Inch-level single crystal diamond wafer and closed-loop batch production method and application thereof

Abstract

The disclosure belongs to the technical field of diamond material preparation, and provides an inch-level single crystal diamond wafer and a closed-loop batch preparation method and application thereof. The preparation method is to splice a plurality of seed crystals to form a substrate, and then perform two-stage differential methane concentration MPCVD gradient crystal growth; the blank is subjected to laser edge cutting, chemical etching and plasma composite impurity removal treatment; after secondary thickening, the blank is subjected to laser dicing to obtain a standardized seed crystal for recycling. The inch-level single crystal diamond wafer prepared according to the above method and the application of the wafer in a semiconductor substrate, a power device heat dissipation substrate or an infrared window are also disclosed. The process of the disclosure effectively reduces the interface stress and carbon impurity pollution, and the finished crystal has high integrity, and can stably batch prepare a large-size single crystal diamond wafer.

Description

Technical Field

[0001] This disclosure relates to the field of diamond material preparation technology, and in particular to an inch-scale single-crystal diamond wafer and its closed-loop batch preparation method and application. Background Technology

[0002] Single-crystal diamond possesses ultra-high thermal conductivity, ultra-wide optical transmission band, excellent carrier mobility, and stable chemical inertness, making it a core material for high-power microwave electronic devices, infrared optical windows, third-generation semiconductor heat dissipation substrates, and quantum computing substrates. Industrial applications have a rigid demand for single-crystal diamond wafers of 2 inches and above with uniform crystal quality throughout. Currently, the mainstream single-crystal diamond fabrication routes are high-temperature high-pressure (HPHT) and microwave plasma chemical vapor deposition (MPCVD) homoepitaxial growth. However, the maximum seed crystal size for both processes generally does not exceed 10mm × 10mm, making direct epitaxy difficult to break through the inch-scale size bottleneck. Mosaic splicing growth has become the core technical path to overcome size limitations. The splicing process uses multiple small-sized single-crystal seed crystals to form a densely packed substrate, and then performs lateral epitaxy via MPCVD to heal the seed crystal seams, which can produce large-area diamond blanks. However, current splicing schemes generally suffer from key defects such as edge tip discharge, thermal stress concentration, edge polycrystalline parasitics, poor wafer thickness uniformity, and inability to mass-produce seed crystals, which seriously restrict the stable mass production of 2-inch high-quality single-crystal diamond wafers.

[0003] Current splicing technologies mostly optimize from a single dimension, such as seed crystal pretreatment, segmented growth, and crystal orientation matching. This makes it difficult to simultaneously address the synergistic challenges of edge plasma effects, stress distribution, thickness uniformity, and cyclic replication production. Representative related technologies exhibit significant limitations: One technology discloses a modified chamfered single-crystal diamond splicing growth process. The entire process completes a three-end continuous growth flow within the same MPCVD cavity, sequentially performing seed crystal diameter reduction and chamfering, lateral diameter expansion splicing, and thick-layer homogeneous epitaxy. By distributing and controlling the oxygen, nitrogen, and methane ratios within the cavity, the growth rate of different diamond crystal orientations is adjusted, thereby successively reducing lattice defects at the splicing seams caused by the seed crystal edges. This process completes all growth steps in a low-power microwave cavity, limiting the plasma's effective range and adapting to smaller sample sizes. The entire process can only complete a single spliced ​​blank formation, lacking subsequent shaping and slab preparation processes. The final product size limit, thickness uniformity, and continuous production capacity all have significant shortcomings. Another technology proposes a seed crystal cloning + step flow directional splicing scheme. This scheme first involves multiple epitaxial peelings of a single standard template seed crystal to obtain multiple cloned seed crystals with uniform crystal orientation. After grinding and polishing to control the height difference between the seed crystals, they are spliced ​​according to a unified direction of surface step flow, reducing the lattice mismatch at the splicing interface and allowing the epitaxial layer at the joint to smoothly heal. However, this scheme relies solely on a single MPCVD epitaxy to achieve thickness increase, and does not perform secondary shaping of the blank contour after splicing. When preparing large blanks approaching 2 inches in size, the growth stability is insufficient, and the thickness of the entire wafer fluctuates greatly, making it difficult to meet the dimensional accuracy standards required for high-end device applications.

[0004] In addition, other splicing solutions in the industry generally suffer from common technical pain points: First, the substrate geometry has defects. The sharp edges of the square seed crystal splicing assembly are prone to tip discharge in the MPCVD plasma environment, causing local overheating, carbon particle deposition, and parasitic growth of polycrystalline edges. Although circular cutting can weaken the sharp edges to some extent, the heat-affected zone at the cutting edge is wide and the microcrack density is high. Second, there is insufficient stress control. The curvature abrupt change at the boundary of the splicing blank is prone to residual thermal stress concentration, and microcracks or even overall breakage frequently occur in the crystal during the growth and cooling stages. Third, the wafer thickness is inconsistent. The plasma density and temperature field of different regions of the substrate are different, and the growth rate of each region is significantly differentiated, resulting in large fluctuations in wafer thickness, which will greatly reduce the processing yield of subsequent devices. Fourth, there is a lack of supporting processes for large-scale mass production. The current technology can only prepare a single splicing blank in one go and cannot produce multiple standardized seed crystals from the finished wafer. It is difficult to build a sustainable and cyclical seed crystal preparation chain and cannot meet the industry demand for stable mass production of 2-inch single-crystal diamond wafers. Summary of the Invention

[0005] This disclosure provides an inch-scale single-crystal diamond wafer and its closed-loop batch preparation method and application, in order to at least solve the above-mentioned technical problems existing in the prior art.

[0006] According to a first aspect of this disclosure, a closed-loop batch fabrication method for inch-scale single-crystal diamond wafers is provided, comprising the following steps: Several single-crystal diamond seed crystals are arranged to form a spliced ​​substrate; The spliced ​​substrate is subjected to microwave plasma chemical vapor deposition (MPCVD) to perform homogeneous epitaxial growth until the seed crystals are laterally connected to form a spliced ​​whole; wherein the microwave power during growth is 50~75kW and the volume concentration of methane is 3%~5%; The assembled whole is cut with a laser to obtain circular, regular octagonal or rounded polygonal inch-sized sheets; the damaged layer in the thickness direction of the inch-sized sheets is first removed, and then the surface is leveled and impurities are removed. MPCVD equipment is used to thicken and grow the planarized and impurity-removed sheet to obtain a regrown wafer. The microwave power during growth is 50~75kW, and the volume concentration of methane is 2%~4%, which is lower than the volume concentration of methane in homoepitaxial growth. The edges of the regenerated wafer are trimmed to obtain an inch-sized single-crystal diamond wafer; the inch-sized single-crystal diamond wafer is then sliced ​​to obtain standardized seed crystals for use in the next round of splicing.

[0007] Specifically, this disclosure adopts a set of coupling processes including high-power MPCVD two-stage gradient methane epitaxy, first cutting and shaping and then secondary thickening, and seed crystal closed-loop recycling, combined with laser shaping process without right angles and sharp corners, to simultaneously achieve large-size seamless splicing, low edge defects, and cyclic mass production of inch-level single crystal diamond wafers. (1) Two independent MPCVD growths are performed, and the equipment uniformly adopts 50~75kW high-power MPCVD, which is different from the existing 3~10kW low-power equipment; high power can form a uniform plasma and temperature field on the surface of large-size splicing substrates, solving the problem of uneven temperature field and joint growth discontinuity in the splicing area of ​​large-area seed crystals; the first round (i.e. homogeneous epitaxial growth) has a high methane concentration of 3%~5%, which prioritizes the carbon source supply rate, quickly fills the seed crystal gaps, and makes multiple seed crystals laterally fuse to form a continuous whole, achieving complete healing of the joints; the secondary thickening adopts a lower methane concentration of 2%~4%, the carbon source deposition rate is slow, and the whole sheet is synchronously and uniformly thickened, greatly reducing the thickness deviation of the entire wafer. The existing splicing process only grows with a fixed methane concentration in a single step, resulting in either poor joint healing or uneven overall thickness. The gradient carbon source process disclosed in this invention solves the two major contradictions of joint defects and thickness uniformity. (2) The traditional process is to grow a thick layer first and then polish and cut the whole thing. The present invention first laser cuts the spliced ​​blank into a circular, regular octagonal or rounded polygonal shape without right angles or sharp corners, eliminating the plasma tip discharge effect caused by square right angles from the root and reducing the parasitic growth of polycrystalline material at the edge. In addition, laser cutting will produce a graphite damage layer and microcracks on the diamond surface. The present invention thoroughly removes cutting damage, impurities and surface undulations before secondary thickening, avoiding the extension and diffusion of defects in the secondary growth stage, and greatly improving the integrity and optical uniformity of the final wafer crystal. (3) Conventional splicing blanks are mostly square right-angled structures. The electric field at the right-angle vertex is highly concentrated, and local discharge is very easy to occur during MPCVD growth. A large number of polycrystalline materials are generated at the edge, and the effective single crystal area of ​​the wafer is low. The cutting contour of this disclosure is limited to three types of non-90° right-angled structures: circle, regular octagon, and rounded polygon. The circle has no vertex, the regular octagon has an obtuse 135° interior angle, and the rounded polygon has a rounded transition at the vertex. All three can significantly weaken the peak value of the edge electric field, suppress the generation of polycrystalline materials at the edge, and increase the effective single crystal area of ​​the finished wafer. (4) After the secondary thickening is completed, the edge of the regrowth wafer is trimmed to remove a small number of polycrystalline defect areas at the edge, and qualified inch-level single crystal diamond finished wafers are obtained. A slicing process is added to slice the finished wafers to prepare standardized seed crystals, which are directly returned to the seed crystal splicing step for the next round of splicing substrate arrangement. Existing technologies rely on purchased, one-time raw materials for splicing seed crystals, which cannot be recycled and produced in-house. This results in high raw material costs and production capacity limited by purchased seed crystals. This disclosure constructs a closed-loop production chain that includes preparing finished wafers, slicing finished wafers to form seed crystals, and splicing seed crystals in a new round. This significantly reduces raw material procurement costs and increases the capacity for large-scale continuous production.

[0008] In one embodiment, the inch-scale single-crystal diamond wafer is a single-crystal diamond wafer of 2 inches or larger.

[0009] In one embodiment, the single-crystal diamond seed crystal is obtained by either high-temperature high-pressure method (HPHT) or chemical vapor deposition (CVD); the number of seed crystals is selected according to the size of the seed crystals, and the shape of the seed crystals is mainly square, but not limited to other shapes, such as hexagonal, octagonal, rectangular, circular, etc.

[0010] In one embodiment, the single-crystal diamond seed crystal is selected from single-crystal diamond seed crystals with any one of the orientations of (100), (111), and (110).

[0011] In a preferred embodiment, the single-crystal diamond seed is selected from (100) oriented single-crystal diamond seeds.

[0012] Specifically, MPCVD homoepitaxial growth has a uniform growth rate on the (100) crystal plane, high lattice matching at the seam, and no large number of dislocations or twin defects at the seam; while (111) orientation growth is prone to pyramidal morphology, and polycrystalline impurities are easily generated at the seam interface; (110) orientation has higher stress, and large-size seams are prone to cracking. Therefore, (100) oriented single-crystal diamond seed crystals are preferred.

[0013] In one embodiment, the single-crystal diamond seed crystal has a side length or diameter of 5-15 mm and a thickness of 0.2-0.5 mm.

[0014] Specifically, if the side length or diameter is less than 5mm, the seed crystal size is too small, the number of splices increases significantly, the total length of the seams rises sharply, the seam defects and interface polycrystalline structures increase, the uniformity of the entire wafer deteriorates, and the efficiency of subsequent wafer splitting is low. If the side length or diameter is greater than 15mm, the growth of a single seed crystal becomes more difficult, and the cost of preparing seed crystals by HPHT / CVD is high and there are more internal defects. If the area of ​​a single seed crystal is too large, the uneven temperature field and plasma field in the MPCVD cavity will cause seed crystal thickness differences, resulting in warping of the entire wafer after splicing. The 5~15mm range is the optimal window for mass production, balancing the total number of splicing seams, seed crystal preparation cost, and uniform temperature field in the cavity.

[0015] If the seed crystal is less than 0.2mm thick, it is too thin and easily deforms and warps during high-temperature growth. The height difference between adjacent seed crystals becomes uncontrollable, and the growth bridging at the joint breaks. It is also prone to breakage during clamping and transportation. If the seed crystal is greater than 0.5mm thick, the heat conduction is too slow, the temperature difference between the surface and the bottom layer is large, the thermal stress is increased, and cracks are easily generated at the splicing interface. At the same time, the cost of consumables increases, the weight increase and the growth cycle is significantly lengthened, and the production efficiency decreases. A thickness of 0.2~0.5mm has moderate rigidity, balanced thermal conductivity, and controllable deformation at high temperatures.

[0016] In one embodiment, the gap between adjacent single-crystal diamond seed crystals is ≤0.1mm, the absolute value of the height difference is ≤25μm, and the absolute value of the misalignment angle is ≤5°; the surface roughness Ra of the single-crystal diamond seed crystal is ≤5nm.

[0017] Specifically, if the gap is >0.1mm, the first round of methane epitaxy cannot completely fill the gap, leaving residual holes and polycrystalline layers at the joint, increasing the Raman full width at half maximum (FWHM) of the finished wafer interface, and degrading thermal conductivity and optical performance; if the gap is too wide, vertical grooves will form, and subsequent thickening growth will produce longitudinal stress cracks; however, by keeping the gap ≤0.1mm, it is ensured that the high-concentration methane lateral epitaxy can completely close the joint, forming a continuous single-crystal transition interface without obvious interface defects.

[0018] When the height difference of the seed crystal is large, the plasma electric field is distorted at the step, the higher part grows rapidly and the lower part grows slowly, resulting in severe surface unevenness after splicing, large loss of subsequent laser damage layer removal, and local thickness non-uniformity exceeding the standard. When the absolute value of the height difference is controlled within 25μm, the growth rate of the entire substrate is synchronized, the overall flatness of the splice is excellent, the amount of removal in the subsequent leveling process is greatly reduced, and the material utilization rate is improved.

[0019] If the seed crystal misalignment angle is too large, there will be an angle between the lattice orientations of the two seed crystals, resulting in a large number of mismatched dislocations at the splicing interface. This leads to polycrystalline interface, an increase in scattering centers, a decrease in infrared transmittance, and an increase in thermal resistance. If the absolute value of the misalignment angle is ≤5°, the degree of lattice mismatch is low, and homoepitaxial growth can achieve a low-defect continuous transition, ensuring the uniformity of the entire wafer crystal.

[0020] If the surface roughness is too high, there are a large number of microsteps, damage layers, and graphite residues on the surface. In the early stage of epitaxy, it is easy to spontaneously nucleate and form polycrystalline points, extending inward from the seed crystal surface defects. Ra≤5nm, mirror polished surface, uniform nucleation, epitaxy only along the original single crystal lattice, no impurities or point defects, ensuring the purity of single crystal in the splicing area.

[0021] In one embodiment, a plurality of single-crystal diamond seed crystals are arranged side-by-side to form the splicing substrate, wherein the effective area of ​​the splicing substrate is greater than or equal to the area of ​​the target inch-sized single-crystal diamond wafer.

[0022] Specifically, the outer contour of the splicing substrate can be any closely packed shape such as square, rectangular, or approximately octagonal, without any specific limitation here.

[0023] The effective area of ​​the splicing substrate is greater than or equal to the area of ​​the target inch-sized single crystal diamond wafer. Its function is: (1) to reserve defect removal margin: during high-power microwave plasma growth, polycrystalline growth, discharge burns and stress cracks are easy to occur at the edge of the substrate. A larger splicing substrate can completely remove the edge defect layer through subsequent laser cutting to ensure that the finished wafer is a high-quality single crystal throughout; (2) to compensate for lateral epitaxial expansion: during the homogeneous epitaxy of diamond, the blank will be widened laterally around the substrate. The reserved size margin of the substrate can offset the size loss caused by the epitaxial expansion, ensuring that the standard inch-sized wafer can be processed in the end; (3) to adapt to laser shaping process: sufficient edge margin makes it easy for the laser to complete the removal of the damage layer, leveling, and rounding / octagonal contour processing, reducing the problem of missing edges and scrapping of the whole piece due to insufficient blank size.

[0024] In one possible implementation, the frequency of the MPCVD device is 915MHz or 2450MHz.

[0025] In one embodiment, during homoepitaxial growth, hydrogen and oxygen are also introduced, with a hydrogen flow rate of 2500~3500 sccm, an oxygen flow rate of 10~30 sccm, and a methane flow rate of 100~150 sccm; the chamber pressure during growth is 15~22 kPa, and the substrate temperature is 980~1100℃.

[0026] In one embodiment, nitrogen gas is also introduced during homoepitaxial growth, with a flow rate of 10-30 sccm.

[0027] In one embodiment, the thickness of the homoepitaxial growth is 0.3~2 mm.

[0028] Specifically, if the growth thickness is less than 0.3 mm, only a thin carbon layer overlaps between the seed crystals, resulting in lattice mismatch and incomplete filling of tiny gaps at the seams, leaving numerous dislocations and micropores at the interface. During subsequent secondary thickening, these gaps continue to extend and expand, deteriorating the Raman full width at half maximum (FWHM) of the finished wafer interface and significantly reducing optical / thermal performance. 0.3 mm is the minimum critical thickness for achieving continuous homogeneous epitaxy of the seed crystals in the lateral direction, allowing the diamond lattice on the surfaces of adjacent seed crystals to be fully connected, eliminating microscopic gaps. If a splicing layer thicker than 2 mm is grown, the interfacial stress caused by the splicing of multiple seed crystals will continue to accumulate. The superposition of high-temperature growth and cooling temperature differences makes the thick billet prone to cracking and edge chipping at the seams, leading to a precipitous drop in yield. The MPCVD equipment disclosed in this invention is a high-power MPCVD equipment with a large splicing substrate. When the billet thickness exceeds 2 mm, the overall height of the substrate increases, the plasma sheath layer distribution becomes disordered, the edge electric field is distorted, and premature tip discharge and a large number of polycrystalline parasites at the edges occur, negating the advantages of the low-edge shaping disclosed in this invention. The 0.3~2mm range can completely weld all seed crystal seams to form a seamless and continuous whole, while controlling internal stress and plasma distortion within a safe threshold, thus balancing crystal quality, finished product yield and mass production cost.

[0029] In one embodiment, the rounded polygon refers to a sheet-like outline where all sharp vertices of a polygon are replaced with smooth, rounded transitions, including various structures such as rounded rectangles, rounded hexagons, and rounded dodecagons; a circle can be understood as a special rounded polygon with an infinite number of sides; a regular octagon has interior angles of 135° and no 90° right angles. Circles, regular octagons, and various rounded polygons all lack sharp right angles, effectively eliminating edge-point discharge effects during MPCVD growth, reducing thermal stress concentration at wafer edges, and suppressing parasitic polycrystalline growth at the edges.

[0030] Specifically, the regular octagonal inch-sized sheet has a centrally symmetrical structure, with the eight sides arranged in two alternating groups. Four of the sides are of equal length, and the remaining four sides are arranged symmetrically with equal length or with slight processing deviations. The diameter of the circumcircle of the vertex of the regular octagonal sheet is 45~47mm.

[0031] Specifically, the diameter of the circular, inch-sized sheet is ≥2 inches.

[0032] In one embodiment, the inch-sized sheet is first subjected to laser edge trimming to remove the damaged layer in the thickness direction along the edge of the inch-sized sheet; then, the surface of the inch-sized sheet is leveled and impurities are removed by laser to make the surface roughness Ra≤1μm and the absolute value of the thickness deviation≤10μm; then, the graphite and impurity layers on the surface of the inch-sized sheet are removed by chemical etching.

[0033] Specifically, the removal depth of the damaged layer is greater than the thickness of the inch-sized sheet.

[0034] The reason for limiting the removal depth of the damaged layer to greater than the thickness of the inch-scale sheet is that the graphitized damaged layer and microcracks generated by laser cutting are distributed vertically along the thickness direction of the sample, and removing only the surface layer cannot eliminate the hidden defects at the bottom edge. By using ultra-thickness cutting, the damaged area containing graphite and microcracks on the top, sides, and bottom of the sheet can be completely peeled off, completely eliminating the heterogeneous nucleation sites and stress defects at the edges, suppressing the parasitic growth of polycrystalline materials at the edges and thermal stress cracking during the secondary growth process of MPCVD, and at the same time weakening the plasma tip discharge effect, ensuring the uniformity of the thickness of the entire wafer and the crystal quality.

[0035] Specifically, controlling the surface roughness Ra ≤ 1 μm and the absolute value of the thickness deviation ≤ 10 μm of the sheet can, on the one hand, eliminate surface microsteps and pits caused by laser processing, balance the distribution of microwave plasma electric field, suppress parasitic nucleation of graphite and polycrystalline diamond during secondary epitaxy, and improve the crystal quality of single crystal epitaxial layer; on the other hand, it can unify the overall heat dissipation conditions of the substrate, so that the growth rate of the entire area during the thickening growth stage tends to be consistent, and finally obtain a high-quality wafer with low thickness non-uniformity; at the same time, the smooth surface can release residual stress from processing, avoid wafer cracking during high-temperature growth, and facilitate the thorough removal of graphite impurities by subsequent chemical etching.

[0036] Specifically, the conditions for chemical etching include: the etching solution is an acid solution of nitric acid and hydrofluoric acid mixed in a volume ratio of 3:1, the etching temperature is 60~80℃, and the etching time is 10~30min.

[0037] In one embodiment, the lasers used for cutting the spliced ​​whole, trimming the inch-sized sheet, and leveling and removing impurities from the surface of the inch-sized sheet are all pulsed lasers with a wavelength of 520~540nm; the laser processing parameters include: pulse frequency of 40~60kHz, power of 10~20W, and scanning speed of 5~30mm / s; when cutting the spliced ​​whole, the width of the heat-affected zone is ≤5μm.

[0038] Specifically, the width of the heat-affected zone mentioned above refers to the maximum radial thickness of the lattice damage and graphitized metamorphic layer caused by high temperature at the cut edge after laser cutting. This disclosure controls it to within 5μm, significantly reducing microcracks and graphite impurities in the cut, and reducing edge polycrystalline and splicing gap defects during subsequent epitaxial growth.

[0039] In one embodiment, after the chemical etching, a plasma cleaning step is further included, comprising: adjusting the power of the plasma equipment to 20-30kW etching condition, and treating it in a hydrogen-oxygen mixed plasma atmosphere for 5-30 minutes; the volume ratio of hydrogen to oxygen is 20-100:1, the flow rate of hydrogen is 1000-2000 sccm, the flow rate of oxygen is 2-10 sccm, and the pressure of the cavity is 5-10 kPa.

[0040] Specifically, plasma cleaning is used to remove surface carbon and graphitized contaminants introduced during cutting and finishing processes.

[0041] In one embodiment, during the thickening growth, hydrogen and oxygen are also introduced, with a hydrogen flow rate of 2500~3500 sccm, an oxygen flow rate of 10~30 sccm, and a methane flow rate of 80~130 sccm; the chamber pressure during growth is 15~22 kPa, and the substrate temperature is maintained at 980~1100°C.

[0042] In one embodiment, nitrogen gas is also introduced during the thickening growth process, with a flow rate of 10-30 sccm.

[0043] In one embodiment, the thickness of the thickened growth is 0.5~5mm.

[0044] Specifically, for thickening growth with a thickness less than 0.5mm, the total thickness of the finished wafer is insufficient, failing to meet the mechanical strength requirements of the heat dissipation substrate and optical window. The thin wafer is prone to warping and breakage during processing. It cannot completely cover the surface micro-damage and micro-grooves remaining from laser processing, and internal defects will be retained in the final wafer, resulting in deterioration of Raman full width at half maximum (FWHM) and excessive polycrystalline edge ratio. The stress at the splicing interface cannot be fully released, and subsequent wafer thinning and cutting are prone to cracking along the seed crystal splicing seam. For thickening growth with a thickness greater than 5mm, the growth cycle is significantly lengthened, the cost of high-power MPCVD is extremely high, and the mass production efficiency drops precipitously. Internal thermal stress accumulates, increasing the overall thickness non-uniformity of the wafer and significantly increasing the polycrystalline parasitic area at the edges. Excessive thickness in the plasma field increases the temperature gradient difference between the upper and lower surfaces, causing crystal quality delamination and reducing optical transmittance and thermal conductivity uniformity. Subsequent slab preparation and edge trimming become significantly more difficult, the heat-affected zone expands, and graphite impurities are introduced a second time. Within the range of 0.5~5mm, it can simultaneously achieve: complete repair of surface / subsurface damage caused by laser processing; effective release of internal stress at the splicing interface, suppressing warping and cracking; stable control of relatively small thickness non-uniformity; and balance between production growth efficiency and single crystal quality.

[0045] In one embodiment, the above-mentioned homogeneous epitaxial growth is the stage of lateral bridging of seed crystal gaps. There are tiny splicing gaps between multiple seed crystals, requiring a higher carbon source concentration to increase the lateral growth rate of diamond. High methane concentration increases the density of methyl carbon groups in the plasma, and the lateral growth rate is much greater than that of vertical growth; diamond connecting layer is quickly formed at the gaps, connecting the discrete seed crystals into a continuous spliced ​​whole. After laser edge cutting, chemical etching, and plasma deep impurity removal, the sheet-like body is a complete single crystal continuous substrate, and there is no need for lateral bridging. The goal is to increase the vertical thickness and ensure the quality of the single crystal: (1) When the methane concentration is too high, the carbon supply is excessive, and graphite is easily precipitated on the crystal surface and splicing interface, and non-diamond carbon is accumulated, introducing stacking faults and dislocations; reducing the methane concentration, the carbon supply matches the normal epitaxial rate of the diamond single crystal, the carbon atoms are arranged in an orderly manner, and the defects are greatly reduced. (2) Under high carbon concentration, the electric field is concentrated at the edge and corner of the wafer, making it easy to grow polycrystalline diamond; a lower methane partial pressure can weaken the carbon deposition at the edge, reduce the polycrystalline coverage area at the edge, and increase the proportion of the effective single crystal area of ​​the wafer. (3) Under low methane concentration, the distribution of carbon groups in the plasma is more uniform, the difference in vertical growth rate of the whole wafer is reduced, and the thickness non-uniformity of the final product is very small; high methane concentration is prone to morphological deviation with thicker middle and thinner edge. (4) 50~75kW high-power microwave plasma itself has high carbon dissociation efficiency. If the high methane concentration is maintained during homoepitaxial growth, carbon supersaturation will be serious; reducing the methane volume concentration can match the carbon dissociation ability of high-power plasma and stabilize the growth interface. Therefore, the high methane concentration during homoepitaxial growth disclosed in this invention can quickly bridge the gaps between seed crystals, shorten the splicing and forming time, and is suitable for large-scale closed-loop seed crystal reuse production; the low methane concentration during thickening growth results in high-quality thickening on a complete single-crystal substrate, with fewer defects and a large effective area of ​​the single crystal, ultimately yielding a high-uniformity, low-impurity inch-scale single-crystal diamond wafer.

[0046] In one embodiment, the thickness non-uniformity of the regrown wafer is controlled within ±5%.

[0047] Specifically, this disclosure achieves a thickness non-uniformity of less than ±5% on the entire inch-scale regrown wafer by using high-power MPCVD in a two-step differentiated methane growth process, combined with laser edge trimming to remove the damaged layer, chemical etching, and plasma cleaning for dual impurity removal pretreatment of the substrate. This effectively solves the technical problems of large differences in epitaxial thickness of spliced ​​substrates and low device processing yield.

[0048] In one embodiment, the edges of the regrowth wafer are trimmed using a laser to obtain an inch-scale single-crystal diamond wafer; the inch-scale single-crystal diamond wafer is then sliced ​​using a laser to obtain standardized seed crystals.

[0049] Specifically, the lasers used for edge trimming and slicing are pulsed lasers with a wavelength of 520~540nm; the laser processing parameters include: pulse frequency of 40~60kHz, power of 10~20W, scanning speed of 5~30mm / s, and the width of the heat-affected zone of the cut is ≤5μm.

[0050] In one embodiment, the edge polycrystalline parasitic coverage area of ​​the inch-scale single-crystal diamond wafer is less than or equal to 2% of the total wafer area.

[0051] In one possible implementation, the thickness non-uniformity of each standardized seed crystal obtained by slicing is controlled within ±10%.

[0052] Specifically, the thickness non-uniformity of each standardized seed crystal is controlled within ±10%, making the surface height difference of the substrate formed by splicing multiple seed crystals controllable. This ensures uniform carbon source and temperature distribution during MPCVD epitaxial growth and effectively suppresses polycrystalline and twin defects at the splicing interface. At the same time, the seed crystal processing window is unified, reducing graphite contamination during laser processing and improving the stability of seed crystal recycling. The final inch-scale single-crystal diamond wafers have uniform thickness, low residual stress, and better consistency in optical transmittance and thermal conductivity.

[0053] According to a second aspect of this disclosure, an inch-scale single-crystal diamond wafer is provided, which is prepared by the above-described preparation method.

[0054] According to a third aspect of this disclosure, applications of the aforementioned inch-scale single-crystal diamond wafer are provided, wherein the inch-scale single-crystal diamond wafer is used as a semiconductor substrate, a heat dissipation substrate for power devices, or an infrared optical window.

[0055] According to one possible implementation of this disclosure, at least the following beneficial effects are achieved: 1. By using multiple seed crystals side-bonded and closely packed spliced ​​substrates for homogeneous epitaxy, a large-area continuous diamond blank is formed in one go, avoiding the defects of limited growth size of single seed crystals and high cost of multiple rounds of repeated crystal growth; the effective area of ​​the spliced ​​substrate is larger than the size of the target wafer, and a laser processing allowance is reserved, which significantly improves the yield of finished products and can stably produce inch-level complete single crystal diamond wafers.

[0056] 2. Two rounds of MPCVD growth are set up with differentiated control of methane concentration: the first round uses high methane concentration to quickly bridge the gaps between seed crystals laterally, achieving integrated splicing of the preform; the second round reduces the methane concentration and slowly thickens the wafer, slowing down the parasitic growth of polycrystalline material at the edges, so that the polycrystalline coverage area at the edge of the final wafer is controlled within 2%; with a uniform high-power microwave source, the cavity temperature field is uniform, the overall thickness non-uniformity of the wafer is controlled within ±5%, and internal dislocations and splicing interface defects are greatly reduced.

[0057] 3. Layered process to remove carbon impurities, forming a double guarantee: ① After laser edge cutting and leveling, chemical etching with a nitric acid-hydrofluoric acid mixture is used to selectively remove surface graphite debris; ② After chemical etching, plasma deep cleaning is added, limiting the hydrogen-oxygen flow ratio, power and pressure range, so that trace amounts of residual carbon and graphite contaminants are completely removed; avoiding the induction of a large number of polycrystalline materials and defects by graphite impurities during secondary crystal growth, and significantly improving the infrared transmittance performance of the wafer.

[0058] 4. Cutting and shaping, blank edge trimming and damage removal, wafer edge trimming, and seed wafer slicing all adopt 520-540nm green pulsed laser, with unified and wide-range process parameters such as pulse frequency 40-60kHz and power 10-20W; the laser edge removal depth is greater than the blank thickness, completely eliminating the subsurface damage layer in the thickness direction, and the width of the heat-affected zone after cutting is ≤5μm; after leveling, the surface roughness Ra≤1μm and the absolute value of the thickness deviation≤10μm, with good processing consistency, no need to change multiple sets of processing equipment, and simplified production line configuration.

[0059] 5. The finished wafers are laser-sliced ​​to obtain standardized small-sized seed crystals, which can be directly used in the next round of splicing substrate preparation, realizing closed-loop production of seed crystals; the seed crystals strictly control the gaps, height differences, and misalignment angles, and the splicing interface has a high degree of matching, which further suppresses splicing defects and takes into account both mass production continuity and product crystal quality.

[0060] 6. The inch-scale single-crystal diamond wafers prepared by the method of this disclosure have high crystal integrity, excellent light transmittance, and good thermal conductivity. They can be adapted to high-end needs in multiple fields such as heat dissipation substrates for high-power microwave devices, infrared optical windows, and quantum computing substrates. They have a wide range of applications and outstanding market value.

[0061] It should be understood that the description in this section is not intended to identify key or essential features of the embodiments of this disclosure, nor is it intended to limit the scope of this disclosure. Other features of this disclosure will become readily apparent from the following description. Attached Figure Description

[0062] The above and other objects, features, and advantages of this disclosure will become readily apparent from the following detailed description of exemplary embodiments, taken in conjunction with the accompanying drawings. Several embodiments of this disclosure are illustrated in the drawings by way of example and not limitation, in which: In the accompanying drawings, the same or corresponding reference numerals indicate the same or corresponding parts.

[0063] Figure 1 Photographs of the spliced ​​substrates in embodiments 1 and 2 of this disclosure are shown; Figure 2 A cross-sectional view of the regular octagonal sheet in Embodiment 1 of this disclosure is shown; Figure 3A photograph of the laser-cut and surface-trimmed regular octagonal sheet-like body in Embodiment 1 of this disclosure is shown; Figure 4 A photographic image of the regrowth wafer obtained after thickening growth in Embodiment 1 of this disclosure is shown; Figure 5 A physical diagram of the standardized seed crystal in Embodiment 1 of this disclosure is shown; Figure 6 The Raman spectrum of the standardized seed crystal in Embodiment 1 of this disclosure is shown; Figure 7 A cross-sectional view of the circular sheet-like body in Embodiment 2 of this disclosure is shown; Figure 8 A photograph of the circular sheet-like body after laser cutting and surface finishing in Embodiment 2 of this disclosure is shown; Figure 9 The image shown is a photograph of the regrowth wafer obtained after thickening growth in Embodiment 2 of this disclosure; Figure 10 A physical image of the standardized seed crystal in Embodiment 2 of this disclosure is shown; Figure 11 The Raman spectrum of the standardized seed crystal in Embodiment 2 of this disclosure is shown. Detailed Implementation

[0064] To make the objectives, features, and advantages of this disclosure more apparent and understandable, the technical solutions in the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this disclosure, and not all embodiments. Based on the embodiments of this disclosure, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this disclosure.

[0065] Limited by the seed crystal size achievable using existing high-temperature high-pressure (HTHP) and plasma-enhanced chemical vapor deposition (MPCVD) techniques (typically not exceeding 10mm × 10mm), the fabrication of large-size (≥2-inch) single-crystal diamond wafers has long faced a "size bottleneck." The splicing method is considered an effective technological path to overcome this bottleneck. However, existing splicing processes share the following common problems: 1. Edge discharge effect: The edges of spliced ​​substrates are prone to tip discharge in MPCVD plasma environment, which leads to local overheating and carbon particle deposition, fragmentation and difficulty in forming, and induces polycrystalline parasitic growth. These factors make large-size substrates a long-standing problem that has not been solved in the field. 2. Thermal stress concentration: Significant residual stress is generated at the abrupt curvature of the traditional square or circular cut edges, which easily leads to microcracks or even breakage during the growth process; 3. Poor thickness uniformity: Differences in growth rates in different regions lead to wafer thickness fluctuations, reducing the yield of subsequent device processing.

[0066] This disclosure aims to provide a high-power microwave plasma splicing method for fabricating inch-scale single-crystal diamond wafers. Through optimized geometric design—that is, cutting the spliced ​​assembly into circles, regular octagons, or rounded polygons after the first growth—and combined with edge trimming, surface finishing, and secondary re-growth processes, it significantly suppresses parasitic growth of polycrystalline material at the edges, reduces residual stress, and improves wafer thickness uniformity and crystal quality. This enables the mass production of high-quality, large-size single-crystal diamond wafers or integrated seed crystals for irregularly shaped wafers, solving the long-standing "size bottleneck" in the fabrication of large-size (≥2-inch) single-crystal diamond wafers.

[0067] The following examples illustrate this in detail.

[0068] Example 1 This embodiment describes the process for preparing a 2-inch single-crystal diamond wafer, specifically including the following steps: Preparation of materials and equipment: 25 (100) oriented single-crystal diamond seed crystals, square in shape and 10mm×10mm×0.35mm in size, were obtained by CVD and the surface was polished to Ra<5nm.

[0069] MPCVD equipment: frequency 915MHz, maximum power 75kW, equipped with an infrared thermometer monitoring system.

[0070] (1) Two groups of 25 (100) oriented single-crystal diamond seed crystals are arranged in close side contact to form a single-group 5×5 matrix splicing substrate. The gap between adjacent single-crystal diamond seed crystals in each group is 0.1 mm, the absolute value of the height difference is 25 μm, and the absolute value of the misalignment angle is 5°. The effective area of ​​the splicing substrate is larger than the area of ​​the target wafer. The size of the splicing substrate is approximately 50 mm × 50 mm. See [reference needed] Figure 1 The splicing substrate on the left side.

[0071] (2) Place the splicing substrate from step (1) on the molybdenum substrate stage in the reaction chamber of the MPCVD equipment with a frequency of 915MHz, introduce hydrogen, oxygen, and methane gas, and introduce nitrogen as an auxiliary gas; control the microwave power to be 60kW, the chamber pressure to be 18kPa, the substrate temperature to be 1050±20℃ (infrared thermometry), the volume concentration of methane to be 4% (flow rate to be 120sccm), the flow rate of hydrogen to be 3000sccm, the flow rate of oxygen to be 20sccm, and the flow rate of nitrogen to be 20sccm, and perform homogeneous epitaxial growth on the splicing substrate until the seed crystals are laterally connected to form a continuous splicing whole, with a growth thickness of 1.5mm.

[0072] (3) Remove the assembled whole obtained in step (2) from the reaction chamber, and cut and trim it into regular octagonal sheets using laser cutting. The laser is a pulsed laser with a wavelength of 532 nm, a pulse frequency of 50 kHz, and a power of 20 W. During laser cutting, the focal position and scanning speed are simultaneously controlled (10 mm / s) to ensure that the width of the heat-affected zone is ≤5 μm. A schematic diagram of the regular octagonal sheet is shown below. Figure 2 As shown, it has a centrally symmetric structure with octagonal sides arranged in two alternating groups. Four sides are of equal length, and the remaining four sides are symmetrically arranged with equal lengths. The diameter of the circumscribed circle of the vertex of this regular octagonal sheet is 46.1 mm. It can be seen that there is a slight lateral extension of the step at the boundary of adjacent seed crystals (the height difference between two adjacent pieces is <10 μm) and a small number of stress cracks appear in local areas.

[0073] (4) The damaged layer in the thickness direction is removed along the edge of the regular octagonal sheet using a laser, with the removal depth greater than the sample thickness; then the upper surface of the regular octagonal sheet after the edge trimming is smoothed and impurities are removed using a laser, so that its surface roughness Ra is 1 μm and the thickness deviation is 9 μm; then the graphite and impurity layer on the surface of the regular octagonal sheet is removed by chemical etching (see Figure 3 The laser described above is a pulsed laser with a wavelength of 532 nm, a pulse frequency of 50 kHz, a power of 20 W, and a scanning speed of 10 mm / s. The etching solution used for chemical etching is a strong acid solution of nitric acid and hydrofluoric acid mixed in a volume ratio of 3:1. The etching temperature is 70 °C, and the etching time is 20 min.

[0074] After chemical etching, the regular octagonal sheet is placed in a plasma device, and the power of the device is adjusted to 25kW etching mode. It is treated for 15 minutes in a mixed hydrogen and oxygen plasma atmosphere to remove surface carbon and graphitized contaminants introduced by the cutting and finishing processes. The volume ratio of hydrogen to oxygen is 20:1, the flow rate of hydrogen is 1000 sccm, the flow rate of oxygen is 10 sccm, and the pressure of the chamber is 8 kPa.

[0075] (5) The octagonal sheet processed in step (4) is placed back into the reaction chamber of the MPCVD equipment, and hydrogen, oxygen, methane, and nitrogen gases are introduced; the microwave power is controlled at 60kW, the chamber pressure at 18kPa, the substrate temperature at 1050±15℃, the volume concentration of methane at 3% (flow rate at 90sccm), the flow rate of hydrogen at 3000sccm, the flow rate of oxygen at 20sccm, and the flow rate of nitrogen at 20sccm. The octagonal sheet is then thickened to a thickness of 2.5mm, and a small amount of polycrystalline parasitic growth is controlled in the edge region to obtain a regrown wafer (see Figure 4 The thickness non-uniformity of the regrown wafer is within ±3%.

[0076] A laser was used to refine the edges of the regrowth wafer, resulting in a 2-inch single-crystal diamond wafer. The laser used was a 532nm pulsed laser with a pulse frequency of 50kHz, a power of 20W, and a scanning speed of 10mm / s. The polycrystalline parasitic coverage area at the edge of the aforementioned 2-inch single-crystal diamond wafer accounted for 1% of the total wafer area.

[0077] A laser is used to divide a 2-inch single-crystal diamond wafer into four standardized seed crystals, which can then be used for the next round of splicing production. The laser used is a 532nm pulsed laser with a pulse frequency of 50kHz, a power of 20W, and a scanning speed of 10mm / s. A physical image of the standardized seed crystals is shown below. Figure 5 As shown, it is a regular octagon, and the thickness non-uniformity of each standardized seed crystal is within ±10%. The standardized seed crystals were Raman-characterized, and the results are as follows... Figure 6 As shown. Figure 6 The peak position of this sample is 1332.52 cm⁻¹. -1 Compared to the standard Raman shift of natural single-crystal diamond (1332 cm⁻¹), -1 Only a very small redshift occurred, with a shift of only 0.52 cm. -1 This indicates that the overall stress level inside the crystal is extremely low, the degree of lattice distortion is weak, and there is no significant accumulation of compressive / tensile stress at the splicing interface and the epitaxial layer; if lattice defects and interface mismatches are severe, the peak position shift will usually exceed 2~5cm. -1 The sample exhibits excellent lattice uniformity. The peak intensity approaches 7000 counts, with high signal strength, extremely low baseline noise, and an excellent signal-to-noise ratio, indicating high diamond phase purity. The main peak is extremely sharp and symmetrical, without significant broadening or tailing, and the peaks descend steeply on both sides. The narrow half-width at half-maximum (HWHM) of this sample directly demonstrates the high lattice matching at the spliced ​​growth interface, the effective suppression of interface defects by gradient crystal growth, and the removal of the damaged layer in all thickness directions by laser cutting, thus eliminating defect broadening caused by the damaged layer.

[0078] Example 2 This embodiment describes the process for preparing a 2-inch single-crystal diamond wafer, specifically including the following steps: Preparation of materials and equipment: 25 (100) oriented single-crystal diamond seed crystals, square in shape and 10mm×10mm×0.35mm in size, were obtained by CVD and the surface was polished to Ra<5nm.

[0079] MPCVD equipment: frequency 915MHz, maximum power 75kW, equipped with an infrared thermometer monitoring system.

[0080] (1) Two groups of 25 (100) oriented single-crystal diamond seed crystals are arranged in close side contact to form a single-group 5×5 matrix splicing substrate. The gap between adjacent single-crystal diamond seed crystals in each group is 0.1 mm, the absolute value of the height difference is 25 μm, and the absolute value of the misalignment angle is 5°. The effective area of ​​the splicing substrate is larger than the area of ​​the target wafer. The size of the splicing substrate is approximately 50 mm × 50 mm. See [reference needed] Figure 1 The splicing substrate on the right side.

[0081] (2) Place the splicing substrate from step (1) on the molybdenum substrate stage in the reaction chamber of the MPCVD equipment with a frequency of 915MHz, introduce hydrogen, oxygen, and methane gas, and introduce nitrogen as an auxiliary gas; control the microwave power to be 60kW, the chamber pressure to be 18kPa, the substrate temperature to be 1050±20℃ (infrared thermometry), the volume concentration of methane to be 4% (flow rate to be 120sccm), the flow rate of hydrogen to be 3000sccm, the flow rate of oxygen to be 20sccm, and the flow rate of nitrogen to be 20sccm, and perform homogeneous epitaxial growth on the splicing substrate until the seed crystals are laterally connected to form a continuous splicing whole, with a growth thickness of 1.5mm.

[0082] (3) Remove the assembled whole obtained in step (2) from the reaction chamber, and cut and trim it into circular sheet-like bodies using laser cutting. The laser is a pulsed laser with a wavelength of 532nm, a pulse frequency of 50kHz, and a power of 20W. During laser cutting, the focal position and scanning speed are simultaneously controlled (10mm / s) to ensure that the width of the heat-affected zone is ≤5μm. A schematic diagram of the circular sheet-like body is shown below. Figure 7 As shown, its diameter is 50.8 mm. It can be seen that there is a slight lateral extension of the step at the boundary of the adjacent seed crystals, and the surface is relatively rough (the height difference between two adjacent pieces is <30 μm); the polycrystalline region is dense.

[0083] (4) The damaged layer in the thickness direction is removed along the edge of the circular sheet using a laser, with the removal depth greater than the sample thickness; then the upper surface of the circular sheet after the edge trimming is smoothed and impurities are removed using a laser, so that its surface roughness Ra is 1 μm and the thickness deviation is 9 μm; then the graphite and impurity layers on the surface of the circular sheet are removed by chemical etching (see Figure 8 The laser described above is a pulsed laser with a wavelength of 532 nm, a pulse frequency of 50 kHz, a power of 20 W, and a scanning speed of 10 mm / s. The etching solution used for chemical etching is a strong acid solution of nitric acid and hydrofluoric acid mixed in a volume ratio of 3:1. The etching temperature is 70 °C, and the etching time is 20 min.

[0084] After chemical etching, the circular sheet is placed in a plasma device, and the power of the device is adjusted to 25kW etching mode. It is treated for 15 minutes in a mixed hydrogen and oxygen plasma atmosphere to remove surface carbon and graphitized contaminants introduced by the cutting and finishing processes. The volume ratio of hydrogen to oxygen is 20:1, the flow rate of hydrogen is 1000 sccm, the flow rate of oxygen is 10 sccm, and the pressure of the chamber is 8 kPa.

[0085] (5) Place the circular sheet processed in step (4) back into the reaction chamber of the MPCVD equipment, and introduce hydrogen, oxygen, methane, and nitrogen gases; control the microwave power to be 60kW, the chamber pressure to be 18kPa, the substrate temperature to be 1050±15℃, the volume concentration of methane to be 3% (flow rate to be 90sccm), the flow rate of hydrogen to be 3000sccm, the flow rate of oxygen to be 20sccm, and the flow rate of nitrogen to be 20sccm, and perform thickening growth on the above circular sheet to a thickness of 2.5mm, control the occurrence of a small amount of polycrystalline parasitic growth in the edge region, and obtain a regrown wafer (see Figure 9 The thickness non-uniformity of the regrown wafer is within ±5%.

[0086] A laser was used to refine the edges of the regrowth wafer, resulting in a 2-inch single-crystal diamond wafer. The laser used was a 532nm pulsed laser with a pulse frequency of 50kHz, a power of 20W, and a scanning speed of 10mm / s. The polycrystalline parasitic coverage area at the edge of the aforementioned 2-inch single-crystal diamond wafer accounted for 2% of the total wafer area.

[0087] A laser is used to divide a 2-inch single-crystal diamond wafer into four standardized seed crystals, which can then be reused in the next round of splicing production. The laser used is a 532nm pulsed laser with a pulse frequency of 50kHz, a power of 20W, and a scanning speed of 10mm / s. A physical image of the standardized seed crystals is shown below. Figure 10 As shown, the seed crystals are circular, and the thickness non-uniformity of each standardized seed crystal is within ±10%. The standardized seed crystals were Raman-characterized, and the results are as follows... Figure 11 As shown. Figure 11 The peak position of this sample is 1333.33 cm⁻¹. -1 Compared to the standard Raman shift of natural single-crystal diamond (1332 cm⁻¹), -1 A redshift occurred, with a shift of 1.33 cm. -1 Compared to Example 1, the seed crystal prepared from the regular octagonal sheet was only offset by 0.52 cm. -1The peak shift in this circular sample is greater. A larger peak shift indicates higher internal lattice stress and distortion, suggesting more significant stress accumulation in the edge forming region of the circular wafer blank. After machining, the internal tensile / compressive stress of the circular sample is higher than that of the regular octagonal sample, and the lattice matching consistency between the splicing interface and the epitaxial layer is weaker. In the industry, when lattice mismatch and processing stress are severe, the shift can exceed 2-5 cm. -1 Although this sample did not reach the severe mismatch range, its stress level was significantly higher than that of the regular octagonal sample. The peak intensity was approximately 7200 counts, and the signal intensity was close to that of the regular octagonal sample. The baseline noise levels were essentially the same. Both samples exhibited high diamond phase purity and good signal-to-noise ratios; however, the stress level at 1400–2000 cm⁻¹ was significantly higher. -1 interval sp 2 The carbon bulge baseline height is significantly higher than that of the regular octagonal sample, and the signals from the graphite and amorphous carbon impurity substrate are stronger, indicating that the circular blank produces more graphite contaminants during laser circumferential cutting at the edge, and the content of residual trace carbon impurities is higher than that of the regular octagonal sample under the same impurity removal process. Although the main peak is equally sharp and symmetrical, the tail on the right side of the main peak is more obvious and the peak descent edge is gentler; the main peak of the regular octagonal sample is steep on both sides and has no tail. The tailing phenomenon originates from the superposition of lattice stress and trace defects, directly causing the Raman full width at half maximum (FWHM) of the circular sample to be larger than that of the regular octagonal sample. The narrow FWHM of the regular octagonal sample proves that the lattice matching degree of the splicing interface is high and the subsurface damage is completely removed; while the laser circumferential cutting path of the circular contour is longer and the laser thermal damage range of the curved edge is larger. Even after laser edge cutting, chemical etching, and plasma cleaning, a small amount of subsurface damage and interface defects remain, which manifests as a broadened FWHM and a tail on the right side of the peak.

[0088] It is evident that segmented gradient MPCVD crystal growth is far more effective at suppressing defects at flat octagonal boundaries than at circular curved boundaries; laser processing of circular curved surfaces tends to introduce a wider thermal damage layer, making it impossible to completely eliminate the peak broadening problem caused by defects.

[0089] In summary, this disclosure employs multi-seed crystal splicing to achieve large-area diamond billet growth. However, multi-seed crystal synchronous epitaxy systems are prone to multiple process challenges: the arrangement of multiple seed crystals can easily lead to uneven substrate deposition temperature field and differences in the growth rate of individual seed crystals, thereby inducing crystal defects such as lattice stress concentration, dislocation multiplication, and edge polycrystalline impurities, significantly increasing the overall experimental difficulty and process risk. Therefore, this disclosure focuses on systematic process optimization and parameter control within a closed-loop process chain: "seed crystal splicing → first-round epitaxial growth → laser precision machining and surface finishing → secondary thickening growth → seed crystal wafer reuse."

[0090] Comparing the finished product quality of circular and regular octagonal profile blanks reveals that: the circular wafer has a more prominent problem of stress concentration at the edge, with a higher number of edge microcracks and overall dislocation density than the regular octagonal sample, and poorer crystal integrity; after the second round of thickening growth, the thickness non-uniformity of the circular sample increases, the polycrystalline parasitic coverage area at the edge is significantly widened, the polycrystalline layer extends from the edge into the wafer interior by about 1-2 mm, accompanied by local microcracks, and crack defects can also be seen in the central area; while the regular octagonal straight profile blank has a more uniform stress distribution and better defect suppression effect.

[0091] Before the two types of preforms undergo secondary thickening growth, there is no obvious polycrystalline covering layer on the surface after the finishing process. After all growth and edge finishing are completed, a single wafer can be divided into four standardized seed crystal blocks of uniform thickness through laser slicing process. These seed crystals can be recycled into a new round of splicing substrate preparation to achieve batch iterative replication production of inch-level single crystal diamond wafers.

[0092] It should be understood that the various forms of processes shown above can be used to rearrange, add, or delete steps. For example, the steps described in this disclosure can be executed in parallel, sequentially, or in different orders, as long as the desired result of the technical solution of this disclosure can be achieved, and this is not limited herein.

[0093] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this disclosure, "a plurality of" means two or more, unless otherwise explicitly specified.

[0094] The above description is merely a specific embodiment of this disclosure, but the scope of protection of this disclosure is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this disclosure should be included within the scope of protection of this disclosure. Therefore, the scope of protection of this disclosure should be determined by the scope of the claims.

Claims

1. A closed-loop batch preparation method for inch-scale single-crystal diamond wafers, characterized in that, Includes the following steps: A splicing substrate is formed by arranging several single-crystal diamond seed crystals; the single-crystal diamond seed crystals have a side length or diameter of 5~15mm and a thickness of 0.2~0.5mm; the gap between adjacent single-crystal diamond seed crystals is ≤0.1mm, the absolute value of the height difference is ≤25μm, and the absolute value of the misalignment angle is ≤5°; the surface roughness Ra of the single-crystal diamond seed crystals is ≤5nm; the effective area of ​​the splicing substrate is greater than or equal to the area of ​​the target inch-scale single-crystal diamond wafer; The spliced ​​substrate is subjected to MPCVD equipment to perform homoepitaxial growth until the seed crystals are laterally connected to form a spliced ​​whole; wherein the microwave power during growth is 50~75kW, the volume concentration of methane is 3%~5%, and the thickness of the homoepitaxial growth is 0.3~2mm; The assembled assembly is cut using a laser to obtain circular, regular octagonal, or rounded polygonal inch-sized sheets. The inch-sized sheets are first laser-trimmed to remove the damaged layer along their thickness direction. Then, the surface of the inch-sized sheets is leveled and impurities removed using a laser, ensuring a surface roughness Ra ≤ 1 μm and an absolute thickness deviation ≤ 10 μm. The removal depth of the damaged layer is greater than the thickness of the inch-sized sheet. The lasers used for cutting the assembled assembly, trimming the inch-sized sheets, and leveling and impurities removal are all pulsed lasers with a wavelength of 520–540 nm. Laser processing parameters include: pulse frequency of 40–60 kHz, power of 10–20 W, and scanning speed of 5–30 mm / s. When cutting the assembled assembly, the width of the heat-affected zone is ≤ 5 μm. MPCVD equipment is used to thicken and grow a planarized and impurity-removed sheet to obtain a regrown wafer. The microwave power during growth is 50~75kW, and the volume concentration of methane is 2%~4%, which is lower than the volume concentration of methane in homoepitaxial growth. The thickness of the thickening growth is 0.5~5mm. The regrowth wafer is edge-trimmed using a laser to obtain an inch-scale single-crystal diamond wafer. The inch-scale single-crystal diamond wafer is then sliced ​​using a laser to obtain standardized seed crystals for the next round of splicing. The lasers used for edge trimming and slicing are pulsed lasers with wavelengths of 520~540nm. The laser processing parameters include: pulse frequency of 40~60kHz, power of 10~20W, scanning speed of 5~30mm / s, and the width of the heat-affected zone being cut is ≤5μm.

2. The closed-loop batch preparation method according to claim 1, characterized in that, The inch-scale single-crystal diamond wafer refers to a single-crystal diamond wafer of 2 inches or larger.

3. The closed-loop batch preparation method according to claim 1, characterized in that, During homoepitaxial growth, hydrogen and oxygen are introduced. The flow rate of hydrogen is 2500~3500 sccm, the flow rate of oxygen is 10~30 sccm, and the flow rate of methane is 100~150 sccm. The chamber pressure during growth is 15~22 kPa, and the substrate temperature is 980~1100℃.

4. The closed-loop batch preparation method according to claim 3, characterized in that, During homoepitaxial growth, nitrogen gas is also introduced at a flow rate of 10-30 sccm.

5. The closed-loop batch production method according to claim 1, characterized in that, After leveling and impurity removal, the graphite and impurity layers on the surface of the inch-sized sheet are removed by chemical etching. The conditions for chemical etching include: the etching solution is an acid solution of nitric acid and hydrofluoric acid mixed in a volume ratio of 3:1; the etching temperature is 60~80℃; and the etching time is 10~30min.

6. The closed-loop batch preparation method according to claim 1, characterized in that, During the thickening growth, hydrogen and oxygen are also introduced. The flow rate of hydrogen is 2500~3500 sccm, the flow rate of oxygen is 10~30 sccm, and the flow rate of methane is 80~130 sccm. The chamber pressure during growth is 15~22 kPa, and the substrate temperature is maintained at 980~1100℃.

7. The closed-loop batch preparation method according to claim 6, characterized in that, During the thickening growth process, nitrogen gas is also introduced at a flow rate of 10-30 sccm.

8. The closed-loop batch preparation method according to claim 1, characterized in that, The thickness non-uniformity of the regenerated wafer is controlled within ±5%.

9. The closed-loop batch preparation method according to claim 1, characterized in that, The edge polycrystalline parasitic coverage area of ​​the inch-scale single-crystal diamond wafer is less than or equal to 2% of the total wafer area.

10. The closed-loop batch preparation method according to claim 1, characterized in that, The thickness non-uniformity of each standardized seed crystal obtained by slicing is controlled within ±10%.

11. An inch-scale single-crystal diamond wafer, characterized in that, The inch-scale single-crystal diamond wafer is prepared by the closed-loop batch preparation method according to any one of claims 1 to 10.

12. The application of the inch-scale single-crystal diamond wafer of claim 11, characterized in that, The inch-scale single-crystal diamond wafer is used as a semiconductor substrate, a heat dissipation substrate for power devices, or an infrared window.

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