value as specified herein. In certain embodiments, bonding the rigid carrier to the crystalline material comprises adhesive bonding utilizing an adhesive material disposed between the rigid carrier and the crystalline material.

[0065] In certain embodiments, the adhesive material has a glass transition temperature T g In certain embodiments, the adhesive material has a Shore D durometer of at least about 70 when the adhesive material is at 25° C. In certain embodiments, the adhesive material has a modulus of elasticity of at least about 7 MPa when the adhesive material is at 25° C.

[0066] In certain embodiments, the rigid carrier comprises a first side and a second side opposite the first side, the adhesive material is disposed in contact with the first side, and the second side is free of the adhesive material and free of the stress-producing material.

[0067] In certain embodiments, at 25° C., the coefficient of thermal expansion (CTE) of the rigid carrier is greater than the CTE of the substrate.

[0068] In certain embodiments, the spalling includes cooling at least the rigid support to promote spalling of the crystalline material along or adjacent to the subsurface laser damage region.

[0069] In certain embodiments, the disrupting comprises applying ultrasonic energy to at least one of the rigid carrier or the substrate.

[0070] In certain embodiments, at least one of a maximum length or width of at least a portion of the rigid support exceeds a corresponding maximum length or width of the substrate, hi certain embodiments, the substrate includes a notch or flat along at least one edge thereof, and at least a portion of at least one edge of the rigid support extends laterally beyond the notch or flat.

[0071] In certain embodiments, the fracturing comprises applying a mechanical force proximate to at least one edge of the rigid support, the mechanical force configured to impart a bending moment to at least a portion of the rigid support.

[0072] In certain embodiments, the crystalline material comprises a hexagonal crystal structure and the bending moment is oriented within ±5 degrees of perpendicular to the <11-20> direction of the hexagonal crystal structure.

[0073] In certain embodiments, the method further includes performing at least one additional processing step on the portion of the crystalline material while the portion of the crystalline material remains part of the joined assembly.

[0074] In certain embodiments, the method further comprises bonding an additional rigid carrier to a second surface of the crystalline material opposite the first surface prior to said fracturing, hi certain embodiments, the method further comprises removing a portion of the crystalline material from the bonded assembly.

[0075] In a particular embodiment, the crystalline material includes SiC.

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

[0077] In certain embodiments, the portion of the crystalline material removed from the substrate comprises a device wafer including at least one epitaxial layer grown thereon.

[0078] In another aspect, the present disclosure provides a method for grinding an edge of a thick wafer of crystalline material to eliminate a non-vertical edge profile and form a vertical edge profile, the method comprising: the thick wafer includes a first surface, a second surface opposite the first surface, and at least one epitaxial layer grown on or over the first surface, the first rigid carrier being temporarily bonded over the at least one epitaxial layer with an adhesive material disposed between the first rigid carrier and the at least one epitaxial layer; and after formation of a vertical edge profile, directing laser radiation through the second surface of the thick wafer to form a subsurface laser damage region in the thick wafer.

[0079] In certain embodiments, the method further includes bonding a second rigid carrier to a second surface of the thick wafer and fracturing the thick wafer along or adjacent to the subsurface laser damage region to obtain (i) a first bonded assembly including the first rigid carrier, the adhesive material, at least one epitaxial layer, and a first thin wafer separated from the thick wafer, and (ii) a second bonded assembly including the second rigid carrier and a second thin wafer separated from the thick wafer.

[0080] In certain embodiments, the method further includes bonding a first rigid carrier to a major surface of the crystalline material, the crystalline material including a substrate having an initial subsurface laser damage region at a depth relative to the major surface; fracturing the crystalline material along or adjacent to the initial subsurface laser damage region to obtain an initial bonded assembly comprising the first rigid carrier and a portion of the crystalline material removed from the substrate; and removing a portion of the crystalline material from the first bonded assembly to produce a thick wafer, the thick wafer including the portion of the crystalline material.

[0081] In certain embodiments, the method further includes forming a non-vertical wafer edge of the thick wafer and epitaxially growing at least one epitaxial layer on or over the first surface of the thick wafer after creating the non-vertical wafer edge.

[0082] In certain embodiments, at least one of the first thin wafer or the second thin wafer comprises a thickness less than 250 microns. In certain embodiments, the crystalline material includes SiC.

[0083] In another aspect, the 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.

[0084] 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.

[0085] 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, At least one grinding wheel having a grinding surface of a grinding diameter of 1000 grit, 7000 grit, 8000 grit, 10,000 grit, 15,000 grit, 20,000 grit, 25,000 grit, 30,000 grit, etc.

[0086] 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.

[0087] In certain embodiments, the surface damage includes laser damage and spallation damage.

[0088] 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.

[0089] In another aspect, the disclosure relates to a method for processing a crystalline material wafer having a first surface with 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, 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 growing 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.

[0090] 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.

[0091] 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.

[0092] 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.

[0093] In a particular embodiment, the protective coating comprises a photoresist.

[0094] In certain embodiments, the surface damage includes laser damage and spallation damage.

[0095] 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.

[0096] In another aspect, the present disclosure provides a method for forming a subsurface layer on a crystalline material substrate fed to a laser processing station. a laser processing station configured to form a laser damage region; a crushing station arranged to receive a crystalline material substrate processed by the laser processing station and configured to fracture 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 portions of the surface damage from the crystalline material portions, at least a first and a second of the plurality of rough grinding stations configured to be operated simultaneously to remove the first portions of the 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 portions of the 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.

[0097] 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.

[0098] 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.

[0099] 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.

[0100] 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.

[0101] In certain embodiments, the laser processing station is configured to simultaneously form subsurface laser damaged regions in multiple crystalline material substrates.

[0102] 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.

[0103] Other aspects, features, and embodiments of the present disclosure will become more fully apparent from the ensuing disclosure and the appended claims.

[0104] 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]

[0105] [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-8D] FIG. 8D provides an example laser tool travel path relative to a crystalline material to form subsurface damage within the crystalline material. FIG. 8D includes superimposed arrows indicating the orientation of the subsurface damage lines relative to the [11-20] direction of the hexagonal crystal structure of the crystalline material, which are also parallel to the surface of the crystalline material. [Figure 9]A schematic side cross-sectional view of an assembly including a crystalline material substrate having subsurface laser damage bonded to a rigid carrier with an adhesive material disposed therebetween, the assembly including an exposed adhesive lip around at least a portion of a peripheral edge of the crystalline material along an interface with the rigid carrier. [Figure 10A] 1 is a schematic cross-sectional side view of a rigid carrier having an adhesive material bonded to a surface thereof; [Figure 10B] FIG. 10B is a schematic cross-sectional view of an assembly including the rigid carrier and adhesive material of FIG. 10A bonded to a crystalline material substrate having a subsurface laser damage region proximate to the adhesive material, the assembly being similar to that shown in FIG. 9 but lacking an exposed adhesive lip. [Figure 10C] FIG. 10C is a schematic cross-sectional view of the assembly of FIG. 10B, where a surface of the rigid carrier is positioned on a cooling device in the form of a water-cooled chuck. [Figure 10D] FIG. 14 is a schematic cross-sectional view of a large portion of a crystalline material substrate separated from its bonded assembly (on a water-cooled chuck), including the rigid carrier and the portion of crystalline material removed from the substrate, following spalling of the crystalline material along the subsurface laser damage region. [Figure 10E] FIG. 10C is a schematic cross-sectional view of the bonded assembly of FIG. 10D after removal from the water-cooled chuck, with residual laser damage along the top-facing surfaces. [Figure 10F] FIG. 1 is a schematic cross-sectional view of a portion of crystalline material supported by a heated vacuum chuck, where the rigid carrier and adhesive material have been laterally translated away from the crystalline material portion following thermal softening and release of the adhesive material. [Figure 11] FIG. 10D is a schematic cross-sectional view of the assembly according to FIG. 10C resting on a cooling device in the form of a water-cooled chuck that is placed in a bath of liquid coolant. [Figure 12] FIG. 1 is a perspective view of a cooling apparatus including a vacuum chuck positioned adjacent a bottom wall of a vessel arranged to receive a liquid refrigerant (e.g., methanol, liquid nitrogen, etc. received from an evaporative cooling system). [Figures 13A-13E] 1A-1C are top views of bonded assemblies including carriers of various shapes each bonded to a substrate of crystalline material. [Fig. 13F-13G] 13D and 13E are schematic cross-sectional side views of the joined assemblies of FIG. 13D and FIG. 13E, respectively. [Figure 14] 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 15A-15D] 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 16A] FIG. 1 is a schematic cross-sectional view of an apparatus for fracturing subsurface laser-damaged crystalline materials bonded to a carrier by applying a mechanical force along both edges of the carrier to impart bending moments to portions of the carrier. [Figure 16B] FIG. 16B is a schematic cross-sectional view of a bonded assembly including a rigid carrier and a substrate that has been separated from a bulk crystal material using the apparatus of FIG. 16A. [Figures 17A-17D] 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. [Figures 18A-18O] 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 19]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 20] FIG. 20 is a schematic cross-sectional view of a portion of the crystalline material substrate of FIG. 19 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 polishing). [Figure 21] 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. [Figure 22] FIG. 22 is a schematic diagram of a material processing apparatus according to an embodiment similar to that of FIG. 21, but in which an edge grinding station is located between the fine grinding station and the coarse grinding station. [Figure 23] 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 24A] 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 24B] FIG. 2 is a schematic cross-sectional side view of a second apparatus for holding an ingot having an end face that is non-perpendicular to a sidewall, according to one embodiment. [Diagram 25] 1 is a line graph for sapphire plotting the linear thermal expansion coefficient as a function of temperature. [Figure 26]1 is a line graph for SiC plotting the linear thermal expansion coefficient as a function of temperature. [Figure 27] 1 is a bar graph providing a comparison of the linear thermal expansion coefficients of various crystalline materials and metals. [Figure 28] A plot of elastic modulus (Young's modulus) values ​​for various materials classified into three groups: (1) metals and alloys, (2) graphite, ceramics, and semiconductors, and (3) polymers. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0106] In an embodiment of the present disclosure, a carrier (e.g., a rigid carrier) is bonded to a surface of a crystalline material having subsurface laser damage at a depth, and the crystalline material is bonded to a surface of the crystalline material along the subsurface laser damage region. A method of processing a crystalline material is provided in which the ingot is fractured to provide a bonded assembly including a carrier and a portion of the crystalline material removed from the substrate. The fracture is performed without the need for a separate stress-producing layer disposed over the carrier. The steps described above can be repeated to remove successive thin layers of crystalline material from the ingot to form wafers. In certain embodiments, the carrier includes the crystalline material. In certain embodiments, a rigid carrier can be bonded to a surface of the crystalline material by adhesive bonding, and the rigid carrier can have an elastic modulus of at least 20 GPa. The adhesive material has a glass transition temperature T greater than 25° C. (or another threshold value specified herein). g The portion of the crystalline material removed from the substrate may embody a wafer, ready to undergo further processing steps while the portion is part of the bonded assembly. In certain embodiments, the fracture of the crystalline material may be facilitated by (i) applying a mechanical force (e.g., optionally localized at one or more locations) proximate at least one edge of the carrier to impart a bending moment to at least a portion of the carrier, (ii) cooling the carrier if it has a larger coefficient of thermal expansion than the crystalline material, and / or (iii) applying ultrasonic energy to at least a portion of the bonded assembly.

[0107] The embodiments described below represent the necessary information to enable those skilled in the art to implement the embodiments and show the best mode for implementing the embodiments. Upon reading the following description in light of the accompanying drawing figures, 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.

[0108] 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.

[0109] 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.

[0110] 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.

[0111] 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.

[0112] Unless otherwise defined, all terms (including technical and / or scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. It will be further understood that terms used herein should be interpreted as having a meaning consistent with their meaning in the context of the present specification and related art, and are not to be interpreted in an idealized or overly formal sense unless expressly defined otherwise herein.

[0113] As used herein, "substrate" refers to a crystalline material, such as an ingot or wafer, that can be split 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 crystalline material, and optionally (ii) to be self-supporting when separated from a rigid carrier. In certain embodiments, the substrate can have a generally cylindrical shape and / or a thickness of about 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 can include a thicker wafer that can be split 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.

[0114] The methods disclosed herein can be applied to substrates of a variety of crystalline materials, both monocrystalline 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 monocrystalline 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). Although various exemplary embodiments described herein below refer generally to SiC or specifically to 4H-SiC, it will be appreciated that any suitable crystalline material can 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 is performed on-axis (i.e., The growth can be performed either on-axis (with no intentional angular deviation from the c-plane, suitable for forming undoped or semi-insulating materials) or off-axis (typically at 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 subranges thereof, such as 2 to 6 degrees), 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 materials. Certain embodiments disclosed herein can utilize on-axis 4H-SiC, or vicinal (off-axis) 4H-SiC with an offcut in the range of 1 to 10 degrees or 2 to 6 degrees, or about 4 degrees.

[0115] 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.

[0116] Although various substrates, carriers, adhesives, and fracturing techniques are disclosed herein, it should be appreciated that for various combinations of substrates, carriers, and / or bonding methods, the fracturing techniques can be used individually, or any combination of the fracturing techniques can be used simultaneously and / or sequentially to achieve the desired separation.

[0117] [Support properties] The carriers are contemplated for use with various carrier-assisted methods for breaking apart crystalline materials along subsurface laser-damaged regions as disclosed herein. Given the various methods for breaking apart (i.e., fracturing) crystalline materials as disclosed herein, desirable carrier properties may vary depending on the particular fracturing method.

[0118] In various embodiments, the carrier is referred to as having rigid properties. In certain embodiments, at least the proximal portion of the crystalline material to be cut, or the entirety of the rigid carrier, has an elastic modulus (also known as Young's modulus) of at least about 20 GPa, at least about 50 GPa, at least about 100 GPa, at least about 200 GPa, or at least about 300 GPa. For example, sapphire has an elastic modulus of 345 GPa. Elastic modulus is a mechanical property that measures the rigidity of a solid material. It defines the relationship between stress (force per unit area) and strain (proportional deformation) in a material in the linear elastic modulus regime of uniaxial deformation.

[0119] While not wishing to be bound by any particular theory as to why the separation method disclosed herein results in an improvement over conventional methods (e.g., using low stiffness mating surface materials such as PDMS or silicone and cryo-fracturing), it is believed that the relatively stiff or rigid high It is believed that a rigid (i.e., high modulus) carrier bonded to the crystalline material to be fractured along the subsurface laser damage region can provide reproducible crystalline material separation results while reducing wafer bowing and / or breakage. In addition to the mechanical aspects required for separation (e.g., by mechanical, CTE-mismatched, and / or ultrasonic means), the carrier also provides mechanical support during and after separation. This is useful for post-separation processing, since the separated crystalline material can be ground, polished, etc., while still attached to and supported by the rigid carrier. This avoids the need to bond the wafer to a rigid carrier after fracture to perform one or more post-separation processing steps.

[0120] In cases where the rigid carrier is to be adhesively bonded to the substrate, in certain embodiments the carrier may generally comprise a broader range of materials, including semiconductors, inorganic materials, metals, semi-metals, non-metals, ceramics, crystalline materials (e.g., monocrystalline or polycrystalline in nature), amorphous materials, polymeric materials, glasses, and composite materials. In certain embodiments, the carrier may comprise two or more materials that are bonded or joined together by a variety of conventional means. Other materials may be used, as one of ordinary skill in the art would recognize.

[0121] A narrower range of carrier materials may be desirable if the rigid carrier is not limited to being adhesively bonded to a substrate using an adhesive. In certain embodiments, carriers that are not limited to being adhesively bonded to a rigid carrier may include single crystal materials (e.g., single crystal or polycrystalline in nature), semiconductor materials, ceramic materials, semi-metals, inorganic materials, and composite materials.

[0122] In certain embodiments, the rigid carrier can have a thickness that is 1, 2, 3, 4, or 5 times greater than the subsurface laser damage depth of the crystalline material bonded to the rigid carrier. In various embodiments, the rigid carrier can have a thickness that is less than, equal to, or greater than the thickness (before separation) of the crystalline material bonded to the rigid carrier. In certain embodiments, the rigid carrier can have a thickness of at least 500 μm, greater than 800 μm, at least 850 μm, at least 900 μm, at least 1 mm, at least 1.5 mm, at least 2 mm, or at least 3 mm, the above ranges optionally being bounded by upper limits of 1 mm, 2 mm, 3 mm, 4 mm, or 5 mm, as appropriate. In certain embodiments, the rigid carrier may have a thickness in the range of 0.5 to 5 mm, or 0.5 to 3 mm, or 0.5 to 2 mm, or 0.8 to 5 mm, or 0.8 to 3 mm, or 0.8 to 2 mm, or 0.85 to 5 mm, or 0.9 to 5 mm, or 1 to 4 mm, or 1 to 3 mm, or 1 to 2 mm.

[0123] In certain embodiments, the rigid support may desirably have a lateral extent (e.g., diameter, or length and width) at least as large as or greater than the corresponding dimensions of the substrate bonded thereto. Providing the rigid support with a diameter at least as large as (or larger than) the diameter of the crystalline substrate is believed to facilitate initiation of fracture during the various fracture processes described herein.

[0124] In certain embodiments, at least one of the maximum length or width of at least a portion of the rigid carrier exceeds the corresponding maximum length or width of the substrate. In certain embodiments, at least a portion of at least one edge of the rigid carrier may extend laterally at least about 100 microns, at least about 200 microns, at least about 500 microns, at least about 1 mm, or at least about 2 mm beyond the corresponding edge of at least one substrate. Such lateral overlap is particularly desirable in embodiments utilizing mechanical separation, since the overlap can receive at least a portion of a tool suitable for applying a moment to the rigid carrier to initiate fracture. In certain embodiments, the substrate may have a notch or a groove along at least one edge of the substrate. The rigid carrier may include a flat, and at least a portion of the edge (or at least one edge) of the rigid carrier may extend laterally beyond the notch or flat.

[0125] Disclosed herein are embodiments including single and two carriers. As the substrate to be separated becomes thinner (e.g., less than about 5 mm thick), two carriers become a practical necessity. The carrier located proximal to the subsurface laser damage region may be referred to as the front carrier, as distinguished from the back carrier located distal therefrom. According to certain embodiments disclosed herein, the front carrier is specifically intended to facilitate separation of crystalline material along or adjacent to the subsurface laser damage region. In contrast, the back carrier is not intended to facilitate separation of the substrate during the spallation process. For this reason, the back carrier may have a different CTE than the front carrier, when a CTE mismatch between the carrier and the substrate is used to facilitate spallation of the substrate along the subsurface damage region. In certain embodiments, the back carrier may have a lower CTE mismatch with respect to the substrate than the front carrier. In certain embodiments, the back carrier may be CTE matched or nearly CTE matched with the substrate.

[0126] [CTE characteristics of supports for crystalline materials] In certain embodiments, a rigid carrier having a first coefficient of thermal expansion, or CTE1, is bonded or joined to a surface of a crystalline material having a subsurface laser damage, having a second coefficient of thermal expansion, or CTE2, where CTE1>CTE2 at a desired temperature (e.g., at 25° C.) or over a desired temperature range). At least the carrier is then cooled, which causes the carrier to shrink in size more quickly than the crystalline material due to the CTE difference. Such differential shrinkage creates stresses (e.g., shear stresses) in the carrier and the crystalline material, which stresses cause the crystalline material to fracture along the subsurface laser damage region. While the inventors have extensively tested the combination of a SiC substrate and a sapphire carrier, one of ordinary skill in the art could readily determine other CTE mismatched material combinations that would benefit from the present disclosure.

[0127] To impart sufficient stress to the substrate, the CTE mismatched substrate according to various embodiments disclosed herein can have rigidity as a characteristic, taking into account not only the mechanical properties (e.g., modulus of elasticity) of the carrier material, but also the carrier thickness. In certain embodiments, the rigid carrier can have a thickness of greater than 800 microns, at least 850 microns, at least 900 microns, at least 1 mm, at least 1.5 mm, or another threshold value disclosed herein.

[0128] For various materials, CTE can change with temperature. In the case of a rigid carrier having a CTE greater than that of a crystalline material, in certain embodiments, the rigid carrier can include a material having a CTE greater than that of a crystalline material at a desired temperature (e.g., at 25°C, at 100°C, at 200°C, at 300°C, at 0°C, and / or at -100°C) or over a desired temperature range (e.g., in a range of -100°C to 300°C, in a range of -100°C to 200°C, in a range of -100°C to 100°C, in a range of 0°C to 200°C, in a range of 50°C to 150°C, or any other suitable temperature range or subrange disclosed herein).

[0129] In certain embodiments, the CTE of the rigid support (which will be located proximate to the subsurface damage region of the crystalline material substrate) is less than 5 times, about 4 times or less, about 3 times or less, about 2 times or less, or about 1.5 times or less than the CTE of the crystalline material substrate. In certain embodiments, the CTE of the rigid support is greater than the CTE of the crystalline material substrate by a factor ranging from about 1.25 to about 4. It is believed that some or all of the above CTE mismatch ratios are significantly less than the CTE mismatch ratios of materials used in conventional nickel-based or polymer-based spalling techniques (as described in the background section of this disclosure). For example, nickel or The CTE mismatch between the nickel-containing metal (which can be used as a support) and the SiC (which can be used as a crystal material) can be at least 5 or more, and the CTE mismatch between the polymer and the SiC can be on the order of 10 to 100 or more.

[0130] Although reference has been made to a rigid carrier bonded to a crystalline material with subsurface damage and having a CTE greater than the CTE, in certain embodiments, the crystalline material with subsurface laser damage may be disposed between a first and a second rigid carrier. In such embodiments, the first rigid carrier is bonded to a first surface of the crystalline material proximate to the subsurface laser damage, and the second rigid carrier is bonded to a second surface of the crystalline material opposite the first surface distal to the subsurface laser damage. In certain embodiments, the first rigid carrier and the second rigid carrier may both have a CTE value greater than the CTE of the crystalline material. In other embodiments, the first rigid carrier has a CTE greater than the CTE of the crystalline material, while the second rigid carrier has a CTE less than or equal to the CTE of the crystalline material. For example, in certain embodiments, the front carrier of a SiC substrate may be made of sapphire, which exhibits a large CTE mismatch to SiC, while the back carrier may be made of SiC with no mismatch to the CTE carrier. Alternatively, the front side carrier for the SiC wafer may be made of sapphire (which has a larger CTE than SiC) while the back side carrier may be made of SiC (which has no CTE mismatch with the SiC wafer).

[0131] In certain embodiments utilizing CTE mismatch to facilitate fracturing, it may be desirable to provide the minimum amount of CTE mismatch necessary to enable the desired separation in order to reduce bowing of the bonded assembly (i.e., the carrier and the fractured substrate portion bonded thereto) after separation. When using SiC substrates and sapphire carriers, bowing on the order of 200 microns for a 150 mm diameter SiC wafer has been observed. Such levels of bowing are within the range that can be easily managed through grinding due to both the mechanical forces imposed by the vacuum chuck used during grinding and the grinding forces that serve to flatten the bonded assembly during processing. In contrast, excessive bowing is a major problem faced by prior art processes.

[0132] [Joining or bonding of the carrier to the crystalline material] A variety of methods can be used to bond or join a rigid carrier to the surface of the crystalline material having the subsurface damage in order to promote fracture along the subsurface damage. One method involves adhesive bonding, which can include applying an adhesive material to the proximal surface of the rigid carrier, bringing the adhesive into intimate contact with the surface of the crystalline material having the subsurface laser damage, and curing the adhesive (e.g., by exposing the carrier / adhesive / crystalline material laminate to elevated temperatures and pressures).

[0133] In certain embodiments, the bond between the rigid carrier and the subsurface laser damaged crystalline material is temporary in nature, for example, by using an adhesive material that attempts to maintain adhesion under certain conditions (e.g., room temperature) but exhibits reduced adhesion under removal conditions (e.g., temperatures sufficient to cause the adhesive material to flow and / or exposure to chemicals configured to weaken or degrade the adhesive material). The use of a temporary bonding medium allows the crystalline material to be bonded to the carrier to enable fracturing in accordance with the methods disclosed herein (e.g., thermally induced fracturing at low temperatures, fracturing induced by application of mechanical force, and / or fracturing induced by ultrasonic energy), yet subsequently allows for removal of the removed portion of the crystalline material bonded to the rigid carrier (optionally after performing one or more other processing steps on the portion of the crystalline material while attached to the rigid carrier). The desired properties of adhesive materials usable with various embodiments of the present disclosure may depend in part on the method used to induce fracturing of the crystalline material.

[0134] Important parameters of the temporary bonding material include (a) cohesive strength, (b) adhesive strength, (c) modulus of elasticity, (d) glass transition temperature, and (e) thickness. A suitable temporary bonding material (e.g., a temporary adhesive) should have the appropriate combination of the above parameters to effectively transfer separation forces between the carrier and the crystalline material to cause fracture along the subsurface damage region, yet be easily removed, destroyed, or rendered inoperable (e.g., chemically decomposed, photodecomposed, thermally decomposed, etc.) under specified conditions, preferably without undue effort required for residue removal.

[0135] With regard to cohesion, a desirable adhesive material should have a sufficiently high cohesion such that the adhesive material maintains its integrity and does not break when subjected to the forces required to fracture the crystalline material with subsurface laser damage. The adhesive strength of the adhesive material should be high enough to maintain adhesion to the surrounding material (e.g., carrier or crystalline material) when the forces required to fracture the crystalline material with subsurface laser damage are applied to the adhesive material. It is noted that some adhesive materials exhibit a decrease in adhesive and cohesive strength at lower temperatures and therefore it may be desirable to employ a fracture technique involving relatively warmer temperatures.

[0136] With respect to the adhesive material's modulus and thickness, a desirable adhesive material should function to adequately transfer an appropriate amount of stress from the carrier to the crystalline material without causing the adhesive material to absorb an excessive amount of the stress required to cause fracture of the crystalline material. This tends to favor adhesive materials with a relatively high modulus (i.e., relatively stiff) that are present as a relatively thin layer to promote stress transfer while preventing stress absorption by the adhesive material.

[0137] Glass transition temperature (T g ), when using the CTE mismatch between the support and the crystal material, T gThe smaller the value, the lower the temperature to which the carrier must be cooled to induce spalling (e.g., spontaneous spalling) of the crystalline material along the subsurface laser damage region. For example, the T g If T is 0° C. and a temperature change of 70° C. is desired to introduce sufficient stress, the carrier must be cooled to −70° C. Unfortunately, at very low temperatures, adhesive material properties (including stress transfer efficiency) may be degraded. Thus, a relatively higher T g Adhesive materials that exhibit value may be preferred.

[0138] In certain embodiments, the adhesive material may include an adhesive compatible with high temperature thermocompression adhesive bonding. For high temperature thermocompression bonding, a lower glass transition temperature (T g However, in certain embodiments, particularly when used in embodiments that utilize cooling in combination with a substrate / carrier CTE mismatch to induce fracture of the crystalline material, the T of the adhesive material may be increased. g should not be too low, because T g Materials with low T g The glass transition temperature of a polymeric material is the temperature range where the polymer transitions from a hard, glassy material to a soft, rubbery material.

[0139] In certain embodiments, the adhesive material may include an ultraviolet (UV) light curable adhesive. Such adhesives have a higher T gmay be used because the adhesive bond can be formed at room temperature (e.g., about 25° C.), thereby minimizing any residual stress in the resulting material separated at room temperature. In certain embodiments, UV-curable adhesive bonds can be formed above room temperature to produce the desired level of residual stress at room temperature in embodiments that utilize cooling in combination with a substrate / carrier CTE mismatch to produce fracture of the crystalline material. In such embodiments, the carrier and the bonded material may be formed at room temperature. This residual stress may be desirable in order to reduce the temperature difference required to achieve separation due to the CTE mismatch between portions of the bonded crystalline material.

[0140] Considering the various adhesive bonding and / or curing processes, in certain embodiments that utilize cooling and the CTE mismatch between the carrier and the crystalline material bonded thereto to induce fracture, the adhesive material has a glass transition temperature (T) of about 25° C. or greater, greater than 25° C., greater than 50° C., greater than 75° C., greater than 100° C., or greater than 150° C. g In certain embodiments, the lower threshold may be bounded by an upper threshold of less than about 250° C., less than about 200° C., less than about 150° C., less than about 125° C., or less than about 100° C. (as appropriate). Furthermore, taking into account various adhesive bonding and / or curing processes, in certain embodiments, the adhesive material may have a melting point greater than 50° C., greater than 100° C., greater than 150° C., or greater than 200° C.

[0141] In certain embodiments, the adhesive material may include a thermoplastic adhesive. At least some thermoplastic adhesives have desirable mechanical and adhesive properties (relatively high T g, high modulus, high cohesion, high adhesive strength to desirable carriers and crystalline materials, and hardness in the desired temperature range (e.g., close to room temperature), while still being easily removable when heated to high temperatures and / or exposed to solutions. Examples of adhesive materials that may be suitable for use with the methods disclosed herein include BrewerBOND® 220, WaferBOND® HT-10.10, and BrewerBOND® 305 thermoplastic adhesives available from Brewer Science, Inc. (Rolla, Missouri, USA), and Crystalbond™ 509 thermoplastic adhesive available from Aremco Products (Valley Cottage, NY, USA). Selected thermal and mechanical property values ​​for these adhesives are tabulated below.

[0142] [Table 1]

[0143] In the above table, the hardness values ​​of the first and second adhesive films are provided by the manufacturer, but such values ​​are typically established using nano-indentation techniques and are expressed in Pascal (e.g., MPa or GPa), while the hardness value of the fourth adhesive is expressed as a durometer, which Applicant determined using the Shore D method. Applicant calculated the elastic modulus value of the fourth adhesive from the Shore D durometer value. While there is no direct theoretical relationship between the Shore scale and Young's modulus, there are empirically derived mathematical formulas that are useful for converting between them. The formula Applicant used (utilizing Microsoft Excel) is: is "EXP((Durometer+50)*0.0235-0.6403)" where Durometer refers to the Shore D durometer value. The Shore D durometer value of the fourth adhesive material (Crystalbond™ 509) of 73.2 is between the Shore D durometer values ​​of heavy-duty truck tires (Shore D value of about 50) and high-density polyethylene helmets (Shore D value of about 75). The Shore D durometer value of the fourth adhesive material is also significantly higher than the Shore D durometer values ​​of 50.51 and 54.25 of the measured waxes (i.e., SHIFTWAX7607 available from Nikka Seiko Co., Ltd. and Galaxy Wax available from Galaxy Technologies, respectively) that were tested by applicant and determined to be unsuitable for inducing fracture of crystalline material along the subsurface damage zone using the thermally induced spontaneous separation method and the mechanically induced separation method described herein. The wax material was observed to separate within itself and was determined to have insufficient cohesion to induce fracture, which is consistent with online descriptions suggesting that wax has very weak intermolecular forces of attraction (London forces) and therefore does not hold onto other molecules very strongly.

[0144] Other adhesives beyond the thermoplastic materials mentioned herein above may be used, as one of skill in the art will recognize after reviewing this disclosure. In certain embodiments, the adhesive material may include a glass transition temperature of greater than 0°C, greater than 5°C, greater than 10°C, greater than 20°C, greater than 25°C, greater than 30°C, greater than 35°C, or any suitable higher threshold. In certain embodiments, the lower threshold may be bounded by an upper threshold of less than about 250°C, less than about 200°C, less than about 150°C, less than about 125°C, or less than about 100°C (as appropriate). Such adhesive materials may avoid the need for cooling at extremely low temperatures (e.g., less than -75°C or less than -100°C, requiring liquid nitrogen or similar refrigerants). When using liquid nitrogen to achieve very low temperatures below minus 100°C, the inventors have observed catastrophic failure of the adhesive as a function of the time of exposure when using the thermoplastic adhesive materials previously disclosed herein. Such thermoplastic materials appear to crack and craze at very low temperatures, suggesting that extremely low temperatures (eg, below -100°C) should be avoided.

[0145] One class of adhesive materials that requires cooling to extremely low temperatures are silicones (including PDMS), which have glass transition temperatures (T) of -110°C to -140°C. g ) range. Easy removal of silicone can be difficult. Silicone exhibits a very low modulus above its glass transition temperature, but this modulus changes by several orders of magnitude into the GPa range as the material cools below its glass transition temperature. The inventors tested silicone as a bonding material between a SiC ingot and a sapphire carrier in an attempt to induce spontaneous spallation along the subsurface laser damage region due to the CTE mismatch by cooling the carrier to a temperature of about -110 °C. Spallation was not successfully achieved. It was found that the silicone material acted as a stress absorber during cooling of the sapphire carrier, adhesive material, and SiC ingot, as well as the T gIt is theorized that the CTE mismatch between the carrier and the crystalline material was insufficient when the SiC ingot was heated to 1000 K. The CTE mismatch between the sapphire carrier and the SiC ingot was large at room temperature, but at temperatures as low as -110 °C, the CTE mismatch decreased to a relatively small value. However, even if silicone is hypothetically assumed to exhibit effective stress transfer properties, it may still be beneficial to avoid cryogenic temperatures (e.g., liquid nitrogen temperatures) during separation of the device wafer, since exposure to these temperatures can damage the devices.

[0146] In certain embodiments, the adhesive material may include a chemically crosslinked adhesive, such as an epoxy. In certain embodiments, a reactive catalyst type adhesive is used to bond the rigid carrier and the crystalline material substrate. A multi-part bonding agent (eg, a two-part epoxy) may be used.

[0147] While any suitable thickness of the layer of adhesive material can be used, in certain embodiments, the adhesive layer can be relatively thin (e.g., less than about 100 microns, less than about 50 microns, less than about 40 microns, less than about 30 microns, less than about 20 microns, or less than about 10 microns (any of the above upper thresholds are optionally subject to a lower threshold of at least about 2 microns, at least about 5 microns, or at least about 10 microns, as appropriate). Providing a thin adhesive layer can promote a more direct transfer of shear stress between the rigid carrier and the crystalline material during fracture, thereby reducing the force and time required to complete fracture. However, the optimal adhesive thickness can depend on several factors, such as the elastic modulus of the adhesive, the bonding method, the separation technique, etc.

[0148] Considering the existence of various types of adhesives that can be used to bond the rigid carrier and the crystalline material, various adhesive bonding methods can be employed. In certain embodiments, thermal compression (including application of a compressive force at elevated temperature) can be used. In one example, a 150 mm diameter crystalline material substrate (e.g., 4HSiC) secured to a rigid carrier (e.g., single crystal sapphire) with an adhesive can be subjected to a force of 1800 to 3000 N while being exposed to a temperature of 180° C. In certain embodiments, a compressive force can be applied while applying UV radiation to a UV-curable adhesive material between the rigid carrier and the crystalline material substrate. When a liquid or flowable bonding medium is used, in certain embodiments, the bonding medium can extend partially up the sidewall of the crystalline material substrate (and along the proximal surface of the rigid carrier) when compressed during bonding, resulting in the formation of a peripheral lip around at least a portion (or all) of the peripheral edge of the crystalline material, which can serve to slightly increase the bond strength between the substrate and the carrier.

[0149] In certain embodiments, plasma activated anodic bonding, or any other suitable anodic bonding process, can be used to bond the rigid carrier and the crystalline material substrate. Details relating to anodic bonding between the crystalline material substrate and the 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.

[0150] In certain embodiments, to facilitate adhesion, the proximal surfaces of the rigid carrier and / or the crystalline material can be roughened, textured, and / or surface activated in any suitable manner prior to bonding (including, for example, adhesive bonding). Examples of surface treatments that can be performed include, but are not limited to, micropatterning, mechanical ablation, chemical etching, reactive ion etching, and plasma treatment. In certain embodiments, the rigid carrier can include single crystal sapphire having a micropatterned surface.

[0151] In certain embodiments, the rigid carrier may include one or more features configured to facilitate debonding when removal of the (already cut) crystalline portion attached to the carrier is desired. Examples of such features may include perforated and / or micropatterned surfaces to provide holes or cavities located adjacent to and / or allowing fluid communication with the proximal surface of the rigid carrier.

[0152] Various processes can be used to facilitate debonding between the (already cut) crystalline material portion and the rigid carrier. In certain embodiments, thermal, mechanical, chemical, and / or photo-induced debonding can be employed. In certain embodiments, debonding can be achieved by thermal slide-off, which involves sliding the adhesively bonded assembly to a sufficient temperature while the rigid carrier is fixed in place (e.g., held by a vacuum chuck). The bonding method includes heating the adhesive to a temperature of 100° C. to soften and / or flow the adhesive material, and applying an external shear stress to a portion of the crystalline material to allow the portion to slide laterally from the rigid carrier. In certain embodiments, the adhesive may contain a UV absorbing material, in which case exposure to UV radiation on the adhesive after cutting may be used to cause decomposition (e.g., by heating) of the adhesive between the crystalline material portion and the carrier to allow removal of the crystalline material portion. Chemical removal of the adhesive may utilize any suitable chemical sufficient to reduce the adhesive force and / or decompose the adhesive material. When chemical debonding is used, the carrier may be provided with one or more access openings (e.g., perforations) to allow chemicals to contact the adhesive material.

[0153] [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 within a crystalline material 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 some depth within the crystalline material substrate. Parameters such as focusing depth, laser power, translation speed, and subsurface damage line spacing can be adjusted to create the laser damage, although adjustment of certain factors involves trade-offs. Increasing laser power tends to create 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 creates larger 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 improved by decreasing the lateral spacing between the subsurface laser damage lines; however, decreasing the spacing between the laser damage lines increases the number of translational paths between the substrate and the laser, which reduces the throughput of the tool.

[0154] 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. If the crystalline material includes SiC, the upper surface 32 through which the laser radiation is directed may be a C-terminated surface. The 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 may be pulsed at any suitable frequency and beam intensity (typically in the nanosecond, picosecond, or femtosecond range) 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 to form 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. Relative lateral 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 various patterns, such as those shown in Figures 8A-8D.

[0155] 8A-8D provide exemplary laser tool translation paths relative to a crystalline material for forming subsurface damage in the crystalline material. In certain embodiments, the laser tool portion (e.g., including 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 moves. The material is moved relative to the tool portion. FIG. 8A shows a linear scanning movement 52 in the y direction suitable for forming subsurface damage in a pattern of laterally spaced parallel lines in a first crystalline material 50A. FIG. 8B shows a linear scanning movement 52 in the y direction and a linear scanning movement 54 in the x direction suitable for forming subsurface damage in a pattern of a first group of laterally spaced parallel lines intersecting a second group of laterally spaced parallel lines in a second crystalline material 50B. FIG. 8C shows a circular movement 56 suitable for forming subsurface damage in a pattern of concentric circles in a third crystalline material 50C. FIG. 8D shows a linear scanning movement 56 in the y direction across (and beyond) the surface of crystalline material 50D sufficient to form parallel subsurface laser damage lines distributed across crystalline material 50D, the damage lines being perpendicular to the [11-20] direction of the hexagonal crystal structure of crystalline material 50D. If desired, other subsurface damage patterns (eg, spirals, honeycomb, herringbone, etc.) may be formed.

[0156] In certain embodiments, the crystalline 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. aThen, laser damage can 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 is bonded to the top surface of the crystalline material substrate. The wafer resulting from the crystalline material substrate can be associated with an identification code or other information linked to the first carrier. Alternatively, a laser marking 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 crystalline 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 crystalline material substrate and the remaining portion of the crystalline material substrate are ground smooth and cleaned as necessary to remove residual subsurface laser damage. The removed portion of the crystalline material substrate can be separated from the carrier. The process can then be repeated using the remaining portion of the crystalline material substrate.

[0157] While wire sawing of SiC wafers typically involves a kerf loss of at least about 250 microns per wafer, the laser-assisted and carrier-assisted separation methods applied to SiC disclosed herein can achieve kerf losses in the range of 80 to 140 microns per wafer.

[0158] FIG. 9 is a schematic cross-sectional side view of an assembly 58 including a crystalline material substrate 60 with a subsurface laser damage 66 bonded to a rigid carrier 72 by an intermediately disposed layer 68 of adhesive material. The assembly 58 is suitable for fracturing the crystalline material substrate 60 along the subsurface laser damage 66 utilizing any or more of the methods disclosed herein to facilitate removal of a portion of the crystalline material substrate 60 along the subsurface laser damage 66. The crystalline material substrate 60 includes a first surface 62 proximate the adhesive material 68 and an opposing second surface 64, the subsurface laser damage 66 being closer to the first surface 62 than to the second surface 64. The rigid carrier 72 also includes a first surface 73 proximate the adhesive material 68 and a second surface 74 opposite the first surface 73. The adhesive material 68 extends between the first surface 62 of the crystalline substrate 60 and the first surface 73 of the rigid carrier 72. As shown, an exposed adhesive lip 70 is provided around at least a portion (or optionally all) of the peripheral edge of the crystalline material substrate 60 proximate the first surface 62 of the crystalline material substrate 60. In certain embodiments, the rigid carrier 72 comprises a material having a CTE greater than the CTE of the crystalline material substrate 60 over a desired temperature range, and fracture of the crystalline material 60 occurs in a cryogenic medium (e.g., This may be initiated by cooling at least the rigid carrier 72 (or the carrier and substrate 60) by exposure to a cooling fluid or condition.

[0159] [Cooling spallation of rigid supports with support / substrate CTE mismatch] 10A-10F illustrate steps of a semiconductor processing method according to one embodiment of the present disclosure utilizing a CTE-mismatched rigid carrier bonded to a crystalline material. FIG. 10A is a schematic cross-sectional side view of a rigid carrier 72 having a layer of adhesion material 68 bonded to a first surface 73 of the rigid carrier 72, and having a second surface 74 opposite the first surface 73. To promote better adhesion to the first surface 73, such surface may be etched (e.g., by reactive ion etching) prior to application of adhesion material 68. Adhesion material 68 may be applied by any suitable method, such as spin-coating, spraying, dipping, rolling, or the like.

[0160] FIG. 10B is a schematic cross-sectional view of an assembly 58' including the rigid carrier 72 and adhesive material 68 of FIG. 10A bonded to a crystalline material substrate 60 having a subsurface laser damage region 66. As shown, the rigid carrier 72 has a larger diameter or lateral extension than the crystalline material substrate 60. The assembly 58' of FIG. 10B is similar to that shown in FIG. 9, but lacks the exposed adhesive lip shown in FIG. 9. With continued reference to FIG. 10B, the crystalline material substrate 60 includes a first surface 62 proximate the adhesive material 68 and an opposing second surface 64, with the subsurface laser damage 66 closer to the first surface 62 than to the second surface 64 of the substrate 60. The rigid carrier 72 also includes a first surface 73 proximate the adhesive material 68, with the adhesive material 68 extending between the first surface 62 of the crystalline substrate 60 and the first surface 73 of the rigid carrier 72. The adhesive material 68 can be cured according to the requirements of the selected bonding method (e.g., high temperature thermal compression adhesive bonding, compression UV bonding, chemically reactive bonding, etc.). Although the second surface of the crystalline material substrate 60 is shown bare, in certain embodiments, a second carrier (not shown) may be bonded (either temporarily or permanently) to the second surface 64 of the substrate 60, where the second carrier is optionally equal to or smaller in width than the substrate 60 and / or CTE matched to the substrate 60.

[0161] 7C is a schematic cross-sectional view of the assembly of FIG. 10B after positioning the second surface 74 of the rigid carrier 72 on a support surface 78 of a cooling device in the form of a cooled chuck 76 configured to receive a cooling fluid. Contact between the rigid carrier 72 and the cooled chuck 76 transfers heat from the rigid carrier 72 to the cooled chuck 76, thereby rapidly cooling the rigid carrier 72. During such cooling process, the rigid carrier 72 will contract laterally to a greater extent than the crystalline material substrate 60, thereby exerting a shear stress on the crystalline material substrate 60. Due to the presence of the subsurface laser damage 66 near the adhesive layer 68 bonding the rigid carrier 72 to the crystalline material substrate 60, the exertion of the shear stress on the substrate 60 will cause the crystalline material to fracture along or adjacent the subsurface laser damage region 66.

[0162] In a particular embodiment, the cooled chuck 76 has a diameter smaller than that of the rigid carrier 72. It has been found that cooling of the assembly of FIG. 10C may only be required from the second surface 74 of the rigid carrier 72 and only to a central portion of the rigid carrier 72 to create a temperature differential in both the lateral (i.e., from the center to the edges) and vertical (i.e., from the crystalline material substrate 60 to the rigid carrier 72). Although the cooled chuck 76 may be supplied with a cooling liquid, it is not necessary for the rigid carrier 72 to reach liquid nitrogen temperatures (−160° C.) to successfully complete the thermally induced fracturing of the crystalline material substrate 60. Favorable separation results have been obtained for the fracturing of a single SiC material supported by a crystalline sapphire substrate using a cooled chuck maintained at −70° C. Such temperatures can be achieved with a variety of cooling liquids, such as liquid methanol (with its freezing point −97° C.) received from a two-phase pumped evaporative cooling system. The temperature may be maintained using a single phase evaporative cooling system, although liquid nitrogen remains fluid above -20°C. 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 may be maintained using a single phase evaporative cooling system. The ability to use a single phase or two phase pumped evaporative cooling system rather than liquid nitrogen greatly reduces operational costs.

[0163] FIG. 10D is a schematic cross-sectional view of the remaining portion of the crystalline material substrate 60A separated from the bonded assembly (on the water-cooled chuck 76), including the rigid carrier 72, the adhesive material 68, and the portion of the crystalline material 80 removed from the remaining portion of the substrate 60A, after fracturing of the crystalline material along the subsurface laser damage region. The remaining portion of the crystalline material substrate 60A is bounded by a new first surface 63 (with residual laser damage 66A) opposite the second surface 64. Correspondingly, the removed portion of the crystalline material 80 is bounded by a new second surface 82 (with residual laser damage 66B) opposite the first surface 62. The bonded assembly 85 including the rigid carrier 72, the adhesive material 68, and the removed portion of the crystalline material 80 can then be retrieved from the cooled chuck 76.

[0164] FIG. 10E is a schematic cross-sectional view of the bonded assembly 85 of FIG. 10D after retrieval from the water-cooled chuck 76. Maintaining the removed portion of crystalline material 80 attached to the rigid carrier 72 advantageously provides mechanical support for the removed portion of crystalline material 80, thereby enabling one or more surface processing steps (e.g., grinding, polishing, etc.) to be performed on the new surface 82 to remove residual laser damage 66B and achieve a desired thickness of the crystalline material 80 (e.g., via grinding and optional subsequent chemical mechanical planarization (CMP) and / or various polishing steps). In certain embodiments, the laser damage removal and thinning may include successive grinding / polishing steps with 2000 grit and 7000 grit polishing pads, as well as any suitable polishing and cleaning steps to prepare the new surface 82 for subsequent steps (e.g., surface implantation, laser marking (e.g., adjacent to the wafer flat), formation of an epitaxial layer, metallization, etc.).

[0165] FIG. 10F is a schematic cross-sectional view of the removed portion 80 of crystalline material supported by an upper surface 88 of a heated vacuum chuck 86, with the rigid carrier 72 and adhesive material 68 having been translated laterally away from the removed portion 82 of crystalline material following high temperature softening and release of the adhesive material 68. That is, the heated vacuum chuck 86 can be heated to a temperature sufficient to soften and / or flow the adhesive material 68 such that application of an external shear stress to the second surface 74 of the rigid carrier 72 can cause the rigid carrier 72 to translate laterally away from the removed portion 82 of crystalline material that is temporarily held in place by the heated vacuum chuck 86. Thereafter, operation of the heated vacuum chuck 86 can be stopped and the removed portion 82 of crystalline material will embody a self-supporting material. If desired, the first surface 73 of the rigid carrier 72 can be cleaned of any adhesive 68 residue, and the rigid carrier 72 can be optionally reused for another fracturing process. The removed crystalline material can then be used as a growth substrate for growing one or more epitaxial and conductive metal layers to form a device wafer, which is singulated to form individual semiconductor devices.

[0166] In certain embodiments, a cooled chuck can be placed in a coolant bath (e.g., a bath of liquid nitrogen or other coolant liquid such as methanol received from a pumped evaporative cooling system) to induce thermally induced fracture in a crystalline material substrate supported by a rigid carrier with an appropriate CTE mismatch.

[0167] FIG. 11 illustrates a cooling fluid (e.g., methanol received from a pumped evaporative cooling system, or 10C is a schematic cross-sectional view of the assembly according to FIG. 10C on a cooling device in the form of a cooled chuck 76A that is disposed in a bath 79 of a cooling medium (such as a liquid nitrogen bath or a liquid nitrogen bath). An adhesive material 68 is disposed between the rigid carrier 72 and a crystalline material substrate 60 having a subsurface laser damaged region 66 that is closer to a first surface 62 than an opposite second surface 64 of the substrate 60, the first surface 62 being in contact with the adhesive material 68. The rigid carrier 72 includes a first surface 73 that is in contact with the adhesive material 68 and an opposite second surface 74 that is disposed in contact with a support surface 78A of the cooled chuck 76A. The cooled chuck 76A has a diameter smaller than that of the rigid carrier 72. The cooled chuck 76A is disposed in a bath of a cooling medium (such as a liquid nitrogen bath) sufficient to reduce the temperature of the cooled chuck 76A to or near the cooling medium temperature. In certain embodiments, the cooled chuck 76A and refrigerant bath 79 may be disposed within a closable insulating container (not shown) that may be selectively opened to allow a rigid carrier 72 having an attached adhesive material 68 and a crystalline material substrate 60 with subsurface laser damage 66 to be placed in contact with the cooled chuck 76A for rapid fracture of a single crystalline material substrate 60 along the subsurface laser damage region 66.

[0168] FIG. 12 is a perspective view of a cooling apparatus 90 including a container 92 having a cylindrical side wall 94 bounded by a bottom wall 96 on which a chuck 100 is supported by a thermally conductive spacer 98 (e.g., an aluminum rail). The chuck 100 is of a type that is sufficient to apply suction to a workpiece, but does not need to provide vacuum suction functionality during the cooling process (provided by suction ports 102 configured to be connected to a vacuum source and perforations 104 disposed along a chuck upper surface 106). In use, a cooling fluid can be supplied to the container 92 in contact with the spacer 98, but not necessarily the entire width of the chuck 100 itself. Heat can be transferred from the chuck 100 through the thermally conductive spacer 98 to the cooling fluid. In experiments, a vacuum chuck 100 of the design shown was maintained at a temperature of around −70° C. The carrier side of the assembly 58′ as shown in FIG. 10B can be placed on the chuck upper surface 106 so that the rigid carrier is rapidly cooled. Due to the CTE mismatch between the carrier and the bonded crystalline substrate, thermally induced spallation occurs along the subsurface laser damage region. The inventors have observed spontaneous delamination of 4H-SiC at temperatures up to about -20 °C using the thermoplastic adhesive disclosed herein without mechanical intervention.

[0169] [Shape of the support and its positioning relative to the crystalline material] As already noted, rigid carriers desirably have lateral dimensions (e.g., diameters, or lengths and widths) at least as large as or larger than the corresponding dimensions of the substrate bonded thereto when used with methods as disclosed herein. Figures 13A-13E are top views of bonded assemblies including carriers of various shapes each bonded to a substrate of crystalline material, and Figures 13F and 13G provide side cross-sectional views of the bonded assemblies of Figures 13D and 13E, respectively. Figure 13A shows a first bonded assembly 110 including a generally circular substrate 112 having a flat 114 and a rounded portion 116 opposite the flat 114, the substrate 112 being bonded to a square shaped carrier 118 that is substantially concentric with the substrate 112. 13B shows a second bonded assembly 120 including a generally circular substrate 122 having a flat 124 and a rounded portion 126 opposite the flat 124, bonded to a rounded carrier 128 that is substantially concentric with the substrate 122. Due to the presence of the flat 124 locally reducing the diameter of the substrate 122, a larger boundary portion 129 of the carrier 128 is provided adjacent the flat 124. FIG. 13C shows a third bonded assembly 130 including a generally circular substrate 132 having a flat 134 and a rounded portion 136 opposite the flat 134, bonded to a rounded carrier 138 that is non-concentric with the substrate 132, with the rounded portion 136 of the substrate 132 being substantially closer to an edge of the carrier 138 than the remainder of the substrate 132. Even if flat 134 is not present, there will be a larger boundary 139 of carrier 138 opposite rounded portion 136, but if flat 134 is present, boundary 139 of carrier 138 will be even larger than boundary 129 shown in FIG. 13B. The presence of a locally larger boundary in one area and a locally smaller boundary in an opposite area, as shown in FIG. 13C, may be advantageous in certain embodiments to enable mechanical fracturing of substrate 132 bonded to carrier 138, where the locally larger boundary accommodates the presence of a prying tool (not shown) and the locally smaller boundary limits overhangs that might otherwise resist tilting movement of the upper substrate (as determined by the geometry of the separation apparatus).

[0170] 13D and 13F show a fourth bonded assembly 140 including a generally circular substrate 142 having a flat 144 and a rounded portion 146 opposite the flat 144, bonded to a primarily circular carrier 148 that is substantially concentric with the substrate 142, but includes a single laterally projecting tab portion 149 that provides a locally enlarged interface adjacent the flat 144 of the substrate 142. The laterally projecting tab portion 149 of the carrier 148 may be aligned with the flat 144 in such a manner that a localized mechanical force may be applied in such a manner that a bending moment is imparted that has a tendency to initiate fracture in a direction perpendicular to the flat 144. As shown in FIG. 13F, a second carrier 148' of the same or different shape may be provided below the substrate 142, with the subsurface laser damage region 143 being closer to the upper carrier 148. The presence of protruding tab portions 149 allows for the insertion of a single pry tool (not shown) between the carriers 148, 148'.

[0171] 13E and 13G show a fourth bonded assembly 150 including a generally circular substrate 152 having a flat 154 and a rounded portion 156 opposite the flat 154, bonded to a primarily circular carrier 158 that is substantially concentric with the substrate 152 but includes opposing first and second laterally projecting tab portions 159A, 159B that provide locally enlarged boundary areas, one locally enlarged boundary area adjacent the flat 154 of the substrate 152. The laterally projecting tab portions 159A, 159B of the carrier 158 may be aligned with the flat 154 in a manner that allows for the application of a localized mechanical force in such a manner that a bending moment is imparted that has a tendency to initiate fracture in a direction perpendicular to the flat 154. As shown in FIG. 13G, a second carrier 158' of the same or different shape can be provided below the substrate 152, with the subsurface laser damage region 153 closer to the upper carrier 158. The presence of laterally protruding tab portions 159A, 159B allows for a tool (not shown) to be inserted between the carriers 158, 158' to apply a mechanical force. Additional details regarding the application of mechanical force to initiate fracture of the crystalline material along the subsurface laser damage region are discussed herein below in connection with FIGS. 15A-15D and 16A-16B.

[0172] 13F and 13G show upper carriers 148, 158 and lower carriers 148', 158' having lateral dimensions that exceed the lateral dimensions of the substrates 142, 152, it should be appreciated that in certain embodiments, the lower carriers 148', 158' are no larger than the corresponding substrates 142, 152 (e.g., to provide a base to resist mechanical forces applied to the upper carriers 148, 158 when the substrates 142, 152 are held by a vacuum chuck or other means).

[0173] [Fracture induced by ultrasonic energy] Another method for inducing spallation along the laser-induced subsurface damage zone of crystalline material bonded to a rigid support involves applying ultrasonic energy to the crystalline material while it is in the bonded state. 14 is a schematic cross-sectional view of an assembly 58A including a crystalline material 60A with subsurface laser damage 66A' bonded to a rigid carrier 72A using an intervening adhesive material 68A, the assembly 58A being disposed within a liquid bath 165 of an ultrasonic generator device 160. The device further includes a container 162 disposed in contact with an ultrasonic generating element 164, the container 162 containing the liquid bath 165. The presence of the rigid carrier 72A can reduce or eliminate fracture of the crystalline material 60A when subjected to ultrasonic energy, particularly if residual stresses remain between the rigid carrier 72A and the crystalline material 60A 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. In this regard, it is noted that combining two or more disruption techniques (e.g., CTE mismatch and ultrasonically induced disruption, or CTE mismatch and mechanical action induced disruption, or ultrasonically induced and mechanical action induced disruption) is specifically contemplated. In certain embodiments, the liquid in the ultrasonic bath can be cooled prior to or during application of ultrasonic energy.

[0174] [Mechanical force-induced fracture] In certain embodiments, fracture of a crystalline material bonded to a rigid carrier can be facilitated by application of a mechanical force (e.g., optionally localized at one or more locations) proximate at least one edge of the carrier. Such force can impart a bending moment to at least a portion of the carrier, and such bending moment can be transferred to the subsurface laser damage region to initiate fracture.

[0175] As previously noted herein, multiple fracturing techniques can be used simultaneously or sequentially. In certain embodiments, CTE mismatch can be utilized in combination with mechanical force. If a large CTE mismatch exists between the substrate and the carrier and the temperature is appropriately reduced, less (or no) mechanical force may be required to facilitate separation. Conversely, if a low (or no) degree of CTE mismatch exists between the substrate and the carrier, a greater mechanical force may be required to complete the separation.

[0176] Exemplary embodiments for promoting fracture of a crystalline material having subsurface damage bonded to a rigid carrier by application of a mechanical force are shown in Figures 15A-15D and 16A-16B.

[0177] 15A-15D are schematic cross-sectional views illustrating steps for fracturing a crystalline material substrate 142 with subsurface laser damage 143 by applying a mechanical force proximate one edge of a carrier 148 to which the substrate 142 is bonded. These figures utilize the same bonded assembly 140 shown in FIGS. 13D and 13F. The bonded assembly includes a crystalline material substrate 142 with a subsurface laser damage region 143 bonded (according to any bonding method disclosed herein) between rigid carriers 148, 148'. Each rigid carrier 148, 148' includes a laterally projecting tab portion 149, 149' aligned with a flat 145 of the substrate 142 to provide a locally enlarged border area defining a recess 141 into which a tool 166 can be inserted. FIG. 15A shows the condition prior to insertion of the tool 166 into the recess 141. FIG. 15B shows the tool 166 after insertion into the recess with the tool 166 tilted upward, which exerts a prying force in a direction that tends to promote separation between the rigid supports 148, 148', which exerts a bending moment M on at least one of the supports 148. In certain embodiments, the substrate 142 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 of the hexagonal crystal structure (or equivalently, within ±5 degrees of parallel to the [1-100] direction). Such an orientation of the bending moment M is particularly desirable when the substrate 142 comprises an off-axis (vicinal) material. This The orientation of the crystalline material may be less important if the substrate 142 includes on-axis material. FIG. 15C shows the state after initial fracturing of the crystalline material substrate 142 along the subsurface laser damage region 143, where the upper portion 142A of the crystalline material remains bonded to the upper carrier 148 and the lower portion 142B of the crystalline material remains bonded to the lower carrier 148', with the upper carrier 148 tilted upwardly relative to the lower carrier 148'. FIG. 15D shows the state after fracturing is completed and the tool 166 is removed, resulting in a first bonded assembly 168A (including the upper carrier 148 and the upper portion 142A of the crystalline material) separated from a second bonded assembly 168B (including the lower carrier 148' and the lower portion 142B of the crystalline material).

[0178] In certain embodiments, mechanical forces can be applied proximate opposite edges of a rigid carrier to which the substrate is bonded to facilitate fracture of the subsurface laser damaged crystalline material bonded to the carrier. FIG. 16A is a schematic cross-sectional view of an apparatus 170 for fracture of a crystalline material substrate 172 along a subsurface laser damaged region 173 by applying mechanical forces along opposite edges of a rigid carrier 176 (bonded to the substrate 172 with an adhesive material 174) to impart bending moments M1, M2 to portions of the carrier 174. A limiting element 171 (e.g., a vacuum chuck, a lower substrate, or other support) can be provided below the substrate 172. The lateral extension (e.g., diameter, or length and width) of the carrier 176 is greater than that of the substrate 172, and the carrier 176 forms opposite laterally protruding lips 179A, 179A that are received by lifting members 175A, 175B. The central portion of the carrier 176 is restricted from lifting (e.g., pressed downward) by the limiting member 177. When a vertical lifting force is applied by the lifting members 175A, 175B to the laterally protruding lips 179A, 179B and the central portion of the carrier 176 is prevented from moving upward by the limiting member 177, bending moments M1, M2 are exerted on both sides of the carrier 176, and such bending moments M1, M2 are transferred by the adhesive material 174 to the substrate 172 to initiate fracturing of the substrate 172 along the subsurface laser damage region 173. The limiting member 177 and the lifting members 175A, 175B can then be released and fracturing can be completed. FIG. 16B shows the completed fracturing state, creating a bonded assembly 178 including the rigid carrier 176, the adhesive material 174, and the crystalline material substrate portion 172A separated from the remainder of the crystalline material 172. The exposed surfaces 173A, 173B of the crystalline material substrate portion 172A and the remainder of the crystalline material 172 may exhibit surface irregularities that can be reduced by conventional surface processing steps (e.g., grinding, CMP, and / or polishing). In certain embodiments, such surface processing steps may be performed on the crystalline material substrate portion 172A while such portion remains bonded to the rigid carrier 176.

[0179] Although Figures 15A-15D and 16A-16B provide examples of specific apparatus for facilitating mechanical spallation of the substrate along the subsurface laser damage region, it should be appreciated that other apparatus can be used to practice the methods disclosed herein, as one of ordinary skill in the art would recognize.

[0180] [Subsurface laser damage formation before or after carrier bonding] Although forming laser subsurface damage in a crystalline material substrate prior to bonding to a rigid carrier has been described herein, in certain embodiments, a rigid carrier transparent to the desired wavelength of laser radiation may be bonded to the crystalline material substrate prior to forming the subsurface laser damage. In such embodiments, the laser radiation may be transmitted through the rigid carrier into the interior of the crystalline material substrate. Different carrier-substrate subsurface laser formation configurations are illustrated in Figures 17A-17C. Figure 17A is a schematic diagram of laser radiation 181 being focused through the surface of a bare substrate 182 to form subsurface laser damage 183 in the substrate 182, to which a rigid carrier may be attached after the formation of the subsurface laser damage. Figure 17B shows the formation of a subsurface laser damage in the substrate 182. FIG. 17C is a schematic diagram of laser radiation 181 being focused through a surface of a substrate 182, the substrate 182 having been previously bonded to a rigid carrier 186 using an adhesive material 184, to form the subsurface laser damage 183. FIG. 17C is a schematic diagram of laser radiation 181 being focused through a rigid carrier 186 and adhesive 184 to form subsurface laser damage 183 in a substrate 182 previously bonded to the rigid carrier 186. In certain embodiments, the surface of the substrate 182 distal from the carrier 186 may include one or more epitaxial and / or metallization layers, and the substrate 182 embodies an operational electrical device prior to the formation of the subsurface laser damage 183. FIG. 17D is a schematic diagram of laser radiation 181 being focused through a rigid carrier 186 into a substrate 182 (without an intervening adhesive layer) to form subsurface laser damage 183 in a substrate 182 that has been previously bonded (e.g., via anodic bonding or other adhesive-free means) to a rigid carrier 186.

[0181] [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.

[0182] 18A-18O 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.

[0183] FIG. 18A illustrates a crystalline material substrate 190 having a first surface 191 and a subsurface laser damage 193 disposed at a predetermined depth relative to the first surface. FIG. 18B illustrates the substrate 190 of FIG. 18A after adding an adhesive material 194 to cover the first surface 191. FIG. 18C illustrates the items depicted in FIG. 18B after bonding a rigid carrier 196 to the substrate 190 using the adhesive material 194. FIG. 18D illustrates the items of FIG. 18D after fracturing the substrate 190 (e.g., using one or more methods disclosed herein) along the subsurface laser damage 193, resulting in a remaining portion of the substrate 190 separated from the bonded assembly, including the carrier 196, the adhesive material 194, and the crystalline material portion (e.g., thick wafer) 192 removed from the substrate 190. In certain embodiments, the thick wafer 192 may have a thickness in the range of approximately 350 to 750 microns. The exposed surface 193A of the thick wafer 192 and the exposed surface 193B of the remaining portion of the substrate 190 may exhibit surface irregularities that can be reduced by surface processing steps such as grinding, CMP, polishing, etc. FIG. 18E shows the thick wafer 192 after debonding and removal from the carrier 196, where the thick wafer 192 includes a vertical edge profile. The vertical edges of the wafer can easily fracture during handling of the wafer, 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. 18F shows the thick wafer 192 supported by a turntable 198 in close proximity to a rotating profile grinding tool 199 having a concave cutting surface 199A (e.g., impregnated with diamond particles) configured to impart a rounded edge profile 197 to the thick wafer 192. FIG. 18G shows thick wafer 192 after edge grinding (also known as edge profiling), which includes rounded edge 197 that provides an interface between first wafer surface 201 and second wafer surface 202. .

[0184] FIG. 18H shows the item of FIG. 18G after one or more epitaxial layers 203 have been grown on or over the first surface 201 of the thick wafer 201. Due to the incompatibility of the adhesive with the high temperatures inherent in epitaxy, the carrier shown in FIG. 18D is not present. FIG. 18I shows the structure FIG. 18H after forming conductive (e.g., metal) contacts 204 on the epitaxial layers 203 to form at least one operational semiconductor device, with the thick wafer 192 still having rounded edges 197. Traditionally, grinding is performed against the second surface 202 to thin the thick wafer 192 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.

[0185] The inventors have found that the presence of rounded edges 197 on the thick wafer 192 inhibits control of the formation of subsurface laser damage proximate the edges 197 because the rounded profile adversely affects laser focus and depth control. To address this issue, the rounded edges 197 of the thick wafer 192 can be removed prior to further laser processing. FIG. 18J shows the structure of FIG. 18I having been ground with an edge grinder 206 to grind away the rounded edges 197 and provide a substantially vertical edge 205 extending between the first surface 201 and the second surface 202 of the thick wafer 192, with the epitaxial layer 203 and contacts 204 disposed on the first surface 201.

[0186] FIG. 18K shows the structure of FIG. 18J after adding a temporary adhesive material 207 covering the first surface 201, epitaxial layer 203, and contacts 204 of the thick wafer 192 in preparation for receiving and bonding a first carrier. FIG. 18L shows the structure of FIG. 18K after adding a first carrier 208 over the temporary adhesive material 207 and after forming a subsurface laser damage 209 in the thick wafer 192 by directing focused laser radiation through the second surface 202 of the thick wafer 192. FIG. 18M shows the structure of FIG. 18L after bonding a second rigid carrier 210 to the second surface 202 of the thick wafer 192 in proximity to the subsurface laser damage 209. For separation purposes, the second rigid carrier 210 serves as a front carrier intended to remove a portion (i.e., a layer) of the thick wafer 192.

[0187] 18N illustrates the items of FIG. 18M after applying at least one fracturing process disclosed herein to fractur e the thick wafer 192 along the subsurface laser damage 209 to obtain a first bonded subassembly 212A and a second bonded subassembly 212B. The first bonded subassembly 212A includes the first thin wafer portion 192A (separated from the thick wafer 192 of FIG. 18M), the epitaxial layer 203, the contacts 204, the temporary adhesive material, and the first carrier 208. The second bonded subassembly 212B includes the second thin wafer portion 192B (separated from the thick wafer 192 of FIG. 18M) and the second carrier 210. Exposed surface 209A of thin wafer portion 192A and exposed surface 209B of thin wafer portion 192B 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. 18O illustrates an operational semiconductor device 214 obtained from first bonded subassembly 212A by removing temporary adhesive 207 and first carrier 208. Such figure also illustrates the preparation of second thin wafer portion 192B for further processing (e.g., epitaxial growth). The second thin wafer portion 192B after removal of the second carrier 210 in preparation.

[0188] Exemplary methods involving reuse of carrier wafers FIG. 19 is a flow chart outlining the steps of a method according to the present disclosure. Starting at the top left, a laser 216 can focus laser radiation below a first surface 222 of a thick crystalline material substrate 220 (e.g., a SiC ingot) to create a subsurface laser damage region 218. If the substrate 220 is a SiC material, the laser radiation is directed to a C-terminated face of the SiC substrate 220. A carrier wafer 224 can then be bonded to the first surface 222 of the crystalline material substrate 220, the carrier wafer 224 including a first surface 226 (proximal to the first surface 222 of the substrate 220) and a second surface 228 opposite the first surface 226 of the carrier wafer 224. Such bonding between the carrier wafer 224 and the crystalline material substrate 220 can be performed by any method disclosed herein, such as adhesive bonding or anodic bonding. 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 220 along the subsurface laser damage region 218, separating the crystalline material portion 230 attached to the carrier wafer 224 from the remainder of the crystalline material substrate 220A. The newly exposed surface 232A of the remaining portion of the crystalline material substrate 220A with the residual laser damage is ground smooth, cleaned, and returned to the beginning of the process (top left in FIG. 19 ). Additionally, the newly exposed surface 234 of the removed crystalline material 230 is ground smooth while still attached to the carrier 224. The carrier wafer 224 can then be separated from the removed portion of crystalline material 230 and one or more layers can be epitaxially grown on the crystalline material 230 to form epitaxial device 230', while the carrier wafer 224 is cleaned and returned to the beginning of the process (top left of Figure 19) to allow for the removal of another relatively thin slice of crystalline material substrate 220.

[0189] 20 is a schematic cross-sectional view of a portion of the crystalline material substrate (e.g., SiC ingot) 220 of FIG. 19 showing the subsurface laser damage 218 with the superimposed dashed line identifying the expected kerf loss material region 240. The expected kerf loss material region 240 includes the laser damage 218 and also material 234 to be mechanically removed (e.g., by grinding and polishing) from the bottom surface 238 (e.g., Si-terminated surface) of the crystalline material portion 230 (e.g., SiC wafer) that will be separated from the substrate 220 and also material 236 to be mechanically removed (e.g., by grinding and polishing) from the top surface 232A (e.g., C-terminated) surface of the remaining portion 220A of the substrate 220. The bottom surface 238 of the crystalline material portion 230 is opposite its top surface 222. 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 232A and wafer bottom surface 238 for further processing.

[0190] [Material processing using multiple grinding stations / steps] In certain embodiments, the crystalline material that has undergone laser processing and spalling 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 spalling station, multiple coarse grinding stations arranged in parallel downstream of the spalling 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 is not possible to perform edge grinding on wafers that have laser damage. It has been found by the inventors that edge grinding of a substrate portion (e.g., a wafer) combined 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 the exposed cleavage planes resulting from surface spallation make the surface more susceptible to cracking, at least when edge grinding is performed prior to any surface processing (grinding and / or polishing). 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.

[0191] It has been found that the rough grinding step (i.e., to remove laser damage and spallation damage along the substrate portion and the spallation surface of the bulk substrate) tends to take significantly longer to complete than the preceding laser processing and spallation steps, and significantly longer than the subsequent fine grinding step. For this reason, multiple rough grinding stations are provided in parallel to eliminate bottlenecks in the fabrication of multiple wafers from bulk crystalline material (e.g., ingots). In certain embodiments, robotic handlers may be located upstream and downstream of the multiple rough grinding stations to control the loading and unloading of substrate portions. In certain embodiments, a carrier attachment station may be provided between the laser processing station and the spallation station, and a carrier removal station may be provided upstream (either directly or indirectly) of the edge grinding station. The carrier may desirably remain attached to the substrate portion during at least some of the surface grinding steps to reduce the possibility of breakage, especially for thin substrate portions (e.g., wafers), although the carrier is preferably removed prior to edge grinding (or prior to coating the wafer with a protective coating prior to edge grinding).

[0192] 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.

[0193] FIG. 21 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 the 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 crushing 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 portions received from the crushing 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 portions (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 separates the ground substrate portions from the carrier. Downstream of the carrier removal station 313 is a chemical mechanical planarization (CMP) station 314 for cleaning and preparing the substrate portion 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 a particular embodiment, 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 a particular embodiment, each coarse grinding station 308A, 308B is configured to remove crystalline material from the crystalline material portion (e.g., a wafer) between 20 microns and 100 microns thick, and the fine grinding station 312 is configured to remove crystalline material from the crystalline material portion (e.g., a wafer) between 3 and 15 microns thick. In certain embodiments, each coarse grinding station 308A, 308B and / or fine grinding station 312 can include multiple grinding sub-stations, with different sub-stations equipped with grinding wheels of different grits.

[0194] The apparatus according to the embodiment of Figure 21 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.

[0195] FIG. 22 illustrates a material processing apparatus 320 according to an embodiment similar to that of FIG. 21 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. 18F). Gripping the wafer in this manner may cause undesirable damage to the wafer surface (e.g., the Si-terminated surface of a SiC wafer). 22 is located 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.

[0196] The apparatus 320 according to Fig. 22 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 comprises 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 after edge grinding. In a particular embodiment, the first grinding device is a rough grinding station 328A, a 3 28B, the edge grinding can be performed by edge grinding station 332, and the second grinding device can be embodied in precision grinding station 312. In certain embodiments, after grinding of the first surface with at least one first grinding device and before edge grinding the edges to form a chamfered or rounded edge profile, a carrier removal step can be performed.

[0197] 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.

[0198] FIG. 23 is a schematic diagram of an embodiment of a material processing apparatus 340 similar to that of FIG. 21 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 configured to apply a protective coating (e.g., photoresist) by methods such as spin coating, dip coating, spray coating, or the like. The protective coating should be of sufficient thickness and robustness to absorb any damage that may be inflicted by the edge grinding station 365. In the case of SiC wafers, the Si-terminated surface may be coated with a protective coating since this is the surface on which epitaxial growth typically occurs. The coating removal station 358 may be configured to strip the coating by chemical, thermal, and / or mechanical means.

[0199] The apparatus 340 according to Fig. 23 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.

[0200] 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.

[0201] 24A 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.

[0202] FIG. 24B is a schematic cross-sectional side view of a second gripping device 362' for holding an ingot 364' having end faces 366', 368' that are non-perpendicular to a side wall 370', according to one embodiment. The upper end face 366' is arranged horizontally to receive a laser beam 376, while the lower end face 368' may have a carrier 372' attached thereto and held by a chuck 374'. To grip the side wall 370' of the ingot 364', a gripping effector 378' having a non-perpendicular face is provided, which is arranged at a non-perpendicular angle A1, A2 to a horizontal actuation rod 380'. A pivot joint 382' is provided between the actuation rod 380' and the gripping effector 378', which facilitates automatic alignment between the gripping effector 378' and the side wall 370' of the ingot 364'.

[0203] FIG. 25 is a line graph of the linear thermal expansion coefficient as a function of temperature for sapphire, with a plot of the CTE parallel to the c-axis of sapphire and a plot of the CTE perpendicular to the c-axis of sapphire superimposed. FIG. 26 is a line graph of the linear thermal expansion coefficient as a function of temperature for SiC, with a plot of the CTE along the c-axis of SiC and the a-axis of SiC superimposed. Comparing FIG. 25 and FIG. 26, sapphire (in FIG. 25) exhibits a larger variation in CTE between axes than SiC. It can be seen that sapphire has a larger CTE than SiC over a wide temperature range.

[0204] FIG. 27 is a bar graph providing a comparison of the linear thermal expansion coefficients of various crystalline materials and metals as seen at 25° C. It can be seen that the CTE of SiC is about 3, while the CTE of sapphire is about 7 (about 2.3 times larger). Although not shown in FIG. 27, the CTE of the PDMS polymer is about 3.0x10 over the temperature range of -55 to 150° C. -4 / C. Such a value is approximately 7.0x10 for sapphire, as shown in Figure 27. -6 This is two orders of magnitude larger than the CTE value of / C.

[0205] FIG. 28 plots the elastic modulus (Young's modulus) values ​​of various materials categorized into three groups: (1) metals and alloys, (2) graphite, ceramics, and semiconductors, and (3) polymers. Elastic modulus is a mechanical property that measures the stiffness of a solid material in the linear modulus regime of uniaxial deformation and defines the relationship between stress and strain of the material. As can be seen in FIG. 28, metals and semiconductors exhibit elastic modulus values ​​at least an order of magnitude greater than those of polymers. Although the exact values ​​are not shown in FIG. 28, it has been determined separately that sapphire has an elastic modulus of 345 GPa, while nickel has an elastic modulus of 190 GPa. In contrast, the polymer PDMS has an elastic modulus range between 0.57 MPa and 3.7 MPa, with such variation linearly dependent on the amount of crosslinker present in the polymer.

[0206] The following examples disclose further non-limiting embodiments of the present disclosure.

[0207] [Example 1] A single crystal SiC substrate with a thickness of 640 μm and a diameter of 150 mm was used as the starting material. A 10 μm thick SiC epitaxial layer was grown on the first side of the SiC substrate to obtain a 650 μm SiC structure. The laser radiation was focused to a depth of 240 μm from the SiC surface to create multiple substantially parallel subsurface laser damage lines at that depth. A single crystal sapphire carrier was bonded to the opposite second side of the SiC substrate using WaferBOND® HT-10.10 thermoplastic adhesive (Brewer Science, Inc., Rolla, MO, USA), and a thermal compression process (including application of a force of 1800 N and maintenance at 180 °C) was applied to complete the adhesive curing. Thermally induced spallation was performed by contacting the sapphire carrier to a vacuum chuck cooled with liquid nitrogen and maintained at −70 °C. Fracturing yielded a 240 μm section of SiC bonded to a sapphire carrier, which separated from the 410 μm section of SiC (forming the bonded assembly). Residual laser damage on the 410 μm section of SiC was removed by lapping and CMP to yield a 350 μm thick SiC wafer ready for epitaxy. Separately, the bonded assembly with the 240 μm thick SiC was also lapped and CMPed to reduce the SiC to a thickness of 180 μm. The bonded assembly was then subjected to carrier removal, which involves applying a lateral force to the SiC while the carrier is placed in contact with a heated vacuum chuck to soften the adhesive, following a thermal slide-off process. The resulting 180 μm thick SiC wafer now has a SiC epitaxial layer and is suitable for MOSFET fabrication. The result of this process is the formation of 350 μm thick SiC wafers ready for epitaxy from the 640 micron thick SiC substrate used as the starting material, and 180 μm thick SiC wafers that now have a SiC epitaxial layer on their surface.

[0208] [Example 2] A single crystal SiC substrate with a thickness of 570 μm and a diameter of 150 mm was used as the starting material. A 2 μm thick SiC epitaxial layer was grown on the first side of the SiC substrate to obtain a 572 μm SiC structure. Laser radiation was focused to a depth of 160 μm from the SiC surface to create multiple substantially parallel subsurface laser damage lines at that depth. A single crystal sapphire carrier was bonded to the opposite second side of the SiC substrate using the same bonding process as in Example 1. Thermally induced spallation was performed by contacting the sapphire carrier to a vacuum chuck cooled with liquid nitrogen and maintained at −70° C. Spallation yielded a 160 μm thick section of SiC bonded to the sapphire carrier (forming a bonded assembly) that was separated from the 412 μm thick section of SiC. Residual laser damage on the 412 μm thick section of SiC was removed by lapping and CMP to obtain a 350 μm thick SiC wafer ready for epitaxy. Separately, the bonded assembly containing 160 μm thick SiC was also lapped and CMPed to reduce the SiC to a thickness of 100 μm. The bonded assembly was then subjected to carrier removal, which involves applying a lateral force to the SiC while the carrier is in contact with a heated vacuum chuck to soften the adhesive, following a thermal slide-off process. The resulting 100 μm thick SiC wafer now has a SiC epitaxial layer and is suitable for RF device fabrication. The result of this process is a 350 μm thick SiC wafer ready for epitaxy from the 570 micron thick SiC substrate used as the starting material, and a 100 μm thick SiC wafer now has a SiC epitaxial layer on its surface.

[0209] [Example 3] As starting material for producing SiC wafers with a thickness of 355 microns, single crystal SiC substrates (ingots) with a diameter of 150 mm and a thickness of more than 10 mm are used. 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 as 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., a metal, vitreous, 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 greater (e.g., up to 30,000 grit or greater) to obtain a smoother surface, preferably with an average roughness (Ra) of less than 4 nm, and more preferably within the range of 1-2 nmRa. The remaining part of the ingot requires a smooth surface 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 fine 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 remaining part 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. Edge grinding can be performed between the rough and fine surface grinds to avoid any risk of scratching the fine ground Si surface. Material removal during CMP may be in the approximately 2 micron thickness range. Total material consumed from the substrate (ingot) may be less than 475 microns. If the final wafer thickness is 355 microns, the kerf loss is less than 120 microns.

[0210] Potential technical benefits obtained by one or more embodiments of the present disclosure may include: reduced crystalline material kerf loss when compared to wire sawing; reduced processing time and increased throughput of crystalline material wafers and resulting devices when compared to wire sawing; reduced bowing of the resulting semiconductor wafers when compared to conventional post-laser fragmentation methods; reduced need for consumed liquid nitrogen when compared to conventional post-laser fragmentation methods; and improved ability to obtain thin crystalline layers with reduced need for thinning by abrasive material removal (e.g., grinding).

[0211] 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.

[0212] 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. Temporarily bonding a rigid carrier to a first surface of a crystalline material with an intervening adhesive material, the crystalline material comprising a substrate having a subsurface laser damage region at a depth relative to the first surface, the adhesive material having a glass transition temperature T greater than 25° C. ｇ and fracturing the crystalline material along or adjacent to the subsurface laser damage region to obtain a bonded assembly comprising the rigid carrier, the adhesive material, and a portion of the crystalline material removed from the substrate; and A method for processing a crystalline material comprising:

2. the rigid carrier has a thickness greater than 800 microns; said rigid carrier having an elastic modulus of at least 20 GPa; In the bonded assembly, the portion of the crystalline material removed from the substrate has a thickness of at least 160 μm. The method for processing a crystalline material according to claim 1.

3. The method for processing crystalline materials according to claim 1 or 2, wherein the adhesive material comprises a thermoplastic material.

4. The adhesive material has a glass transition temperature T ｇ The method for processing a crystalline material according to any one of claims 1 to 3, comprising:

5. 5. The method of claim 1, wherein the adhesive material has a Shore D durometer value of at least about 70 when the adhesive material is at 25°C.

6. A method according to any one of claims 1 to 5, wherein the adhesive material has a thickness of less than about 50 microns.

7. the rigid carrier having a first surface and a second surface opposite the first surface; the adhesive material is disposed in contact with the first surface; the second surface being free of adhesive material and free of stress-producing material; A method for processing a crystal material according to any one of claims 1 to 6.

8. A method according to any one of claims 1 to 7, wherein the rigid support comprises a crystalline material.

9. The rigid carrier has a coefficient of thermal expansion (CTE) greater than a CTE of the substrate at 25° C., and the spalling includes cooling at least the rigid carrier to promote spalling of the crystalline material along or adjacent the subsurface laser damage region. A method for processing a crystal material according to any one of claims 1 to 8.

10. A method for processing crystalline materials according to any one of claims 1 to 8, wherein the fracturing comprises applying ultrasonic energy to at least one of the rigid carrier or the substrate.

11. 9. A method for processing a crystalline material according to any one of claims 1 to 8, wherein at least one of a maximum length or width of at least a portion of the rigid support exceeds a corresponding maximum length or width of the substrate, and the fracturing comprises applying a mechanical force adjacent to at least one edge of the rigid support, the mechanical force being configured to impart a bending moment to at least a portion of the rigid support.

12. 12. A method for processing crystalline materials according to any one of claims 1 to 11, further comprising performing at least one additional processing step on said portion of crystalline material whilst said portion remains part of the joined assembly.

13. 9. A method for processing a crystalline material according to any one of claims 1 to 8, further comprising bonding an additional rigid carrier to a second surface of the crystalline material opposite the first surface prior to said fracturing.

14. The method of claim 1 , wherein the crystalline material comprises SiC.

15. 15. A method for processing a crystalline material according to any one of claims 1 to 14, further comprising roughening, texturing and / or etching at least one of (i) the first surface of the crystalline material, or (ii) an adjacent surface of the rigid carrier, prior to the temporary bonding of the rigid carrier to the first surface of the crystalline material with the adhesive material.

16. 16. A method of processing crystalline materials according to any one of claims 1 to 15, wherein the portion of the crystalline material removed from the substrate comprises a free-standing wafer configured to have at least one epitaxial layer grown thereon.

17. 16. A method of crystalline material processing according to any one of claims 1 to 15, wherein the portion of the crystalline material removed from the substrate comprises a device wafer including at least one epitaxial layer grown thereon.

18. bonding a first crystal carrier to a first surface of a crystalline material, the crystalline material comprising a substrate having a subsurface laser damage region at a depth relative to the first surface; bonding a second crystal carrier to a second surface of the crystalline material; fracturing the crystalline material along or adjacent to the subsurface laser damage region to obtain a bonded assembly comprising the first crystal carrier and the portion of the crystalline material removed from the substrate after the bonding step; A method for processing a crystalline material comprising:

19. 20. The method of claim 18, wherein at least one of the bonding of the first crystal carrier to the first surface of the crystalline material or the bonding of the second crystal carrier to the second surface of the crystalline material comprises anodic bonding.

20. 20. The method of claim 18, wherein at least one of the bonding of the first crystal carrier to the first surface of the crystalline material or the bonding of the second crystal carrier to the second surface of the crystalline material comprises adhesive bonding utilizing an adhesive material.

21. the first crystal support having a first surface and a second surface opposite the first surface; the adhesive material is disposed in contact with the first surface; the second surface being free of adhesive material and free of stress-producing material; The method for processing a crystalline material according to claim 20.

22. The adhesive material has one or more of the following properties (a) to (c): (a) the adhesive material comprises a thermoplastic material; (b) the adhesive material has a Shore D durometer value of at least about 70 when the adhesive material is at 25° C.; or (c) the adhesive material has a Shore D durometer value of at least about 70 when the adhesive material is at 25° C.

21. The method of claim 20, comprising at least one of: having an elastic modulus of at least about 7 MPa at some time.

23. bonding a rigid carrier to a first surface of a crystalline material, the crystalline material comprising a substrate having a subsurface laser damaged region at a depth relative to the first surface, the rigid carrier having a thickness greater than 850 microns, the rigid carrier having at least one of the following characteristics (i) or (ii): the carrier comprises a crystalline carrier, or (ii) the carrier has an elastic modulus of at least 20 GPa; fracturing the crystalline material along or adjacent to the subsurface laser damage region to obtain a bonded assembly comprising the rigid carrier and a portion of the crystalline material removed from the substrate; A method for processing a crystalline material comprising:

24. 24. A method for processing crystalline materials according to claim 23, wherein the rigid carrier comprises a crystalline carrier.

25. 25. A method of processing crystalline materials according to claim 23 or 24, wherein said bonding of said rigid carrier to said crystalline material comprises adhesive bonding utilising an adhesive material disposed between said rigid carrier and said crystalline material.

26. The adhesive material has the following properties (a) to (d): (a) the adhesive material has a glass transition temperature T ｇ 26. The method of claim 25, comprising at least one of: (a) the adhesive material has a Shore D durometer value of at least about 70 when the adhesive material is at 25°C; (b) the adhesive material has a modulus of elasticity of at least about 7 MPa when the adhesive material is at 25°C; or (d) the adhesive material comprises a thermoplastic material.

27. 27. A method of processing crystalline materials according to any one of claims 23 to 26, further comprising performing at least one additional processing step on said portion of crystalline material whilst said portion remains part of the joined assembly.

28. 27. A method for processing a crystalline material according to any one of claims 23 to 26, further comprising bonding an additional rigid carrier to a second surface of the crystalline material opposite the first surface prior to said fracturing.

29. bonding a first crystal carrier to a first surface of a crystalline material, the crystalline material comprising a substrate having a subsurface laser damage region at a depth relative to the first surface; bonding a second crystal carrier to a second surface of the crystalline material; fracturing the crystalline material along or adjacent to the subsurface laser damage region to obtain a bonded assembly after the bonding step, the bonded assembly comprising the first crystal carrier and a portion of the crystalline material removed from the substrate; and A method for processing a crystalline material comprising:

30. 30. A method of crystalline material processing as claimed in claim 29, wherein at least one of the first crystal support or the second crystal support comprises an elastic modulus of at least 100 GPa.

31. 31. A method of processing crystalline materials according to claim 29 or 30, wherein at least one of the first crystal carrier or the second crystal carrier has a thickness greater than 800 microns.

32. At 25° C., the coefficient of thermal expansion (CTE) of the first crystalline support is greater than the CTE of the substrate. Large, and cooling at least the first crystal carrier to promote spalling of the crystalline material along or adjacent the subsurface laser damage region. A method for processing a crystalline material according to any one of claims 29 to 31.

33. 33. A method according to any one of claims 29 to 32, wherein the crushing comprises applying ultrasonic energy to at least one of the first crystal carrier or the substrate.

34. 34. A method for processing a crystalline material according to any one of claims 29 to 33, wherein at least one of a maximum length or a maximum width of at least a portion of the first crystalline support exceeds a corresponding maximum length or maximum width of the substrate.

35. 35. A crystalline material processing method as claimed in claim 34, wherein the substrate comprises a notch or flat along at least one edge of the substrate, and at least a portion of at least one edge of the first crystal carrier extends laterally beyond the notch or flat.

36. 36. A method of processing crystalline materials as claimed in claim 34 or 35, wherein the fracturing comprises applying a mechanical force adjacent to at least one edge of the first crystal carrier, the mechanical force being configured to impart a bending moment to at least a portion of the first crystal carrier.

37. the crystalline material comprises a hexagonal crystal structure; the bending moment is oriented within ±5 degrees of the perpendicular to the <11-20> direction of the hexagonal crystal structure; 37. A method for processing a crystalline material according to claim 36.

38. 38. A method of processing a crystalline material according to any one of claims 29 to 37, wherein at least one of the bonding of the first crystal carrier to the first surface of the crystalline material or the bonding of the second crystal carrier to the second surface of the crystalline material comprises anodic bonding.

39. 38. A method of processing a crystalline material according to any one of claims 29 to 37, wherein at least one of the bonding of the first crystal carrier to the first surface of the crystalline material or the bonding of the second crystal carrier to the second surface of the crystalline material comprises adhesive bonding utilising an adhesive material.

40. The adhesive material has a glass transition temperature T ｇ 40. The method of claim 39, comprising:

41. the first crystal support having a first surface and a second surface opposite the first surface; the adhesive material is disposed in contact with the first surface; the second surface being free of adhesive material and free of stress-producing material; 40. A method for processing a crystalline material according to claim 39.

42. 42. A method for processing a crystalline material according to any one of claims 39 to 41, wherein the adhesive material comprises a thermoplastic material.

43. 43. A method of processing a crystalline material according to any one of claims 39 to 42, wherein the adhesive material has a Shore D durometer value of at least about 70 when the adhesive material is at 25°C.

44. 44. A method for processing a crystalline material according to any one of claims 39 to 43, wherein the adhesive material has an elastic modulus of at least about 7 MPa when the adhesive material is at 25°C.

45. 45. A method of processing crystalline materials according to any one of claims 29 to 44, further comprising performing at least one additional processing step on said portion of crystalline material whilst said portion remains part of the joined assembly.

46. 46. ​​A crystalline material processing method according to any one of claims 29 to 45, wherein the subsurface laser damage region comprises a plurality of substantially parallel subsurface laser damage lines.

47. 47. A method of crystalline material processing according to any one of claims 29 to 46, further comprising removing said portion of said crystalline material from said bonded assembly.

48. 48. A method for processing a crystalline material according to any one of claims 39 to 47, wherein the crystalline material comprises SiC.

49. 49. A method of crystalline material processing according to any one of claims 39 to 48, wherein the portion of the crystalline material removed from the substrate comprises a free-standing wafer configured to have at least one epitaxial layer grown thereon.

50. 49. A crystalline material processing method according to any one of claims 39 to 48, wherein the portion of the crystalline material removed from the substrate comprises a device wafer including at least one epitaxial layer grown thereon.

51. bonding a rigid carrier to a first surface of a crystalline material, the crystalline material comprising a substrate having a subsurface laser damaged region at a depth relative to the first surface, at least a portion of at least one edge of the rigid carrier extending laterally beyond a corresponding at least one edge of the substrate; applying a mechanical force adjacent to at least one edge of the rigid carrier to impart a bending moment to at least a portion of the rigid carrier and fracture the crystalline material along or adjacent to the subsurface laser damage region to obtain a bonded assembly including the rigid carrier and the portion of the crystalline material removed from the substrate; A method for processing a crystalline material comprising:

52. 52. A crystalline material processing method according to claim 51 , wherein said applying a mechanical force proximate to said at least one edge of said rigid support comprises locally applying a mechanical force at a single location proximate to said at least one edge of said rigid support.

53. 52. A crystalline material processing method according to claim 51 , wherein said applying a mechanical force proximate to said at least one edge of said rigid support comprises locally applying a mechanical force at a plurality of spatially isolated locations proximate to said at least one edge of said rigid support and exerting an opposing mechanical force at a central location of said rigid support.

54. 54. A crystalline material processing method according to any one of claims 51 to 53, wherein said at least a portion of said at least one edge of said rigid support extends laterally at least about 100 microns beyond said corresponding at least one edge of said substrate.

55. The at least a portion of the at least one edge of the rigid carrier is 54. A method of processing a crystalline material according to any one of claims 51 to 53, wherein the at least one edge extends laterally at least about 500 microns beyond the corresponding edge.

56. 56. A crystalline material processing method according to any one of claims 51 to 55, wherein the substrate comprises a notch or flat along the at least one edge of the substrate, and the at least a portion of the at least one edge of the rigid support extends laterally beyond the notch or flat.

57. the crystalline material comprises a hexagonal crystal structure; the bending moment is oriented within ±5 degrees of the perpendicular to the <11-20> direction of the hexagonal crystal structure; A method for processing a crystalline material according to any one of claims 51 to 56.

58. 58. A method of processing a crystalline material according to any one of claims 51 to 57, wherein the joining of the rigid carrier to the surface of the crystalline material comprises adhesive bonding utilising an adhesive material disposed between the rigid carrier and the surface of the crystalline material.

59. 59. A method of processing a crystalline material according to any one of claims 51 to 58, further comprising bonding an additional rigid carrier to a second surface of the crystalline material opposite the first surface prior to said application of a mechanical force.

60. 60. A crystalline material processing method as claimed in claim 59, wherein said applying a mechanical force comprises exerting a localised prying force between said first rigid support and said additional rigid support to increase separation between said first rigid support and said additional rigid support.

61. 61. A method for processing a crystalline material according to any one of claims 51 to 60, wherein the crystalline material comprises SiC.

62. 62. A method of processing a crystalline material according to any one of claims 51 to 61, wherein the portion of the crystalline material removed from the substrate comprises a free-standing wafer configured to have at least one epitaxial layer grown thereon.

63. 62. A crystalline material processing method according to any one of claims 51 to 61, wherein the portion of the crystalline material removed from the substrate comprises a device wafer including at least one epitaxial layer grown thereon.

64. grinding an edge of a thick wafer of crystalline material to eliminate a non-vertical edge profile and form a vertical edge profile, the thick wafer including a first surface, a second surface opposite the first surface, and at least one epitaxial layer grown on or over the first surface, the first rigid carrier being temporarily bonded over the at least one epitaxial layer with an adhesive material disposed between the first rigid carrier and the at least one epitaxial layer; after forming the vertical edge profile, directing laser radiation through the second surface of the thick wafer to form a subsurface laser damage region in the thick wafer; A method comprising:

65. bonding the first rigid carrier to a major surface of the crystalline material, the crystalline material including a substrate having an initial subsurface laser damage region at a predetermined depth relative to the major surface; To join and fracturing the crystalline material along or adjacent to the initial subsurface laser damage region to obtain an initial bonded assembly comprising the first rigid carrier and a portion of the crystalline material removed from the substrate; removing the portion of the crystalline material from the first bonded assembly to produce the thick wafer, the thick wafer including the portion of the crystalline material; 65. The method of claim 64, further comprising:

66. bonding a second rigid carrier to the second surface of the thick wafer; fracturing the thick wafer along or adjacent to the subsurface laser damage region to obtain: (i) a first bonded assembly including the first rigid carrier, the adhesive material, the at least one epitaxial layer, and a first thin wafer separated from the thick wafer; and (ii) a second bonded assembly including the second rigid carrier and a second thin wafer separated from the thick wafer; 66. The method of claim 64 or 65, further comprising:

67. forming the non-vertical wafer edge of the thick wafer; epitaxially growing the at least one epitaxial layer on or over the first surface of the thick wafer after creating the non-vertical wafer edge; 67. The method of claim 66, further comprising:

68. 68. A crystalline material processing method according to claim 66 or 67, wherein at least one of the first thin wafer or the second thin wafer comprises a thickness less than 250 microns.

69. 69. A method for processing a crystalline material according to any one of claims 64 to 68, wherein the crystalline material comprises SiC.

70. 1. A method for processing a crystalline material wafer having a first surface with surface damage, the first surface being edge-bounded, the method comprising: grinding the first surface with at least one first grinding device to remove a first portion of the surface damage; after said grinding of said first surface with said at least one first grinding device, edge grinding said edge to form a chamfered or rounded edge profile; and after the 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.

71. 71. The method of claim 70, further comprising, after the 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 suitable for epitaxial growth of one or more layers of semiconductor material thereon.

72. 72. The method of claim 70 or 71, wherein 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.

73. 73. The method of any one of claims 70 to 72, wherein the grinding of the first surface with the at least one first grinding device comprises removal of the crystalline material to a thickness of from 20 microns to 100 microns, and the grinding of the second surface with the at least one second grinding device comprises removal of the crystalline material to a thickness of from 3 to 15 microns.

74. 74. The method of any one of claims 70 to 73, wherein the surface damage includes laser damage and spallation damage.

75. 75. The method of any one of claims 70 to 74, wherein the crystalline material comprises a silicon carbide material and the first surface comprises a Si-terminated surface of the silicon carbide material.

76. 1. A method for processing a crystalline material wafer having a first surface with surface damage, the first surface being edge-bounded, the method comprising: grinding the first surface with at least one first grinding device to remove a first portion of the surface damage; After the grinding of 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. forming a protective coating on the first surface after the grinding of the first surface with the at least one second grinding device; after said depositing said sacrificial material on said first surface, edge grinding said edge to form a chamfered or rounded edge profile; removing the protective coating from the first surface after the edge grinding.

77. 77. The method of claim 76, further comprising, after the 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.

78. 78. The method of claim 76 or 77, wherein 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.

79. 79. The method of any one of claims 76 to 78, wherein the grinding of the first surface with the at least one first grinding device comprises removal of the crystalline material to a thickness of from 20 microns to 100 microns, and the grinding of the second surface with the at least one second grinding device comprises removal of the crystalline material to a thickness of from 3 to 15 microns.

80. 80. The method of any one of claims 76 to 79, wherein the protective coating comprises a photoresist.

81. 81. The method of any one of claims 76 to 80, wherein the surface damage includes laser damage and spallation damage.

82. 82. The method of any one of claims 76 to 81, wherein the crystalline material comprises a silicon carbide material and the first surface comprises a Si-terminated surface of the silicon carbide material.

83. a laser processing station configured to form a subsurface laser damage region in a crystalline material substrate supplied to the laser processing station; a fragmentation station disposed to receive the crystalline material substrate processed by the laser processing station and configured to fragment the crystalline material substrate along the subsurface laser damage regions to form crystalline material portions removed from the crystalline material substrate, each crystalline material portion comprising a surface damage; a plurality of rough grinding stations arranged in parallel downstream of the crushing station and configured to remove the first portions 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 being configured to be operated simultaneously to remove the first portions of surface damage of different crystalline material portions; at least one fine grinding station disposed downstream of the plurality of rough grinding stations and configured to remove a second portion of the 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; A material processing apparatus comprising:

84. 84. The material processing apparatus of claim 83, further comprising 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.

85. 85. A material processing apparatus according to claim 83 or 84, further comprising at least one edge grinding station configured to grind an edge of each crystalline material portion to form a chamfered or rounded edge profile.

86. 86. A material processing apparatus according to any one of claims 83 to 85, wherein each coarse grinding station comprises at least one grinding wheel having a grinding surface of less than 5000 grit, and wherein the at least one fine grinding station comprises at least one grinding wheel having a grinding surface of at least 5000 grit.

87. 87. A material processing apparatus as claimed in any one of claims 83 to 86, wherein each coarse grinding station is configured to remove a thickness of crystalline material from each crystalline material portion from 20 to 100 microns, and each fine grinding station is configured to remove a thickness of crystalline material from each crystalline material portion from 3 to 15 microns.

88. 88. A material processing apparatus according to any one of claims 83 to 87, wherein the laser processing station is configured to simultaneously form subsurface laser damage regions in a plurality of crystalline material substrates.

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