SiC crystal substrate with optimal lattice plane orientation for crack reduction and its manufacturing method

Abstract

To provide a single crystal 4H-SiC substrate having a specific orientation of crystal structures that is set so as to reduce or even eliminate occurrence of cracks or fissures during mechanical processing, and a manufacturing method thereof.SOLUTION: A single crystal 4H-SiC substrate has a longitudinal axis C and a side face parallel to the longitudinal axis and curved at least partially. Crystal structures of the 4H-SiC substrate are oriented so that a line segment that crosses a parallel cleavage surface having at least a prescribed minimum number per unit length with a prescribed shape exists at each position on the side face of a semi-product with respect to the longitudinal axis, and the line segment is defined by a plane that is in contact with the side surface at one point at the position.SELECTED DRAWING: Figure 13B

Description

[Technical Field]

[0001] The present invention relates to bulk SiC single crystals having a particular crystal structure orientation to reduce or eliminate cracking and fissure formation during machining, and to methods for producing single crystal SiC substrates having such orientation. [Background technology]

[0002] Silicon carbide (SiC) substrates are commonly used in the fabrication of electronic components for a wide range of applications, including power electronics, radio frequency, and optoelectronics. SiC substrates are typically fabricated from bulk SiC single crystals, which can be grown by standard methods, such as physical vapor deposition (PVD), and suitable source materials. In this case, SiC substrates are produced from the grown crystal by cutting wafers with a wire saw and then polishing the wafer surface in multiple polishing steps. In a subsequent epitaxy process, thin single-crystalline layers of semiconductor materials (e.g., SiC, GaN) are deposited on the SiC substrate. The properties of these epitaxial layers, and therefore the components made from them, depend critically on the quality of the underlying SiC substrate.

[0003] A standard method for producing SiC crystals by physical vapor deposition is described in U.S. Patent No. 8,865,324. Bulk SiC crystals produced in this manner are then oriented, e.g., using X-ray irradiation, to ensure that the crystal structure has the necessary orientation for further mechanical processing. As an example, the desired substrate diameter is then established for the single-crystal SiC semi-finished product through various surface treatment steps, e.g., grinding, of the bulk SiC crystal. One or more orientation flats (OFs) are then ground into its lateral surfaces, and the front surface of the thus-processed crystal cylinder is prepared for wafer separation, e.g., by wire sawing. As shown in FIG. 1, the SiC semi-finished product 100 resulting from such mechanical processing of the bulk SiC crystal is an oriented cylinder with a diameter equal to the diameter of the future substrate wafer, one or two orientation flats 110 (or notches) defined in the lateral cylindrical surfaces 130, and parallel, flat front surfaces 120a, 120b.

[0004] The SiC semi-finished product 100 is then separated into individual original single-crystal SiC substrates, for example, using a wire sawing process. After quality control, the single-crystal SiC substrates are subjected to further mechanical processing. As an example, the following processing sequence can be used: After the edge mechanical processing, a single-stage or multi-stage grinding or polishing process is performed to remove the destroyed layer created during the substrate separation process and to gradually reduce the roughness of the substrate. Then, a chemical-mechanical polishing process (CMP) is performed on one or both sides of the substrate to finish the respective surfaces.

[0005] SiC single crystals and substrates made from them are known to exhibit high brittleness (or respectively low ductility). During the multi-stage mechanical processing of the bulk SiC crystals and SiC substrates described above, these crystals and substrates are subjected to large mechanical forces. In particular, for example, 4H-SiC, the shape

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[0008] In the mechanical processing of single crystal SiC semi-finished cylinders, setting the outer diameter by grinding is the most critical processing step, since most of the forces exerted by the grinding tool, e.g., a grinding wheel, are applied perpendicular to the cylinder outer diameter.

[0009] In the mechanical processing of single-crystal SiC substrates, both the machining and polishing steps of the substrate edge are crucial. For example, when chamfering the substrate edge, a radial force is applied to the substrate outer diameter by the cup grinding wheel. During polishing, in which the substrate is guided by rotor disks, a radial force is also exerted on the substrate outer diameter from these rotor disks.

[0010] As a result, special attention must be paid to the high brittleness of SiC material, combined with the presence of cleaved lattice planes, during mechanical processing of the respective bulk crystals and substrates.

[0011] So far, existing prior art techniques have not addressed the anisotropy of the mechanical properties of the SiC crystal lattice, and so in practice it has generally been accepted that there will always be some waste of bulk crystals and substrates due to cracks that develop during mechanical processing, which in turn negatively impact the yield of the entire processing chain.

[0012] During the mechanical processing of the SiC semi-finished cylinder's outer periphery, it is possible to reduce, but not completely eliminate, the occurrence of cracks or fissures within certain limits by adjusting the parameters of the mechanical processing step itself, such as the applied force and grinding speed. However, this has adverse effects on other processing parameters, such as an increase in processing duration and costs. Breaks or cracks during mechanical processing of the raw SiC substrate obtained after cutting the SiC semi-finished cylinder with a wire saw (e.g., during edge chamfering, mechanical grinding, mechanical or chemical-mechanical polishing, etc.) can also be reduced, but not completely avoided, by adjusting the processing parameters. Such adjustments also have adverse effects on other processing parameters, such as a significant increase in the duration of mechanical processing of the substrate.

[0013] Several solutions have been attempted to reduce the amount of defective SiC semi-finished cylinders and substrates.

[0014] For example, DE 102009048868 A1 describes a method for thermal post-treatment of SiC crystals, which makes it possible to reduce stresses in the crystals and therefore also to reduce the susceptibility of the SiC crystals to cracking.

[0015] CN Patent No. 110067020 describes a treatment that reduces the inherent stress in the crystals already during manufacturing, which should make them less susceptible to cracking.

[0016] However, none of these prior art methods take into account the special requirements regarding crystal orientation that are imposed on the processing of single crystal SiC semi-finished products or substrates due to the anisotropy of their mechanical properties. Furthermore, the influence of crystal orientation on the susceptibility of SiC semi-finished products and / or SiC substrates is not taken into account by these prior art methods. Both methods describe a reduction in internal stresses and, therefore, a general reduction in cracking due to a reduction in crystal stresses.

[0017] However, no solution is disclosed for reducing the occurrence of cracks that may appear during mechanical processing in low-stress or even stress-free SiC semi-finished products or SiC substrates depending on the applied mechanical forces.

[0018] Therefore, there is a need for a solution that can efficiently reduce the amount of defective SiC semi-finished products and / or SiC substrates caused by crack generation during mechanical processing, while improving the quality and yield of SiC semi-finished products and SiC substrates, without significantly increasing the overall cost and time of the mechanical processing. [Prior art documents] [Patent documents]

[0019] [Patent Document 1] U.S. Patent No. 8,865,324 [Patent Document 2] German Patent Application Publication No. 102009048868 [Patent Document 3] Chinese Patent No. 110067020 Summary of the Invention [Problem to be solved by the invention]

[0020] The present invention has been made in consideration of the drawbacks and shortcomings of the prior art, and its object is to provide a single crystal 4H—SiC substrate having improved mechanical robustness against forces applied during fabrication and / or mechanical processing of the outer surface of the 4H—SiC substrate, and a method for fabricating such a single crystal 4H—SiC substrate. [Means for solving the problem]

[0021] This object is solved by the subject matter of the independent claims. Advantageous embodiments of the invention are the subject matter of the dependent claims.

[0022] A single crystal 4H—SiC substrate with improved mechanical robustness against cleavage is provided, the 4H—SiC substrate having a substrate axis and at least partially curved side surfaces parallel to the substrate axis, wherein the crystal structure of the 4H—SiC substrate lattice is such that the crystalline structure of the 4H—SiC substrate lattice is curved at each position on the side surfaces of the substrate relative to the substrate axis.

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[0024] According to another result,

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[0026] Another result was that the principal axis of the basal plane of the 4H-SiC crystal structure is tilted by a first angle with respect to the substrate axis.

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[0031] According to another achievement, the single crystal 4H—SiC substrate further comprises first and second front surfaces, each of which is perpendicular to the at least partially curved side of the 4H—SiC substrate, and / or one or both of the first and second front surfaces is perpendicular to the substrate axis.

[0032] In another outcome, the at least partially curved side surface has a curvature that defines a cylindrical surface, the substrate axis having an axis of symmetry for the cylindrical surface, the cylindrical surface having an outer diameter that substantially corresponds to a given diameter of a substrate wafer obtained by slicing the 4H—SiC substrate, and / or the outer diameter of the cylindrical surface is 150.0 mm±0.5 mm, 200.0 mm±0.5 mm, or 250.0 mm±0.5 mm, and / or the single crystal 4H—SiC substrate has a thickness greater than 250 μm, or preferably greater than 325 μm, and / or the single crystal 4H—SiC substrate has a thickness greater than 1×10 18 cm -3 The 4H-SiC semi-finished product having greater nitrogen doping and / or single crystal has an orientation flat or notch having a length of 47.5 mm±1.0 mm.

[0033] The present invention also provides a method for producing a single crystal 4H—SiC substrate with improved mechanical robustness against cleaving, the single crystal 4H—SiC substrate having a substrate axis and at least partially curved side surfaces parallel to the substrate axis, the method comprising:

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[0035] In another work, a predetermined orientation of the 4H—SiC crystal structure is

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[0037] In another implementation, the method involves the

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[0039] According to another result, the process of setting the predetermined orientation of the 4H—SiC crystal structure of a 4H—SiC substrate includes the steps of providing a single crystal 4H—SiC semi-finished product for producing at least one original 4H—SiC substrate, the 4H—SiC semi-finished product being set to the predetermined orientation of the 4H—SiC crystal structure with respect to a substrate axis of the 4H—SiC semi-finished product and a reference plane of the single crystal 4H—SiC semi-finished product; attaching the 4H—SiC semi-finished product with the reference plane to a support surface; and cutting the attached 4H—SiC semi-finished product transversely or parallel to the support surface to obtain at least one original 4H—SiC substrate.

[0040] In another outcome, the process of establishing the predetermined orientation of the 4H—SiC crystal structure of a 4H—SiC substrate includes the steps of providing a single crystal 4H—SiC semi-finished product for producing at least one original 4H—SiC substrate; spatially orienting the 4H—SiC crystal structure with a predetermined tilt in direction and amount of a basal plane 0001 axis relative to a predetermined alignment axis; and, after spatially orienting the 4H—SiC crystal structure, cutting the 4H—SiC semi-finished product substantially transversely to the predetermined alignment axis to obtain at least one original 4H—SiC substrate.

[0041] According to another result, the method further comprises the steps of: determining a crystallographic orientation of a 4H—SiC crystal structure of the original 4H—SiC substrate relative to a front surface of the original 4H—SiC substrate by performing angle measurements; and, if the determined crystallographic orientation deviates from a predetermined orientation relative to a substrate axis of the original 4H—SiC substrate, spatially orienting the original 4H—SiC substrate such that the crystallographic orientation of the 4H—SiC crystal structure is spatially oriented at a predetermined tilt in direction and amount of a 0001 axis of the basal plane of the 4H—SiC crystal structure relative to a predetermined alignment axis; and machining an outer surface of the spatially oriented 4H—SiC single crystal wafer with reference to the alignment axis to form at least one of the at least partially curved side surfaces substantially parallel to the alignment axis and at least one front surface substantially orthogonal to the alignment axis, wherein the substrate axis of the 4H—SiC substrate after machining is substantially coincident with or parallel to the alignment axis used for spatially orienting the 4H—SiC crystal structure.

[0042] In another result, the step of spatially orienting the 4H—SiC crystal structure at the predetermined tilt includes the steps of orienting a basal plane of the 4H—SiC crystal structure to an initial orientation, and tilting the basal plane of the 4H—SiC crystal structure from the initial orientation to the first orientation.

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[0046] According to another result, the first tilt angle is 4° and the tolerance is ±0.5°, and / or the second tilt angle intersects the line segment.

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[0049] According to another result, the spatial orientation process includes the steps of orienting the basal plane of the 4H—SiC crystal structure to match the initial orientation, rotating the basal plane clockwise by a predetermined rotation angle about the initial orientation, and aligning the rotated basal plane with the 4H—SiC crystal structure.

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[0051] According to another result, the spatial orientation process includes the steps of orienting the basal plane of the 4H—SiC crystal structure to match the initial orientation, rotating the basal plane counterclockwise by a predetermined rotation angle about the initial orientation, and aligning the rotated basal plane with the 4H—SiC crystal structure.

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[0053] In another outcome, the predetermined rotation angle is 0.33° or a value within the range 0.22° to 2.19°, and / or the third tilt angle is 4° with a tolerance of ±0.5°, and / or the orientation of the 4H—SiC crystal structure after rotating by the predetermined rotation angle and / or tilting by the third tilt angle is verified by angle measurement.

[0054] The accompanying drawings are incorporated into and form a part of this specification for the purpose of explaining the principles of the invention, and are not to be construed as limiting the invention to only the shown and described examples of how the invention can be made and used.

[0055] Further features and advantages will be apparent from the following more detailed description of the invention, as illustrated in the accompanying drawings. [Brief explanation of the drawings]

[0056] FIG. 1 is a schematic perspective view of a single-crystal SiC semi-finished product. [Figure 2] On-axis orientation of a conventional 4H-SiC semi-finished product or substrate (viewed from the top, front) Schematic diagram, where the basal plane (0001) is parallel to the front surface and the crystallographic direction

[0001] is inclined at 0° with respect to the cylindrical symmetry axis C.

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[0001] direction on the plane of FIG. [Figure 3B]

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[0057] Please note that because atomic scale is discussed in this application, the dimensions and relative angles shown in the drawings are for purposes of understanding only and are not drawn to scale.

[0058] The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which illustrative embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout.

[0059] The principle underlying the present invention is based on the inventors' realization that by establishing a given crystal structure orientation relative to an external reference surface (e.g., front facet and / or side face) of the SiC crystal and / or SiC substrate that improves the mechanical robustness of the SiC crystal and substrate without affecting the quality of the epitaxial layers grown on the single crystal SiC substrate, the occurrence of cracks or fissures in the SiC crystal and substrate during their respective mechanical processing can be significantly reduced or even eliminated.

[0060] The present invention thus achieves optimal orientation of the lattice planes of the SiC crystal and substrate, which ensures higher mechanical robustness and improved yield in mechanical processing.

[0061] In SiC crystals, cracks and fissures can affect the shape of the 4H-SiC single crystal.

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[0064] For example, FIG. 2 shows a polar 4H—SiC semi-finished product 200 (or 4H—SiC substrate) having an on-axis crystal orientation, with a shape

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[0087] Basal plane (0001)

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[0001] are inclined at an inclination angle δ of 4° (±0.5°) relative to the central axis C of the 4H—SiC substrate.

[0096] As mentioned above, the basal plane (0001)

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[0001] is also reflected in the crystal orientation of some cleavage planes. For example, the 4° tilt in the direction of the basal plane (0001) depicted in Figure 2 for on-axis orientation

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[0102] A similar situation occurs with a single crystal 4H—SiC preform 400 with a standard 4° off-axis orientation, as shown in Figures 4A-4B.

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[0001] orientation, and cleavage plane

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[0109] Figure 4B shows

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[0123] However, with either an on-axis or 4° off-axis orientation, 4H-SiC semi-finished products or 4H-SiC substrates may experience deformation of the cleavage planes mentioned above during mechanical processing, especially when radial mechanical forces are applied in the regions where the cleavage planes intersect with the respective cylindrical planes aligned with the symmetry axis C.

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[0125] As illustrated in Figure 5, during mechanical processing of a single-crystal SiC semi-finished product (or substrate), it can be assumed, to a first approximation, that the tool used during mechanical processing, such as grinding, applies a mechanical force F along line segment L (force line segment) to the surface of the single-crystal body, and that this force propagates radially towards the single-crystal body. The determining factor in terms of cleavability is the strength of the force acting inward on the single-crystal SiC semi-finished product, i.e., the radial component F of the total force F. rad The tangential force component (F tang ) can be ignored for the purpose of evaluating their influence on cleavage. The length of the line segment L is approximately the length of the contact area with the respective processing tool, such as the thickness h of the grinding wheel, as shown in FIG. 6. In fact, during machining, the mechanical force is not applied along a single line segment L of length h, but rather to a very narrow region of the same h. This narrow region can be considered to be formed by a series of parallel line segments. The conditions for achieving the reduction of cleavage along the line segments according to the principles of the present invention, as described below, are thus applicable to each of these individual line segments.

[0126] To evaluate the effect of the radial mechanical force applied inward to the cleavage plane at the contact area, both the contact area and the actual length of the line segment L along which the mechanical force is actually applied are taken into account. The length h of the line segment L and / or the narrowed area is essentially determined by the thickness h of the processing tool.

[0127] During mechanical processing of SiC semi-finished products with the standard 4° off-axis orientation described above with reference to FIGS. 4A-4B, or with an on-axis orientation as illustrated in FIG. 2, a radial force is applied laterally at several locations along the circumference of the crystal's cylindrical face, e.g., by a grinding wheel. The effect of the applied force on whether the crystal will crack or not depends heavily on the location / region along the cylindrical circumference where this force is applied. As illustrated in FIGS. 7 and 8, the following extreme situations can be characterized with respect to different cleavage plane orientations relative to the region of application of the radial force:

[0128] Figure 7 shows the direction

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[0138] Figure 8 shows the

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[0147] shape

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[0153] From the above, the cleavage plane

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[0156] The present invention provides a method for producing 4H-SiC substrates and semi-finished products with off-axis orientations, such as the 4° off-axis orientation described above, that utilizes crystal cleavage planes, i.e., cleavage planes.

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[0158] In the following, for ease of explanation, the principle of the present invention will be explained as follows:

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[0160] The principle underlying the present invention is to set a specific crystal orientation of the 4H-SiC crystal structure on a 4H-SiC semi-finished product (or 4H-SiC substrate) so that the 4H-SiC crystal structure is aligned in a plane direction, while maintaining the advantages that an off-axis orientation in the direction

[0001] brings to the epitaxy quality of the respective 4H-SiC substrate.

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[0162] To reduce or avoid the formation of cracks on 4H-SiC semi-finished products with a 4° off-orientation (4°±0.5°), the present invention establishes a specific orientation of the crystal structure on the 4H-SiC semi-finished product (or 4H-SiC substrate) with respect to each outer surface, such as one or both of the side and / or front surfaces of the 4H-SiC semi-finished product. Crack initiation occurs when the radial force applied during mechanical processing does not create at least a predetermined minimum number of parallel cleavage planes per unit length of the force line segment L.

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[0165] cleavage plane

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[0169] Many parallel cleavage planes per unit length of the force line

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[0173] The present invention improves mechanical robustness of the underlying 4H—SiC crystal structure, more specifically the cleavage plane.

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[0175] 9A-9B schematically illustrate a 4H—SiC preform 500 according to one exemplary embodiment, in which the spatial orientation of the 4H—SiC crystalline structure relative to a longitudinal axis C of 4H—SiC preform 500 (or relative to one or both of front ends 520 a, 520 b and / or side surfaces 530) is oriented in a direction according to a first tilt angle δ1 (e.g., δ1=4°±0.5° depicted in FIG. 9A ).

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[0181] Therefore, the radial force applied during the grinding process, as described above with reference to FIG. 4B, may be limited to only one or a few cleavage planes at a particular location.

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[0183] moreover,

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[0185] 10A-10B schematically illustrate a 4H—SiC preform 600 having another predetermined orientation for improved mechanical robustness, according to another exemplary embodiment. In this configuration, the 4H—SiC preform has a predetermined spatial orientation relative to the longitudinal axis C (or relative to one or both of the front end faces 620 a, 620 b and / or side faces 630 of the 4H—SiC preform 600), thereby providing an off-axis orientation in the 0001 direction and an orientation according to a first tilt angle δ1 (e.g., δ1=4°±0.5° depicted in FIG. 10A ).

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[0191] The second tilt angle δ2 is

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[0194] Both exemplary embodiments utilize multiple equal parallel cleavage planes per unit length of the force line L to reduce or even eliminate cracking.

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[0196] Similar improvements in mechanical robustness to cleaving are also achieved in 4H—SiC substrates or wafers having the same spatial orientation of the 4H—SiC crystal structure described above with reference to FIGS. 9A-9B and 10A-10B.

[0197] A predetermined orientation of the 4H—SiC crystal structure can be set in the 4H—SiC semi-finished product by the method described below.

[0198] In the original 4H—SiC crystal (pretreated 4H—SiC crystal) obtained after crystal growth and / or the first rough mechanical treatment, the lattice planes and the reference plane (e.g., one of the treated front facets or cylindrical faces) are not yet aligned with each other in the precise orientation required, as in the final 4H—SiC semi-finished product.

[0199] For this reason, at the beginning of the mechanical processing, the raw 4H-SiC crystal (or the pre-processed 4H-SiC crystal) is prepared by aligning one of its front facets (Si side (0001) or C side (0001)).

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[0202] In a subsequent step, the so-oriented raw SiC crystal (or pre-treated SiC single crystal) is orientated using a goniometer to obtain the desired 4° off-axis orientation of the basal plane, which is required for good quality epitaxy of future SiC substrates.

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[0204] The outer diameter of the cylinder is then set to the diameter of the future substrate, for example, by a grinding process. The diameter setting process is one of the most critical steps with regard to crack occurrence, as explained above. During this setting process, it is ensured that the orientation of the grating plane relative to the cylinder surface, previously adjusted with a goniometer, is accurately transferred. Furthermore, primary or secondary orientation flats and / or notches can be ground during this process step. The desired orientation of the grating plane relative to the cylinder surface is then inspected / controlled using an X-ray device before any further processing.

[0205] After processing the outer diameter and / or orientation flat and controlling the desired orientation of the lattice planes relative to the cylindrical plane, processing is carried out to define the front end face of the SiC single crystal, thereby obtaining a final SiC semi-finished product with an outer shape similar to that shown in FIG. 1.

[0206] Grating surfaces that improve mechanical robustness, such as the predetermined orientation depicted in FIGS. 9A-9B or 10A-10B

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[0208] According to a first orientation processing sequence for setting a predetermined orientation of the SiC crystal structure of 4H—SiC preform 500 as illustrated in FIGS. 9A-9B , the original or preprocessed 4H—SiC crystal is spatially oriented so that the basal plane is initially aligned with an initial orientation in which the basal plane is substantially perpendicular to the direction of the central alignment axis C (which corresponds to the direction of the future cylindrical side surface of final 4H—SiC preform 500). In a subsequent step, the basal plane is aligned with

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[0213] According to an alternative second orientation processing sequence for setting a predetermined orientation of the SiC crystal structure in a 4H—SiC semi-finished product 600 as shown in FIGS. 10A-10B, the basal planes are also first oriented to an initial orientation perpendicular to the direction of the central axis C (which direction coincides with the direction of the future cylindrical side surface 630).

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[0217] In the first and second alignment processing sequences described above, the value of the first tilt angle is preferably 4°±0.5°. This ±0.5° error is related to the allowable tolerance of the first tilt angle value, which still allows for the desired improvement in the epitaxy characteristics of the respective semiconductor substrate. The value of the second tilt angle δ2 is preferably 0.023°. However, any value within the range of 0.015° to 0.153° that achieves the desired alignment effect on mechanical robustness may be used for the second tilt angle δ2. In particular, the value of the second tilt angle δ2 to be used can be estimated based on the distance between the equivalent parallel cleavage planes of the 4H-SiC lattice that are intended to minimize their cleavage effect, and by reference to at least the predetermined minimum number of intersecting cleavage planes per unit length of the aforementioned lines of force.

[0218] According to a third orientation sequence for establishing another predetermined orientation that improves mechanical robustness, the basal planes are first aligned with an initial orientation perpendicular to the direction of the central axis C, i.e., the direction of the future cylindrical side faces. The basal planes are then rotated clockwise around this initial orientation by a predetermined rotation angle, which is 0.33° or a value in the range 0.22° to 2.19°. In a subsequent step, the basal planes are aligned with the 4H-SiC crystal structure.

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[0220] Alternatively, a fourth orientation sequence can be used, in which the basal planes are also first aligned with an initial orientation perpendicular to the direction of the central axis C, i.e., the direction of the future cylindrical side faces. The basal planes are then rotated counterclockwise around this initial orientation by a predetermined rotation angle. The predetermined rotation angle is preferably 0.33°, but may be any value in the range 0.22° to 2.19° to achieve the desired orientation effect on mechanical robustness. In a subsequent step, the basal planes are aligned with the 4H-SiC crystal structure.

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[0222] After the crystallographic direction of the original SiC crystal (or pre-processed SiC crystal) has been aligned by any of the orientation processing sequences described above, one or more external reference surfaces of the final 4H—SiC semi-finished product may be machined relative to the alignment axis C. For example, an at least partially curved side surface may be machined on the oriented original or pre-processed SiC crystal in a direction parallel to the alignment axis C. Additionally or alternatively, one or two front surfaces of the final 4H—SiC semi-finished product may be machined in a direction perpendicular to the C-axis.

[0223] In this way, a predetermined orientation of the basal plane (0001) and other lattice planes of the 4H—SiC structure can be precisely set relative to at least one reference plane of the 4H—SiC semi-finished product, i.e., one or both of the curved side faces and / or its front face.

[0224] The diameter of the curved side surface can be set to substantially match the intended diameter of the substrate wafer to be sliced ​​from the 4H-SiC semi-finished product. In particular, the techniques of the present invention can be applied to improve the mechanical robustness of 4H-SiC semi-finished products and the resulting 4H-SiC substrates having outer diameters of 150.0 mm ± 0.5 mm, 200.0 mm ± 0.5 mm, or 250.0 mm ± 0.5 mm. The ± 0.5 mm error in the outer diameter corresponds to the tolerance associated with standard grinding processes. However, depending on the techniques used to set the side surface and / or adjust the outer diameter of the 4H-SiC semi-finished product, the diameter tolerance can be greater or less than 0.5 mm.

[0225] Furthermore, the techniques of the present invention can be applied to improve the mechanical robustness of 4H—SiC semi-finished products having heights along the longitudinal axis C greater than 20 mm, or preferably greater than 15 mm, however, the present invention is also applicable to 4H—SiC semi-finished products or raw 4H—SiC crystals of any height, preselected to yield a desired number of 4H—SiC substrate slices.

[0226] The set of SiC semi-finished products with a predetermined orientation of the 4H-SiC lattice for improved mechanical robustness can then be separated into substrate wafers using commonly known wafer separation processes such as multi-wire sawing with diamond-based slurries, wire-based spark erosion, or other alternative separation processes. This predetermined orientation of the 4H-SiC lattice can be transferred to the substrate wafers by referencing one of the reference planes of the SiC semi-finished products during the separation process.

[0227] An alternative exemplary embodiment for supporting a SiC workpiece during wafer separation processing and transferring a predetermined orientation of the underlying 4H—SiC lattice to a SiC substrate is illustrated in FIGS.

[0228] 11 illustrates a configuration in which the crystal orientation of a single-crystal SiC preform 700, such as one of the single-crystal SiC preforms 500, 600 described above, is transferred to a SiC substrate 740 via a cylindrical side surface 730. In a splitting process in which the single-crystal SiC preform 700 to be processed is supported by the cylindrical side surface 730, the cylindrical side surface 730 requires precise alignment with the orientation of the SiC lattice planes. In this splitting method, the orientation of the lattice planes is thus transferred via their respective orientations relative to the cylindrical side surface 730.

[0229] FIG. 12 illustrates a configuration in which the single-crystal SiC semifinished product 700 is supported by one of its front faces 720b. In separation processes in which the single-crystal SiC semifinished product to be processed is supported by its front face, the front face must be precisely aligned with the orientation of the lattice planes. In these separation methods, the orientation of the SiC lattice planes is transferred by aligning one of the cylindrical front faces 720b with the lattice planes. In this case, the orientation of the lattice planes with respect to the support front face 720b is preferably measured using X-ray photography set up with a goniometer and then precisely transferred during mechanical processing, for example, using a grinding process. To precisely transfer the predetermined orientation of the 4H-SiC lattice planes to the substrate wafer 740, the single-crystal SiC semifinished product 700 must satisfy one of the following basic conditions:

[0230] At least one of the two front end faces 720a and / or 720b (reference plane) is oriented perpendicular to the side surface 730 of the cylinder, i.e. the grating orientation is precisely transferred via one of the reference planes. Both front end faces 720a, 720b (reference faces) are oriented perpendicular to the cylindrical side face 730, i.e. the grating orientation can be accurately transferred via both reference faces. One of the front end faces 720a or 720b (reference face) is oriented exactly perpendicular to the cylindrical side face 730, and the second front end face 720b or 720a is oriented in the direction

[0231]

number

[0232] However, even when individual 4H—SiC substrates or wafers 740 are produced from a 4H—SiC preform 700 that meets any of the ideal transfer conditions described above, these 4H—SiC substrates or wafers 740 may not be cut precisely parallel to one or both of the edge faces 720 a and 720 b of the 4H—SiC preform 700 and / or perpendicular to the curved lateral surface 730. For example, when using a diamond-based wire saw, the saw wire may deviate during the cutting process, resulting in individual substrates 740 that are wedge-shaped and / or exhibit significant thickness irregularities. Similar geometric distortions can also be observed in substrates obtained using other conventional separation processes.

[0233] Because the top and bottom surfaces of the original substrate 740 obtained from the SiC preform 700 using conventional cleaving methods are not precisely planar and / or parallel to one another, the orientation of the 4H—SiC crystal lattice on one or both front surfaces of the original 4H—SiC substrate 740 is not precisely transferred from the 4H—SiC preform 700 during the slicing process.

[0234] Such geometric distortions in the sliced ​​4H—SiC substrate 740 are typically corrected by flattening the top and bottom surfaces using polishing and / or grinding processes, but even in this case, the orientation of the 4H—SiC crystal lattice relative to the substrate reference surfaces (i.e., the side, top, and / or bottom surfaces) no longer matches the predetermined orientation of the 4H—SiC crystal structure preset in the 4H—SiC semifinished product 700.

[0235] For example, in a conventional process for grinding the front surface of a SiC substrate, the sliced ​​original substrate 740 is mounted with one front surface facing toward the mounting surface of a support, such as a chuck, and the opposite top surface is ground without any further substrate alignment. As a result, the top surface of the ground 4H—SiC substrate 740 is in a plane parallel to the surface of the support, thereby reproducing the orientation of the 4H—SiC lattice relative to the bottom surface of the substrate mounted on the chuck. Thus, depending on the degree to which the front surface mounted on the chuck deviates from a plane perpendicular to the c-axis of symmetry of the 4H—SiC preform 700, the orientation of the 4H—SiC crystal structure of the 4H—SiC substrate, and consequently, the orientation of the 4H—SiC cleavage plane relative to the ground top surface, may exhibit significant deviations from the predetermined orientation established in the 4H—SiC preform 700. If 4H—SiC substrate 740 is then rotated and the previously chuck-mounted face is ground, a second front face will be set parallel to the now chuck-mounted first, ground face, so that the orientation of the basal plane and the 4H—SiC cleavage plane relative to the second front face will also no longer match the predetermined orientation set in 4H—SiC preform 700. Because the predetermined orientation of the SiC crystal structure for increased mechanical robustness, according to the present invention, is possibly no longer present for one or both front faces of 4H—SiC substrate 740 after grinding, further cracks and / or fissures may occur during final processing of the edges of the 4H—SiC substrate (e.g., by grinding with a cup wheel).

[0236] A similar problem can occur during polishing of a 4H—SiC substrate 740 using a conventional polishing process, in which the substrate is processed using a rotor disk that applies a radial force to the substrate to remove material from both sides of the substrate. If the 4H—SiC substrate 740 does not have a plane-parallel front surface and / or the orientation of the cleavage lattice planes relative to the front surface does not match a predetermined orientation that improves mechanical robustness, cracks / fissures can also occur in the 4H—SiC substrate 740 during polishing of the substrate.

[0237] Thus, even if a 4H—SiC substrate is obtained from 4H—SiC semi-finished product 700 having a predetermined orientation of the cleavage plane that improves mechanical robustness against cleaving according to the present invention, cracks or fissures may occur during mechanical processing of 4H—SiC substrate 740 due to deviations of the substrate front surface from the ideal plane-parallel orientation after the slicing process.

[0238] To compensate for such manufacturing-related deviations of the SiC lattice orientation of SiC substrate 740 from the predetermined lattice orientation of the present invention, the predetermined orientation of the 4H—SiC crystal structure relative to an axis substantially perpendicular to one or both front surfaces of the finished 4H—SiC substrate 800 can be set (or reoriented) in the original 4H—SiC substrate 740 sliced ​​from the 4H—SiC semi-finished product 700 by applying a pre-alignment planarization process, as described below.

[0239] 13A and 13B show a finished 4H—SiC substrate 800 having a predetermined SiC crystal orientation established to improve the mechanical robustness of the substrate against cleaving, essentially corresponding to the predetermined orientation described above with respect to 4H—SiC preform 500 of FIGS. 9A-9B.

[0240] At each position on the side of the final 4H—SiC substrate 800, at least a predetermined minimum number of

[0241]

number

[0242] When source substrate 4H—SiC 740 is fabricated from a single-crystal 4H—SiC preform 700 that has already been set to a desired predetermined orientation, such as 4H—SiC crystal preforms 500 and 600 described above with reference to FIGS. 9A-9B and 10A-10B, the predetermined orientation of the SiC crystal lattice is already set relative to at least one reference surface of 4H—SiC preform 700, e.g., lateral cylindrical surface 730 and / or one or both of front surfaces 720a and 720b. This relative orientation of the SiC crystal lattice is then transferred to the original 4H—SiC substrate 740 during slicing of 4H—SiC preform 700 by using one of these reference surfaces, as illustrated in FIGS. 11 and 12. For example, in the configuration shown in FIG. 11, the reference surface for transferring the crystal orientation is lateral surface 730 of 4H—SiC preform 700. In the configuration shown in FIG. 12, one of the front surfaces 720a and 720b of the 4H—SiC workpiece 700 is used as a reference surface.

[0243] After slicing, the crystal orientation of the original 4H—SiC substrate 740 can then be determined using goniometer and X-ray measurements to determine whether the desired orientation has been accurately transferred in accordance with the principles of the present invention. If deviations from the desired orientation are evident, the process of establishing a predetermined orientation of the SiC crystal structure of 4H—SiC substrate 800 may then include applying a pre-alignment planarization process to the original 4H—SiC substrate 740 to correct the orientation of the SiC crystal lattice relative to the front and / or side surfaces of the 4H—SiC substrate.

[0244] During the pre-alignment planarization process, the original 4H—SiC substrate 740 is spatially oriented relative to a planarization tool (or reference alignment axis C) so that one or more crystallographic axes of the 4H—SiC crystal lattice are aligned in a particular orientation prior to planarization. The front surface of the 4H—SiC substrate 740 can then be planarized, for example, by grinding as described above, while maintaining the spatial orientation of the substrate 740 during the planarization step. In addition to, or as an alternative to, the front surface, the side surface of the 4H—SiC substrate 740 may be formed parallel to the reference alignment axis C and / or set to the desired substrate diameter of the spatially oriented 4H—SiC substrate 740.

[0245] The pre-alignment planarization process is preferably performed by mounting the 4H—SiC substrate 740 on a goniometer and measuring the crystallographic orientation of the respective 4H—SiC crystal lattice using, for example, X-ray radiation. The original 4H—SiC substrate 740 is then spatially oriented in three-dimensional space to align the crystallographic axes and / or lattice planes of the SiC crystal, e.g., the 0001 crystallographic axis and / or the respective basal plane (0001), with a reference alignment direction C. This reference alignment direction is preferably selected to be coincident with or parallel to the axis C of the final 4H—SiC substrate 800, i.e., the axis of symmetry C of the cylindrical surface, including the at least partially curved side surface 830, of the 4H—SiC substrate 800 after grinding, polishing, and / or other finishing processes that prepare the substrate 800 for use in layer deposition and electronic component fabrication.

[0246] In the pre-alignment planarization process of the original 4H—SiC substrate 740, any of the first through fourth orientation processing sequences described above can be used to set a predetermined orientation of the SiC crystal lattice of the original (or pre-processed) 4H—SiC crystal semi-finished product. For example, when using the first orientation processing sequence described above, the original 4H—SiC substrate 740 is spatially oriented so that the basal plane (0001) is initially aligned with the initial orientation, in which the basal plane is substantially perpendicular to the reference alignment direction (i.e., the 0001 axis is substantially parallel to the reference alignment direction). The 4H—SiC substrate 740 is then orientated such that the basal plane is aligned from the initial orientation to a predetermined orientation.

[0247]

number

[0248]

number

[0249]

number

[0250]

number

[0251]

number

[0252]

number

[0253] Once the original 4H—SiC substrate 740 has been spatially oriented so that the SiC crystal lattice is precisely aligned with respect to the reference alignment axis, one or both front surfaces 820 a and 820 b of the substrate 800 are flattened, for example by grinding, along a plane transverse to the reference alignment axis while maintaining the 4H—SiC crystal in a second orientation. This results in flat front surfaces 820 a and / or 820 b that are substantially perpendicular to the axis of symmetry C and with the 4H—SiC crystal orientation relative to the axis of symmetry precisely set to a desired, predetermined orientation. Additionally or alternatively, the shape and / or diameter of the side surfaces of the spatially oriented original 4H—SiC substrate 740 may be ground parallel to the reference alignment axis to set the lateral curved surfaces 830 of the finished 4H—SiC substrate 800 that extend parallel to the axis of symmetry C, as depicted in FIGS. 13A-13B .

[0254] As a result, the resulting 4H—SiC substrate 800 after the pre-alignment planarization process exhibits a precise orientation of the 4H—SiC lattice relative to the substrate side surface 830 and / or one or both front surfaces 820, 820b, consistent with a predetermined orientation that enhances mechanical robustness against cleaving.

[0255] In an alternative embodiment, the process of establishing a predetermined crystallographic orientation in 4H—SiC substrate 800 to enhance mechanical robustness can begin with a single-crystal 4H—SiC substrate having a standard crystallographic orientation other than the predetermined orientation of the present invention, such as 4H—SiC substrate 100 having the on-axis orientation illustrated in FIG. 2 . In this case, establishing the predetermined crystallographic orientation in 4H—SiC substrate 800 involves spatially orienting 4H—SiC substrate 100 with respect to a reference alignment axis, e.g., using a goniometer and X-ray radiometry, so that the 4H—SiC crystal lattice is oriented in the desired predetermined orientation with a predetermined tilt in direction and amount of the basal plane 0001 axis relative to the reference alignment axis. This spatial orientation of 4H—SiC substrate 100 can be achieved using any of the first through fourth orientation process sequences described above for establishing the predetermined orientation of the SiC crystal lattice in 4H—SiC substrate 500 or 600. However, in this embodiment, the original 4H—SiC substrate is obtained by slicing wafers directly from the spatially oriented 4H—SiC preform 100. Starting with the conventional 4° off-axis oriented 4H—SiC preform 400 described above with reference to FIGS. 4A-4B, the first and second orientation sequence processes described above are performed.

[0256]

number

[0257] The 4H—SiC wafer is then cut substantially transversely with respect to a reference alignment axis selected to be substantially coincident with or parallel to the central axis C of the final 4H—SiC substrate 800 after spatial orientation of the 4H—SiC crystal preform 100 or 400. As in the previous embodiment, the crystal orientation of the resulting original 4H—SiC substrate after slicing can also be determined using goniometer and X-ray measurements to determine whether the desired orientation of the SiC crystal lattice in accordance with the principles of the present invention has been accurately transferred.

[0258] If deviations from the desired orientation are evident, establishing a predetermined orientation of the SiC crystal structure of 4H—SiC substrate 800 may include applying the above-described pre-alignment planarization process to correct the SiC crystal lattice orientation for the front and / or side surfaces of the 4H—SiC substrate. If deviations from the desired orientation are not detected and / or are within a predetermined tolerance that is not expected to significantly affect the cleavage robustness of 4H—SiC substrate 800, the pre-alignment planarization process is omitted.

[0259] In conclusion, the present invention makes it possible to reduce the occurrence of cracks during mechanical processing of 4H—SiC single crystals and / or 4H—SiC substrates by establishing an optimal orientation of the preferred cleavage planes relative to the side surfaces and / or one or both front surfaces of the SiC semi-finished product or 4H—SiC substrate such that the radial mechanical force applied to a given area during mechanical processing is always distributed over at least a predetermined minimum number of preferred cleavage planes, regardless of the position around the periphery of the 4H—SiC semi-finished product or 4H—SiC substrate to which the mechanical force is applied.

[0260] As a result, this optimal orientation of the 4H-SiC crystal structure allows for achieving higher mechanical robustness during mechanical processing of bulk SiC crystals and SiC substrates, and therefore higher yields of single crystal semi-finished and final products, without compromising the epitaxy quality of the future substrates and without significantly increasing the cost and / or time of the respective mechanical processing.

[0261] While certain features of the above exemplary embodiments have been described using terms such as "downward," "top," "bottom," and "horizontal," these terms are used solely to facilitate the description of the respective features and their relative orientation within the 4H—SiC single crystal and / or 4H—SiC substrate, and should not be construed as limiting the claimed invention or any of its components to any particular spatial orientation. Furthermore, while the invention has been described above with respect to 4H—SiC crystals, the principles of the invention may also be advantageously applied to other modified SiC single crystals and / or other semiconductor single crystals such as AlN and GaN. [Explanation of symbols]

[0262] C Geometric longitudinal axis L line segment h is the height of the grinding wheel, L is the length of the line segment 100 SiC semi-finished products 110 Orientation Flat (OF) 120a, 120b Upper and lower front faces of the cylinder 130 Lateral cylindrical surface 200 SiC semi-finished product with on-axis orientation (prior art) 220 Front 230 Cylinder Side 240 Grinding Wheel 300 SiC substrate with 4° off-orientation (conventional technology) 320a, 320b Upper and lower front faces of the cylinder 330 Cylinder Side 400 SiC semi-finished product with 4° off-orientation (prior art) 420a, 420b Upper and lower front faces of the cylinder 430 Cylinder Side 500 SiC semi-finished products 520a, 520b Upper and lower front faces of the cylinder 530 Cylinder side 600 SiC semi-finished products 620a, 620b Upper and lower front faces of the cylinder 630 Cylinder side 700 Single crystal SiC semi-finished products 710 Support 720a, 720b, and 730 front and side faces 740 substrate wafer 800 Finished 4H-SiC substrate 820a, 820b Upper and lower front faces of the board 830 Cylindrical side of the board

Claims

1. A single crystal 4H—SiC substrate with improved mechanical robustness to cleaving, the single crystal 4H—SiC substrate having at least partially curved side surfaces parallel to the substrate axis; The crystal structure of the 4H—SiC substrate has the following structure at each position on the side of the substrate with respect to the substrate axis: [Equation 1] line segments intersecting the cleavage planes of the shape, oriented such that there are at least a predetermined minimum number of parallel line segments intersecting the cleavage planes per unit length of the line segments; the line segment is parallel to the substrate axis, wherein the predetermined orientation of the 4H—SiC crystal structure is a principal axis of the basal plane of the 4H—SiC crystal structure tilted at a first angle with respect to the substrate axis; [Number P] tilted in a direction, wherein the first tilt angle is 4° and has a tolerance of ±0.5°; and a major axis of the basal plane of the 4H—SiC crystal structure tilted at a second angle with respect to the substrate axis; [Number Q] direction, or [Number R] and tilted in a direction, wherein the second tilt angle is a value selected from the range of 0.015° to 0.153°. By doing so, The aforementioned [Equation 2] the predetermined minimum number of parallel cleavage planes of the shape per unit length of the line segments is at least 1000 planes per millimeter; Parallel cleavage planes intersecting the line segment [Number x] the number of parallel cleavage planes per millimeter of said line segment length is less than 10,000.

2. 2. The single crystal 4H—SiC substrate of claim 1, wherein the substrate axis is the axis of symmetry of a cylinder defined by the curvature of the at least partially curved side surface of the 4H—SiC substrate.

3. further comprising first and second front surfaces; the first and second front surfaces are each perpendicular to the at least partially curved side surface of the 4H—SiC substrate; and / or 3. The single crystal 4H-SiC substrate of claim 1, wherein one or both of the first and second front surfaces are perpendicular to the substrate axis.

4. the at least partially curved side has a curvature that defines a cylindrical surface, the substrate axis having an axis of symmetry for the cylindrical surface; the outer diameter of the cylindrical surface is 150.0 mm ± 0.5 mm, 200.0 mm ± 0.5 mm, or 250.0 mm ± 0.5 mm; and / or the thickness of the single crystal 4H—SiC substrate is greater than 250 μm, or preferably greater than 350 μm; and / or The single crystal 4H—SiC substrate is 1×10 １８ cm －３ have a greater nitrogen doping, and / or 4. The single crystal 4H-SiC substrate according to claim 1, wherein the single crystal 4H-SiC substrate has an orientation flat or notch with a length of 47.5 mm±1.0 mm.

5. 1. A method for producing a single crystal 4H—SiC substrate with improved mechanical robustness to cleaving, the single crystal 4H—SiC substrate having a substrate axis and at least partially curved sides parallel to the substrate axis, the method comprising: At each position on the side of the 4H—SiC substrate, [Equation 7] performing a process to set a predetermined orientation of the 4H—SiC crystal structure of the 4H—SiC substrate relative to the substrate axis such that there are at least a predetermined minimum number of line segments intersecting the cleavage plane of the shape per unit length of the line segments that are parallel to the cleavage plane; the line segment is parallel to the substrate axis, wherein the predetermined orientation of the 4H—SiC crystal structure is a principal axis of the basal plane of the 4H—SiC crystal structure tilted at a first angle with respect to the substrate axis; [Number S] tilted in a direction, wherein the first tilt angle is 4° and has a tolerance of ±0.5°; and a major axis of the basal plane of the 4H—SiC crystal structure tilted at a second angle with respect to the substrate axis; [Number of Tons] direction, or [Number U] and tilted in a direction, wherein the second tilt angle is a value selected from the range of 0.015° to 0.153°. By doing so, The aforementioned [Equation 8] the predetermined minimum number of parallel cleavage planes of the shape per unit length of the line segment is at least 1000 planes per millimeter of the line segment length; Parallel cleavage planes intersecting the line segment [Number y] wherein the number of parallel cleavage planes is less than 10,000 per millimeter of said line segment length.

6. the treatment for setting a predetermined orientation of the 4H—SiC crystal structure of the 4H—SiC substrate comprises: providing a single crystal 4H—SiC semi-finished product for producing at least one original 4H—SiC substrate; setting the 4H—SiC semi-finished product to the predetermined orientation of the 4H—SiC crystal structure with respect to a reference plane of the single crystal 4H—SiC semi-finished product; attaching the 4H—SiC workpiece having the reference surface to a support surface; and cutting the attached 4H—SiC semi-finished product transversely or parallel to the support surface to obtain the at least one original 4H—SiC substrate.

7. the treatment for setting a predetermined orientation of the 4H—SiC crystal structure of the 4H—SiC substrate comprises: providing a single crystal 4H—SiC semi-finished product for producing at least one original 4H—SiC substrate; spatially orienting the 4H—SiC crystal structure at a predetermined tilt in direction and amount of the [0001] axis of the basal plane relative to a predetermined alignment axis of the single crystal 4H—SiC semi-finished product; and after spatially orienting the 4H—SiC crystal structure, cutting the 4H—SiC semi-finished product substantially transversely to the predetermined alignment axis to obtain the at least one original 4H—SiC substrate.

8. determining a crystallographic orientation of the 4H—SiC crystal structure of the original 4H—SiC substrate relative to a front surface of the original 4H—SiC substrate by performing an angular measurement; if the determined crystalline orientation deviates from the predetermined orientation relative to the substrate axis of the original 4H—SiC substrate, spatially orienting the original 4H—SiC substrate such that the crystalline orientation of the 4H—SiC crystal structure is spatially oriented at a predetermined tilt in direction and amount of a [0001] axis of the basal plane of the 4H—SiC crystal structure relative to a predetermined alignment axis of the original 4H—SiC substrate; machining an outer surface of the spatially oriented 4H—SiC single crystal wafer relative to the alignment axis; the at least partially curved side being substantially parallel to the alignment axis; and forming at least one of the at least one front surface substantially perpendicular to the alignment axis; 7. The method of claim 6, wherein the substrate axis of the 4H—SiC substrate after machining is substantially coincident with or parallel to the alignment axis used to spatially orient the 4H—SiC crystal structure.

9. the step of spatially orienting the 4H—SiC crystalline structure at the predetermined tilt comprises: orienting the basal plane of the 4H—SiC crystal structure to an initial orientation; the basal plane from the initial orientation to a first orientation; [Equation 10] tilting the optical axis in a direction by the first tilt angle; the basal plane from the first orientation to a second orientation of the 4H—SiC crystal structure; [0011] Direction or said [0012] and tilting the second tilt angle in a direction 9. The method of claim 7, wherein in the initial orientation, the basal plane is substantially perpendicular to the predetermined alignment axis.

10. 10. The method of claim 9, wherein the orientation of the 4H—SiC crystal structure after tilting through the first tilt angle and / or the second tilt angle is verified by goniometry.

Images