Silicon carbide crystal with optimal crystal plane orientation for crack reduction and method for producing the same

Abstract

The present invention relates to a silicon carbide crystal having an optimal crystal plane orientation for reducing cracks and a method for producing the same. In particular, a single-crystal 4H-SiC semi-finished product having a crystal structure specifically oriented to reduce or even eliminate the occurrence of cracks or fissures during machining and a method for producing the same are provided. The single-crystal 4H-SiC semi-finished product having a longitudinal axis and at least partially curved side surfaces parallel to the longitudinal axis is characterized in that the crystal structure of the 4H-SiC semi-finished product is oriented relative to the longitudinal axis such that at each location on the side surface of the semi-finished product, a line segment intersects at least a predetermined minimum number of parallel cleavage planes per unit length, wherein the line segment is defined by a plane tangent to the side surface at the location.

Description

Technical Field

[0001] The present invention relates to bulk silicon carbide (SiC) single crystals having a specific crystal structural orientation for reducing or eliminating the occurrence of cracks or fissures during machining, and methods for producing single crystal SiC semi-finished products having such an orientation. Background Art

[0002] Silicon carbide (SiC) substrates are commonly used to produce electronic components with a wide range of applications, such as power electronics, radio frequency and optoelectronic applications. They are typically produced from bulk SiC single crystals, which can be grown using standard methods such as physical vapor deposition (PVT) and suitable source materials. SiC substrates are then produced from the grown crystals by cutting the wafers using a wire saw and then refining the wafer surface in a multi-stage polishing step. In the subsequent epitaxial process, thin single crystal layers of semiconductor materials such as SiC, GaN (gallium nitride) are then deposited onto the SiC substrate. The properties of these epitaxial layers and the properties of the components made therefrom depend primarily on the quality of the underlying SiC substrate.

[0003] A standard method for producing SiC crystals by physical vapor deposition is described in patent US 8,865,324 B2. The bulk SiC crystals produced in this way are then oriented, for example by using X-ray radiation, so that the crystal structure has the orientation required for further mechanical processing. For example, by various surface treatment steps of the bulk SiC crystal (for example by grinding), the desired substrate diameter is then set on the single-crystal SiC semi-finished product, one or more orientation planes (OF) are ground into its side surface, and the front side of the crystal cylinder processed in this way is prepared for the wafer separation process (for example by wire sawing). Figure 1 As shown, the SiC semi-finished product 100 resulting from such machining of a bulk SiC crystal is an oriented cylinder having a diameter equal to the diameter of the future substrate wafer and having one or two orientation flats 110 (or notches) defined on the cylinder side surface 130 and having parallel and flat front faces 120a, 120b.

[0004] The SiC semi-finished product 100 is then separated into individual original single-crystal SiC substrates, for example, using a wire saw process. After quality control, the single-crystal SiC substrates undergo further mechanical processing. For example, the following processing sequence can be used. After mechanical processing of the edges, a single-stage or multi-stage grinding or polishing process is performed to remove the (one or more) damage layers formed during the substrate separation process and gradually reduce the substrate roughness. A chemical mechanical polishing process (CMP) is then applied to one or both sides of the substrate to finally finish the corresponding (one or more) surfaces.

[0005] It is known that SiC single crystals and substrates made from them exhibit high brittleness (or correspondingly low ductility). During the multi-stage machining of bulk SiC crystals and the above-mentioned SiC substrates, they are subjected to large mechanical forces. In particular, cracks or fissures can easily form along the preferred crystal cleavage planes (e.g., in the case of 4H-SiC, Type and In particular, in mechanical processes where mechanical forces are applied radially (i.e., perpendicular to the outer diameter), the increased likelihood of cracking along the cleavage plane leads to cracks in the crystal and substrate, resulting in an undesirable reduction in yield.

[0006] In the machining of single-crystal SiC semi-finished cylinders, setting the outer diameter by grinding is the most critical process step, since the high forces exerted by the grinding tool (eg grinding wheel) are applied perpendicularly to the outer diameter of the cylinder.

[0007] In the machining of single-crystal SiC substrates, both substrate edge machining and polishing are crucial steps. For example, when chamfering the substrate edge, a cup grinding wheel applies radial forces to the substrate's outer diameter. During polishing, where the substrate is guided in rotor disks, radial forces are also applied to the substrate's outer diameter by these rotor disks.

[0008] Therefore, special attention must be paid to the high brittleness of SiC materials and the presence of cleavage planes during the mechanical processing of corresponding bulk crystals and substrates.

[0009] To date, existing technologies have not addressed the anisotropy of the mechanical properties of the SiC lattice, which is why it is generally accepted that in practice a certain amount of bulk crystal or substrate is always wasted due to cracks that appear during machining. However, this has a negative impact on the yield of the entire process chain.

[0010] During the machining of the outer periphery of the SiC semi-finished cylinder, the occurrence of cracks or fissures can be reduced to a certain extent by adjusting the parameters of the machining step itself (e.g., the applied force or the grinding speed), but they cannot be completely eliminated. However, this has a negative impact on other process parameters, such as an increase in process duration and costs. Fractures or cracks during the machining of the raw SiC substrate obtained after wire sawing the SiC semi-finished cylinder (e.g., during edge chamfering, mechanical grinding, mechanical or chemical mechanical polishing, etc.) can also be reduced by adjusting the process parameters, but cannot be completely avoided. Such adjustments also have an adverse effect on other process parameters, such as significantly increasing the duration of substrate machining.

[0011] Several solutions have been attempted to reduce the amount of defective SiC semi-finished cylinders and substrates.

[0012] For example, patent application DE 10 2009 048 868 describes a method for thermal post-treatment of SiC crystals which allows reducing the stresses in the crystals and therefore also the susceptibility of the SiC crystals to cracking.

[0013] Patent CN110067020A describes a method for reducing the intrinsic stresses already present in a crystal during production, which in turn should reduce the crystal's sensitivity to cracking.

[0014] However, none of these prior art methods take into account the specific requirements regarding crystal orientation imposed on the processing of single-crystal SiC semi-finished products or substrates due to the anisotropy of their mechanical properties. Furthermore, these prior art methods do not consider the influence of crystal orientation on the crack susceptibility of the SiC semi-finished products and / or SiC substrates. Both methods describe a reduction in internal stresses and, therefore, a general reduction in cracks due to a reduction in crystal stresses.

[0015] However, no solution is disclosed for reducing the occurrence of cracks which, depending on the mechanical forces applied, may even appear on low-stress or unstressed SiC semi-finished products or SiC substrates during machining.

[0016] Therefore, a solution is needed that allows effectively reducing the amount of defective SiC semi-finished products and / or corresponding SiC substrates due to the appearance of cracks during the machining of the SiC semi-finished products and / or corresponding SiC substrates, without significantly increasing the costs and time of the overall machining, while improving the quality and yield of the SiC semi-finished products and corresponding SiC substrates. Summary of the Invention

[0017] The present invention has been made in view of the drawbacks and disadvantages of the prior art, and an object of the present invention is to provide a single-crystal 4H-SiC semi-finished product and a method for producing such a single-crystal 4H-SiC semi-finished product, which has improved mechanical robustness against forces applied during machining of the outer surface of a 4H-SiC single crystal.

[0018] This object is achieved by the subject matter of the independent claim. Advantageous embodiments of the invention are the subject matter of the dependent claims.

[0019] A single-crystal 4H-SiC semi-finished product with improved mechanical robustness against cleavage is provided, the 4H-SiC semi-finished product having a longitudinal axis and at least partially curved side surfaces parallel to the longitudinal axis being characterized in that the crystal structure of the 4H-SiC semi-finished product is oriented relative to the longitudinal axis such that at every position on the side surface of the semi-finished product there is a line segment which is aligned with at least a predetermined minimum number of The line segments are defined by planes tangential to the side surfaces at said positions.

[0020] According to a further refinement, the predetermined minimum number of The number of parallel cleavage planes of the type is at least 1000 planes per millimeter; and / or the longitudinal axis is the axis of symmetry of a cylinder defined by the curved portion of the at least partially curved side surface of the 4H-SiC semi-finished product.

[0021] According to a further development, the main axis of the basal plane of the 4H-SiC crystal structure is oriented relative to the longitudinal axis. and / or the main axis of the basal plane of the 4H-SiC crystal structure is tilted toward the longitudinal axis. The second tilt angle is tilted in the direction, and / or the first tilt angle is 4° with a tolerance of ±0.5°; and / or wherein the second tilt angle is based on The distance between the parallel cleavage planes of the type is estimated to produce the at least predetermined minimum number of intersections per unit length with the line segment. The parallel cleavage plane of the type, and / or the second tilt angle is a value selected from the interval [0.015°; 0.153°] or preferably 0.023°.

[0022] According to a further improvement, the single crystal 4H-SiC substrate further comprises a first front side and a second front side; wherein one or both of the first front side and the second front side are perpendicular to the longitudinal axis; or wherein the first front side is perpendicular to the longitudinal axis and the second front side is oriented such that The measurement of the direction results in a total thickness variation of the second front side relative to the first front side of between 40 μm and 340 μm.

[0023] In a further development, the at least partially curved side surface has a curved portion defining a cylindrical surface with the longitudinal axis, the curved portion having its axis of symmetry, wherein the outer diameter of the cylindrical surface substantially corresponds to a given diameter of a substrate wafer obtainable by slicing the 4H-SiC semi-finished product, and / or the outer diameter of the cylindrical surface is 150.0 mm ± 0.5 mm, or 200.0 mm ± 0.5 mm; and / or the height of the single-crystalline 4H-SiC semi-finished product is greater than 20 mm, or preferably greater than 15 mm, and / or the nitrogen doping of the single-crystalline 4H-SiC semi-finished product is greater than 1×10 18 cm -3 , and / or the single crystal 4H-SiC semi-finished product has a notch or an orientation flat with a length of 47.5 mm ± 1.0 mm.

[0024] The present invention also provides a method for producing a single-crystal 4H-SiC semi-finished product with improved mechanical robustness against cleavage, the single-crystal 4H-SiC semi-finished product having a longitudinal axis and at least partially curved side surfaces parallel to the longitudinal axis, the method comprising: performing a process for setting a predetermined orientation of the 4H-SiC crystal structure relative to the longitudinal axis so that at each position on the side surface of the 4H-SiC semi-finished product there is a line segment which is aligned with at least a predetermined minimum number of lines per unit length. The line segments are defined by planes tangential to the side surfaces at said positions.

[0025] In a further refinement, the predetermined orientation of the 4H-SiC crystal structure is such that the predetermined minimum number of The parallel cleavage planes of the type are at least 1000 per millimeter.

[0026] In a further refinement, the method further comprises estimating said predetermined orientation so as to produce said at least predetermined minimum number of intersections per unit length with the line segment. Type of parallel cleavage planes.

[0027] According to a further improvement, the process of setting the predetermined orientation of the 4H-SiC crystal structure relative to the longitudinal axis of the 4H-SiC semi-finished product includes: spatially orienting the 4H-SiC single crystal relative to an alignment axis so that the orientation of the 4H-SiC crystal structure is set to be a predetermined tilt of the

[0001] axis of the basal plane in the 4H-SiC crystal structure relative to the alignment axis in a direction and amount; processing the outer surface of the spatially oriented 4H-SiC single crystal with reference to the alignment axis to form at least one of the following: the at least partially curved side surface substantially parallel to the alignment axis, and at least one front surface substantially orthogonal to the alignment axis; wherein the longitudinal axis of the 4H-SiC semi-finished product substantially corresponds to the alignment axis of the spatially oriented 4H-SiC single crystal.

[0028] In a further improvement, the process of setting the predetermined orientation of the 4H-SiC crystal structure comprises: orienting the basal plane of the 4H-SiC crystal structure in an initial orientation; ... The basal plane is tilted from the initial orientation to the first orientation at a first tilt angle; and toward the 4H-SiC crystal structure Direction or The direction tilts the basal plane from the first orientation to the second orientation at a second tilt angle; wherein in the initial orientation, the basal plane is substantially perpendicular to the longitudinal axis of the 4H-SiC semi-finished product after the final orientation.

[0029] In a further refinement, the first tilt angle is 4° with a tolerance of ±0.5°; and / or wherein based on The second tilt angle is estimated based on the distance between the parallel cleavage planes of the type, thereby generating the at least predetermined minimum number of intersections per unit length with the line segment. The parallel cleavage plane of the type, and / or the second tilt angle is a value selected from the interval [0.015°; 0.153°] or preferably 0.023°.

[0030] According to a further improvement, the process of setting the predetermined orientation of the 4H-SiC crystal structure includes: orienting the basal plane of the 4H-SiC crystal structure with an initial orientation; rotating the basal plane in a clockwise direction around the initial orientation by a predetermined rotation angle; and orienting the rotated basal plane toward the 4H-SiC crystal structure. The direction is tilted at a third tilt angle; and wherein in the initial orientation, the basal plane is substantially perpendicular to the longitudinal axis of the 4H-SiC semi-finished product after the final orientation.

[0031] In a further improvement, the process of setting the predetermined orientation of the 4H-SiC crystal structure includes: orienting the basal plane of the 4H-SiC crystal structure with an initial orientation; rotating the basal plane in a counterclockwise direction around the initial orientation by a predetermined rotation angle; and orienting the rotated basal plane toward the 4H-SiC crystal structure. The direction is tilted at a third tilt angle; and wherein in the initial orientation, the basal plane is substantially perpendicular to the longitudinal axis of the 4H-SiC semi-finished product after the final orientation.

[0032] According to a further improvement, the predetermined rotation angle is 0.33° or a value within the range of [0.22°, 2.19°], and / or the third tilt angle is 4° with a tolerance of ±0.5°.

[0033] According to a further improvement, the process of setting the predetermined orientation of the 4H-SiC crystal structure is performed on an original 4H-SiC single crystal and includes performing angle measurements on the 4H-SiC crystal structure to determine the orientation of the main axis of the basal plane, and wherein, after the setting process is completed on the original 4H-SiC single crystal, a 4H-SiC semi-finished product is obtained by performing the following steps: machining at least one front face along the initial orientation, and machining the at least partially curved surface in a direction transverse to the initial orientation.

[0034] The accompanying drawings are incorporated in and form a part of the specification for the purpose of explaining the principles of the invention. The drawings are not to be construed as limiting the invention to the examples shown and described of how the invention may be made and used. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Further features and advantages will become apparent from the following more detailed description of the invention and as illustrated in the accompanying drawings, in which:

[0036] Figure 1 is a schematic perspective view of a single crystal SiC semi-finished product;

[0037] Figure 2 is a schematic diagram of a conventional 4H-SiC semi-finished product or substrate (viewed from the top, front side) with an on-axis orientation, wherein the basal plane (0001) is parallel to the front side and the crystal direction

[0001] is tilted 0° relative to the cylindrical symmetry axis C; depicts Type and Two sets of cleavage planes of type Type includes and crystal face, Type includes and crystal plane;

[0038] Figure 3A is a schematic top view (viewed from the front) of a conventional 4H-SiC substrate with a standard 4° off-axis orientation, where the basal plane (0001) of the 4H-SiC crystal faces The direction is tilted by an angle δ of 4° relative to the front side of the 4H-SiC substrate; the short arrow in the inset depicts Figure 2 The vector component of the

[0001] direction on the plane of ;

[0039] Figure 3B yes Figure 3A The 4H-SiC substrate shown is from a Schematic side view of the crystal direction, and depicts the basal plane (0001) and the corresponding

[0001] axis toward direction (i.e., parallel to Figure 3A The direction of the main plane OF in the figure is tilted by an angle δ of 4°;

[0040] Figure 4A From the included Schematic side view of a 4H-SiC semi-finished product with a standard deviation of 4° from the orientation as viewed from the side of the crystallographic direction (i.e. the side of the main plane OF), and depicting the basal plane (0001) and the corresponding

[0001] crystallographic direction towards the initial The direction is tilted by an inclination angle δ of 4°;

[0041] Figure 4B From the initial Observed from the opposite side Figure 4AAnother schematic side view of a 4H-SiC semi-finished product shown in FIG, and depicting a cleavage plane parallel to the central symmetry axis C of the 4H-SiC cylinder orientation;

[0042] Figure 5 is a top view depicting the components of the mechanical force F exerted by the grinding wheel on the side surface of the 4H-SiC semi-finished product (or substrate);

[0043] Figure 6 is a side view depicting the radial mechanical force exerted on the 4H-SiC semi-finished product (or substrate) by the grinding wheel;

[0044] Figure 7 When from the direction Another schematic side view of a 4H-SiC semi-finished product having a standard orientation deviating by 4° when viewed (ie viewed from the side of the main plane OF) and depicting the force line segment L and the crystal plane The intersection of

[0045] Figure 8 It is now along Direction of observation Figure 7 Another schematic side view of the 4H-SiC semi-finished product is shown, and another force line segment L and the crystal plane are depicted. The intersection of

[0046] Figure 9A is a schematic side view (along the direction of the 4H-SiC semi-finished product) having a predetermined crystal orientation according to an exemplary embodiment. direction), where the base plane (0001) faces The direction is tilted by a first tilt angle δ1, and further rotates counterclockwise toward The second inclination angle δ2 is tilted in the direction; an exemplary force line segment L is also depicted, along which a radial force can be applied to the side surface of the 4H-SiC semi-finished product during machining;

[0047] Figure 9B yes Figure 9A Another schematic side view of a 4H-SiC semi-finished product shown, and depicting the basal plane (0001) and the cleavage plane resulting from tilting at a second tilt angle δ2 The tilt (from Direction observation);

[0048] Figure 10A is a schematic side view (along the direction of the 4H-SiC semi-finished product) according to another exemplary embodiment having a predetermined crystal orientation. direction), where the base plane (0001) faces The direction is tilted by a first tilt angle δ1, toward The direction is tilted by a second tilt angle δ2;

[0049] Figure 10B yes Figure 10A Another schematic side view (along the direction of the 4H-SiC semi-finished product (or substrate) shown) direction), and depicts the basal plane (0001) and the cleavage plane caused by tilting the second tilt angle δ2 The tilt;

[0050] Figure 11 Schematically illustrates a support structure for a single-crystal SiC semi-finished product according to an embodiment, which is used to transfer a predetermined crystal orientation from the SiC semi-finished product to individual SiC wafers by referring to a cylindrical side surface of the SiC semi-finished product during a wafer separation process; and

[0051] Figure 12 Another support structure for a single-crystal SiC semi-finished product according to an embodiment is schematically shown, which is used to transfer a predetermined crystal orientation from the SiC semi-finished product to individual SiC wafers by referring to one of the front sides of the single-crystal SiC semi-finished product during the wafer separation process.

[0052] It should be noted that since this application discusses atomic scales, the sizes and relative angles shown in the drawings are for understanding purposes only and are not drawn to scale. DETAILED DESCRIPTION

[0053] The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. However, the present invention may 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 the present invention will be thorough and complete and will fully convey the scope of the invention to those skilled in the art. Like reference numerals refer to like elements throughout.

[0054] The basic principle of the invention comes from the fact that the inventors have realized that by setting a given orientation of the crystal structure relative to an external reference surface (e.g. the front and / or side surfaces) of the SiC crystal and / or SiC substrate, the occurrence of cracks or fissures in the SiC crystal and substrate during various mechanical processes can be significantly reduced or even eliminated, which improves their mechanical robustness without affecting the quality of the epitaxial layer to be grown on the single-crystal SiC substrate.

[0055] The present invention thus provides an optimal orientation of the crystal planes of the SiC crystal and the substrate, which ensures higher mechanical robustness and increased yield in machining.

[0056] In SiC crystals, cracks or fissures can easily form along preferred cleavage planes (e.g., for 4H-SiC single crystals, Type and The formation of cleavage planes (of different types) can lead to damage or destruction of single-crystal SiC semi-finished products and final products. In particular, during the rapid application of mechanical forces in the radial direction (i.e., perpendicular to the side surfaces of the SiC crystal cylinder), the higher sensitivity to cracking along the cleavage plane can lead to cracking of the SiC crystal and substrate, resulting in an undesirable reduction in the corresponding yield.

[0057] For example, Figure 2 A polar 4H-SiC semi-finished product 200 (or 4H-SiC substrate) having an on-axis crystal orientation is depicted. Type and The orientation of the cleavage plane of the type. Figure 2 In the illustrated on-axis orientation, the basal plane (0001) of the 4H-SiC crystal structure is parallel to one of the front faces 220 of the cylinder, and thus the

[0001] crystallographic direction forms an angle of 0° with the longitudinal axis C of the 4H-SiC cylinder 200. The longitudinal axis C, as referred to hereinafter, is defined as the axis of symmetry of the cylindrical surface defined by the curved side surfaces of the 4H-SiC semi-finished product or 4H-SiC substrate. Figure 2 It is shown that when the corresponding front side 220 (eg Figure 1 The polar 4H-SiC semi-finished product or substrate is viewed from the Si side (0001) when viewed from the front side 120a). The orientation plane (OF) is defined in the crystal direction On. Can be optionally provided in the crystal direction The secondary plane on the In the direction of the notch (ie, a lateral indentation in the substrate wafer for precise positioning in a semiconductor production plant) instead of the main plane OF. Figure 2 Two types of cleavage planes are depicted, showing The three symmetry equivalent crystal planes of type The three symmetry equivalent crystal planes of the type. The type specification can be obtained by symmetry operation from The set of crystal planes obtained by the plane describes the ideal crystal structure of SiC (point group 6nn) and therefore includes the plane and Crystal plane and Included in Type, The type specifies that the symmetry operation can be performed from The set of crystal planes obtained by the plane. Type and All cleavage planes of the type are aligned with the front side (0001) of the Si side of the 4H-SiC semi-finished product 200 and the opposite C side. The front faces of (not shown) intersect at an angle of 90°. Type and The cleavage plane of the depicted type also intersects the side surfaces of the 4H-SiC semi-finished product 200 at right angles, which means that the 4H-SiC semi-finished product 200 will be susceptible to cracking when a radial force is applied along the depicted cleavage plane.

[0058] exist Figure 3A and Figure 3B Depicted in FIG. 3 is an example of a 4H-SiC substrate 300 having an off-axis orientation of 4° from the standard basal plane (0001) in the direction of FIG. This 4° orientation has become the standard orientation for 4H-SiC substrates used in the prior art because it allows for optimal quality in epitaxial layers grown thereon and in subsequently processed components. Figure 3A Depicted is a standard 4° off-axis orientation of a 4H-SiC substrate 300 when viewed from the top, front side (i.e., from the Si side (0001)), showing the direction parallel to the substrate front side 320a. crystal direction and along the front surface 320a The inclination of the axis is determined by Figure 3A The short arrows in the illustration depict the vector component along the

[0001] axis of the front face 320a. The principal plane is generally defined as indicating Directions, although markers can be used Direction notch instead. Can also be provided in Direction of the secondary plane. Figure 3B yes Figure 3A The 4H-SiC substrate 300 depicted in FIG. Side view when viewed from the direction (one side of the main plane OF). Figure 3B It can be seen that the basal plane (0001) of the 4H-SiC crystal faces the crystal direction The plane parallel to the front surface 320a is tilted out, and the corresponding crystal axis

[0001] is tilted at a tilt angle δ of 4° (+ / - 0.5°) relative to the central axis C of the 4H-SiC half substrate.

[0059] As mentioned above, the base plane (0001) faces The 4° tilt in the direction allows for optimal step flow during epitaxy, thus ensuring the best quality of the epitaxial layers subsequently grown on substrates that deviate by 4°. This tilt of the basal plane (0001) and the main axis

[0001] is also reflected in the crystal orientation of some cleavage planes. For example, in the case of an axially oriented Figure 2 Depicted in Type and Five of the six cleavage planes of the 4H-SiC substrate are no longer orthogonal to the front side 320a, 320b of the 4H-SiC substrate having an off-axis orientation of 4° and therefore no longer intersect the cylinder side surface 330 at right angles. Still intersecting the front surface 320a, 320b of the 4H-SiC substrate 300 at an angle of 90°, and remaining parallel to the longitudinal axis C. On the other hand, the cleavage plane The largest change in crystal orientation relative to the front side 320a is shown.

[0060] A similar situation occurs in a single crystal 4H-SiC semi-finished product 400 having a standard 4° off-axis orientation, such as Figure 4A-4B As shown in . Figure 4A Shown from A side view of the 4H-SiC semi-finished product 400 viewed from the main plane OF (ie, from the side of the main plane OF) and depicting the crystal orientation and The orientation relative to the front surface 420a (on the Si side (0001)) and the central axis C of the cylinder, and the cleavage plane The tilt. Figure 4A It can be seen that the cleavage surface No longer intersects the front face 420a at right angles and, therefore, is no longer aligned parallel to the central axis C, but rather exhibits a 4° tilt relative to the central axis C due to the 4° off-axis orientation of the basal plane (0001) and the corresponding

[0001] crystal axis. On the other hand, The direction remains transverse to the central axis C.

[0061] Figure 4B Shown Figure 4A The 4H-SiC semi-finished product shown in the figure is now The crystal direction is 90° (i.e. from the tilted base plane (0001) to the front The other side view (from the opposite direction). Figure 4B It can be seen that The direction remains transverse to the central axis C of the 4H-SiC semi-finished product 400, and the cleavage plane Is not along the base (0001) towards The only crystal plane that changes its orientation by tilting 4°. Continue to intersect the front surface 420a (and 420b) at a right angle and remain parallel to the central axis C of the cylinder. It is no longer perpendicular to the central axis C because it is tilted downward by 4° relative to the front face 420a (this is Figure 4B In the direction of The intersection of the parallel basal plane (0001) and the side surface 430 of the 4H-SiC semi-finished product 400 is at Figure 4B Indicated by a horizontal line. Outside the plane, all other corresponding Type and The cleavage planes of the type change their orientation relative to the front surface 420a after the 4° tilt of the base plane (0001), and the corresponding tilt angle falls on the cleavage plane The maximum change of 4° and the cleavage plane between zero changes.

[0062] However, whether oriented on-axis or 4° off-axis, the 4H-SiC semi-finished product or 4H-SiC substrate is still susceptible to cracking during machining, especially when radial mechanical forces are applied to the region where the cleavage plane intersects its corresponding cylindrical surface aligned with the symmetry axis C, as in the above-mentioned cleavage plane. The same situation.

[0063] like Figure 5 As shown, during the machining of a single-crystal SiC semi-finished product (or substrate), it can be assumed, in a first approximation, that the tool used during machining (e.g. grinding) applies a mechanical force F along a line segment L (force line segment) on the surface of the single crystal and that the mechanical force F propagates radially into the single crystal. The decisive factor with regard to cleavage is the force applied inwards to the single-crystal SiC semi-finished product (i.e. the radial component F of the total force F). rad ) strength. The tangential force component (F tang ) can be ignored for the purpose of evaluating its effect on cleavage. The length of the line segment L is approximately the length of the contact area with the corresponding machining tool, such as the thickness h of the grinding wheel, as Figure 6 As shown. In fact, during processing, the mechanical force is not applied along a single line segment L of length h, but rather on a very narrow area with the same length h. This narrow area can be considered as formed by a series of parallel line segments. The conditions for achieving reduced cleavage along the line segments according to the principles of the present invention (to be explained below) can then be applied to each of these individual lines.

[0064] In order to evaluate the effect of the radial mechanical force applied inwards to the cleavage plane in the contact area, the actual length of the contact area and the line segment L to which the mechanical force is actually applied is considered. The length h of the line segment L and / or the narrow area is mainly determined by the thickness h of the processing tool.

[0065] In machining with reference Figure 4A-4B The standard 4° off-axis orientation shown or with Figure 2 During the production of the SiC semi-finished product oriented on the axis shown, radial forces are applied transversely at multiple locations along the circumference of the cylindrical surface of the crystal, for example by a grinding wheel. The effect of the applied force on the development of cracks in the crystal is highly dependent on the location / area along the circumference of the cylinder where the force is applied. The following extreme cases can be distinguished regarding the orientation of the different cleavage planes relative to the area where the radial force is applied, such as Figure 7 and Figure 8 shown.

[0066] Figure 7 Shows when from the direction Another schematic side view of a 4H-SiC semi-finished product 400 having a standard 4° off-axis orientation when viewed (ie, viewed from the principal plane OF), and which shows the cleavage plane It intersects with the force line segment L along which the mechanical force is applied (where h represents the thickness of the grinding wheel). Figure 7 As shown, the inventors have realized that because the cleavage plane In a standard 4° off-axis orientation not parallel to the cylinder axis C and therefore not transverse to the front face 420a of the 4H-SiC semi-finished product 400, so in a first approximation for example by a grinding wheel in the direction The radial force applied along the line segment L is not only applied in one plane and simultaneously applied to a plurality of parallel cleavage planes intersecting with the side surface of the 4H-SiC semi-finished product 400 at the force line segment L of length h. Based on the atomic distances in the 4H-SiC crystal structure, the radial force actuated along the line segment L is estimated to be distributed in multiple equivalent, parallel On the cleavage plane of the type, for example, in the case of the 4° off-axis orientation shown, the number of 5 Planar cleavage plane This means that the applied The forces on the steel are greatly reduced, and therefore the risk of cracks propagating within parallel cleavage planes can be significantly reduced.

[0067] Figure 8 yes Figure 7 The 4H-SiC semi-finished product 400 shown is now obtained from Another schematic side view viewed from the opposite side shows that when a radial force is applied along a line segment L parallel to the C axis and toward Another extreme case occurs when the direction. Figure 8 As shown, the inventors have realized that the cleavage plane The front face 420a of the 4H-SiC semi-finished product 400 is oriented at right angles and along a line parallel to the central axis C, from the bottom front face 420b to the upper front face 420a intersecting the cylindrical side surface 430. In this case, in a first approximation, the grinding wheel is rotated along the line segment L in the direction A radial force is applied to the cleavage plane, but the radial force can only be distributed on a single or very few parallel cleavage planes. Therefore, since in this case, Figure 7 The cleavage plane shown in In contrast, the applied force is not distributed over a large number of cleavage planes. Therefore, the maximum force applied during machining is actually applied on a single or reduced number of cleavage planes. This results in a very high probability of cracking, which can easily cause the single crystal SiC semi-finished product 400 to break during machining.

[0068] Because the base plane (0001) is in the direction It is tilted 4° upwards. Type and All other remaining cleavage planes of the type are not parallel to the C-axis and exhibit a behavior in terms of robustness to cleavage that is intermediate between the above for the cleavage planes and between the two extremes described.

[0069] From the above, we can see that so far, the cleavage plane The cleavage planes remain the most sensitive to cracks and cracks during machining, and therefore the likelihood of cracks occurring along these cleavage planes is high. Therefore, the inventors have realized that the standard 4° off-axis orientation of 4H-SiC semi-finished products used in the prior art for various purposes, such as improving the epitaxial quality of material to be grown onto 4H-SiC substrates, may have a beneficial and surprising effect in reducing cleavage along certain crystal directions, but this positive effect is not present at every location along the periphery of the cylindrical surface of the 4H-SiC semi-finished product or 4H-SiC half substrate, particularly along the cleavage planes. The position of intersection with the outer cylindrical surface is achieved.

[0070] The present invention provides a method and a single-crystal 4H-SiC semi-finished product, which solves the problem of the cleavage plane along the crystal (i.e., the cleavage plane in the case of a 4H-SiC semi-finished product with an off-axis orientation (such as the above-mentioned 4° off-axis orientation) ) related to cracks / cracks formed.

[0071] In the following, for the sake of simplicity, the principle of the present invention will be directed to The present invention is described with reference to the case of a 4H-SiC semi-finished product having an off-axis orientation of 4° in the direction of the substrate. However, the present invention can be applied to variations of single-crystal SiC semi-finished products (or substrates) other than 4H-SiC, and / or other single-crystal semiconductor materials having other off-axis orientations and exhibiting a preferred cleavage plane oriented transversely to the front face of the bulk crystal and / or substrate.

[0072] The basic principle of the present invention is that by setting a specific crystal orientation of the 4H-SiC crystal structure on the 4H-SiC semi-finished product (or 4H-SiC substrate), the 4H-SiC crystal structure can be reduced or even prevented from being cleaved along the preferred cleavage plane (such as the plane). ) cracking sensitivity while maintaining the benefits of the off-axis orientation in direction

[0001] on the epitaxial quality of the corresponding 4H-SiC substrates.

[0073] In order to reduce or avoid crack formation on a 4H-SiC semi-finished product having an off-axis orientation of 4° (4°±0.5°), the present invention sets a specific orientation of the crystal structure on the 4H-SiC semi-finished product (or 4H-SiC substrate) relative to the corresponding (one or more) external surfaces (e.g., the side surface and / or one or both front surfaces of the 4H-SiC semi-finished product). For a cleavage plane that satisfies the condition The occurrence of cracks can be reduced or even avoided by orienting the 4H-SiC semi-finished product such that the radial force applied during machining is distributed over at least a predetermined minimum number of parallel cleavage planes per unit length of the force line segment L and independently of the position around the periphery of the semi-finished product. superior.

[0074] The minimum number of cleavage planes per unit length of force line segment L It can be estimated based on the atomic distances in the 4H-SiC lattice. The inventors have found that the minimum number of 1000 equivalent parallel cleavage planes per millimeter of force line segment L is A reduction in the occurrence of cracks / fissures can be achieved. The preferred number corresponds to 1500 equivalent parallel cleavage planes per millimeter of force line segment length. It is further estimated that for any number of intersecting cleavage planes up to a maximum number of 10,000 equivalent parallel cleavage planes per millimeter of force line segment, the desired increase in cleavage robustness can be achieved without affecting the epitaxial properties of the SiC semi-finished product or substrate that deviates from 4°.

[0075] The applied mechanical force produces a large number of parallel cleavage planes per unit length of force line segment The distribution on allows to reduce the probability of cracking. However, due to the cleavage plane intersecting with the force line segment L The amount of is closely related to its inclination relative to the front face of the cylinder, so it is desirable to maintain the cleavage plane The inclination is as low as possible so as not to negatively influence the quality of the epitaxial growth on the final substrate and, therefore, the number of planes intersecting the force line segments, while still achieving the desired effect of increasing the cleavage robustness of the 4H-SiC semi-finished product and the substrate made therefrom.

[0076] Figure 9A-9B and Figures 10A-10B A 4H-SiC semi-finished product, more specifically a cleavage plane, is shown having a predetermined orientation of the basic 4H-SiC crystal structure for improved mechanical robustness according to the invention. An exemplary embodiment of . Figure 9A-9B and Figures 10A-10B The relative dimensions and angles used in the drawings are only for facilitating understanding and are not drawn to scale. These exemplary predetermined orientations are also applicable to 4H-SiC substrates.

[0077] Figure 9A-9B Schematically illustrates a 4H-SiC semi-finished product 500 according to an exemplary embodiment, wherein the spatial orientation of the 4H-SiC crystal structure relative to the longitudinal axis C of the 4H-SiC semi-finished product 500 (or relative to one or both of the front faces 520a, 520b and / or the side surface 530 thereof) is as follows: At a first tilt angle δ1 (e.g. δ1 = 4° ± 0.5°, Figure 9A In addition to the off-axis orientation shown in FIG, the base plane (0001) is also oriented toward The direction is tilted at a non-zero second tilt angle δ2, such as Figure 9B Therefore, not only the cleavage plane The 4H-SiC semi-finished product 500 is tilted at an angle δ1 (eg Figure 9A shown), and the cleavage plane The tilt angle δ2 is tilted relative to the central axis C (as Figure 9B As shown in FIG. 1 ). Therefore, assuming, in a first approximation, that the radial force exerted by the machining tool along a line segment L of length h on the curved side surface 530 (the line segment L is defined as a line segment on a plane tangent to the side surface 530 in the contact region), then regardless of the position of the line segment L along the periphery of the 4H-SiC semi-finished product 500 (i.e., the region where the radial force is exerted), there are always multiple per unit length. The parallel cleavage plane of the type intersects with the force line segment L.

[0078] Therefore, the radial force applied during grinding is applied to a single or only a few cleavage planes at certain locations. The situation (such as the above reference Figure 4B described) does not occur in the 4H—SiC semi-finished product 500 having the above-mentioned predetermined orientation.

[0079] Furthermore, the occurrence of cracks during machining of the 4H-SiC semi-finished product 500 or a 4H-SiC substrate having the same predetermined orientation can be significantly reduced or even avoided in a controlled manner by estimating the value of the second tilt angle δ2, which produces at least a predetermined minimum number of cracks per unit length of the line segment. The intersecting parallel cleavage planes of the type are formed, and the radial force applied per unit plane at this second tilt angle δ2 becomes lower than a given cleavage characteristic threshold of a specific cleavage plane.

[0080] Figures 10A-10BA 4H-SiC semi-finished product 600 having another predetermined orientation for improving mechanical robustness according to another exemplary embodiment is schematically shown. In this configuration, the 4H-SiC crystal structure has a predetermined spatial orientation relative to the longitudinal axis C (or relative to one or both of the front faces 620a, 620b and / or the side surface 630 of the 4H-SiC semi-finished product 600), such that, in addition to the

[0001] direction and the corresponding basal plane (0001) facing The direction is tilted at a first angle δ1 (e.g., δ1 = 4° ± 0.5°, as shown in FIG. Figure 10A In addition to the off-axis orientation shown in the figure, it also includes the base plane (0001) facing direction with a non-zero second tilt angle δ2, such as Figure 10B As shown. In this spatial orientation, the cleavage plane Then, the 4H-SiC semi-finished product 600 is tilted at an angle δ2 relative to the central axis C. Therefore, similar to Figure 9A-9B In the embodiment, any force line segment L on the side surface 630 parallel to the central axis C will be connected to at least a predetermined minimum number of force line segments L per unit length. The parallel cleavage planes of the type intersect, regardless of the position on the side surface 630 where the line segment L is defined, and therefore, regardless of the position where the radial force is applied during the grinding process. Also in this case, the value of the second tilt angle δ2 can be estimated so as to achieve at least a predetermined minimum number of line segments per unit length. The radial force of each cleavage plane becomes lower than a given cleavage threshold at the second inclination angle δ2.

[0081] The second tilt angle δ2 may be based on Two equivalent parallel cleavage planes of the type (e.g. The second tilt angle δ2 can be estimated based on the known distance between the two planes, and / or considering the parameters of the mechanical process (e.g., the height h of the grinding tool in the contact area, the force usually applied and the grinding speed, etc.), and / or the known cleavage threshold of a specific type of cleavage plane. Alternatively, the second tilt angle δ2 can be determined and adjusted by experiment.

[0082] The two exemplary embodiments share the following principle of the present invention: the external mechanical force is distributed to multiple equivalent parallel cleavage planes per unit length of the force line segment L. The occurrence of cracks can be reduced or even eliminated regardless of the position around the entire periphery of the SiC semi-finished product to which such external mechanical force is to be applied.

[0083] With the above reference Figure 9A-9B and Figures 10A-10B Similar improvements in mechanical robustness against cleavage are also achieved in 4H-SiC substrates or wafers having the same spatial orientation of the 4H-SiC crystal structure.

[0084] The predetermined orientation of the 4H-SiC crystal structure can be set on the 4H-SiC semi-finished product by the following method.

[0085] In the original 4H-SiC crystal obtained after crystal growth and / or first rough machining (pre-machined 4H-SiC crystal), the crystal face and the reference surface (e.g. one of the machined front faces or a cylindrical surface) are not yet aligned with the desired exact orientation relative to each other, as in the final 4H-SiC semi-finished product.

[0086] For this reason, at the beginning of machining, the original 4H-SiC crystal (or pre-machined 4H-SiC crystal) is oriented with one of its front sides (Si side (0001) or C side) to ) is mounted on a goniometer and / or a holder and glued or bonded thereto in order to precisely set the crystal orientation for machining. For this orientation, commercial X-ray equipment can be used, and with this equipment the orientation of the crystal planes can be accurately determined and aligned. Therefore, in order to set an off-axis orientation of 4°, in a first step, the original crystal orientation is adjusted in the X-ray equipment using a goniometer so that the basal plane (0001) (or plane) is accurately oriented in a direction normal to the future cylindrical surface (ie the

[0001] axis is aligned along the C axis), which will be defined in a subsequent machining process (eg by a grinding process).

[0087] In the subsequent step, the raw SiC crystal (or pre-processed SiC single crystal) thus oriented is oriented in the direction of Tilt 4° (+ / - 0.5°) to provide the desired 4° off-axis orientation of the basal plane as required for high quality epitaxy of future SiC substrates. Figure 4A and Figure 4B In this case, the angle between the

[0001] axis of the base surface and the future cylinder axis C is 4° (+ / - 0.5°).

[0088] Afterwards, the outer diameter of the cylinder is set to the diameter of the future substrate, for example, by a grinding process. As mentioned above, this diameter setting process is one of the most critical steps with regard to crack initiation. During this setting process, the previously goniometer-adjusted orientation of the crystal planes relative to the cylindrical surface can be accurately transferred. Furthermore, orientation major or minor planes and / or notches can be ground during this process step. X-ray equipment is then used to check / control the desired orientation of the crystal planes relative to the cylindrical surface before any further processing.

[0089] After the processing of the outer diameter and / or orientation plane and the control of the desired orientation of the crystal plane relative to the cylindrical surface, a process for defining the front side of the SiC single crystal is performed, resulting in a final SiC semi-finished product having an external shape similar to Figure 1 The shape shown in .

[0090] To set the crystal plane to improve mechanical robustness A predetermined spatial orientation (e.g. Figure 9A-9B or Figures 10A-10B The original SiC crystal (or pre-processed SiC crystal) is subjected to a process for setting the desired predetermined orientation, which includes spatially orienting the original (or pre-processed) SiC crystal, for example, by using any of the following orientation process sequences. Each step of the orientation process sequence is preferably performed using a goniometer and commercial X-ray equipment to ensure precise orientation in each step of the process sequence.

[0091] like Figure 9A-9B As shown, according to a first sequence of orientation processes for setting a predetermined orientation of the SiC crystal structure in the 4H-SiC semi-finished product 500, the raw or pre-processed 4H-SiC crystal is spatially oriented so that the basal plane is first aligned with an initial orientation in which the basal plane is substantially at right angles to the direction of the alignment center axis C (corresponding to the direction of the future cylindrical side surface of the final 4H-SiC semi-finished product 500). Tilt the same amount δ1 in the direction, and move the base surface toward The direction is tilted from the initial orientation by a first tilt angle δ1 and becomes the first orientation. Then the SiC crystal oriented in this way is directed toward The second tilt angle δ2 is tilted in the direction, which causes the base plane (0001) to pass toward The direction is tilted by a second tilt angle δ2 from the first orientation to the second orientation.

[0092] like Figures 10A-10B According to the alternative second orientation process sequence for setting a predetermined orientation of the SiC crystal structure in the 4H-SiC semi-finished product 600, the basal plane is also first oriented in an initial orientation at right angles to the direction of the central axis C (which corresponds to the direction of the future cylindrical side surface 630). The direction is tilted from the initial orientation by a first tilt angle δ1 to the first orientation. Then the original or pre-processed SiC crystal oriented in this way is directed toward The second tilt angle δ2 is tilted in the direction so that the base plane (0001) passes through the The direction is tilted by an additional tilt angle δ2 from the first orientation to the second orientation.

[0093] In the above-mentioned first orientation process sequence and second orientation process sequence, the value of the first tilt angle is preferably 4°±0.5°, where the error of ±0.5° is associated with an acceptable tolerance for the value of the first tilt angle that still allows the desired improvement in the epitaxial characteristics of the respective semiconductor substrates to be obtained. The value of the second tilt angle δ2 is preferably 0.023°. However, any value within the range of [0.015°; 0.153°] can be used for the second tilt angle δ2, at which the desired orientation effect on mechanical robustness can be achieved. In particular, the value of the second tilt angle δ2 to be used can be estimated based on the distance between equivalent parallel cleavage planes of the 4H-SiC lattice and with reference to the above-mentioned at least a predetermined minimum number of intersecting cleavage planes on the force line segment per unit length, and the cleavage effects of these cleavage planes are intended to be minimized.

[0094] According to a third orientation process sequence for setting another predetermined orientation to improve mechanical robustness, the base surface is first aligned in an initial orientation that is at right angles to the direction of the central axis C, i.e., the direction of the future cylindrical side surface. The base surface is then rotated clockwise around this initial orientation by a predetermined rotation angle. The predetermined rotation angle is 0.33° or a value within the range [0.22°; 2.19°]. In subsequent steps, the base surface is aligned in the direction of the 4H-SiC crystal structure. The direction is further tilted by a third tilt angle δ3. The third tilt angle is preferably 4° with a tolerance of ±0.5°.

[0095] Alternatively, a fourth orientation process sequence can be used, in which the base surface is also first aligned in an initial orientation that is at right angles to the direction of the central axis C, i.e., the direction of the future cylinder side surface. The base surface is then rotated counterclockwise about this initial orientation by a predetermined rotation angle. This predetermined rotation angle is preferably 0.33°, but can also be any value within the range [0.22°; 2.19°] to achieve the desired orientation effect on mechanical robustness. In a subsequent step, the base surface is aligned in the 4H-SiC crystal structure. The first embodiment further inclines at a third inclination angle δ3 in the direction of the first embodiment, preferably at 4°±0.5°.

[0096] After the crystallographic orientation of the raw SiC crystal (or pre-machined SiC crystal) has been aligned by any of the above-described sequences of orientation processes, one or more external reference surfaces of the final 4H-SiC semi-finished product may be machined with reference to the alignment axis C. For example, at least partially curved side surfaces may be machined on the oriented raw or pre-machined SiC crystal in a direction parallel to the alignment axis C. Additionally or alternatively, one or both front sides of the final 4H-SiC semi-finished product may be machined in a direction orthogonal to the C-axis.

[0097] Therefore, the predetermined orientation of the basal plane (0001) and other crystal planes of the 4H-SiC structure can be accurately set relative to at least one reference surface of the 4H-SiC semi-finished product, i.e., the curved side surface and / or one or both front sides thereof.

[0098] The diameter of the curved side surface can be set to substantially correspond to the expected diameter of the substrate wafer to be sliced ​​from the 4H-SiC semi-finished product. In particular, the technology of the present invention can be applied to improve the mechanical robustness of 4H-SiC semi-finished products having an outer diameter of 150.0 mm ± 0.5 mm, 200.0 mm ± 0.5 mm, or 250.0 mm ± 0.5 mm, and 4H-SiC substrates obtained therefrom. An error of ± 0.5 mm in the outer diameter corresponds to the tolerance associated with standard grinding processes. However, the diameter tolerance can be higher or lower than 0.5 mm, depending on the technology used to set the side surface of the 4H-SiC semi-finished product and / or adjust its outer diameter.

[0099] Furthermore, the technology of the present invention can be applied to improve the mechanical robustness of 4H-SiC semi-finished products having a height in the direction of 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 having a height preselected to produce the desired number of 4H-SiC substrate slices.

[0100] The SiC semi-finished product having a predetermined orientation of the 4H-SiC crystal lattice for improved mechanical robustness can then be separated into substrate wafers using well-known wafer separation processes, such as multi-wire sawing using diamond-based slurry, wire-based spark erosion, or other alternative separation processes. This predetermined orientation of the 4H-SiC crystal lattice can be transferred to the substrate wafers by referencing any reference surface of the SiC semi-finished product during the separation process.

[0101] An alternative exemplary embodiment for supporting a SiC semi-finished product during a wafer separation process and transferring a predetermined orientation of the substantially 4H-SiC lattice into a SiC substrate is described in Figure 11 and Figure 12 Shown in.

[0102] Figure 11 A configuration is shown in which the crystal orientation of a single-crystal SiC semi-finished product 700 (e.g., any of the single-crystal SiC semi-finished products 500 and 600 described above) is transferred to a SiC substrate 740 via a cylindrical side surface 730. In the case of a separation process in which the support of the single-crystal SiC semi-finished product 700 to be processed is achieved via the support of the cylindrical side surface 730, the cylindrical side surface 730 needs to be accurately aligned with respect to the orientation of the SiC crystal plane. Therefore, in this separation method, the orientation of the crystal plane is transferred by correspondingly aligning them with respect to the cylindrical side surface 730.

[0103] Figure 12 A configuration is shown in which a single-crystal SiC semi-finished product 700 is supported on one of the front faces 720b. In the case of a separation process in which the support of the single-crystal SiC semi-finished product to be processed is achieved by the support of the front face, the front face needs to be accurately aligned with respect to the orientation of the crystal face. In these separation methods, the orientation of the SiC crystal face is transferred by aligning one of the front faces 720b of the cylinder with respect to the crystal face. In this case, the orientation of the crystal face relative to the front face 720b for support is preferably measured using an X-ray radiographic method, set using a goniometer, and accurately transferred during mechanical processing, for example using a grinding process. In order to accurately transfer the predetermined orientation of the 4H-SiC crystal face to the substrate wafer 740, the single-crystal SiC semi-finished product 700 should meet one of the following basic conditions:

[0104] At least one of the two front faces 720a and / or 720b (reference surfaces) is oriented at right angles to the cylinder side surface 730, i.e. the lattice orientation is exactly transferred via one of the reference surfaces;

[0105] Both front faces 720a and 720b (reference surfaces) are oriented at right angles to the cylinder side surface 730, i.e. the lattice orientation can be accurately transferred via the two reference surfaces;

[0106] One of the front faces 720a or 720b (reference surface) is oriented exactly at right angles to the cylindrical side surface 730, while the second front face 720b or 720a is oriented so that The measurements showed that the total thickness variation (TTV) of the second front side relative to the first front side was between 40 μm and 340 μm, i.e., the lattice orientation could be accurately transferred through two reference surfaces, with one front side accurately oriented and the other within the expected orientation.

[0107] In summary, the present invention allows reducing the occurrence of cracks during the machining of 4H-SiC single crystals and / or 4H-SiC substrates by setting 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) so that the radial mechanical force applied to a given area is always distributed over at least a predetermined minimum number of preferred cleavage planes, regardless of the location of the application of the mechanical force on the periphery of the SiC semi-finished product.

[0108] Therefore, by means of this optimal orientation of the 4H-SiC crystal structure, a higher mechanical robustness can be achieved during the mechanical processing of bulk SiC crystals and SiC substrates and, as a result, a higher yield of single-crystal semi-finished products and end products can be achieved without compromising the epitaxial quality of future substrates and without significantly increasing the costs and / or time of the corresponding mechanical processes.

[0109] While certain features of the exemplary embodiments described above have been described using terms such as "downward" and "horizontally," these terms are used solely for convenience in describing the corresponding 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 component thereof to a particular spatial orientation. Furthermore, while the present invention has been described above with reference to a 4H-SiC crystal, the principles of the present invention may also be advantageously applied to other variations of SiC single crystals and / or other semiconductor single crystals, such as AlN and GaN.

[0110] Reference numerals

[0111] C Geometric longitudinal axis

[0112] L segment

[0113] h is the height of the grinding wheel and the length of the line segment L

[0114] 100 SiC semi-finished products

[0115] 110 Orientation Plane (OF)

[0116] 120a, 120b upper and lower front faces of the cylinder

[0117] 130 cylinder side surface

[0118] 200 SiC semi-finished product with axial orientation (prior art)

[0119] 220 front

[0120] 230 cylinder side surface

[0121] 240 Grinding Wheel

[0122] 300 SiC substrate with 4° off-axis orientation (prior art)

[0123] 320a, 320b upper and lower front faces of the cylinder

[0124] 330 cylinder side surface

[0125] 400 SiC semi-finished product with 4° off-axis orientation (prior art)

[0126] 420a, 420b upper and lower front faces of the cylinder

[0127] 430 cylinder side surface

[0128] 500 SiC semi-finished products

[0129] 520a, 520b upper and lower front faces of the cylinder

[0130] 530 cylinder side surface

[0131] 600 SiC semi-finished products

[0132] 620a, 620b upper and lower front faces of the cylinder

[0133] 630 cylinder side surface

[0134] 700 Single crystal SiC semi-finished products

[0135] 710 bracket

[0136] 720a, 720b and 730 front and side surfaces

[0137] 740 substrate wafer

Claims

1. A single-crystal 4H-SiC semi-finished product with improved mechanical robustness against cleavage, the single-crystal 4H-SiC semi-finished product having a longitudinal axis and at least partially curved side surfaces parallel to the longitudinal axis, It is characterized by: The crystal structure of the 4H-SiC semi-finished product is oriented relative to the longitudinal axis so that at each position on the side surface of the semi-finished product there is a line segment with at least 1000 { } type parallel cleavage planes intersect, The main axis of the basal plane of the 4H-SiC crystal structure is oriented relative to the longitudinal axis. The direction is tilted by a first tilt angle, wherein the first tilt angle is 4° with a tolerance of ±0.5°; and The main axis of the base surface is oriented relative to the longitudinal axis. The direction is tilted by the second tilt angle, The second tilt angle is a value selected from the interval [0.015°, 0.153°], The line segment is defined by a plane tangent to the side surface at the position.

2. The single crystal 4H-SiC semi-finished product according to claim 1, wherein: The longitudinal axis is the axis of symmetry of the cylinder defined by the curved portion of the at least partially curved side surface of the 4H-SiC semi-finished product.

3. The single crystal 4H-SiC semi-finished product according to claim 1 or 2, wherein: The second tilt angle is based on the { } type of parallel cleavage planes, thereby generating said at least 1000 { } type parallel cleavage planes, and / or The second inclination angle is 0.023°.

4. The single crystal 4H-SiC semi-finished product according to claim 1 or 2, further comprising a first front side and a second front side; in, One or both of the first front side and the second front side are perpendicular to the longitudinal axis; or wherein the first front face is perpendicular to the longitudinal axis and the second front face is oriented such that The measurement of the direction results in a total thickness variation of the second front side relative to the first front side of between 40 μm and 340 μm.

5. The single crystal 4H-SiC semi-finished product according to claim 1 or 2, wherein: said at least partially curved side surface having a curvature defining a cylindrical surface having said longitudinal axis as its axis of symmetry, wherein the outer diameter of the cylindrical surface substantially corresponds to a given diameter of a substrate wafer that can be obtained by slicing the 4H-SiC semi-finished product, 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 height of the single crystal 4H-SiC semi-finished product is greater than 15 mm, and / or The nitrogen doping of the single crystal 4H-SiC semi-finished product is greater than 1×10 18 cm -3 , and / or The single crystal 4H-SiC semi-finished product has a notch or an orientation flat with a length of 47.5 mm±1.0 mm.

6. A method for producing a single-crystal 4H-SiC semi-finished product with improved mechanical robustness against cleavage, the single-crystal 4H-SiC semi-finished product having a longitudinal axis and at least partially curved side surfaces parallel to the longitudinal axis, the method comprising: The process of setting the predetermined orientation of the 4H-SiC crystal structure relative to the longitudinal axis is performed so that at each position on the side surface of the 4H-SiC semi-finished product there is a line segment that has at least 1000 { } type parallel cleavage planes intersect, wherein the line segment is defined by a plane tangent to the side surface at the position, The process of setting the predetermined orientation of the 4H-SiC crystal structure relative to the longitudinal axis of the 4H-SiC semi-finished product comprises: spatially orienting a 4H-SiC single crystal relative to an alignment axis such that the orientation of the 4H-SiC crystal structure is set such that a [0001] axis of a basal plane in the 4H-SiC crystal structure is tilted in a direction and by a predetermined amount relative to the alignment axis; and processing the outer surface of the spatially oriented 4H-SiC single crystal with reference to the alignment axis to form at least one of the following: an at least partially curved side surface substantially parallel to the alignment axis, and at least one front face substantially orthogonal to said alignment axis, wherein the longitudinal axis of the 4H-SiC semi-finished product corresponds to the alignment axis of the 4H-SiC single crystal after spatial orientation, and Wherein, in the predetermined orientation of the 4H-SiC crystal structure: The main axis of the basal plane of the 4H-SiC crystal structure is oriented relative to the longitudinal axis. The direction is tilted by a first tilt angle, wherein the first tilt angle is 4° with a tolerance of ±0.5°; and The main axis of the base surface is oriented relative to the longitudinal axis. The direction is tilted by the second tilt angle, The second inclination angle is a value selected from the interval [0.015°, 0.153°].

7. The method of claim 6, further comprising: Estimating the predetermined orientation so as to generate the at least 1000 { } type parallel cleavage planes.

8. The method according to claim 6 or 7, wherein: The process of setting the predetermined orientation of the 4H-SiC crystal structure, spatially orienting the 4H-SiC single crystal includes: orienting the basal plane of the 4H-SiC crystal structure in an initial orientation; Towards the 4H-SiC crystal structure tilting the base surface from the initial orientation to a first orientation at the first tilt angle; and Towards the 4H-SiC crystal structure Direction or tilting the base surface from the first orientation to a second orientation at the second tilt angle; Wherein, in the initial orientation, the basal plane is substantially perpendicular to the longitudinal axis of the 4H-SiC semi-finished product after final orientation.

9. The method of claim 8, wherein: Based on the { The second tilt angle is estimated by the distance between the parallel cleavage planes of the type, thereby generating the at least 1000 { } type parallel cleavage planes.

10. The method according to claim 6 or 7, wherein: The process of setting the predetermined orientation of the 4H-SiC crystal structure, spatially orienting the 4H-SiC single crystal includes: orienting a basal plane of the 4H-SiC crystal structure in an initial orientation; Rotating the base surface clockwise around the initial orientation by a predetermined rotation angle; The rotated base plane faces the 4H-SiC crystal structure The direction is tilted by a third tilt angle; and Wherein, in the initial orientation, the basal plane is substantially perpendicular to the longitudinal axis of the 4H-SiC semi-finished product after final orientation.

11. The method according to claim 6 or 7, wherein: The process of setting the predetermined orientation of the 4H-SiC crystal structure, spatially orienting the 4H-SiC single crystal includes: orienting a basal plane of the 4H-SiC crystal structure in an initial orientation; Rotating the base surface counterclockwise around the initial orientation by a predetermined rotation angle; The rotated base plane faces the 4H-SiC crystal structure. The direction is tilted by a third tilt angle; and Wherein, in the initial orientation, the basal plane is substantially perpendicular to the longitudinal axis of the 4H-SiC semi-finished product after final orientation.

12. The method of claim 10, wherein: The predetermined rotation angle is a value in the range of [0.22°, 2.19°], and / or The third inclination angle is 4°, and the tolerance is ±0.5°.

13. The method of claim 11, wherein: The predetermined rotation angle is a value in the range of [0.22°, 2.19°], and / or The third inclination angle is 4°, and the tolerance is ±0.5°.

14. The method according to claim 6 or 7, wherein: The process of setting the predetermined orientation of the 4H-SiC crystal structure is performed on a raw 4H-SiC single crystal and includes performing an angular measurement on the 4H-SiC crystal structure to determine the orientation of the principal axis of the basal plane, and After the spatial orientation in the setting process is completed on the original 4H-SiC single crystal, the 4H-SiC semi-finished product is obtained by performing the following steps: processing at least one front face in an initial orientation, and The at least partially curved side surface is machined in a direction transverse to the initial orientation.

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