A method for processing and using a SiC substrate without a positioning edge

Abstract

The present invention proposes a method for processing a SiC substrate without a positioning edge, including: orienting the outer circle of a SiC crystal; crystal cutting; cutting and taking a piece: baking the cutting piece from a cutting base, taking out and marking the carbon-silicon surface of the head piece or tail piece of the cutting piece, and cleaning the cutting piece to remove the cutting fluid remaining on the surface; head and tail piece orientation: orienting the head and tail cutting pieces of the SiC crystal, verifying the [1-100] and [11-20] directions of the marked head piece or tail piece; non-head and tail piece orientation: overlapping the non-head and tail pieces with the head piece and / or tail piece so that their knife marks overlap, and then orienting along the off-axis direction of the wafer to determine the off-axis direction and polarity plane of the wafer; carbon / silicon surface marking and crystal direction marking; performing subsequent process processing on the marked wafer to obtain a SiC substrate without a positioning edge. When the SiC substrate without a positioning edge prepared in the present invention is used as a seed crystal or substrate to grow SiC crystals or epitaxial wafers, it can effectively reduce defects such as micropipes and stress in the crystal, and greatly improve the quality of the material.

Description

Technical Field

[0001] The invention belongs to the technical field of single crystal processing, and in particular relates to a method for processing and using a SiC substrate without a positioning edge. Background Art

[0002] The statements in this section merely provide background information related to the present invention and do not necessarily constitute prior art.

[0003] Silicon carbide (SiC) is a relatively mature third-generation semiconductor material with excellent semiconductor properties such as high temperature resistance, high thermal conductivity, and high breakdown voltage, which enables SiC-based devices to work under extreme conditions. At the same time, SiC, as an important substrate material, can be used for epitaxial growth of gallium nitride, graphene, etc. At present, β-SiC substrates such as 4H-SiC and 6H-SiC are widely used in high-power power electronic devices, microwave radio frequency devices, and optoelectronic devices.

[0004] SiC is a group IV compound semiconductor, and its basic structural unit is SiC4 or Si4C. Due to the different electronegativity of C atoms and Si atoms, there is charge transfer between Si atoms and C atoms, which makes it have strong ionicity. Therefore, SiC is a typical polar crystal, and its (0001) face is a polar face. The Si atom is on the Si face at the outermost layer, and the C atom is on the C face at the outermost layer. The surface activation energy of the Si face and the C face is different, so the polar face of the SiC substrate has an important influence on the growth of SiC single crystals and the epitaxy of other materials. For example, when a SiC substrate is used as a seed crystal to grow a SiC single crystal, the crystal grown on the C face is generally a 4H-SiC single crystal, and the crystal grown on the Si face is generally a 6H-SiC single crystal. When graphene is prepared by SiC thermal decomposition method, the Si face is used as the growth face, and the graphene morphology and layer uniformity are more controllable. In addition, when using a biased SiC substrate for SiC homoepitaxial growth, a substrate with a 4° offset from the axial direction [11-20] is generally selected for epitaxy to obtain a high-quality epitaxial layer; when a substrate with a 4° offset from the axial direction [1-100] is selected for epitaxy, 3C-SiC inclusions and stacking faults are likely to appear, and the epitaxial layer morphology is poor. Therefore, how to accurately mark the crystal orientation and polarity of the SiC substrate is of great significance to the application of the SiC substrate.

[0005] At present, in this field, two positioning edges (main positioning edge and auxiliary positioning edge) are usually made on the SiC substrate to distinguish the crystal orientation and polarity surface of the SiC substrate. In this process, it is generally necessary to grind the SiC crystal to the target diameter, and then use an orientation instrument to orient the end face of the single crystal to find the (1-100) and (11-20) crystal planes of the SiC single crystal, and use a surface grinder to grind the two crystal planes of the crystal to obtain the main positioning edge and the auxiliary positioning edge respectively. There are three problems when using this method:

[0006] (1) When the positioning edge is ground on the crystal end face, the probability of crystal cracking is high;

[0007] (2) The crystal after grinding is no longer a complete circle. When this type of substrate is used as a seed crystal, defects such as micropipes and stress accumulation will appear in the grown SiC single crystal, affecting the quality of the single crystal;

[0008] (3) As the crystal diameter increases, in order to intuitively distinguish the main positioning edge from the auxiliary positioning edge, the lengths of the two positioning edges also need to be increased accordingly, resulting in a reduction in the available area of ​​the substrate.

[0009] Chinese patent CN107991230B discloses a method for identifying the carbon-silicon surface of SiC wafers. The method performs surface grinding and rounding on the grown SiC ingot; orients the rounded ingot to determine the reference axis direction as the <11-20> direction; processes an asymmetric V-groove along the <11-20> direction; processes the ingot into a wafer; the V-groove of the processed wafer forms an angle θ, and the two oblique sides forming the angle θ are set as a and b respectively, and the lengths of the two oblique sides satisfy a≠b; the corresponding wafer surface can be judged as a carbon surface or a silicon surface by whether the two oblique sides ab.

[0010] However, in this method, (1) the crystal still needs to be V-grooved. The V-grooves are generally processed by wire cutting, which is a point contact process. As a result, the crystal is subjected to greater mechanical stress during this process and is very prone to cracking. (2) The crystal is still not a standard circle. When this method is used to obtain a substrate as a seed crystal to grow SiC single crystals, the single crystal corresponding to the V-grooves of the seed crystal will have defects such as microtubes and stress.

[0011] Chinese patent CN109037307A discloses a SiC wafer and a method for processing its positioning edge. The method provides an R angle with an optimal radius range at the junction of the first flat edge and the second flat edge of the SiC wafer with the edge of the silicon carbide wafer, which can reduce the stress at the location and avoid the wafer from breaking during transportation and packaging, thereby improving the processing yield and quality of the SiC wafer.

[0012] However, in this method, there are still two positioning edges on the SiC substrate, and the stress near the positioning edges has not been substantially improved. Summary of the invention

[0013] In order to overcome the above-mentioned deficiencies of the prior art, the present invention provides a method for processing and using a SiC substrate without a positioning edge, which realizes the orientation of all cutting pieces and the distinction between carbon and silicon surfaces.

[0014] To achieve the above objectives, one or more embodiments of the present invention provide the following technical solutions:

[0015] In a first aspect, a method for processing and using a SiC substrate without a positioning edge is disclosed, comprising:

[0016] Rolling: The grown SiC crystal is subjected to external cylindrical grinding to make the outer diameter of the SiC crystal reach the target size;

[0017] Orientation: Orient the outer circle of the SiC crystal, determine the [1-100] and [11-20] directions of the SiC crystal, and mark the outer circle of the SiC crystal;

[0018] Crystal cutting: Bond the SiC crystal to the cutting base in the set direction and process the SiC crystal into cutting pieces;

[0019] Cutting and taking out the slices: bake the cutting slices from the cutting base, take out and mark the carbon silicon surface of the head or tail slice of the cutting slice, and clean the cutting slice to remove the cutting fluid remaining on the surface;

[0020] Head and tail piece orientation: Orient the head and tail cut pieces of SiC crystals to verify the [1-100] and [11-20] directions of the marked head or tail cut pieces;

[0021] Orientation of non-head and tail pieces: overlap the non-head and tail pieces with the head piece and / or tail piece so that their cut marks overlap, and then orient them along the off-axis direction of the wafer to determine the off-axis direction and polarity plane of the wafer;

[0022] Carbon / silicon surface marking and crystal orientation marking: marking the determined crystal orientation and carbon / silicon surface;

[0023] Substrate processing: The marked wafer is subjected to subsequent process processing to obtain a SiC substrate without positioning edges.

[0024] As a further technical solution, the SiC crystal subjected to external cylindrical grinding is a SiC crystal that has not been subjected to surface grinding or a SiC crystal that has been subjected to surface grinding.

[0025] As a further technical solution, the SiC crystal for external cylindrical grinding is an axially oriented crystal, and the silicon surface or carbon surface of the crystal deviates from the c-axis along [11-20] or [1-100], with a deviation angle of 0.1 to 8°.

[0026] As a further technical solution, an orientation instrument is used to determine the crystal [1-100] and [11-20], with an accuracy within ±0.2°.

[0027] As a further technical solution, when the crystal is bonded to the cutting base, the [1-100] and [11-20] directions are marked on the native surface of the crystal and / or the seed crystal surface.

[0028] Preferably, when bonding the crystal to the cutting base, the [1-100] or [11-20] direction is bonded opposite the graphite base;

[0029] By adjusting the cutting machine's feed speed, wire feed speed, slurry flow rate, and swing angle parameters, the SiC cutting blade has asymmetric roughness and cutter marks along the feed direction.

[0030] Further preferably, by increasing the feed speed at 1 / 8 to 1 / 3 of the total cutting thickness, and / or reducing the wire feed speed, and / or reducing the mortar flow rate, and / or reducing the swing angle, the roughness of a part of the cutting blade is increased and the knife marks are obvious, so that the feed direction of the cutting blade is easily identified without significantly affecting the cutting quality of the cutting blade;

[0031] When cutting a SiC crystal into a cutting piece with uneven knife mark distribution along the cutting direction, it is preferred to process the SiC crystal into a cutting piece with a rougher exit point than the cutting point and heavier knife marks.

[0032] As a further technical solution, when the cut piece is baked off the cutting base, the carbon surface and / or silicon surface of the wafer and the specific crystal orientation are clearly marked;

[0033] According to the preferred embodiment of the present invention, the cutting fluid remaining on the cutting disc is cleaned by ultrasonic cleaning with kerosene solvent, and then the cutting disc is rinsed with ethanol and tap water;

[0034] As a further technical solution, an orienting instrument is used to orient the cut head and tail pieces. By taking advantage of the asymmetry of the off-axis crystal orientation, the crystal direction is marked and the accuracy of the off-axis direction is controlled within 0.1°.

[0035] As a further technical solution, the head / tail pieces with determined directions are bonded together with the non-head / tail pieces according to the marks of the knife marks, and then the wafer is oriented using an orientator. With the help of the asymmetry of the off-axial crystal orientation, the test surface is determined to be the carbon surface or the silicon surface, and then the two directions of the cutting piece are determined.

[0036] As a further technical solution, the marking machine is a laser marking machine or an etching machine;

[0037] Marking is performed on the carbon surface and / or the silicon surface of the substrate, or marking is performed in a specific direction of the substrate, and the marking content is graphics, text or numbers;

[0038] When the silicon surface of the substrate is the growth surface or epitaxial surface, the mark is engraved on the carbon surface of the substrate;

[0039] When the carbon surface of the substrate is the growth surface or epitaxial surface, the mark is engraved on the silicon surface of the substrate.

[0040] As a further technical solution, a double-sided grinder and / or a wheel grinder is used to thin the cutting blade.

[0041] One or more of the above technical solutions have the following beneficial effects:

[0042] 1) The method of the present invention skillfully combines crystal cutting with off-axial crystal orientation and carbon / silicon surface distinction, and uses the orientation result of the crystal end face before cutting to determine the crystal orientation of the cutting head / tail piece, and then determines the crystal orientation of the cutting head / tail piece; by making full use of the characteristics of the roughness and deep knife marks of the cutting piece at the knife exit point of the existing cutting technology, or intentionally increasing the roughness and knife marks of some areas of the cutting piece without significantly affecting the quality of the cutting piece, the knife marks of the non-head and tail piece cutting pieces are matched with the knife marks of the head and tail piece cutting pieces, and with the help of the asymmetric characteristics of the off-axial crystal crystal orientation, the orientation of all cutting pieces and the distinction of carbon and silicon surfaces are achieved;

[0043] 2) The method of the present invention does not require the edge grinding of the crystal to be cut, which simplifies the crystal processing process, reduces the probability of cracking during the crystal processing, reduces the crystal processing cost to a certain extent, and improves the crystal processing yield;

[0044] 3) The method of the present invention can obtain a wafer substrate without a positioning edge, which can effectively increase the utilization area of ​​the substrate and reduce the preparation cost of related devices; the growth of SiC crystals using the substrate prepared by the present invention can avoid the problem of micropipe proliferation in the crystal caused by stress difference and diameter expansion difference in the positioning edge area, which is conducive to improving crystal stress;

[0045] 4) When the substrate obtained in the present invention is used to make SiC seed crystals, since the substrate is a complete round wafer, when the substrate is bonded to graphite paper, the graphite paper will not have creases or indentations, which can improve the quality and yield of seed crystal production;

[0046] 5) The method of the present invention involves cutting pieces and orienting them, including a cutting machine, an orienting instrument, etc., which are conventional equipment in the art. Therefore, the method is simple, practical, and easy to promote.

[0047] Advantages of additional aspects of the present invention will be given in part in the following description, and in part will become obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0049] Figure 1 The flowchart of the processing and use of SiC substrate without positioning edge in the present invention.

[0050] Figure 2The knife marks and crystal directions of the cutting head sheet in Example 2; wherein 2-1 is the marked [11-20] direction, 2-2 is the marked [1-100] direction, 2-3 is the cutting head sheet, and 2-4 is the knife mark of the cutting sheet;

[0051] Figure 3 These are the test results of the cut marks and crystal orientation of the non-head and tail pieces of the cut pieces in Example 2. DETAILED DESCRIPTION

[0052] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0053] It should be noted that the terms used herein are for describing specific embodiments only and are not intended to be limiting of exemplary embodiments according to the present invention.

[0054] In the absence of conflict, the embodiments of the present invention and the features of the embodiments may be combined with each other.

[0055] Terminology Note:

[0056] Seed crystal face: refers to the side of the crystal that contains the seed crystal;

[0057] Native surface: refers to the growth surface of the crystal. Generally, this surface is not flat and has growth stripes and small faces.

[0058] Cutting head piece: refers to the first cutting piece close to or / and containing the seed crystal, usually with a carbon ring on the periphery;

[0059] Cutting tail piece: refers to the first cutting piece close to or / and including the natural surface. Generally, the diameter is smaller than the target diameter and has a "slope edge";

[0060] Axially biased SiC crystal: refers to a crystal whose surface normal does not coincide with the c-axis and deviates from the c-axis by a certain small angle along the [11-20] or [1-100] direction.

[0061] According to the prior art, the presence of V-grooves or positioning edges on the marked SiC substrate causes stress accumulation on the substrate and reduces the utilization area. This embodiment provides a method for processing a SiC substrate without positioning edges.

[0062] Example 1

[0063] Attached Figure 1 As shown, this embodiment discloses a method for processing and using a SiC substrate without a positioning edge, including:

[0064] 1) Rounding: The grown SiC crystal is subjected to cylindrical grinding to make the outer diameter of the SiC crystal reach the target size;

[0065] 2) Orientation: Use an orientator to orient the outer circle of the crystal, accurately determine the [1-100] and [11-20] directions of the crystal, and mark the outer circle of the crystal;

[0066] 3) Crystal cutting: Bond the crystal to the cutting base in a specific direction, use a multi-wire saw to set the cutting process parameters, and process the SiC crystal into cutting pieces;

[0067] 4) Cutting and taking out the slices: Use a heating platform to bake the cutting slices from the cutting base, take out and mark the carbon silicon surface of the head or tail slice of the cutting slice, and clean the cutting slice to remove the residual cutting fluid on the surface;

[0068] 5) Orientation of head and tail pieces: Orient the head and tail SiC cut pieces to verify the [1-100] and [11-20] directions of the marked head or tail pieces;

[0069] 6) Orientation of non-head and tail pieces: Overlap the non-head and tail pieces with the head piece and / or tail piece so that their cut marks overlap, and then orient along the off-axis direction of the wafer to determine the off-axis direction and polarity plane of the wafer;

[0070] 7) Carbon / silicon surface marking and crystal orientation marking: Use a marking machine to mark the determined crystal orientation and carbon / silicon surface;

[0071] 8) Substrate processing: The marked wafer is subjected to thinning, mechanical polishing, chemical mechanical polishing, cleaning, packaging and other process treatments to obtain a SiC substrate without positioning edges.

[0072] In step 1) of this embodiment, there is no strict requirement for the surface flatness of the SiC crystal that is subjected to external cylindrical grinding; specifically, the SiC crystal may be one that has not been ground after growth, in order to omit a step, reduce the probability of crystal cracking, and improve crystal processing efficiency.

[0073] In sub-step 1) of this embodiment, the SiC crystal subjected to external cylindrical grinding is an off-axis crystal, where the silicon surface or carbon surface of the crystal deviates from the c-axis along [11-20] or [1-100], with a deviation angle of 0.1 to 8°.

[0074] Since the maximum substrate off-angle used for epitaxy at present is generally 8°, the method of the embodiment of the present disclosure can only be applied to off-angle crystals, so the minimum off-angle is stipulated to be 0.1°.

[0075] In sub-step 2) of this embodiment, when determining the crystals [1-100] and [11-20], an orientation instrument is required to ensure the accuracy of orientation, and the accuracy is strictly required to be controlled within ±0.2°. The accuracy of this step determines the accuracy of the subsequent cutting piece orientation.

[0076] In sub-step 3) of this embodiment, when the crystal is bonded to the cutting base, the [1-100] and [11-20] directions are marked on the native surface of the crystal and / or the seed crystal surface.

[0077] In sub-step 3) of this embodiment, when the crystal is bonded to the cutting base, the [1-100] or [11-20] direction is bonded opposite the graphite base or on the left and right sides of the graphite base, in order to avoid the influence of the bonding between the crystal and the graphite on the crystal orientation mark.

[0078] In sub-step 3) of this embodiment, by adjusting the cutting machine's parameters such as feed speed, wire feed speed, mortar flow rate, and swing angle, the SiC cutting blade has obvious asymmetric roughness and knife marks along the feed direction. Specifically, by increasing the feed speed and / or reducing the wire feed speed and / or reducing the mortar flow rate and / or reducing the swing angle at 1 / 8 to 1 / 3 of the total cutting thickness, the roughness of some areas of the cutting blade is increased and the knife marks are obvious. The purpose is to easily identify the feed direction of the cutting blade without significantly affecting the quality of the cutting blade.

[0079] In sub-step 3) of this embodiment, when the SiC crystal is cut into a cutting piece with uneven knife mark distribution along the cutting direction, the characteristics of the existing cutting technology that the cutting point of the cutting piece is rougher than the cutting point and the knife mark is obvious can be fully utilized, and the SiC crystal is preferentially processed into a cutting piece with a rougher cutting point than the cutting point and heavy knife mark.

[0080] In sub-step 4) of this embodiment, when the cut piece is baked off the cutting base, the carbon surface and / or silicon surface of the wafer and the specific crystal orientation need to be clearly marked.

[0081] In sub-step 4) of this embodiment, the cutting fluid remaining on the cutting blade is ultrasonically cleaned with a solvent such as kerosene, and then the cutting blade is rinsed with ethanol, tap water, etc.

[0082] In sub-step 5) of this embodiment, an orienting instrument is used to orient the cut head and tail pieces, and the crystal orientation marked in step 4) is verified by utilizing the asymmetry of the off-axis crystal orientation, and the accuracy of the off-axis direction is controlled within 0.1°.

[0083] In sub-step 6) of this embodiment, the head piece / tail piece with a determined orientation is bonded together with the non-head and tail pieces according to the marks of the knife marks, and then the wafer is oriented using an orientation instrument. By using the asymmetry of the off-axial crystal orientation, the test surface is determined to be the carbon surface or the silicon surface, thereby determining the two directions of the cut piece.

[0084] In sub-step 7) of this embodiment, the marking machine may be a laser marking machine, an etching machine, etc.

[0085] In sub-step 7) of this embodiment, the carbon surface and / or the silicon surface of the substrate may be marked, or a specific direction of the substrate may be marked, and the marking content may be graphics, text or numbers.

[0086] In sub-step 7) of this embodiment, when the silicon surface of the substrate is the growth surface or the epitaxial surface, the mark is engraved on the carbon surface of the substrate; when the carbon surface of the substrate is the growth surface or the epitaxial surface, the mark is engraved on the silicon surface of the substrate. The purpose is to minimize the degradation of the substrate quality caused by the mark.

[0087] In sub-step 8) of this embodiment, the cutting blade may be thinned by using a double-sided grinder and / or a wheel grinder.

[0088] Except for special instructions, the existing technology is used in the technical scheme of this embodiment. In addition to being able to prepare axially oriented SiC substrates without positioning edges, this method can also be used to distinguish crystal directions or polar surfaces for other polar crystals (such as aluminum nitride, gallium nitride, and gallium arsenide).

[0089] Example 2

[0090] The purpose of this embodiment is to provide a method for processing and using a 4H-SiC substrate without a positioning edge, which specifically includes the following operating steps:

[0091] 1) Rolling: The grown silicon surface is subjected to external cylindrical grinding along the [11-20] direction with a 4° deflection from the axis, so that the outer diameter of the 4H-SiC crystal is processed to 150 mm;

[0092] 2) Orientation: Use an orienting instrument to orient the outer circle of the crystal, accurately determine the <1-100> and [11-20] directions of the crystal, and mark the crystal directions on the outer circle of the crystal with a marker pen, and mark the silicon surface and carbon surface on the seed crystal surface and native surface of the crystal respectively;

[0093] 3) Crystal cutting: The [11-20] direction of the crystal mark is vertically upward, and then the crystal is bonded to a graphite cutting base. The cutting process parameters are set using a multi-wire saw. The feed speed is increased to 10% of the original feed speed at 1 / 5 of the cutting thickness, and the SiC crystal is processed into a cutting piece with an asymmetric cut.

[0094] 4) Cutting disc removal: Use a heating platform to bake the cutting disc from the cutting base, take out and mark the carbon silicon surface of the head or tail of the cutting disc, and clean the cutting fluid remaining on the surface of the cutting disc with kerosene ultrasound, ethanol, tap water, etc.;

[0095] 5) Verification of the orientation of the head and tail pieces: Orient the head and tail pieces of the 4H-SiC cut pieces, verify the [1-100] and [11-20] directions of the marked cut pieces, and control the deviation angles of the [11-20] and [1-100] directions within 0.1°. Take the silicon surface of the cut head piece as an example. Figure 2 As shown, OA is the [11-20] direction. When the X-ray of the orientation instrument is incident on the wafer along AO, the diffraction angle is 21.8°.

[0096] 6) Orientation of non-head and tail pieces: Overlap the non-head and tail pieces with the head piece and / or tail piece so that their cut marks overlap. Then use an orientator to orient the non-head and tail pieces along the off-axis direction (i.e. Figure 3 If the X-ray is incident on the wafer along A'O, the diffraction angle is 21.8°, indicating that OA' is in the [11-20] direction, the oriented surface is the silicon surface, and OC is in the [1-100] direction; if the X-ray is incident on the wafer along A'O, the diffraction angle is 13.8°, indicating that OA' is in the [11-20] direction, the oriented surface of the wafer is the carbon surface, and OB is in the [1-100] direction.

[0097] 7) Carbon / silicon surface marking and crystal orientation marking: Use a laser marking machine to mark the edge of the silicon surface [1-100] direction of the substrate;

[0098] 8) Substrate processing: The marked wafer is processed by double-sided grinding, mechanical polishing, chemical mechanical polishing, cleaning, packaging and other processes to obtain a 6-inch 4H-SiC substrate without a positioning edge.

[0099] The substrate without positioning edge prepared by the above method is used as a seed crystal to grow a 6-inch 4H-SiC single crystal. Since there is no positioning edge in the substrate and the mark is on the silicon surface, and the single crystal growth adopts carbon surface growth, the obtained 6-inch SiC single crystal will not have incremental micropipes, voids, and obvious stress at the mark. The crystal achieves true zero micropipes, has high quality, and can be used for the preparation of high-voltage and high-power devices.

[0100] Example 3

[0101] A method for processing and using a 4H-SiC substrate without a positioning edge, specifically comprising the following operating steps:

[0102] 1) Rolling: The grown silicon surface is subjected to external cylindrical grinding along the [11-20] direction with an 8° axial deviation from the 4H-SiC crystal, so that the outer diameter of the SiC crystal is processed to 200 mm;

[0103] 2) Orientation: Use an orienting instrument to orient the outer circle of the crystal, accurately determine the [1-100] and [11-20] directions of the crystal, and mark the crystal directions on the outer circle of the crystal with a marker pen, and mark the silicon surface and carbon surface on the seed crystal surface and native surface of the crystal respectively;

[0104] 3) Crystal cutting: The [11-20] direction of the crystal mark is vertically upward, and then the crystal is bonded to the graphite cutting base. The cutting process parameters are set using a multi-wire saw. The mortar flow rate is reduced to 90% of the original mortar flow rate at 1 / 8 of the cutting thickness, and the SiC crystal is processed into a cutting piece with an asymmetric knife mark;

[0105] 4) Cutting disc removal: Use a heating platform to bake the cutting disc from the cutting base, take out and mark the carbon silicon surface of the head or tail of the cutting disc, and clean the cutting fluid remaining on the surface of the cutting disc with kerosene ultrasound, ethanol, tap water, etc.;

[0106] 5) Verification of the orientation of the head and tail pieces: Orient the head and tail pieces of the 4H-SiC cut pieces, verify the [1-100] and [11-20] directions of the marked cut pieces, and control the deviation angles of the [11-20] and [1-100] directions within 0.1°. Take the silicon surface of the cut head piece as an example. Figure 2 As shown, OA is the [11-20] direction. When the X-ray of the orientation instrument is incident on the wafer along AO, the diffraction angle is 25.8°.

[0107] 6) Orientation of non-head and tail pieces: Overlap the non-head and tail pieces with the head piece and / or tail piece so that their cut marks overlap. Then use an orientator to orient the non-head and tail pieces along the off-axis direction (i.e. Figure 3 If the X-ray is incident on the wafer along A'O, the diffraction angle is 25.8°, indicating that OA' is in the [11-20] direction, the oriented surface is the silicon surface, and OC is in the [1-100] direction; if the X-ray is incident on the wafer along A'O, the diffraction angle is 9.8°, indicating that OA' is in the [11-20] direction, the oriented surface of the wafer is the carbon surface, and OB is in the [1-100] direction.

[0108] 7) Carbon / silicon surface marking and crystal orientation marking: Use a laser marking machine to mark the carbon surface [11-20] direction of the substrate;

[0109] 8) Substrate processing: The marked wafer is subjected to thinning, mechanical polishing, chemical mechanical polishing, cleaning, packaging and other process treatments to obtain an 8-inch 4H-SiC substrate without a positioning edge.

[0110] The substrate without positioning edges prepared by the above method is used as a substrate for homoepitaxial growth to grow an 8-inch 4H-SiC epitaxial wafer. Since there is no positioning edge in the substrate and the mark is on the carbon surface, and the epitaxial wafer is grown on the silicon surface, the obtained 8-inch 4H-SiC epitaxial wafer has no value-added micropipes, voids, and obvious stress at the mark. The epitaxial wafer has a regular morphology within an area of ​​8 inches, without polymorphic wrapping, triangular defects, etc., and can be used for the preparation of high-reliability, high-voltage, and high-power power electronic devices. In addition, since there is no positioning edge or notch in the substrate, the utilization area of ​​the substrate is greatly improved, which reduces the preparation cost of related devices to a certain extent.

[0111] Example 4

[0112] A method for processing and using a 6H-SiC substrate without a positioning edge, specifically comprising the following operating steps:

[0113] 1) Rolling: The grown silicon surface is subjected to cylindrical grinding with an axial angle of 0.1° along the [1-100] direction on the 6H-SiC crystal, so that the outer diameter of the 6H-SiC crystal is processed to 50.8 mm;

[0114] 2) Orientation: Use an orienting instrument to orient the outer circle of the crystal, accurately determine the [1-100] and [11-20] directions of the crystal, and mark the crystal directions on the outer circle of the crystal with a marker pen, and mark the silicon surface and carbon surface on the seed crystal surface and native surface of the crystal respectively;

[0115] 3) Crystal cutting: The [1-100] direction of the crystal mark is vertically upward, and then the crystal is bonded to a graphite cutting base. The cutting process parameters are set using a multi-wire saw, and the wire feed speed is reduced to 80% of the original wire feed speed at 1 / 3 of the cutting thickness, and the 6H-SiC crystal is processed into a cutting piece with an asymmetric knife mark;

[0116] 4) Cutting disc removal: Use a heating platform to bake the cutting disc from the cutting base, take out and mark the carbon silicon surface of the head or tail of the cutting disc, and clean the cutting fluid remaining on the surface of the cutting disc with kerosene ultrasound, ethanol, tap water, etc.;

[0117] 5) Verification of the orientation of the head and tail pieces: Orient the head and tail cut pieces of 6H-SiC, verify the [1-100] and [11-20] directions of the marked cut pieces, and control the deviation angles of the [11-20] and [1-100] directions within 0.1°. Take the carbon surface of the cut tail piece as an example. Figure 2 As shown, OA is the [1-100] direction. When the X-ray of the orientation instrument is incident on the wafer along AO, the diffraction angle is 17.9°.

[0118] 6) Orientation of non-head and tail pieces: Overlap the non-head and tail pieces with the head piece and / or tail piece so that their cut marks overlap. Then use an orientator to orient the non-head and tail pieces along the off-axis direction (i.e. Figure 3 If the X-ray enters the wafer along A'O, the diffraction angle is 17.9°, indicating that OA' is in the [1-100] direction, the oriented surface is the carbon surface, and OC is in the [11-20] direction; if the X-ray enters the wafer along A'O, the diffraction angle is 17.7°, indicating that OA' is in the [1-100] direction, the oriented surface of the wafer is the silicon surface, and OB is in the [11-20] direction;

[0119] 7) Carbon / silicon surface marking and crystal orientation marking: Use an etching machine to mark the carbon surface with a certain crystal orientation;

[0120] 8) Substrate processing: The marked wafer is subjected to wheel grinding, thinning, mechanical polishing, chemical mechanical polishing, cleaning, packaging and other process treatments to obtain a 2-inch 6H-SiC substrate without a positioning edge.

[0121] The substrate without positioning edges prepared by the above method is used as a seed crystal to grow a 2-inch 6H-SiC single crystal. Since there is no positioning edge in the substrate and the mark is on the carbon surface, and the 6H-SiC single crystal is grown on the silicon surface, the obtained 2-inch 6H-SiC single crystal has no micropipes, voids, and obvious stress at the mark. The crystal achieves true zero micropipes, has high quality, and can be used for the preparation of high-voltage and high-power devices.

[0122] Comparative Example 1

[0123] Different from Example 2, the crystal is first surface ground, and then the grown silicon surface is cylindrically ground along the [11-20] direction with an axial angle of 4° to the 4H-SiC crystal, so that the outer diameter of the 4H-SiC crystal is processed to 150 mm, and then the end face of the crystal is oriented [11-20] and [1-100], and two positioning edges are ground on the end face of the crystal according to the existing processing technology in the field, and then the crystal is cut, ground and polished, and the carbon surface of the substrate is marked, and finally the substrate is cleaned and packaged to obtain a 6-inch SiC substrate with two positioning edges.

[0124] The substrate without positioning edges prepared by the above method was used as a seed crystal to grow a 6-inch 4H-SiC single crystal. Due to the presence of two positioning edges in the substrate, the seed crystal is not a complete circle. Therefore, during the growth of the single crystal, the single crystal grown near the positioning edges will produce micropipe proliferation and obvious stress concentration stripes. At the same time, since the carbon surface of the SiC substrate is marked, and the 4H-SiC single crystal growth adopts carbon surface growth, defects such as voids and micropipes will be generated in the growing crystal at the marked position. Therefore, the 6-inch SiC single crystal obtained by growing the substrate has problems such as micropipe proliferation, void proliferation, and stress concentration, which seriously deteriorates the quality of the crystal. High-voltage and high-power devices prepared using this substrate have problems such as high-voltage breakdown and poor device reliability.

[0125] Comparative Example 2

[0126] Different from Example 3, the crystal is first surface ground, and then the grown silicon surface is cylindrically ground along the [11-20] direction with an axial angle of 4° to the 4H-SiC crystal, so that the outer diameter of the SiC crystal is processed to 150 mm, and then the end faces of the crystal are oriented [11-20] and [1-100], and according to the existing processing technology in the field, two positioning edges are ground on the end faces of the crystal or a notch is performed. Finally, the crystal is cut, ground and polished, and the carbon surface of the substrate is marked. The substrate is then cleaned and packaged to obtain an 8-inch 4H-SiC substrate with two positioning edges or notches.

[0127] The 8-inch SiC substrate prepared by the above method is used as a substrate for homoepitaxial growth to grow an 8-inch 4H-SiC epitaxial wafer. Due to the presence of two non-positioning edges or notches in the substrate, the morphology of the obtained 8-inch SiC epitaxial wafer near the positioning edges or notches is poor, and even triangular defects appear, and the overall quality of the epitaxial wafer is not high. In addition, in the subsequent device preparation process, due to the presence of positioning edges or notches on the substrate, the available area of ​​the substrate is reduced, which leads to poor device reliability and high cost.

[0128] Although the above describes the specific implementation mode of the present invention in conjunction with the accompanying drawings, it is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art on the basis of the technical solution of the present invention without creative work are still within the scope of protection of the present invention.

Claims

1. A method for processing a SiC substrate without a positioning edge, characterized in that: include: Rolling: The grown SiC crystal is subjected to external cylindrical grinding to make the outer diameter of the SiC crystal reach the target size; Orientation: Orient the outer circle of the SiC crystal, determine the [1-100] and [11-20] directions of the SiC crystal, and mark the outer circle of the SiC crystal; Crystal cutting: Bond the SiC crystal to the cutting base in the set direction and process the SiC crystal into cutting pieces; Cutting and taking out the slices: bake the cutting slices from the cutting base, take out and mark the carbon silicon surface of the head or tail slice of the cutting slice, and clean the cutting slice to remove the cutting fluid remaining on the surface; Head and tail piece orientation: Orient the head and tail cut pieces of SiC crystals to verify the [1-100] and [11-20] directions of the marked head or tail cut pieces; Orientation of non-head and tail pieces: overlap the non-head and tail pieces with the head piece and / or tail piece so that their cut marks overlap, and then orient them along the off-axis direction of the wafer to determine the off-axis direction and polarity plane of the wafer; Carbon / silicon surface marking and crystal orientation marking: marking the determined crystal orientation and carbon / silicon surface; Substrate processing: The marked wafer is subjected to subsequent process processing to obtain a SiC substrate without positioning edges.

2. A method for processing a SiC substrate without a positioning edge as claimed in claim 1, characterized in that: The SiC crystal subjected to external cylindrical grinding is a SiC crystal that has not been subjected to surface grinding or a SiC crystal that has been subjected to surface grinding.

3. A method for processing a SiC substrate without a positioning edge as claimed in claim 1, characterized in that: The SiC crystal for external cylindrical grinding is an off-axis crystal, in which the silicon surface or carbon surface of the crystal deviates from the c-axis along [11-20] or [1-100], and the deviation angle is 0.1 to 8°.

4. A method for processing a SiC substrate without a positioning edge as claimed in claim 1, characterized in that: The crystal [1-100] and [11-20] were determined using an orientation meter, with the accuracy controlled within ±0.2°.

5. A method for processing a SiC substrate without a positioning edge as claimed in claim 1, characterized in that: When bonding the crystal to the cutting mount, mark the [1-100] and [11-20] directions on the native face of the crystal and / or the seed face.

6. A method for processing a SiC substrate without a positioning edge as claimed in claim 1, characterized in that: When bonding the crystal to the cut mount, bond the [1-100] or [11-20] orientation opposite the graphite mount.

7. A method for processing a SiC substrate without a positioning edge as claimed in claim 1, characterized in that: By adjusting the cutting machine's feed speed, wire feed speed, slurry flow rate, and swing angle parameters, the SiC cutting blade is made to have asymmetric roughness and cutter marks along the cutting direction.

8. A method for processing a SiC substrate without a positioning edge as claimed in claim 1, characterized in that: By increasing the feed speed at 1 / 8 to 1 / 3 of the total cutting thickness, and / or reducing the wire feed speed, and / or reducing the mortar flow, and / or reducing the swing angle, the roughness of some areas of the cutting blade is increased and the knife marks are obvious. While the feed direction of the cutting blade is easy to identify, the quality of the cutting blade is not significantly affected.

9. A method for processing a SiC substrate without a positioning edge as claimed in claim 1, characterized in that: When cutting a SiC crystal into a cutting piece with uneven knife mark distribution along the cutting direction, it is preferred to process the SiC crystal into a cutting piece with a rougher exit point than the cutting point and heavier knife marks.

10. A method for processing a SiC substrate without a positioning edge as claimed in claim 1, characterized in that: When the cut pieces are baked out of the cutting base, the carbon side and / or silicon side of the wafer and the specific crystal orientation are clearly marked.

11. A method for processing a SiC substrate without a positioning edge as claimed in claim 1, characterized in that: The residual cutting fluid on the cutting disc was cleaned by ultrasonic cleaning with kerosene solvent, and then the cutting disc was rinsed with ethanol and tap water.

12. A method for processing a SiC substrate without a positioning edge as claimed in claim 1, characterized in that: An orienting instrument is used to orient the cutting head and tail pieces. By taking advantage of the asymmetry of the off-axis crystal orientation, the crystal direction is marked and the accuracy of the off-axis direction is controlled within 0.1°.

13. A method for processing a SiC substrate without a positioning edge as claimed in claim 1, characterized in that: The head / tail pieces with determined orientation are bonded together with the non-head / tail pieces according to the marks of the knife. Then the wafer is oriented using an orientation instrument. With the help of the asymmetry of the off-axial crystal orientation, the test surface is determined to be the carbon surface or the silicon surface, thereby determining the two directions of the cut piece.

14. A method for processing a SiC substrate without a positioning edge as claimed in claim 1, characterized in that: The marking machine is a laser marking machine or an etching machine.

15. The method for processing a SiC substrate without a positioning edge according to claim 1, characterized in that: The carbon surface and / or silicon surface of the substrate is marked, or a specific direction of the substrate is marked, and the marking content is graphics, text or numbers.

16. A method for processing a SiC substrate without a positioning edge as claimed in claim 1, characterized in that: When the silicon surface of the substrate is the growth surface or the epitaxial surface, the mark is engraved on the carbon surface of the substrate.

17. A method for processing a SiC substrate without a positioning edge as claimed in claim 1, characterized in that: When the carbon surface of the substrate is the growth surface or epitaxial surface, the mark is engraved on the silicon surface of the substrate.

18. The method for processing a SiC substrate without a positioning edge according to claim 1, characterized in that: Use double-sided grinders and wheel grinders to thin the cutting discs.

19. A method for processing a SiC substrate without a positioning edge as claimed in claim 1, characterized in that: The method can process SiC substrate sheets larger than 2 inches.

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