Method for processing silicon carbide wafers with relaxed positive curvature

Abstract

The present invention provides a crystal material processing method for separating wafers from silicon carbide ingots that have been curved by gravity or stress. [Solution] The method comprises the steps of providing a bulk crystalline material comprising silicon carbide (SiC), and separating a SiC wafer 122 from the bulk crystalline material, wherein the SiC wafer forms a relaxed positive curvature from the silicon surface 124 of the SiC wafer, and the kerf loss associated with the formation of the SiC wafer from the bulk crystalline material is less than 250 microns (μm). Another method comprises the steps of providing a bulk crystalline material comprising silicon carbide (SiC), forming a subsurface laser damage pattern within the bulk crystalline material, and separating the SiC wafer from the bulk crystalline material along the subsurface laser damage pattern such that the SiC wafer has a relaxed positive curvature from the silicon surface of the SiC wafer.

Description

Technical Field

[0001] Related Applications

[0001] This application claims the benefit of U.S. Patent Application No. 16 / 784,311, filed Feb. 7, 2020, and U.S. Patent Application No. 16 / 415,721, filed May 17, 2019, the disclosures of which are incorporated herein by reference in their entireties.

[0002]

[0002] The present disclosure relates to a method for processing crystalline materials, and more particularly, to a method for forming wafers from bulk crystalline materials.

Background Art

[0003]

[0003] Various microelectronics, optoelectronics, and microfabrication applications require thin film layers of crystalline materials as starting structures for manufacturing various useful systems. Conventional methods for cutting thin film layers (e.g., wafers) from large-diameter crystalline ingots of crystalline materials have involved the use of wire saws. Wire saw technology has been applied to various crystalline materials such as silicon (Si), sapphire, and silicon carbide (SiC). Wire saw tools include ultrafine steel wires (usually having a diameter of 0.2 mm or less) that pass through grooves of one or more guide rollers. Two slicing methods exist: abrasive slicing and fixed abrasive slicing. Abrasive slicing involves applying slurry (usually a suspension of abrasive in oil) to a steel wire traveling at high speed, thereby the rolling motion of the abrasive between the wire and the workpiece cuts the ingot. Unfortunately, the slurry has a considerable environmental impact. To mitigate such effects, a wire fixed with diamond abrasive can be used in a fixed abrasive slicing method that requires only a water-soluble coolant (not a slurry). High-efficiency parallel slicing allows for the production of a large number of wafers in a single slicing procedure. Figure 1 shows a system extending between rollers 4A–4C, simultaneously sawing (cutting) the ingot 2 into multiple thin cross-sections (e.g., wafers 8A–8G), each having a plane substantially parallel to the end face 6 of the ingot 2. A conventional wire saw tool 1 is shown, which includes parallel wire sections 3 arranged as shown. During the sawing process, the wire sections 3, supported by rollers 4A-4C, can be pressed downward 5 toward a holder 7 located beneath the ingot 2. If the end face 6 is parallel to the crystallographic c-plane of the ingot 2, and the wire sections 3 pass through the ingot 2 parallel to the end face 6, then each resulting wafer 8A-8G will have an "axial" end face 6' parallel to the crystallographic c-plane.

[0004]

[0004] It is also possible to manufacture adjacent (also known as off-cut or "off-axis") wafers having end faces that are not parallel to the crystallographic c-plane. Adjacent wafers (e.g., of SiC) with a 4-degree off-cut are frequently used as growth substrates for high-quality epitaxial growth of other materials (e.g., AlN and other Group III nitrides). Adjacent wafers can be manufactured by growing an ingot away from the c-axis (e.g., by growing it on an adjacent seed material and sawing the ingot perpendicular to the ingot sidewall), or by starting the ingot from an on-axis seed material and growing it, and cutting the ingot at an angle perpendicular to the ingot sidewall.

[0005]

[0005] Wire sawing of semiconductor materials involves various limitations. Kerf loss, based on the width of material removed with each cut, is inherent to saw cutting and is a significant factor for semiconductor materials. This represents the loss. Wire saw cutting applies moderately high stress to the wafer, resulting in non-zero curvature and warp characteristics. The processing time for a single boule (or ingot) is very long, and events such as wire breakage increase the processing time, leading to undesirable material loss. There is a possibility that chips or cracks may occur on the cut surface of the wafer, reducing its strength. At the end of the wire sawing process, it is necessary to remove any remaining fragments from the resulting wafer.

[0006]

[0006] In the case of SiC, which has high wear resistance (and hardness comparable to diamond or boron nitride), wire sawing requires considerable time and resources, which can result in considerable manufacturing costs. SiC substrates enable the manufacture of desirable power electronics, radio frequency, and optoelectronic devices. SiC occurs in many different crystal structures called polytypes, and certain polytypes (e.g., 4H-SiC or 6H-SiC has a hexagonal crystal structure.

[0007]

number

[0008]

[0008] Figure 4A is a perspective wafer orientation diagram showing the orientation of the adjacent wafer 11A with respect to the c-plane ((0001) plane), where the vector 10A (perpendicular to the wafer plane 9A) is tilted at an angle β from the

[0001] direction. This tilt angle β is equal to the orthogonal tilt angle (or misorientation angle) β between the (0001) plane and the projection 12A of the wafer plane 9A. Figure 4B is a simplified cross-sectional view of the adjacent wafer 11A superimposed on a portion of the defined ingot 14A (for example, an axial ingot having an end face 6A parallel to the (0001) plane). Figure 4B shows that the wafer plane 9A of the adjacent wafer 11A is tilted at an angle β with respect to the (0001) plane.

[0009]

number

[0010]

[0010] Due to the problems associated with the fabrication and processing of SiC, SiC device wafers are more expensive than wafers made of various other semiconductor materials. Typical kerf loss obtained from wire-sawed SiC is significantly larger than the resulting wafer thickness when considering material loss during the sawing process and subsequent thinning, grinding, or polishing of the wafer after sawing. Given the problems with wire sawing and device manufacturing, slicing wafers thinner than approximately 350 μm has not been practical.

[0011]

[0011] To address the limitations associated with wire sawing, alternative techniques have been developed for removing thin film layers of semiconductor material from bulk crystals. One technique involving the removal of a layer is described by Kim et al. in “4H-SiC wafer slicing by using femtosecond laser double pulses,” Optical Materials Express 2450, Vol. 7, No. 7 (2017). Such a technique involves inducing subsurface damage by bombarding the SiC with laser pulses, and then bonding the crystal to a rocking jig. By applying tensile force, fracture occurs along the subsurface damage zone. This involves the formation of laser writing tracks. By using a laser to weaken specific areas of the material and then performing fracture between those areas, the laser scanning time is reduced.

[0012]

[0012] Another separation technique, which involves the formation of laser subsurface damage, is disclosed in U.S. Patent No. 9,925,619 of Disco. Laser subsurface damage lines are formed by moving the SiC ingot in a forward pass, indexing at the laser focal point, then moving the ingot in a backward pass, indexing at the laser focal point, and so on. The formation of laser subsurface damage causes internal cracks to occur in the ingot that run parallel to the c-plane, and ultrasonic vibrations are applied to the ingot, causing fracture.

[0013]

[0013] A similar separation technique, including the formation of laser subsurface damage, is disclosed in U.S. Patent No. 10,155,323 by Disco. A pulsed laser beam is fed into a SiC ingot, each forming multiple consecutive modified sections with a diameter of 17 μm and an 80% overlap in the feed direction, and indexing is performed at the laser focal point. The modified section formation step and the indexing step are performed alternately to generate a separation layer in which adjacent cracks in the index direction are connected. Subsequently, ultrasonic vibrations are applied to the ingot to break it up.

[0014]

[0014] Another technique for removing a thin film layer of semiconductor material from a bulk crystal is disclosed in U.S. Patent Publication 2018 / 0126484A1 of Siltectra, Inc. Laser radiation strikes a solid material to create a delamination zone or a plurality of partial delamination zones, followed by the formation of a polymer receiving layer (e.g., PDMS), which is then cooled (optionally in combination with high-speed rotation) to induce mechanical stress and separate the thin film layer of solid material from the rest of the material along the delamination zone.

[0015]

[0015] Tools for forming laser subsurface damage in semiconductor materials are known in the art and are commercially available from various providers such as Disco (Tokyo, Japan). Such tools allow laser radiation to be focused into the interior of a crystalline substrate and allow the laser to move laterally relative to the substrate. Typical laser damage patterns involve the formation of parallel lines spaced laterally apart from one another at a depth within the crystalline material substrate. Parameters such as focal depth, laser power, and translation speed can be adjusted to produce laser damage, but adjusting certain factors involves trade-offs. Increasing the laser power tends to result in larger subsurface damage and easier fracturing (for example, by reducing the stress required to complete the fracturing), but larger subsurface damage results in greater surface roughness along the surface exposed by the fracturing, so additional processing may be required to render such surfaces smooth enough for subsequent processing (e.g., incorporation into electronic devices). Narrowing the lateral spacing between subsurface laser damage lines may facilitate fragmentation, but it also increases the number of translational passes between the substrate and the laser, reducing tool throughput. In addition, the results obtained by laser processing may vary within the substrate depending on the lateral or radial position at a particular vertical position, and / or the perpendicular position of the substrate surface to the original growth position as part of the ingot. [Overview of the project] [Problems that the invention aims to solve]

[0016]

[0016] Accordingly, the art continues to pursue improved methods for separating or removing relatively thin layers of crystalline material from a substrate, addressing the problems associated with conventional methods. [Means for solving the problem]

[0017]

[0017] The device is configured to reduce manufacturing problems associated with such wafer deformation, bending, or sagging due to gravity or existing crystal stresses. Silicon carbide (SiC) containing a graphic, or forced, wafer shape. Wafers and related methods are disclosed. In certain embodiments, an intentional, or forced, wafer shape may comprise a SiC wafer having a relaxed positive bow from its silicon plane. In this way, effects associated with deformation, bending, or sagging of SiC wafers, particularly large-area SiC wafers, can be reduced. In certain embodiments, a method is disclosed for providing a SiC wafer having a relaxed positive bow that reduces kerf loss of bulk crystalline material. Such a method may include laser-assisted separation of the SiC wafer from the bulk crystalline material. .

[0018]

[0018] In one embodiment, the crystalline material processing method comprises providing a bulk crystalline material comprising SiC and separating a SiC wafer from the bulk crystalline material, wherein the SiC wafer has a relaxed positive curvature from the silicon plane of the SiC wafer, and the kerf loss associated with the formation of the SiC wafer from the bulk crystalline material is less than 250 microns (μm). In certain embodiments, the kerf loss is less than 175 μm or is in the range of 100 μm to 250 μm. In certain embodiments, the relaxed positive curvature is in the range of greater than 0 μm and up to 50 μm, or greater than 0 μm and up to 40 μm, or greater than 0 μm and up to 15 μm, or in the range of 30 μm to 50 μm, or in the range of 8 μm to 16 μm. In certain embodiments, the SiC wafer has a diameter-to-thickness ratio of at least 250, or at least 300, or at least 400, or in the range of 250 to 1020. In certain embodiments, the SiC wafer includes an n-type conductive SiC wafer, or a semi-insulating SiC wafer, or an unintentionally doped SiC wafer. In certain embodiments, the carbon surface of the SiC wafer has a shape corresponding to a relaxed positive curvature from the silicon surface. In certain embodiments, the contour of the silicon surface defined by the relaxed positive curvature is different from the contour of the carbon surface of the SiC wafer.

[0019] In another aspect, a method of processing a crystalline material comprises providing a bulk crystalline material comprising silicon carbide (SiC), forming a subsurface laser damage pattern within the bulk crystalline material, and separating a SiC wafer from the bulk crystalline material along the subsurface laser damage pattern such that the SiC wafer has a relaxed positive curvature from the silicon face of the SiC wafer. In certain embodiments, the relaxed positive curvature is in the range greater than 0 μm up to 50 μm, or in the range greater than 0 μm up to 15 μm, or in the range including 30 μm to 50 μm, or in the range including 8 μm to 16 μm. In certain embodiments, forming the subsurface laser damage pattern comprises variably adjusting a laser output across the bulk crystalline material to form a non-linear profile of the subsurface laser damage pattern such that after separation, a relaxed positive curvature is provided. In certain embodiments, forming the subsurface laser damage pattern comprises variably adjusting a focus of a laser across the bulk crystalline material to form a non-linear profile of the subsurface laser damage pattern such that after separation, a relaxed positive curvature is provided. In certain embodiments, laser absorption during formation of the subsurface laser damage pattern forms a non-linear profile of the subsurface laser damage pattern and, after separation, the bulk crystalline material is arranged in a radial doping profile such that a relaxed positive curvature is provided. In certain embodiments, the SiC wafer has a diameter-to-thickness ratio in the range of at least 250, or at least 300, or at least 400, or including 250 to 1020. In certain embodiments, the kerf loss associated with forming the SiC wafer from the bulk crystalline material is less than 250 micrometers (μm). Afterwards, the bulk crystalline material is arranged in a radial doping profile such that a relaxed positive curvature is provided. In certain embodiments, the SiC wa fer has a diameter-to-thickness ratio in the range of at least 250, or at least 300, or at least 400, or including 250 to 1020. In certain embodiments, the kerf loss associated with forming the SiC wafer from the bulk crystalline material is less than 250 micrometers (μm).

[0020] In another aspect, additional advantages can be obtained by combining any of the foregoing aspects and / or various distinct aspects and features described herein. Any of the various features and elements disclosed herein can be combined with one or more other disclosed features and elements, unless indicated to the contrary herein.

[0021] Those skilled in the art will understand the scope of the present disclosure and will be able to implement additional aspects after reading the following detailed description of the preferred embodiments in relation to the accompanying drawings.

[0022] The accompanying drawings, which are incorporated herein and form a part hereof, illustrate some aspects of the present disclosure and, together with the description, serve to explain the principles of the present disclosure.

Brief Description of the Drawings

[0022] [Figure 1]

[0023] FIG. 1 is a diagram including a first frame providing a perspective view of an ingot received by a conventional wire saw tool and wire saw processed, and a second frame providing a perspective view of a plurality of wafers obtained by wire saw processing. [Figure 2]

[0024] FIG. 2 is a first perspective crystal plane view showing a hexagonal coordinate system such as 4H silicon carbide (SiC). [Figure 3]

[0025] FIG. 3 is a second perspective crystal plane view of a hexagonal crystal showing an adjacent plane non-parallel to the c-plane. [Figure 4A]

[0026] FIG. 4A is a perspective wafer orientation diagram showing the orientation of adjacent wafers with respect to the c-plane. [Figure 4B]

[0027] FIG. 4B is a simplified cross-sectional view of the adjacent wafer of FIG. 4A superimposed on a part of the ingot. [Figure 5]

[0028] FIG. 5 is a top view of an exemplary SiC wafer with arrows indicating crystallographic orientation directions superimposed. [Figure 6A]

[0029] Figure 6A is a schematic side elevation view of an axial ingot of a crystalline material. [Figure 6B]

[0030] Figure 6B is a schematic side elevation view of the ingot shown in Figure 6A, rotated by 4 degrees using an overlapping pattern for cutting the end of the ingot. [Figure 6C]

[0031] Figure 6C is a schematic side elevation of the ingot after the end has been removed to provide an end face that is not perpendicular to the c-direction. [Figure 7]

[0032] Figure 7 is a schematic perspective view of a movable laser tool configured to focus laser radiation into the interior of a crystalline material to create subsurface damage. [Figure 8]

[0033] Figure 8A shows an exemplary laser tool movement path through a crystalline material to form subsurface damage within the crystalline material. Figure 8B shows the hexagonal crystal structure of the crystalline material.

number

[0034] Figure 9 is a schematic perspective view of the surface structure of a 4H-SiC crystal after fracture but before smoothing, showing terraces and steps on the fractured surface, either off-axis or adjacent to the c-axis. [Figure 10]

[0035] Figure 10A is a schematic cross-sectional view of the formation of subsurface laser damage in a crystalline material substrate by focusing laser radiation onto a bare substrate. Figure 10B is a schematic cross-sectional view of the formation of subsurface laser damage in a crystalline material substrate by focusing laser radiation through the surface of a carrier-supported substrate. Figure 10C is a schematic cross-sectional view of the formation of subsurface laser damage in a crystalline material substrate by focusing laser radiation onto the substrate through a carrier and adhesive layer. Figure 10D is a schematic cross-sectional view of the formation of subsurface laser damage in a crystalline material substrate by focusing laser radiation onto the substrate through a carrier. [Figure 11]

[0036] Figure 11 is a schematic cross-sectional view of the bulk crystalline material, including the first subsurface laser damage pattern formed therein. [Figure 12]

[0037] Figure 12 is a schematic cross-sectional view of the bulk crystalline material of Figure 11 after the formation of the second subsurface laser damage pattern recorded by the first subsurface laser damage pattern, where the vertical ranges of the first and second subsurface laser damage patterns overlap. [Figure 13]

[0038] Figure 13 is a schematic cross-sectional view of a portion of a bulk crystalline material showing subsurface laser damage, with superimposed dashed lines identifying the expected kerf loss material region. [Figure 14]

[0039] Figure 14 is a schematic cross-sectional view of a portion of a bulk crystalline material showing curved subsurface laser damage, with superimposed dashed lines identifying the expected kerf-loss material region. [Figure 15]

[0040] Figure 15 is a schematic cross-sectional view of a variable laser output laser beam focused across a portion of a bulk crystalline material, forming a curved shape of subsurface laser damage. [Figure 16]

[0041] Figure 16 is a schematic cross-sectional view of a laser beam with variable height adjustment that is focused across a portion of the bulk crystalline material, forming a curved shape of subsurface laser damage. [Figure 17]

[0042] Figure 17 is a schematic cross-sectional view of laser radiation focused across a variably doped region of the bulk crystalline material, forming a curved shape of subsurface laser damage. [Figure 18]

[0043] Figure 18 is a schematic side cross-sectional view of a bulk SiC crystalline material on a seed crystal, showing a cylindrical, higher-doping region extending upward from the seed crystal along its central portion across the entire thickness of the bulk crystalline material. [Figure 19]

[0044] Figure 19 is a schematic top view along the cross-sectional portion of the SiC wafer derived from the bulk crystalline material in Figure 18. [Figure 20]

[0045] Figure 20 is a schematic side cross-sectional view of a bulk SiC crystalline material on a seed crystal, showing a frustoconically shaped, higher-doping region extending upward from the seed crystal along its central portion across the entire thickness of the bulk crystalline material. [Figure 21]

[0046] Figure 21 is a schematic side cross-sectional view of a bulk SiC crystalline material on a seed crystal, showing a more doped region in the shape of a Furst cone extending upward from the seed crystal at a non-center position relative to the center of the seed crystal, and extending upward across the entire thickness of the bulk crystalline material. [Figure 22]

[0047] Figure 22 is a schematic side cross-sectional view of a SiC wafer having a positive curvature relaxed from its silicon surface and a corresponding carbon surface shape, according to an embodiment disclosed herein. [Figure 23]

[0048] Figure 23 is a schematic side cross-sectional view of a SiC wafer having a positive curvature relaxed from its silicon surface and an overall flat carbon surface, according to an embodiment disclosed herein. [Figure 24]

[0049] Figure 24A is a schematic side cross-sectional view of a SiC wafer during edge-supported measurement for quantifying relaxed positive curvature while correcting for gravity effects. Figure 24B is a schematic side cross-sectional view of a SiC wafer during edge-supported measurement for quantifying relaxed positive curvature while correcting for gravity effects. Figure 24C is a schematic side cross-sectional view of a SiC wafer during edge-supported measurement for quantifying relaxed positive curvature while correcting for gravity effects. [Figure 25]

[0050] Figure 25 is a schematic side cross-sectional view of a SiC wafer during vertical orientation measurement to quantify relaxed positive curvature. [Figure 26]

[0051] Figure 26 is a schematic side cross-sectional view of a conventional laser focusing device that uses a lens to focus an incident horizontal beam and forms an outgoing beam having a beam waist pattern with minimum width at a downstream position corresponding to the focal length of the lens. [Figure 27]

[0052] Figure 27 is a schematic side cross-sectional view of a vertically oriented focused laser beam showing the beam waist within a crystalline material, illustrating the resolution thresholds at different perpendicular positions to the beam waist. [Modes for carrying out the invention]

[0023]

[0053] The embodiments described below represent the information necessary to enable those skilled in the art to practice the embodiments and illustrate the best mode of practice. Those skilled in the art will understand the concepts of this disclosure and recognize the applications of those concepts not specifically addressed herein by reading the following description in reference to the accompanying drawings. It should be understood that these concepts and applications are included in this disclosure and the accompanying claims.

[0024]

[0054] In this specification, various elements may be described using terms such as "first," "second," etc., but it will be understood that these elements should not be limited by these terms. These terms are used solely to distinguish one element from another. For example, without departing from the scope of this disclosure, the first element may be called the second element, and similarly, the second element may be called the first element. Where used herein, the term "and / or" includes any one or more and all combinations of the associated listed items.

[0025]

[0055] When an element such as a layer, region, or substrate is said to be "on" or "extending" "above" another element, it will be understood that it may be directly on or extend directly "above" another element, or that there may also be an intervening element. In contrast, when an element is said to be "directly" on or extend "above" another element, there is no intervening element. Similarly, when an element such as a layer, region, or substrate is said to be "above" or "extending" another element, it will be understood that it may be directly above or extend directly to another element, or that there may be an intervening element. In contrast, when an element is said to be "directly above" or extend "above" another element, there is no intervening element. When an element is said to be "connected" or "joined" to another element, it will be understood that it may be directly connected to or joined to another element, or that there may be an intervening element. In contrast, when an element is said to be "directly connected" or "directly coupled" to another element, there is no intermediary element.

[0026]

[0056] Relative terms such as "below" or "above" or "upper side" or "lower side" or "horizontal" or "vertical" may be used herein to describe the relationship of one element, layer, or region to another, as shown in the drawings. It will be understood that these terms and the terms discussed above are intended to encompass different orientations of the device, in addition to the orientation shown in the drawings.

[0027]

[0057] The technical terms used herein are for the sole purpose of describing specific embodiments and are not intended to limit the disclosure. Where used herein, the singular forms “a,” “an,” and “the” are intended to include the plural form unless the context clearly indicates otherwise. Where used herein, the terms “equip,” “equip,” “contain,” and / or “contain” specify the presence of the described features, integers, steps, actions, elements, and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, actions, elements, components, and / or groups thereof.

[0028]

[0058] Unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as those generally understood by those skilled in the art to which this disclosure belongs. Terms used herein should be construed to have meanings consistent with their meanings in the context of this specification and related art, and it should be further understood that they should not be construed in an idealized or overly formal sense unless expressly defined herein.

[0029]

[0059] Disclosed are silicon carbide (SiC) wafers including intentional, or forced, wafer shapes configured to reduce manufacturing problems associated with deformation, bending, or sagging of such wafers due to gravity or pre-existing crystalline stresses, and related methods. In certain embodiments, the intentional, or forced, wafer shape may comprise a SiC wafer having a relaxed positive curvature from its silicon plane. In this way, effects associated with deformation, bending, or sagging of SiC wafers, particularly large-area SiC wafers, can be reduced. In certain embodiments, a method is disclosed for providing a SiC wafer having a relaxed positive curvature that reduces kerf loss in bulk crystalline material. Such a method may include laser-assisted separation of the SiC wafer from the bulk crystalline material.

[0030]

[0060] In this way, a processing technique is disclosed that provides a SiC wafer with an intentional, or forced, shape while simultaneously reducing kerf loss compared to conventional wafer separation and shaping processes.

[0031]

[0061] As used herein, “substrate” refers to a crystalline material such as a single-crystal semiconductor material, optionally comprising an ingot or wafer. In certain embodiments, the substrate may (i) be surface-treated (e.g., lapped and polished) to support the epitaxial deposition of one or more semiconductor material layers, and optionally (ii) be sufficiently thick to be free-standing when separated from rigid carriers. In certain embodiments The substrate may have an overall cylindrical or circular shape and / or may have a thickness of at least about one or more of the following: 200 microns (μm), 300 μm, 350 μm, 500 μm, 750 μm, 1 millimeter (mm), 2 mm, 3 mm, 5 mm, 1 centimeter (cm), 2 cm, 5 cm, 10 cm, 20 cm, 30 cm, or more. In certain embodiments, the substrate may include a thicker wafer that can be divided into two thinner wafers. In certain embodiments, the substrate may be part of a thicker substrate or wafer having one or more epitaxial layers (in conjunction with one or more metal contacts, optionally) disposed thereon as part of a device wafer having a plurality of electrically operating devices. The device wafer may be divided according to embodiments of the present disclosure to produce a thinner device wafer and a second thinner wafer on which one or more epitaxial layers (in conjunction with one or more metal contacts, optionally) may be formed. In certain embodiments, the substrate may have a diameter of 150 mm or more, or 200 mm or more. In certain embodiments, the substrate may comprise 4H-SiC having a diameter of 150 mm, 200 mm or more, and a thickness in the range of 100 to 1000 μm, or 100 to 800 μm, or 100 to 600 μm, or 150 to 500 μm, or 150 to 400 μm, or 200 to 500 μm, or any other arbitrary thickness range, or any other arbitrary thickness value specified herein. In certain embodiments, the terms “substrate” and “wafer” may be used interchangeably, as a wafer is typically used as the substrate for a semiconductor device that may be formed thereon. Thus, a substrate or a wafer may refer to a larger or bulk crystalline material or a self-supporting crystalline material separated from the substrate.

[0032]

[0062] As used herein, "kerf loss" refers to the individual welds from the bulk crystalline material. Kerf loss refers to the total amount of material loss associated with forming a wafer. Kerf loss can be based on the total width or height of the material removed from the bulk crystalline material minus the final thickness of the resulting wafer. Kerf loss can be associated with the wafer separation process from the bulk crystalline material and subsequent processing steps applied to the wafer, including grinding or polishing one or more wafer surfaces.

[0033]

[0063] As used herein, “positive curvature” of a wafer generally refers to a shape in which the wafer is bent, curved, or warped outward from the device surface, for example, a convex shape from the device surface. Also as used herein, “relaxed positive curvature” refers to a positive curvature of a wafer that is established while gravity-induced wafer bending is ignored. SiC wafers generally have a silicon surface facing a carbon surface, with the wafer thickness formed between them. In many semiconductor applications, the device is typically formed on the silicon surface of the SiC wafer. Wafer curvature, warping, etc., occurs when one or more of the silicon surface and / or carbon surface form a surface misalignment from a reference plane. Therefore, positive curvature or relaxed positive curvature of a SiC wafer generally refers to a shape in which the SiC wafer is bent, curved, or warped outward from the silicon surface, for example, a convex shape from the silicon surface. In certain embodiments, the shape of the carbon surface may correspond to the positive curvature or relaxed positive curvature of the silicon surface of the SiC wafer. In other embodiments, only the silicon surface may form the positive curvature or relaxed positive curvature.

[0034]

[0064] Wafers for semiconductor applications can be subjected to many different semiconductor device manufacturing techniques for forming devices on them. One such manufacturing technique is the epitaxial growth of thin films to form device structures, including, among other things, chemical vapor deposition and metal-organic chemical vapor deposition. During epitaxial growth, the wafer is typically supported on a susceptor in a growth chamber. The chamber and susceptor are heated to a suitable temperature to induce the deposition of a thin film on the wafer from the decomposed source gas in the growth chamber. During growth, the wafer may be supported in individual pockets of the susceptor. In particular, the susceptor may provide an edge-supported configuration within a pocket where the wafer is supported by multiple points along the periphery of the wafer. This configuration provides separation between the central portion of the wafer and the bottom surface of the susceptor within the pocket. For wafers with a relatively thin thickness (e.g., 800 μm or less) and a larger diameter (e.g., 150 mm or more in certain embodiments), gravity and / or various operating conditions may cause the wafer to sag or deform towards the bottom of the susceptor pocket during processing. In this way, wafer sag can create a variable distance between the wafer and the susceptor, thereby creating a non-uniform temperature profile across the wafer during deposition, which may contribute to the non-uniform growth of the thin film thereon. In addition, other temperature-related steps in epitaxy, including cleaning and sublimation steps, may also be affected by wafer sag.

[0035]

[0065] According to embodiments disclosed herein, SiC wafers and related methods for providing SiC wafers have an intentional, or forced, shape configured to reduce manufacturing problems associated with wafer deformation or sag that may arise from gravity or existing crystalline stresses within the wafer. The forced shape may comprise a SiC wafer having a positive curvature relaxed from the silicon plane. Thus, for epitaxial growth applications, the silicon plane of the SiC wafer may be configured to initially curve away from the susceptor, and then, during growth, the wafer sag positions the silicon plane relative to the susceptor to have a flatter configuration, thereby improving the uniformity of the epitaxial layer grown thereon. In certain embodiments, a method for separating a SiC wafer from a bulk crystalline material comprises forming a laser subsurface damage within the bulk crystalline material, and subsequently separating the SiC wafer from the bulk crystalline material along the laser subsurface damage. In certain embodiments, the shape of the resulting SiC wafer is the shape of the formed laser subsurface damage region. The kerf loss is determined at least partially by the shape. For example, laser subsurface damage can be introduced in a curving manner within the bulk crystalline material such that, when separated, the wafer is formed with a positive curvature relaxed from the silicon surface. Thus, a processing technique is disclosed that provides a SiC wafer with an intentional, or forced, shape while simultaneously reducing kerf loss compared to conventional wafer separation and shaping processes.

[0036]

[0066] The methods disclosed herein may be applied to substrates or wafers of various crystalline materials of both single-crystal and polycrystalline types. In certain embodiments, the methods disclosed herein may utilize cubic, hexagonal, and other crystalline structures and relate to crystalline materials having on-axial and off-axial crystallographic orientations. In certain embodiments, the methods disclosed herein may be applied to semiconductor materials and / or wide-bandgap materials. Exemplary materials include, but are not limited to, Si, GaAs, and diamond. In certain embodiments, such methods may utilize single-crystal semiconductor materials having a hexagonal crystalline structure, such as 4H-SiC, 6H-SiC, or Group III nitride materials (e.g., GaN, AlN, InN, InGaN, AlGaN, or AlInGaN). While the various exemplary embodiments described below generally refer to SiC or specifically 4H-SiC, it should be understood that other suitable crystalline materials can be used. Among the various SiC polytypes, the 4H-SiC polytype is characterized by its high thermal conductivity and wide bandgap. Due to its high molecular weight and isotropic electron mobility, it is particularly attractive for power electronics devices. Bulk SiC can be grown on-axial (without intentional angular deviation from the c-plane, suitable for forming undoped or semi-insulating materials) or off-axial (typically in the range of 0.5 to 10 degrees (or its sub-range such as 2 to 6 degrees, or another sub-range) such that it deviates from the growth axis at a non-zero angle, such as the c-axis, and can be suitable for forming N-doped or highly conductive materials). Embodiments disclosed herein may apply to on-axial and off-axial crystalline materials, as well as doped and unintentionally doped crystalline semiconductor materials. In certain embodiments, crystalline materials may include single-crystal materials. Certain embodiments disclosed herein may utilize on-axial 4H-SiC or adjacent (off-axial) 4H-SiC with offcuts in the range of 1 to 10 degrees, or 2 to 6 degrees, or about 4 degrees.

[0037]

[0067] Figures 6A, 6B, and 6C schematically show on-axial and off-axial bulk crystalline materials in the form of ingots that may be used in the manner disclosed herein. Figure 6A shows the c direction (i.e., the

[0001] direction in the case of hexagonal crystalline materials such as 4H-SiC). Figure 6B is a schematic side elevation of an on-axial ingot 15 of a crystalline material having a first end face 16 and a second end face 17 perpendicular to the c-direction. Figure 6B is a schematic side elevation of the ingot 15 of Figure 6A, rotated by 4 degrees and featuring an overlapping pattern 18 (shown by dashed lines) for cutting and removing the end of the ingot 15 adjacent to the end faces 16, 17. Figure 6C is a schematic side elevation of an off-axial ingot 15A formed from the ingot 15 of Figure 6B, after which the end is removed to provide new first end faces 16A and second end faces 17A that are not perpendicular to the c-direction. When laser radiation of a first depth is supplied through the end face 16 of the ingot 15 to form subsurface laser damage, carriers (not shown) are coupled to the end face 16, causing the ingot 15 to break along the subsurface laser damage, after which an on-axial wafer may be formed. Conversely, if laser radiation of a first depth is supplied through the end face 16A of the off-axis ingot 15A and forms subsurface laser damage, carriers (not shown) may couple to the end face 16A, causing the ingot 15A to break along the subsurface laser damage, and subsequently forming an off-axis wafer.

[0038]

[0068] Tools for creating laser-subsurface damage in crystalline materials are known in the art and are commercially available from various providers such as Disco (Tokyo, Japan). Such tools allow laser radiation to be focused into the interior of a crystalline material substrate, thereby creating damage to the substrate. This allows for lateral movement of the laser. Typical laser damage patterns in this art involve the formation of parallel lines spaced laterally apart from one another at a depth within a crystalline substrate. Laser damage can be induced by adjusting parameters such as focal depth, laser power, translation speed, and subsurface damage line spacing, but adjusting certain factors involves trade-offs. Increasing the laser power tends to increase subsurface damage, which can increase the ease of fracturing (for example, by reducing the stress required to complete the fracturing). However, larger subsurface damage results in greater surface roughness along the surface exposed by fracturing, which may require additional processing to render such surfaces smooth enough for subsequent processing (e.g., integration into electronic devices), and this additional processing results in additional kerf loss. Narrowing the lateral spacing between subsurface laser damage lines may facilitate fracturing, but this increases the number of translational paths between the substrate and the laser, reducing tool throughput.

[0039]

[0069] Figure 7 is a schematic perspective view of an example of a laser tool 29 configured to focus laser radiation into the interior of 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 between the upper surface 32 and the lower surface 34 inside the crystalline material 30. The laser radiation 36 is focused by a lens assembly 35 to produce a focused beam 38, whose focal point is inside the crystalline material 30. Such laser radiation 36 can be pulsed at a wavelength lower than the band gap of the crystalline material 30 with any suitable frequency (typically in the range of nanoseconds, picoseconds, or femtoseconds) and beam intensity, allowing the laser radiation 36 to be focused to a target depth below its surface. At the focal point, the beam size and short pulse width result in a sufficiently high energy density, causing very localized absorption that forms the subsurface damage. By modifying one or more properties of the lens assembly 35, the focal point of the focused beam 38 can be adjusted to a desired depth within the crystalline material 30. As schematically shown by the dashed line 42, relative lateral movement (e.g., lateral translation) between the lens assembly 35 and the crystalline material 30 can be caused to propagate subsurface damage 40 in a desired direction. Such lateral movement can be repeated in various patterns, including those described below.

[0040]

[0070] Figures 8A and 8B provide exemplary laser tool movement paths toward a crystalline material for forming subsurface damage within the crystalline material. In certain embodiments, the laser tool portion (including, for example, a lens assembly) may be configured to move while the crystalline material is stationary, and in other embodiments, the laser tool portion may remain stationary while the crystalline material moves toward the tool portion. Figure 8A shows a reversing y-direction linear scanning motion 46 suitable for forming subsurface damage in a pattern of transversely spaced parallel lines within a first crystalline material 45A. Figure 8B shows a y-direction linear scanning motion 48 (slightly advancing in the x-direction at each reversal in the y-direction) across (and beyond) the entire surface of a second crystalline material 45B, sufficient to form parallel subsurface laser damage lines distributed across the crystalline material 45B. As illustrated, the laser damage lines are due to the hexagonal crystal structure of the crystalline material 45B along the surface of the crystalline material 45B.

[0041]

number

[0042] The laser lines are perpendicular to the direction and substantially parallel to the surface of the crystalline material 45B. In certain embodiments, additional subsurface laser damage lines may be interspersed with the parallel subsurface laser damage lines. In other embodiments, various combinations and patterns of subsurface laser damage lines and interspersed subsurface laser damage lines can be provided.

[0043]

[0071] Coverage of the entire surface of a crystalline material using a laser beam formed in the y-direction and advancing unidirectionally in the x-direction after each reversal in the y-direction can be called a single pass of laser damage formation. In certain embodiments, the laser treatment of the crystalline material to form subsurface damage may be performed in 2, 3, 4, 5, 6, 7, or 8 passes, or any other suitable number of passes. Increasing the number of passes with lower laser power can reduce kerf loss. To achieve the desired balance between material loss and process speed, the desired number of laser subsurface damage formation passes before performing the fracturing step is known to be 2 to 5 passes, or 3 to 4 passes.

[0044]

[0072] In certain embodiments, the lateral spacing between adjacent laser subsurface damage lines (whether formed in a single or multiple pass) may range from 80 to 400 μm, 100 to 300 μm, or 125 to 250 μm. The lateral spacing between adjacent laser subsurface damage lines affects the laser processing time, the ease of fracturing, and (depending on the orientation or misorientation of the c-plane) the effective laser damage depth.

[0045]

[0073] When subsurface laser damage lines are formed in crystalline materials, it has been observed that small cracks are formed within the material, propagating outward from the laser damage lines (e.g., outward in the transverse direction). Such cracks appear to spread substantially, or mainly, along the c-plane. The length of such cracks appears to be functionally related to the laser power level (which can be calculated as the product of pulse frequency and energy per pulse). For adjacent laser subsurface damage lines placed at a certain distance apart, it has been observed that increasing the laser power when forming such laser subsurface damage lines tends to increase the ability of cracks to connect or bond between them, which is desirable to facilitate fracturing.

[0046]

[0074] If the crystalline material subjected to laser damage formation includes off-axis (i.e., non-c-plane) orientations (e.g., in the range of 0.5–10 degrees, 1–5 degrees, or other mis-orientations), such mis-orientations may affect the desired laser damage line spacing.

[0047]

[0075] A SiC substrate may include, for example, a surface that is not aligned off-axis at an oblique angle to the c-plane. Off-axis substrates are sometimes called adjacent substrates. After such a substrate is fractured, the fractured surface may include terraces and steps (these can then be smoothed by surface treatments such as grinding and polishing). Figure 9 is a schematic perspective view of the surface structure of an off-axis 4H-SiC crystal 50 (with angle A relative to the c-axis base plane 56) after fracture and before smoothing. The fractured surface shows steps 52 and terraces 54 relative to the c-axis base plane 56. For a 4-degree off-axis plane, with a terrace width of 250 μm, the step height is theoretically about 17 μm. For a 4H-SiC crystal with subsurface laser damage, between laser rays... When the spacing is 250 μm, a terrace with a width of 250 μm is formed. After crushing, the step-like surface is smoothed, planarized, and polished in preparation for the epitaxial growth of one or more layers on top of it.

[0048]

number

[0049]

[0077] If the spacing between adjacent subsurface laser damage lines is too large, the fragmentation of the crystalline material is suppressed. If the spacing between adjacent subsurface laser damage lines is too small, it tends to reduce the step height, but the number of vertical steps increases, and an increase in the number of vertical steps usually requires a greater separation force to complete the fragmentation.

[0050]

[0078] Reducing the spacing between adjacent laser-damaged lines to too small a distance can decrease yield and significantly increase processing time and cost. A minimum laser energy threshold is required for SiC decomposition. If this minimum energy level creates connected cracks between two laser lines spaced approximately 100 μm apart, reducing the laser line spacing below this threshold offers little benefit in terms of reducing kerf loss.

[0051]

[0079] The surface roughness of crystalline material exposed by fracturing can affect not only subsequent handling, such as with robotic vacuum cleaners, but also the wear of grinding wheels, which are a major consumable cost. Roughness is influenced by both the spacing of subsurface laser damage lines relative to the crystalline structure of the semiconductor material and the orientation of such subsurface damage lines. Reducing the gaps between subsurface damage lines simply reduces the potential step height. Providing off-axis laser subsurface damage lines tends to split long, parallel steps that would otherwise be present in the laser-damaged area, and also helps to mitigate, at least to some extent, the effects of c-plane inclination or curvature. If the laser beam is perpendicular to the plane of the substrate, the cleave plane parallel to the laser beam along the c-plane extends approximately 150 mm from the plane to the curved end on the opposite side of the wafer. Slight deviations in c-plane inclination or curvature (common to SiC substrates) can cause significant variation in the fracture surface, as they force a jump in the plane as the fracturing propagates. A drawback of providing off-axis laser subsurface damage lines is that such subsurface damage lines generally require increasing the laser power to form connected cracks between adjacent laser lines. Therefore, in certain embodiments, forming a combination of on-axis laser subsurface damage lines (perpendicular to the primary plane) and off-axis laser subsurface damage lines provides a good balance while avoiding excessive fluctuations in the fracture surface without requiring an excessive increase in laser power to form connected cracks between adjacent laser lines.

[0052]

[0080] In certain embodiments, the method disclosed herein can be carried out using a laser having a wavelength of 1064 nanometers (nm), and the inventors have experience in processing 4H-SiC. In certain embodiments, a wide range of pulse frequencies can be used, but pulse frequencies from 120 kilohertz (kHz) to 150 kHz have been successfully applied. A translational stage speed of 936 millimeters per second (mm / s) between the laser and the substrate being processed has been successfully applied, but in certain embodiments, higher or lower translational stage speeds can be used by appropriately adjusting the laser frequency to maintain the desired laser pulse overlap. The average laser power range for forming subsurface laser damage in doped SiC material is in the range of 3 watts (W) to 8 W, and for undoped SiC material, it is in the range of 1 W to 4 W. Laser pulse energy can be calculated as power divided by frequency. Laser pulse widths of 3 ns to 4 ns can be used, but other pulse widths can be used in other embodiments. In certain embodiments, laser lens numerical apertures (NA) in the range of 0.3 to 0.8 can be used. In embodiments relating to the processing of SiC, considering the change in refractive index from air (about 1) to SiC (about 2.6), a significant change in the angle of refraction occurs within the SiC material to be processed, and laser lens NA and aberration correction become important to achieve the desired results.

[0053]

[0081] In certain embodiments, the semiconductor material processing method disclosed herein may include some or all of the following items and / or steps: A second carrier wafer may be attached to the bottom side of a crystalline material substrate (e.g., an ingot). Next, the upper surface of the crystalline material substrate may be ground or polished to provide an average surface roughness Ra of less than approximately 5 nm in order to prepare a surface for transmitting laser energy. Then, laser damage may be given at one or more desired depths within the crystalline material substrate, and the spacing and direction of the laser damage traces may optionally depend on the crystal orientation of the crystalline material substrate. A first carrier may be bonded to the upper surface of the crystalline material substrate. An identification code or other information linked to the first carrier is associated with the wafer derived from the crystalline material substrate. Alternatively, laser marking may be applied to the wafer (rather than the carrier) before separation to facilitate traceability of the wafer during and after manufacturing. Next, the crystalline material substrate is separated or crushed along the subsurface laser damage region to provide a portion of the semiconductor material substrate bonded to the first carrier and the remaining portion of the crystalline material substrate bonded to the second carrier. Both the removed portion of the semiconductor material substrate and the remaining portion of the semiconductor material substrate are smoothly polished and, if necessary, cleaned to remove any remaining subsurface laser damage. The removed portion of the semiconductor material substrate can be separated from the carriers. This process can then be repeated using the remaining portion of the semiconductor material substrate.

[0054]

[0082] In certain embodiments, subsurface laser damage can be formed on a crystalline material substrate before the substrate is coupled to a rigid carrier. In certain embodiments, a rigid carrier transparent to laser radiation of a desired wavelength can be coupled to the crystalline material substrate before the formation of subsurface laser damage. In such embodiments, the laser radiation can optionally be transmitted through the rigid carrier into the interior of the crystalline material substrate. Different carrier-substrate subsurface laser formation configurations are shown in Figures 10A to 10D. Figure 10A is a schematic diagram of laser radiation 61 focused through the surface of a bare substrate 62 to form subsurface laser damage 63 within the substrate 62, thereby allowing the rigid carrier to be fixed to the substrate 62 after the formation of the subsurface laser damage. Figure 10B is a schematic diagram of laser radiation 61 focused through the surface of a substrate 62 to form subsurface laser damage 63 within the substrate 62, where the substrate 62 is pre-bonded to a rigid carrier 66 using an adhesive 64. Figure 10C is a schematic diagram of laser radiation 61 focused through a rigid carrier 66 and adhesive 64 to form subsurface laser damage 63 within a substrate 62 that is pre-bonded to the rigid carrier 66. In certain embodiments, the surface of the substrate 62 distal to the rigid carrier 66 may include one or more epitaxial layers and / or metallization layers, and the substrate 62 embodies an operable electrical device before the formation of the subsurface laser damage 63. Figure 10D is a schematic diagram of laser radiation 61 focused onto the substrate 62 (without an intervening adhesive layer) via the rigid carrier 66 to form subsurface laser damage 63 within the substrate 62 that is pre-bonded to the rigid carrier 66 (e.g., by anode coupling or other non-adhesive means).

[0055]

[0083] In certain embodiments, an initial subsurface laser damage centered on a first depth may be formed within a crystalline material substrate, an additional subsurface laser damage centered on a second depth may be formed within the substrate, the additional subsurface laser damage is substantially recorded in the initial subsurface laser damage, and at least a portion of the vertical range of the additional subsurface laser damage overlaps with at least a portion of the vertical range of the initial laser damage. In other words, one or more subsequent passes configured to give laser damage at different depths can be added on top of one or more preceding passes to provide subsurface laser damage with overlapping vertical ranges. In certain embodiments, the addition of overlapping subsurface damage may be performed in response to determining, before fracturing (e.g., by optical analysis), that one or more previous subsurface laser damage formation steps were incomplete. The formation of subsurface laser damage overlapping at different depths may be performed in combination with any other method steps specified herein, including (but not limited to) the formation of multiple scattered subsurface laser damage patterns.

[0056]

[0084] Figure 11 shows the first surface formed on the first surface 74 of the bulk crystalline material 70. This is a schematic cross-sectional view of a bulk crystalline material 70 including a subsurface laser damage pattern 72, the first subsurface laser damage pattern 72 being generated by focused radiation from a laser 76. The first subsurface laser damage pattern 72 is formed by a plurality of laser damage regions 72', each region having a vertical range 78 that remains within the bulk crystalline material 70 between the first surface 74 and the opposing second surface 80. In certain embodiments, the bulk crystalline material 70 comprises bulk SiC, the first surface 74 comprises the carbon surface of the bulk crystalline material 70, and the second surface 80 comprises the silicon surface of the bulk crystalline material 70. As illustrated, the first subsurface laser damage pattern 72 may be formed in a nonlinear shape. In particular, the first subsurface laser damage pattern 72 is shown as a curved shape within the bulk crystalline material 70. In this way, when the bulk crystalline material 70 is separated along the first subsurface laser damage pattern 72, the shape of the silicon surface of the resulting SiC wafer is at least partially defined by the first subsurface laser damage pattern 72. For example, the curvature of the first subsurface laser damage pattern 72 may provide a relaxed positive curvature from the silicon surface of the resulting SiC wafer.

[0057]

[0085] Figure 12 is a schematic cross-sectional view of the bulk crystalline material 70 of Figure 11 after the formation of a second subsurface laser damage pattern 82 recorded by a first subsurface laser damage pattern 72, centered at different depths, where the vertical range 84 of the second subsurface laser damage pattern 82 overlaps with the vertical range 78 of the first subsurface laser damage pattern 72 in the damage overlap region 86. In certain embodiments, subsequent fracture of the bulk crystalline material 70 is performed along or through the damage overlap region 86 to at least partially form a SiC wafer having a positive curvature relaxed from the silicon surface. In certain embodiments, additional manufacturing steps, such as grinding or polishing, can be applied to the first surface 74 after separation to consequently provide a SiC wafer in which both the silicon and carbon surfaces have similar nonlinear shapes.

[0058]

[0086] In certain embodiments, subsurface laser damage lines may be formed at different depths within the substrate without being recorded by other (e.g., pre-formed) subsurface laser damage lines, and / or without the vertical ranges of the initial and subsequent laser damage characteristically overlapping. In certain embodiments, the scattered pattern of subsurface laser damage may include groups of laser beams, each group focused to different depths relative to the substrate surface. In certain embodiments, the focusing depths of laser radiation within the substrate differ by a distance ranging from about 2 μm to about 5 μm (i.e., about 2 μm to about 5 μm) between different groups of laser beams (e.g., at least two different groups of first and second groups, first to third groups, first to fourth groups, etc.). After forming subsurface laser damage within the bulk crystalline material, the bulk crystalline material is fractured along the subsurface laser-damaged region by applying a fracturing process as disclosed herein (e.g., cooling of CTE mismatch carriers, application of ultrasonic energy, and / or application of mechanical force), thereby separating a portion of the crystalline material from the rest of the bulk crystalline material.

[0059]

[0087] Figure 13 is a schematic cross-sectional view of a portion of bulk crystalline material 92, showing subsurface laser damage 94 with superimposed dashed lines identifying the expected kerf-loss material region 104. The expected kerf-loss material region 104 includes, in addition to the subsurface laser damage 94, material 106 removed mechanically (e.g., by grinding and polishing) from the underside or surface 108 (e.g., silicon end face) of the crystalline material portion 102 (e.g., SiC wafer) separated from the bulk crystalline material 92, and further, material 109 removed mechanically (e.g., by grinding and polishing) from the surface 90A (e.g., carbon end face) of the remaining portion of the bulk crystalline material 92A. The underside or surface 108 of the crystalline material portion 102 faces its first surface or surface 90. In certain embodiments, the entire kerf-loss material region 104 may have a thickness of less than 250 μm for SiC.

[0060]

[0088] Figure 14 is a schematic cross-sectional view of a portion of bulk crystalline material 92, showing curved subsurface laser damage 94 with superimposed dashed lines identifying the expected kerf loss material region 104. As illustrated, the subsurface laser damage 94 is located in a nonlinear (e.g., curved) contour across the bulk crystalline material 92, providing a SiC wafer with relaxed positive curvature after separation. After separation, one or more surfaces of the SiC wafer, as well as the surface of the remaining bulk crystalline material 92, may be polished or ground to remove damage associated with the separation process. In certain embodiments, the expected kerf loss material region 104 may be similar to the planar configuration shown in Figure 13. Thus, the entire kerf loss material region 104 may have a thickness of less than 250 μm for SiC. Wire sawing of SiC wafers typically involves a kerf loss of at least about 250 μm per individual wafer separated from the bulk crystalline material. However, laser and carrier-assisted separation methods disclosed herein and applied to SiC can achieve kerf losses of less than 250 μm, or less than 175 μm, or in the range including 100–250 μm, or in the range including 80–250 μm per wafer, or in the range including 80–140 μm per wafer. In particular, for shape-forced SiC wafers, conventional methods typically involve wire cutting thicker portions of the SiC material, followed by grinding, polishing, or other mechanical material removal processes to form the desired shape. According to embodiments disclosed herein, a SiC wafer can be separated from the bulk crystalline material 90 having a forced shape at least partially determined by the shape of the subsurface laser damage 94 and the subsequent separation process, while preferably providing a low kerf loss.

[0061]

[0089] According to embodiments disclosed herein, subsurface laser damage having various nonlinear contours or shapes, including curvature, can be provided within a bulk crystalline material in various ways. In certain embodiments, the laser power used to form subsurface laser damage may be applied variably across the bulk crystalline material to form curved subsurface laser damage. In other embodiments, the laser focus or height used to form subsurface laser damage may be variably adjusted across the crystalline material to form curved subsurface laser damage. In yet another embodiment, the bulk crystalline material may be formed with a variable doping profile that changes the laser absorption across the bulk crystalline material. In particular, generally higher doping concentrations may be formed at the center of the bulk crystalline material than at the periphery of the bulk crystalline material. Once subsurface laser damage is formed, the differences in laser absorption due to the change in doping concentration may form curved subsurface laser damage. In certain embodiments, the method comprises one or more combinations of variable laser power, variable laser focus or height, and a variable doping profile of the bulk crystalline material to form a molded subsurface laser damage region.

[0062]

[0090] Figure 15 is a schematic cross-sectional view of a variable laser output laser radiation 61 that is focused across a portion of the bulk crystalline material 92 to form a curved shape 110 of subsurface laser damage. As illustrated, the laser radiation 61 consists of a first laser output P1 near the periphery of the bulk crystalline material 92 and a second laser output P2 near the center of the bulk crystalline material 92. In certain embodiments, the second laser output P2 is configured to be greater than the first laser output P1, thereby forming deeper subsurface laser damage in the region of the bulk crystalline material 92 recorded at the second laser output P2. Although only two laser outputs P1, P2 are shown in Figure 15, any number of laser outputs can be provided across the bulk crystalline material 92 to form a curved shape 110 of subsurface laser damage. Depending on the laser tool, the target wafer thickness, and the material properties of the bulk crystalline material, the average laser output may be configured to vary in a range including 2W to 6W or 3W to 5.5W. In certain embodiments, higher or lower power ranges can be used. In addition, the curved shape 110 of the subsurface laser damage is shown in Figure 15. However Depending on how the laser power across the bulk crystalline material 92 changes, other shapes of subsurface laser damage may be formed.

[0063]

[0091] Figure 16 is a schematic cross-sectional view of a laser emission 61 with variable height adjustment that is focused across a portion of the bulk crystalline material 92 to form a curved shape 110 of subsurface laser damage. As illustrated, the laser emission 61 consists of a first laser height Z1 near the periphery of the bulk crystalline material 92 and a second laser height Z2 near the center of the bulk crystalline material 92, with varying heights (e.g., the "Z" position of the laser focal point). In certain embodiments, the second laser height Z2 is configured to provide deeper subsurface laser damage in the bulk crystalline material 92 than the first laser height Z1. Variable laser heights Z1, Z2 may be provided by adjusting the laser focal position Z relative to the surface of the bulk crystalline material 92 and / or optical elements in the laser lens to move the focal point to a target depth for the formation of subsurface laser damage in the bulk crystalline material 92. The curved shape 110 of the subsurface laser damage is shown in Figure 16, but other shapes of subsurface laser damage may be formed depending on how the height or focal point of the laser traversing the bulk crystalline material 92 changes.

[0064]

[0092] Figure 17 is a schematic cross-sectional view of laser radiation 61 focused across a variably doped portion of the bulk crystalline material 92, forming a curved shape 110 of subsurface laser damage. A simple doping profile plot is provided below the schematic cross-sectional view of the bulk crystalline material 92. The y-axis represents the relative doping concentration (ccn) within the bulk crystalline material 92, while the x-axis represents the lateral position of the bulk crystalline material 92. As illustrated, the doping of the bulk crystalline material 92 is configured to have a radial doping profile that is higher near the center of the bulk crystalline material 92 and lower near the periphery of the bulk crystalline material 92. Thus, as the laser radiation 61 passes along the bulk crystalline material 92, the laser radiation 61 may exhibit a laser absorption level that varies with respect to the horizontal position within the bulk crystalline material 92, thereby forming a curved shape 110 of subsurface laser damage. A variable doping profile of the bulk crystalline material 92 may be provided during the crystal growth of the bulk crystalline material 92. In certain embodiments, the bulk crystalline material 92 is arranged with a central doping ring having a higher doping concentration. A curved shape 110 of subsurface laser damage is shown in Figure 17, but other shapes of subsurface laser damage may be formed depending on how the doping profile is arranged within the bulk crystalline material 92.

[0065]

[0093] Figures 18–21 show various diagrams of bulk crystalline materials with various doping profiles. Figure 18 is a schematic side section view of a bulk crystalline material 92 of SiC on a seed crystal 112, showing a cylindrical higher doping region 114 extending upward from the seed crystal 112 along its central portion across the entire thickness of the bulk crystalline material 92. In certain embodiments, the higher doping region 114 is laterally bounded by a lower doping region 116 positioned along the periphery of the bulk crystalline material 92. In certain embodiments, the lower doping region 116 may be intentionally doped, unintentionally doped, or undoped. Figure 18 shows the size (e.g., width or diameter) of the higher doping region 114, assuming it is substantially constant across the entire thickness of the bulk crystalline material 92, although the size of the doping region may vary with its vertical position within the bulk crystalline material 92 (e.g., typically larger in width or diameter closer to the seed crystal and smaller further away from the seed crystal). In addition, the magnitude of doping within the higher doping region 114 can vary depending on its vertical position in the bulk crystalline material 92. A thin cross-sectional portion 118 of the bulk crystalline material 92 is shown by a dashed line and can define the SiC wafer 120 as shown in Figure 19. Figure 19 is a schematic top view along the cross-sectional portion 118 of the SiC wafer 120 derived from the bulk crystalline material 92 of Figure 18. As illustrated, the higher doping region 114 forms a circular shape within the ring shape of the SiC wafer 120, around the lower doping region 116. In such embodiments, the variable surface The lower laser-damaged region is provided along the cross-sectional portion 118 in Figure 18, which can provide the SiC wafer 120 with the relaxed positive curvature described above.

[0066]

[0094] Figure 20 is a schematic side cross-sectional view of a bulk crystalline material 92 of SiC on a seed crystal 112, showing a Furst cone-shaped higher doping region 114 extending upward from the seed crystal 112 along its central portion across the entire thickness of the bulk crystalline material 92. In certain embodiments, the lateral position and shape of the higher doping region 114 may differ from the configuration shown in Figure 20 if an adjacent seed crystal (e.g., off-cut at an angle nonparallel to the c-plane) is used for the growth of the bulk crystalline material 92. For example, if an adjacent seed crystal is used, the higher doping region 114 may be more elliptical than circular in shape and / or may be laterally offset with respect to the center of the bulk crystalline material 92. Figure 21 is a schematic side cross-sectional view of a bulk crystalline material 92 of SiC on a seed crystal 112, showing a Furst cone-shaped higher doping region 114 extending upward from the seed crystal 112 at a non-center position with respect to the center of the seed crystal 112 and across the entire thickness of the bulk crystalline material 92. In Figure 21, the seed crystal 112 may have adjacent (e.g., off-cut) seed crystals, and the higher doping region 114 may form an overall elliptical shape when viewed from above. As demonstrated by the variable shape of the higher doping region 114 in Figures 20 and 21, the lateral dimensions of the higher doping region 114 and the lower doping region 116 may vary depending on their vertical position within the bulk crystalline material 92. Thus, in order to uniformly manufacture multiple SiC wafers with the same relaxed positive curvature, the laser conditions used to form the subsurface laser-damaged region (e.g., one or more of the focal height and laser power) may need to be modified to compensate for the vertical variations in the higher and lower doping regions 114, 116.

[0067]

[0095] Figure 22 is a schematic side cross-sectional view of a SiC wafer 122 having a relaxed positive curvature according to embodiments disclosed herein. The SiC wafer 122 includes a silicon surface 124 and an opposing carbon surface 126. As illustrated, the SiC wafer 122 is formed with a relaxed positive curvature from the silicon surface 124 according to the manufacturing techniques described above. In particular, the carbon surface 126 is formed with a similar or parallel curvature. In certain embodiments, one or more combinations of laser subsurface damage followed by grinding or polishing may form such corresponding shapes on the silicon surface 124 and the carbon surface 126. A theoretically flat wafer 128 is superimposed on the SiC wafer 122 by a dashed line. The amount of relaxed positive curvature of the silicon surface 124 can be quantified by the distance or deviation 130 at the highest point of the silicon surface 124 (e.g., the center in Figure 22) compared to the silicon surface 124' of a theoretically flat wafer 128 unaffected by gravity. In a similar manner, the curvature of the carbon surface 126 can be quantified as the distance or deviation from the carbon surface 126' of the theoretically flat wafer 128.

[0068]

[0096] Figure 23 is a schematic side cross-sectional view of a SiC wafer 132 having a relaxed positive curvature according to an embodiment disclosed herein. The SiC carbide wafer 132 includes a silicon surface 124 and an opposing carbon surface 126. As illustrated, the SiC wafer 132 is formed with a relaxed positive curvature from the silicon surface 124 according to the manufacturing techniques described above, while the carbon surface 126 is formed with an overall flat profile. Thus, the profile of the silicon surface 124, defined by the relaxed positive curvature, differs from the profile of the carbon surface 126, such that the SiC wafer 132 has a localized thickness variation from the periphery of the SiC wafer 132 to the thicker central portion of the SiC wafer 132. In certain embodiments, one or more combinations of laser subsurface damage followed by grinding or polishing may form such shapes of the silicon surface 124 and the carbon surface 126. As explained in Figure 22, the amount of relaxed positive curvature of silicon surface 124 is compared to the silicon surface 124' of theoretically flat wafer 128, which is unaffected by gravity. This can be quantified by the distance or deviation 130 at the highest point of the silicon surface 124.

[0069]

[0097] Various techniques may be used to measure the amount of relaxed positive curvature of a wafer according to the embodiments disclosed herein. Such techniques include configurations for compensating for wafer deformation or sag caused by gravity. One such measurement technique described in the International Semiconductor Equipment and Materials (SEMI) standard MF1390, entitled "Test Method for Measuring Warp on Silicon Wafers by Automated Non-Contact Scanning," is used to compensate for gravity effects by comparing a first wafer measurement with an inverted second wafer measurement, such that the difference between the two corresponds to the effect of gravity. Other measurement techniques can be found in SEMI standard 3D4-0915, titled "Guide for Metrology for Measuring Thickness, Total Thickness Variation (TTV), Bow, Warp / Sori, and Flatness of Bonded Wafer Stacks," which describes various gravity compensation techniques for horizontally and vertically supported wafers. In certain embodiments, such measurement techniques may include interferometry. In certain embodiments, the measurement technique may include the use of an optical plane used to determine the flatness or lack thereof of the wafer.

[0070]

[0098] Figures 24A–24C are schematic side cross-sectional views of the SiC wafer 122 of Figure 22 during measurement to quantify relaxed positive curvature while correcting for gravity effects. Figure 24A is a schematic side cross-sectional view of the SiC wafer 122 of Figure 22 forming relaxed positive curvature from the silicon surface 124 facing the carbon surface 126 without gravity effects. In Figure 24B, the SiC wafer 122 is placed on an edge support 134 for characterization of wafer curvature or warpage. In certain embodiments, the edge support 134 is placed to estimate how the SiC wafer 122 may be supported during subsequent device manufacturing processes, including epitaxial growth of a thin film on the SiC wafer 122. The edge support 134 may have any number of configurations, including three-point support, four-point support, or a continuous ring for support. As illustrated, when the SiC wafer 122 is placed on the edge support 134, gravity can cause the SiC wafer 122 to deform, bend, or sag in the direction from the silicon surface 124 to the carbon surface 126. In particular, gravity can cause a relaxed positive curvature, as shown in Figure 24A, which can form a flattened or even convex shape on the silicon surface 124. Such a configuration may be desirable to provide improved temperature uniformity of the SiC wafer 122 during epitaxial device growth, as previously mentioned. In Figure 24C, the SiC wafer 122 is flipped or inverted so that the silicon surface 124 faces downward toward the edge support 134 and the carbon surface 126 faces upward. As illustrated, gravity can cause the SiC wafer 122 to deform, bend, or sag to a greater extent than shown in Figure 24B. In this regard, characterization measurements of wafer curvature or warpage are obtained from both the silicon side 124 and the carbon side 126 of the SiC wafer 122 and can be compared to compensate for gravity effects. For example, if the sag measurement from the silicon side 124 (e.g., Figure 24B) is equal to the sag measurement from the carbon side 126 (e.g., Figure 24C), the SiC wafer 122 may be characterized as generally flat or as having no relaxed positive curvature.Therefore, if the measured amount of sag from the silicon surface 124 (e.g., Figure 24B) is smaller than the measured amount of sag from the carbon surface 126 (e.g., Figure 24C), the SiC wafer 122 can be quantified as the difference between the two measurements and can be characterized as having a relaxed positive curvature, with gravity effects during measurement compensated for.

[0071]

[0099] Figure 25 is a schematic side cross-sectional view of the SiC wafer 122 of Figure 22 during a vertical orientation measurement to quantify the relaxed positive curvature. As illustrated, the SiC wafer 122 is positioned perpendicularly on the optical plane 136 for characterization. During the flatness measurement, the optical plane 136 and the SiC wafer 122 are illuminated with light 138, such as monochromatic or white light, among other things, to form interference fringes, which are used to quantify the flatness of the SiC wafer 122 relative to the optical plane 136. Because it is oriented vertically, the effect of gravity is reduced.

[0072]

[0100] In certain embodiments, the relaxed positive curvature is in the range of greater than 0 μm and up to 50 μm, or greater than 0 μm and up to 40 μm, or greater than 0 μm and up to 25 μm, or greater than 0 μm and up to 15 μm, or greater than 0 μm and up to 10 μm, or from 5 μm to 50 μm. In certain applications, a relaxed positive curvature greater than 50 μm may result in wafers that maintain positive curvature during subsequent manufacturing steps such as epitaxial growth, which may adversely affect the uniformity of the device. As stated above, the SiC wafers disclosed herein may include diameters in the range of at least 100 mm, at least 150 mm, at least 200 mm or more, or from 150 mm to 205 mm, and thicknesses in the range of 100 to 1000 μm. In certain embodiments, the SiC wafer includes a diameter-to-thickness ratio of at least 250, or at least 300, or at least 400, or in the range of 250 to 1020. In a particular example, a 152.4 mm (6 inch) SiC wafer has a thickness of 200 μm (0.2 mm) when the diameter-to-thickness ratio is 762, or a thickness of 350 μm (0.35 mm) when the diameter-to-thickness ratio is 435 (rounded), or a thickness of 500 μm (0.5 mm) when the diameter-to-thickness ratio is 305 (rounded). In other examples, a 203.2 mm (8-inch) SiC wafer may have a thickness of 200 μm (0.2 mm) when the diameter-to-thickness ratio is 10¹⁶, or a thickness of 500 μm (0.5 mm) when the diameter-to-thickness ratio is 40⁶ (rounded), or a thickness of 800 μm (0.8 mm) when the diameter-to-thickness ratio is 25⁴. Each of the above examples of 152.4 mm (6-inch) and 203.2 mm (8-inch) SiC wafers may be configured with a relaxed positive curvature according to the embodiments described above. In a particular embodiment, the amount of relaxed positive curvature may be configured differently based on the diameter and thickness dimensions of the wafer. In one example, a 152.4 mm (6-inch) SiC wafer with a thickness of 350 μm (0.35 mm) may have a relaxed positive curvature ranging from 8 μm to 16 μm to compensate for sag, warp, or other deformation effects.For the same wafer thickness, relaxed positive curvature can increase as the wafer diameter increases. For example, a 203.2 mm (8 inch) SiC wafer with a thickness of 350 μm (0.35 mm) may have relaxed positive curvature ranging from 30 μm to 50 μm to compensate for sag, warp, or other deformation effects. For the same wafer diameter, relaxed positive curvature can decrease as the wafer thickness increases. For example, a 203.2 mm (8 inch) SiC wafer with a thickness of 500 μm (0.5 mm) may have relaxed positive curvature ranging from 10 μm to 30 μm, and a 203.2 mm (8 inch) SiC wafer with a thickness of 800 μm (0.8 mm) may have relaxed positive curvature ranging from 4 μm to 12 μm to compensate for sag, warp, or other deformation effects. In certain embodiments, other ranges of relaxed positive curvature are possible depending on the type of material and / or the dimensions of the material (e.g., thickness and diameter) and / or any crystalline stresses that may be present. In this regard, the large-area SiC wafer of the above thickness is disclosed with relaxed positive curvature, thereby reducing sagging, warping, or other deformation effects associated with the effects of gravity or from existing crystalline stresses of the SiC wafer of such dimensions.

[0073]

[0101] As described above in this specification, the process starts distal to the seed crystal, and the seed crystal By obtaining wafers at cross-sectional positions that gradually approach the crystal and then fracturing them, progressively higher laser power levels may be required to form laser damage sufficient to split the crystalline material. Using high laser power at each continuous depth position when forming subsurface damage would result in unnecessary material loss and a significant increase in the thickness spread between wafers due to variations in both damage depth and the point at which disintegration is reached relative to the laser beam waist. Such concepts can be understood by referring to Figures 26 and 27.

[0074]

[0102] Figure 26 shows how the incident horizontal beam 400 is focused in the propagation direction using lens 404, and the minimum width W is at position 406 corresponding to the focal length f of lens 404. f Figure 27 is a schematic side cross-sectional view of a conventional laser focusing device that forms an outgoing beam 402 having a beam waist pattern having a beam waist pattern having a beam waist pattern having a beam waist pattern having a beam waist pattern having a beam width having a beam width having a beam width having a beam waist pattern having a beam width having a beam width having a beam width having a beam width having a beam width having a beam width having a beam width having a beam width having a beam width having a beam width having a beam width having a beam width having a beam width having a beam width having a beam width having a beam width having a beam waist pattern having a beam width having a beam width having a beam width having a beam width having a beam width having a beam width having a beam width having a beam waist pattern having a beam waist pattern having a beam width

[0075]

[0103] The methods and apparatus disclosed herein enable addressing the aforementioned problem by imaging the upper surface of a crystalline material having subsurface laser damage to detect crack-free regions, analyzing one or more images to identify conditions indicating the presence of crack-free regions within the crystalline material, and performing one or more actions in response to the analysis (for example, when appropriate conditions are met). Such actions may include performing additional laser passes at the same depth location and / or modifying the instruction set to generate subsurface laser damage at subsequent depth locations. Such methods and apparatus facilitate the manufacture of shape-forced substrate or wafer portions without unnecessary material loss.

[0076]

[0104] The technical benefits that can be obtained by one or more embodiments of the present disclosure may include, compared to conventional techniques, the formation of wafers having relaxed positive curvature from the device surface and reduced crystalline material kerf loss, reduced processing time and improved throughput between the crystalline material wafer and the resulting device, and / or improved reproducibility of thin wafers with relaxed positive curvature separated from bulk crystalline material.

[0077]

[0105] Those skilled in the art will recognize improvements and modifications to preferred embodiments of this disclosure. All such improvements and modifications are considered within the scope of the concepts disclosed herein and the following claims.

Claims

1. The steps include providing a bulk crystalline material containing silicon carbide (SiC), A crystal material processing method comprising the steps of separating a SiC wafer from the bulk crystal material, wherein the SiC wafer forms a relaxed positive curvature from the silicon surface of the SiC wafer, and the kerf loss associated with the formation of the SiC wafer from the bulk crystal material is less than 250 microns (μm).

2. The crystal material processing method according to claim 1, wherein the kerf loss is less than 175 μm.

3. The crystal material processing method according to claim 1, wherein the kerf loss is within the range of 100 μm to 250 μm.

4. The crystal material processing method according to claim 1, wherein the relaxed positive curvature is in the range greater than 0 μm and up to 50 μm.

5. The crystal material processing method according to claim 1, wherein the relaxed positive curvature is in the range greater than 0 μm and up to 40 μm.

6. The crystal material processing method according to claim 1, wherein the relaxed positive curvature is in the range greater than 0 μm and up to 15 μm.

7. The crystal material processing method according to claim 1, wherein the relaxed positive curvature is within the range of 30 μm to 50 μm.

8. The crystal material processing method according to claim 1, wherein the relaxed positive curvature is within the range of 8 μm to 16 μm.

9. The crystalline material processing method according to claim 1, wherein the SiC wafer has a diameter-to-thickness ratio of at least 250.

10. The crystalline material processing method according to claim 1, wherein the SiC wafer has a diameter-to-thickness ratio of at least 300.

11. The crystalline material processing method according to claim 1, wherein the SiC wafer has a diameter-to-thickness ratio of at least 400.

12. The crystalline material processing method according to claim 1, wherein the SiC wafer has a diameter-to-thickness ratio in the range of 250 to 1020.

13. The crystal material processing method according to claim 1, wherein the SiC wafer comprises an n-type conductive SiC wafer.

14. The crystal material processing method according to claim 1, wherein the SiC wafer comprises a semi-insulating SiC wafer.

15. The crystal material processing method according to claim 1, wherein the SiC wafer comprises an unintentionally doped SiC wafer.

16. The carbon surface of the SiC wafer is relative to the relaxed positive curvature from the silicon surface. A method for processing a crystalline material according to claim 1, comprising a corresponding shape.

17. The crystal material processing method according to claim 1, wherein the contour of the silicon surface defined by the relaxed positive curvature is different from the contour of the carbon surface of the SiC wafer.

18. The steps include providing a bulk crystalline material containing silicon carbide (SiC), The steps include forming a subsurface laser damage pattern within the bulk crystalline material, A crystal material processing method comprising the steps of separating the SiC wafer from the bulk crystalline material along the subsurface laser damage pattern such that the SiC wafer has a positive curvature relaxed from the silicon surface of the SiC wafer.

19. The crystal material processing method according to claim 18, wherein the relaxed positive curvature is in the range greater than 0 μm and up to 50 μm.

20. The crystal material processing method according to claim 18, wherein the relaxed positive curvature is in the range greater than 0 μm and up to 15 μm.

21. The crystal material processing method according to claim 18, wherein the relaxed positive curvature is in the range of 30 μm to 50 μm.

22. The crystal material processing method according to claim 18, wherein the relaxed positive curvature is in the range of 8 μm to 16 μm.

23. The step of forming the subsurface laser damage pattern is, A method for processing a crystalline material according to claim 18, comprising the step of variably adjusting the laser output across the bulk crystalline material to form a nonlinear contour of the subsurface laser damage pattern such that the relaxed positive curvature is provided after separation.

24. The step of forming the subsurface laser damage pattern is, A method for processing a crystalline material according to claim 18, comprising the step of variably adjusting the focus of a laser crossing the bulk crystalline material to form a nonlinear contour of the subsurface laser damage pattern such that the relaxed positive curvature is provided after separation.

25. The crystalline material processing method according to claim 18, wherein the bulk crystalline material is arranged in a radial doping profile such that the laser absorption during the step of forming the subsurface laser damage pattern forms a nonlinear contour of the subsurface laser damage pattern and, after separation, provides the relaxed positive curvature.

26. The crystalline material processing method according to claim 18, wherein the SiC wafer has a diameter-to-thickness ratio of at least 250.

27. The crystalline material processing method according to claim 18, wherein the SiC wafer has a diameter-to-thickness ratio of at least 300.

28. The crystalline material processing method according to claim 18, wherein the SiC wafer has a diameter-to-thickness ratio of at least 400.

29. The crystalline material processing method according to claim 18, wherein the SiC wafer has a diameter-to-thickness ratio in the range of 250 to 1020.

30. The crystal material processing method according to claim 18, wherein the kerf loss associated with forming the SiC wafer from the bulk crystal material is less than 250 microns (μm).

31. The steps include providing a bulk crystalline material containing silicon carbide (SiC), The steps of forming a subsurface laser damage pattern within the bulk crystalline material by variably adjusting at least one of the laser power and the laser focus in order to form a nonlinear contour of the subsurface laser damage pattern from the periphery of the bulk crystalline material to the center of the bulk crystalline material, A crystal material processing method comprising the step of separating a SiC wafer from the bulk crystal material along the subsurface laser damage pattern.

32. The crystal material processing method according to claim 31, wherein the nonlinear contour forms a curved shape from the periphery of the bulk crystal material to the center of the bulk crystal material.

33. The crystal material processing method according to claim 31, wherein the laser output is variably adjusted so that the laser output differs between the periphery of the bulk crystal material and the center of the bulk crystal material.

34. The crystal material processing method according to claim 33, wherein the laser output is greater at the center of the bulk crystal material than along the periphery of the bulk crystal material.

35. The method for processing crystalline materials according to claim 31, wherein the laser output is variably adjusted within a range including 2 watts (W) to 6 watts (W).

36. The crystal material processing method according to claim 31, wherein the laser focus is variably adjusted so that the height position of the laser focus differs between the periphery of the bulk crystal material and the center of the bulk crystal material.

37. The crystal material processing method according to claim 36, wherein the height position of the laser focal point is configured to be deeper into the bulk crystal material at the center of the bulk crystal material than along the periphery of the bulk crystal material.

38. The crystal material processing method according to claim 31, wherein the step of forming the subsurface laser damage pattern in the bulk crystal material comprises the step of variably adjusting the laser output and the laser focus to form the nonlinear contour of the subsurface laser damage pattern.

39. The crystalline material processing method according to claim 31, wherein the bulk crystalline material has a radial doping profile that is variable from the periphery of the bulk crystalline material to the center of the bulk crystalline material.

40. The crystal material processing method according to claim 39, wherein the radial doping profile comprises a lower doping region near the periphery of the bulk crystal material and a higher doping region closer to the center of the bulk crystal material than to the periphery of the bulk crystal material.

41. The crystal material processing method according to claim 40, wherein the higher doping region is located at the center of the bulk crystal material.

42. The crystal material processing method according to claim 40, wherein the higher doping region is positioned offset from the center of the bulk crystal material.

43. The crystal material processing method according to claim 31, wherein the subsurface laser damage pattern comprises a plurality of subsurface laser damage lines formed at different depths within the bulk crystal material.

44. The crystal material processing method according to claim 43, wherein the plurality of subsurface laser damage lines are formed at different depths including 2 microns (μm) and 5 μm.

45. The plurality of subsurface laser damage lines of SiC [Math 1] A method for processing a crystalline material according to claim 43, wherein the material is formed not perpendicular to the crystal direction.

46. The crystalline material processing method according to claim 31, wherein the SiC comprises 4-H SiC.

47. The crystal material processing method according to claim 31, wherein the SiC comprises off-axis 4-H SiC in a range including 0.5 to 10 degrees from the c-axis of the SiC.

48. The crystalline material processing method according to claim 31, wherein the SiC comprises axial 4-H SiC.

49. The crystal material processing method according to claim 31, wherein the SiC wafer forms a positive curvature that is relaxed from the silicon surface of the SiC wafer.

50. The crystal material processing method according to claim 49, wherein the relaxed positive curvature is in the range of greater than 0 microns (μm) and up to 15 μm.

51. The crystal material processing method according to claim 49, wherein the relaxed positive curvature is in the range of 30 microns (μm) to 50 μm.

52. The crystal material processing method according to claim 49, wherein the relaxed positive curvature is in the range of 8 microns (μm) to 16 μm.

53. The crystalline material processing method according to claim 31, wherein the SiC wafer has a diameter-to-thickness ratio of at least 250.

54. The crystalline material processing method according to claim 31, wherein the SiC wafer has a diameter-to-thickness ratio of at least 300.

55. The crystalline material processing method according to claim 31, wherein the SiC wafer has a diameter-to-thickness ratio of at least 400.

56. The crystalline material processing method according to claim 31, wherein the SiC wafer has a diameter-to-thickness ratio in the range of 250 to 1020.

57. The crystal material processing method according to claim 31, wherein the kerf loss associated with forming the SiC wafer from the bulk crystal material is less than 250 microns (μm).

58. The crystal material processing method according to claim 57, wherein the kerf loss is in the range of 100 μm to 250 μm.

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