Method for producing a polycrystalline silicon carbide wafer

Abstract

This invention relates to a method for preparing polycrystalline silicon carbide wafers. A mixture of MTS and H2 is introduced into the reaction chamber of a chemical vapor deposition (CVD) apparatus through a first inlet, and N2 is introduced into the reaction chamber through a second inlet. CVD is performed on a substrate surface, resulting in a polycrystalline silicon carbide wafer. The shortest distance between the second inlet and the substrate is less than that between the first inlet and the substrate. The flow rate ratio of H2 to MTS is greater than 10:1, and the flow rate ratio of N2 to MTS is greater than 10:1. The total flow rate of H2, MTS, and N2 is Q. The substrate is placed on a rotating stage of the CVD apparatus, and the rotating stage is controlled to rotate at a speed N. The rotation speed N and the total flow rate Q of the gas introduced into the reaction chamber satisfy the following condition: 5 × 10⁻⁶. 5 L·rpm / (min·m 2 )≤(Q / A)×N≤1×10 6 L·rpm / (min·m 2 A is the surface area of ​​the substrate. Using the described preparation method, polycrystalline silicon carbide wafers of arbitrary size with a resistivity not exceeding 1 mΩ·cm can be fabricated.

Description

Technical Field

[0001] This invention relates to the field of semiconductor technology, and in particular to a method for preparing polycrystalline silicon carbide wafers. Background Technology

[0002] Silicon carbide (SiC), as a typical wide-bandgap semiconductor material, possesses high breakdown electric field, high thermal conductivity, and excellent high-temperature stability, making it promising for applications in power devices, radio frequency devices, and other fields. Low-resistivity silicon carbide wafers are a core material for realizing high-efficiency, high-power-density, and high-reliability power electronic systems. By reducing the resistance of the substrate itself, they can significantly reduce device conduction and switching losses, thus finding applications in various fields with stringent requirements for energy consumption, heat dissipation, and size.

[0003] Currently, silicon carbide wafers are mainly single-crystal, but their long growth cycle, high cost, and limited crystal size make it difficult to meet the demands of large-size, low-cost applications. In contrast, polycrystalline silicon carbide wafers have advantages such as short fabrication cycle, low cost, and good scalability, and are considered an important development direction for power device substrates. However, existing polycrystalline silicon carbide wafers generally suffer from problems such as high resistivity and poor in-plane uniformity, especially in the fabrication of large-size wafers.

[0004] In existing technologies, although the resistivity of polycrystalline silicon carbide wafers can be reduced by introducing nitrogen as a doping gas, the doping efficiency is low and grain boundary scattering is severe, making it difficult to obtain 12-inch and larger polycrystalline silicon carbide wafers with resistivity below 1 mΩ·cm. Although using highly reactive ammonia as a doping gas can improve the doping efficiency, the rapid reaction between ammonia and the precursor not only poses safety concerns but also results in silicon carbide wafers with poor uniformity and high roughness.

[0005] Therefore, there is an urgent need for a method that can achieve ultra-low resistivity and is particularly suitable for the fabrication of large-size polycrystalline silicon carbide wafers. Summary of the Invention

[0006] Therefore, it is necessary to provide a method for preparing polycrystalline silicon carbide wafers to address the above problems. The method can obtain polycrystalline silicon carbide wafers with a resistivity of no more than 1 mΩ·cm, and is especially suitable for the preparation of large-size wafers with strict requirements on resistivity.

[0007] A method for preparing a polycrystalline silicon carbide wafer includes the following steps:

[0008] A mixture of methyltrichlorosilane and hydrogen is introduced into the reaction chamber of the chemical vapor deposition equipment through the first feed port, and nitrogen is introduced into the reaction chamber through the second feed port. Chemical vapor deposition is performed on the substrate surface, and polycrystalline silicon carbide wafers are obtained after the deposition is completed.

[0009] Wherein, the shortest distance between the second feed inlet and the substrate is less than the shortest distance between the first feed inlet and the substrate; the flow rate ratio of hydrogen to methyltrichlorosilane is greater than 10:1; the flow rate ratio of nitrogen to methyltrichlorosilane is greater than 10:1; the total flow rate of hydrogen, methyltrichlorosilane, and nitrogen is Q; the substrate is placed on the rotating stage of the chemical vapor deposition apparatus; the rotating stage is controlled to rotate at a speed N; and the speed N of the rotating stage and the total flow rate Q of the gas entering the reaction chamber satisfy: 5 × 10⁻⁶. 5 L·rpm / (min·m 2 )≤(Q / A)×N≤1×10 6 L·rpm / (min·m 2 A is the surface area of ​​the substrate.

[0010] In one embodiment, the ratio of the flow rate of hydrogen to that of methyltrichlorosilane is 15:1 to 50:1.

[0011] In one embodiment, the ratio of the nitrogen flow rate to the methyltrichlorosilane flow rate is 15:1 to 100:1.

[0012] In one embodiment, the flow rate of the methyltrichlorosilane is 0.5 L / min to 3 L / min;

[0013] And / or, the hydrogen delivery flow rate is 25 L / min to 200 L / min;

[0014] And / or, the nitrogen flow rate is 10L / min to 200L / min.

[0015] In one embodiment, the rotational speed N of the rotating stage is 500 rpm to 5000 rpm.

[0016] In one embodiment, the chemical vapor deposition temperature is 1200°C to 1600°C, and the pressure is 10 kPa to 30 kPa.

[0017] In one embodiment, during the heating process, when the temperature reaches 800°C to 1200°C, nitrogen gas is first introduced into the reaction chamber. When the temperature reaches 1200°C to 1600°C, hydrogen gas is then introduced into the reaction chamber. After the temperature and pressure stabilize, methyltrichlorosilane is mixed with hydrogen gas to form a mixed gas and then introduced.

[0018] In one embodiment, the axis of the first feed port is parallel to the substrate surface, and the axis of the second feed port is perpendicular to the substrate surface.

[0019] In one embodiment, the shortest distance between the first feed inlet and the substrate is 10mm to 100mm;

[0020] And / or, the shortest distance between the second feed port and the substrate is 5mm to 50mm.

[0021] In one embodiment, the diameter of the substrate is greater than or equal to 12 inches.

[0022] This invention achieves efficient nitrogen doping in polycrystalline silicon carbide wafers by independently feeding nitrogen closer to the substrate surface, controlling the flow ratio of hydrogen to methyltrichlorosilane and nitrogen to methyltrichlorosilane to be greater than 10:1, and combining this with the coordinated control of high-speed rotation of the rotating stage and the total gas flow rate. This results in polycrystalline silicon carbide wafers with a room temperature resistivity of no more than 1 mΩ·cm, excellent in-plane uniformity, and good adaptability to substrates of different sizes. In particular, it can solve the problem of low resistivity preparation of large-size polycrystalline silicon carbide wafers. At the same time, the process is safe, simple, and highly controllable, making it suitable for large-scale industrial production. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of this application or the conventional technology, the drawings used in the description of the embodiments or the conventional technology will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 This is a schematic diagram of the chemical vapor deposition equipment used in this invention;

[0025] Figure 2 This is a physical image of the polycrystalline silicon carbide wafer prepared in Example 1 of the present invention;

[0026] Figure 3 The resistivity distribution diagram is shown for the polycrystalline silicon carbide wafer prepared in Example 1 of this invention.

[0027] In the figure: 101, reaction chamber; 102, first feed inlet; 103, second feed inlet; 104, rotary motor; 105, rotating shaft; 106, rotating platform; 107, support rod; 108, support lug; 109, base; 110, exhaust port. Detailed Implementation

[0028] To facilitate understanding of the present invention, it will be described in more detail below. However, it should be understood that the present invention can be implemented in many different forms and is not limited to the embodiments or examples described herein. Rather, these embodiments or examples are provided to make the disclosure of the present invention more thorough and complete.

[0029] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the specification of this invention is for the purpose of describing particular embodiments or examples only and is not intended to limit the invention. The optional scope of the term "and / or" as used herein includes any one of two or more of the related listed items, as well as any and all combinations of the related listed items, including any two related listed items, any more related listed items, or a combination of all related listed items.

[0030] In this invention, numerical ranges are involved. Unless otherwise specified, the numerical ranges are considered continuous and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe features or characteristics, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are included.

[0031] This invention reveals that the high resistivity of polycrystalline silicon carbide wafers during chemical vapor deposition (CVD) is fundamentally due to insufficient carrier concentration, which is essentially caused by low nitrogen doping efficiency. Therefore, achieving stable and efficient nitrogen doping is crucial for obtaining low resistivity materials.

[0032] Further research revealed that the core reason for the low nitrogen doping efficiency lies in the difficulty for reactants (nitrogen molecules and their intermediates) to effectively penetrate the gas boundary layer on the substrate surface to reach the deposition interface. This boundary layer is a stagnant region adjacent to the substrate surface, where convective transport is suppressed, and mass transport mainly relies on diffusion. Therefore, the boundary layer is essentially a resistance layer for the mass transfer process. According to Fick's first law, the thicker the boundary layer, the greater the mass transfer resistance, the fewer nitrogen species reach the deposition surface per unit time, and the lower the doping efficiency. Especially on large-size substrates, the boundary layer effect is more prominent. When gas flows through a large surface, the boundary layer gradually thickens along the flow direction, resulting in significant differences in mass transfer conditions between the center and edge regions of the substrate. Consequently, the doping concentration at different locations within the wafer surface deviates, which is the fundamental reason for the high resistivity, poor in-plane uniformity, and difficulty in stably obtaining materials with resistivity below 1 mΩ·cm on large-size wafers.

[0033] Based on this, the present invention starts from boundary layer control, combined with, for example Figure 1 The chemical vapor deposition apparatus shown provides a method for preparing polycrystalline silicon carbide wafers.

[0034] The chemical vapor deposition equipment includes:

[0035] The reaction chamber 101 is provided with a first feed inlet 102, a second feed inlet 103 and an exhaust port 110;

[0036] A rotating stage 106 is disposed inside the reaction chamber 101 to support the substrate 109. The rotating stage 106 is connected to a rotating motor 104 disposed outside the reaction chamber 101 via a rotating shaft 105. The rotating motor 104 drives the rotating stage 106 to rotate.

[0037] A support rod 107 is provided, one end of which is fixed to the rotating platform 106 by a threaded connection. A support ear 108 is provided on the outer side of the base 109, and the support ear 108 is fixed to the support rod 107 by a snap fastener.

[0038] The preparation method includes the following steps: a mixture of methyltrichlorosilane (MTS) and hydrogen (H2) is introduced into the reaction chamber 101 of the chemical vapor deposition equipment through the first feed port 102, and nitrogen (N2) is introduced into the reaction chamber 101 through the second feed port 103. Chemical vapor deposition is performed on the surface of the substrate 109, and a polycrystalline silicon carbide wafer is obtained after the deposition is completed.

[0039] Wherein, the shortest distance between the second feed inlet 103 and the substrate 109 is less than the shortest distance between the first feed inlet 102 and the substrate 109; the flow rate ratio of hydrogen to methyltrichlorosilane is greater than 10:1; the flow rate ratio of nitrogen to methyltrichlorosilane is greater than 10:1; the total flow rate of hydrogen, methyltrichlorosilane, and nitrogen is Q; the substrate 109 is placed on the rotating stage 106 of the chemical vapor deposition apparatus; the rotating stage 106 is controlled to rotate at a rotation speed N; and the rotation speed N of the rotating stage 106 and the total flow rate Q of the gas entering the reaction chamber 101 satisfy: (Q / A)×N≥5×10 5 L·rpm / (min·m 2 A is the surface area of ​​the substrate.

[0040] First, by setting the N2 inlet closer to the surface of the substrate 109 than the mixed gas inlet, the present invention shortens the diffusion distance of nitrogen species from the inlet to the deposition surface, reduces nitrogen loss before reaching the surface, and results in a higher local nitrogen concentration, providing a concentration driving force for efficient doping. At the same time, the mixed gas is introduced from the inlet relatively far from the substrate 109, ensuring that the MTS has sufficient space and time for decomposition before reaching the surface of the substrate 109, and that the supply paths of the main reactants and dopants do not interfere with each other.

[0041] Building upon this, the present invention significantly increases the relative concentration of H2 in reaction chamber 101 by controlling the H2 to MTS flow ratio to be greater than 10:1. The highly chemically active atomic hydrogen generated by H2 dissociation at high temperatures promotes the breaking of the N≡N triple bond, activating chemically inert nitrogen molecules into nitrogen atoms or nitrogen-containing active groups that can directly participate in doping. This fundamentally overcomes the technical bottleneck of effectively incorporating N2 under conventional CVD conditions. Simultaneously, the high concentration of activated hydrogen effectively removes chlorine-containing groups from MTS decomposition products, reducing the competitive adsorption of chlorine on active nitrogen species and ensuring that the activated nitrogen species can successfully reach and adsorb onto the growth interface. Further controlling the N2 to MTS flow ratio to be greater than 10:1 ensures an absolutely abundant nitrogen source within reaction chamber 101. According to Fick's law, the high concentration of nitrogen source increases the concentration gradient of active nitrogen species on both sides of the boundary layer, increasing the diffusion driving force and allowing more active nitrogen species to cross the boundary layer and reach the deposition surface under the drive of the concentration gradient.

[0042] Building upon this, the present invention further discovers that even if N2 is fully activated and supplied adequately, if the gas boundary layer on the surface of substrate 109 is too thick, the mass transfer resistance will still severely restrict the doping efficiency. According to the hydrodynamic boundary layer theory, the boundary layer thickness is inversely proportional to the square root of the rotational angular velocity, i.e., the higher the rotational speed, the thinner the boundary layer; simultaneously, the boundary layer thickness is also inversely proportional to the square root of the total gas flow rate Q, the larger Q is, the stronger the thinning effect of the main gas flow on the boundary layer. Therefore, the product of the total gas flow rate Q and the rotational speed N jointly determines the boundary layer thickness.

[0043] Based on the above theoretical derivation, this invention quantifies the process control conditions as 5×10. 5 L·rpm / (min·m 2 )≤(Q / A)×N≤1×10 6 L·rpm / (min·m 2This invention incorporates Q and N into a unified synergistic control framework. By combining high-flow-rate blowing and high-speed centrifugal suction to thin the boundary layer, the boundary layer is significantly thinned, allowing the activated, high-concentration nitrogen species to be efficiently pushed to the deposition surface for lattice incorporation. Controlling (Q / A)×N within the aforementioned range ensures sufficient boundary layer thinning for efficient nitrogen doping while avoiding problems such as excessively high gas flow rate leading to short MTS residence time and decreased deposition efficiency, and excessively high rotation speed causing excessive equipment load and wafer cracking. This achieves a balance between doping effect and process stability. The equation also incorporates the substrate surface area A for normalization, making the control conditions applicable to the fabrication of wafers of different sizes. When the total gas flow rate per unit area is relatively lower on large-size substrates, this can be compensated for by increasing the rotation speed N, thus ensuring the method is stably applicable to the fabrication of wafers of different sizes.

[0044] Through the synergistic effect of the above mechanisms, high-concentration active nitrogen species are efficiently transported to the growth interface. Nitrogen atoms then replace silicon sites as donor impurities within the SiC grains, significantly increasing the carrier concentration inside the grains. Simultaneously, nitrogen atoms accumulate in the grain boundary regions, effectively reducing the grain boundary barrier and weakening its obstruction to carrier transport. This synergistic improvement in grain conductivity and grain boundary conductivity leads to a substantial decrease in the overall resistivity of the polycrystalline system. Furthermore, the flow field homogenization effect brought about by high-speed rotation makes the boundary layer thickness more uniform across the substrate surface. Combined with the spatial layout advantage of independent nitrogen feeding, this ensures uniform doping flux throughout the wafer plane, thereby achieving excellent in-plane resistivity uniformity.

[0045] Therefore, this invention can stably prepare polycrystalline silicon carbide wafers with a room temperature resistivity of no more than 1 mΩ·cm, and the method has good adaptability to substrates of different sizes, especially solving the problem of preparing large-size polycrystalline silicon carbide wafers with low resistivity. Meanwhile, by using safe and stable nitrogen gas instead of highly reactive ammonia gas as the dopant source, the potential safety hazards of the process are fundamentally eliminated, avoiding problems such as rough wafer surface and poor uniformity caused by the pre-reaction of ammonia gas with the precursor. Furthermore, the process is simple, highly controllable, and suitable for large-scale industrial production.

[0046] In some embodiments, the flow rate ratio of hydrogen to methyltrichlorosilane is preferably 15:1 to 50:1, and the flow rate ratio of nitrogen to methyltrichlorosilane is preferably 15:1 to 100:1. This ensures sufficient activation of nitrogen molecules by hydrogen and an absolutely abundant supply of nitrogen, achieving efficient doping, while avoiding excessive dilution of MTS concentration and reduction of deposition rate due to excessive hydrogen or nitrogen flow rates, thus ensuring a balance between doping efficiency and deposition rate.

[0047] In some embodiments, the preferred flow rate of the methyltrichlorosilane is 0.5 L / min to 3 L / min, the preferred flow rate of the hydrogen is 25 L / min to 200 L / min, the preferred flow rate of the nitrogen is 10 L / min to 200 L / min, and the rotational speed N of the rotating stage 106 is 500 rpm to 5000 rpm, which is beneficial to ensure the doping efficiency while taking into account the deposition rate, raw material utilization rate and equipment stability.

[0048] In some embodiments, the chemical vapor deposition temperature is 1200℃~1600℃, and the pressure is 10kPa~30kPa. This setting ensures that the MTS is fully decomposed to provide sufficient silicon and carbon sources, and also facilitates the effective incorporation of nitrogen atoms into the SiC lattice and their stable occupation of silicon sites. Simultaneously, it avoids problems such as insufficient deposition rate or poor crystal quality due to excessively low temperature, or grain coarsening and increased stress due to excessively high temperature, and decreased deposition rate due to excessively low pressure.

[0049] It is understood that the deposition time of the chemical vapor deposition can be determined based on the target wafer thickness and deposition rate.

[0050] In some embodiments, during the heating process, when the temperature reaches 800℃~1200℃, nitrogen gas is first introduced into the reaction chamber 101 through the second feed port 103, allowing the nitrogen gas to be evenly distributed within the reaction chamber 101 and removing residual air. When the temperature reaches 1200℃~1600℃, hydrogen gas is then introduced into the reaction chamber 101 through the first feed port 102. The hydrogen gas dissociates at high temperature to generate atomic hydrogen, which fully contacts the nitrogen molecules already evenly distributed within the chamber and activates them into active nitrogen species. After the temperature and pressure stabilize, methyltrichlorosilane is mixed with hydrogen to form a mixed gas, which is then introduced into the reaction chamber 101 through the first feed port 102 to begin chemical vapor deposition. Thus, by using a stepwise gas introduction method, each gas can be introduced sequentially and play its role within the optimal temperature window, which is beneficial for improving the activation efficiency of nitrogen gas and the stability of the deposition process, thereby obtaining a high-quality polycrystalline silicon carbide deposition layer.

[0051] In some embodiments, the second feed inlet 103 can be located at the top of the reaction chamber 101 and directly above the substrate 109, while the first feed inlet 102 is located on the side wall of the reaction chamber 101. Thus, the axis of the first feed inlet 102 is parallel to the surface of the substrate 109, allowing the mixed gas to flow in a parallel direction after entering the reaction chamber 101, extending the thermal decomposition path of MTS before reaching the surface of the substrate 109, and ensuring that MTS is fully decomposed into silicon- and carbon-containing active intermediates. The axis of the second feed inlet 103 is perpendicular to the surface of the substrate 109, allowing nitrogen gas to be directly transported towards the surface of the substrate 109 in a vertical direction, shortening the transport distance of nitrogen species, reducing losses during transport, and increasing the concentration and doping efficiency of nitrogen species reaching the deposition surface. Therefore, through the coordination of the feed direction and spatial layout, the supply paths of the main reactants and dopants can be kept separate, which is beneficial for achieving efficient nitrogen doping while ensuring the full decomposition of MTS.

[0052] In order to provide sufficient space and time for the MTS to decompose fully into silicon- and carbon-containing active intermediates before reaching the substrate surface, and to avoid premature gas-phase nucleation or excessive dilution of the active intermediates during transport due to excessive distance, the shortest distance between the first feed port 102 and the substrate 109 is 10mm to 100mm.

[0053] In order to shorten the transport distance of nitrogen species, reduce losses during transport, and improve the concentration and doping efficiency of nitrogen species reaching the deposition surface, the shortest distance between the second feed port and the substrate is 5mm to 50mm.

[0054] It is understood that the specific material and size of the substrate 109 are not limited, and a suitable substrate material and size can be selected according to actual needs during production. Preferably, the substrate 109 is a graphite substrate. Graphite substrates have excellent high-temperature stability and chemical inertness, and are not easily corroded or degraded in high-temperature hydrogen and chlorine-containing precursor environments. They can provide stable support for the deposition of polycrystalline silicon carbide wafers. At the same time, in order to meet the needs of large-size wafer fabrication, the diameter of the substrate 109 is greater than or equal to 12 inches.

[0055] It is understood that after chemical vapor deposition is completed, a polycrystalline silicon carbide deposition layer is formed on the surface of the substrate 109. The substrate 109 with the polycrystalline silicon carbide deposition layer is removed from the reaction chamber 101, and the substrate 109 is removed to obtain the polycrystalline silicon carbide material. The polycrystalline silicon carbide material is then sliced, ground and polished in sequence to obtain a polycrystalline silicon carbide wafer.

[0056] The technical solution of the present invention will be further described below through specific embodiments. However, those skilled in the art will understand that the following embodiments are only for illustrating the present invention and should not be regarded as limiting the scope of the present invention. Unless otherwise specified, specific conditions in the embodiments are performed under conventional conditions or conditions recommended by the manufacturer. Reagents or instruments used without specified manufacturers are all commercially available conventional products.

[0057] Example 1

[0058] A 320mm diameter graphite substrate was selected as the growth substrate, and its surface was subjected to mechanical grinding and fine polishing to reduce surface roughness. Subsequently, the treated graphite substrate was ultrasonically cleaned in a cleaning solution to remove adhering particles and impurities. After cleaning, the graphite substrate was placed in an oven and dried at approximately 200℃ for 6 hours to completely remove residual moisture.

[0059] The pretreated graphite substrate was mounted on the rotating stage of a chemical vapor deposition (CVD) apparatus. In this apparatus, a first inlet is located on the side wall of the reaction chamber, its axis parallel to the substrate surface and 100 mm away from the substrate surface, for introducing a mixture of MTS and H2 gas. A second inlet is located at the top of the reaction chamber, directly above the substrate, its axis perpendicular to the substrate surface and 30 mm away from the substrate surface, for introducing N2 gas. The shortest distance between the second inlet and the substrate is less than that between the first inlet and the substrate. After closing the reaction chamber door, the reaction chamber is evacuated to a vacuum level of approximately 1 × 10⁻⁶. -4 Pa. Then the chamber outlet valve was closed, and the vacuum state was maintained for about 1 hour to conduct a pressure holding test to confirm that there was no gas leakage in the reaction chamber.

[0060] After the pressure holding test is completed, the heating system is activated to heat the reaction chamber. When the chamber temperature reaches 800°C, N2 is first introduced into the reaction chamber through the second feed port. When the temperature further rises to 1400°C, H2 is then introduced into the reaction chamber through the first feed port. Simultaneously, the rotary motor is activated to drive the rotating stage to rotate at a set speed. During the heating and deposition process, the pressure in the reaction chamber is stably controlled at approximately 10 kPa, and the chamber temperature is monitored in real time using thermocouples installed within the chamber.

[0061] After the temperature and pressure of the reaction chamber stabilize, MTS and H2 are mixed in a mixing tank to form a mixed gas, which is then introduced into the reaction chamber through the first feed port. At the same time, N2 is continuously introduced through the second feed port to perform chemical vapor deposition on the substrate surface.

[0062] During deposition, the transport flow rates of MTS were controlled at 1.0 L / min, H2 at 50 L / min, and N2 at 50 L / min, i.e., H2:MTS = 50:1 and N2:MTS = 50:1. The total gas flow rate of H2, MTS, and N2 was Q = 101 L / min. The substrate diameter was 320 mm, and the substrate surface area was A ≈ 0.0804 m². 2 Gas flow rate per unit area q = Q / A ≈ 1256 L / (min·m 2 If the rotational speed of the stage is N = 500 rpm, then (Q / A) × N = 1256 × 500 = 6.28 × 10⁻⁶. 5 L·rpm / (min·m 2 ).

[0063] After 20 hours, the inlet valves for MTS and other gases were closed sequentially, and the heating power was turned off. The reaction chamber was allowed to cool naturally to room temperature under inert gas protection. Once the chamber temperature reached room temperature, the rotating stage was stopped, and argon gas was introduced while keeping the chamber sealed. The chamber door was then opened, and the deposited sample was removed. A polycrystalline silicon carbide layer was formed on the graphite substrate. The substrate with the polycrystalline silicon carbide layer was removed from the reaction chamber, and the graphite substrate was removed to obtain the polycrystalline silicon carbide material. The obtained polycrystalline silicon carbide material was then sequentially sliced, ground, and polished to obtain the desired product. Figure 2 The polycrystalline silicon carbide wafer shown.

[0064] Example 2

[0065] The difference between Example 2 and Example 1 lies only in that, during the deposition process, the MTS delivery flow rate is controlled at 2.0 L / min, the H2 delivery flow rate at 100 L / min, and the N2 delivery flow rate at 100 L / min, i.e., H2:MTS = 50:1 and N2:MTS = 50:1. The total gas flow rate of H2, MTS, and N2 is Q = 202 L / min. The substrate diameter is 320 mm, and the substrate surface area is A ≈ 0.080 m². 2 Gas flow rate per unit area q = Q / A ≈ 2512 L / (min·m 2 The rotational speed of the stage is N = 200 rpm, then (Q / A) × N = 2512 × 200 = 5.02 × 10⁻⁶ 5 L·rpm / (min·m 2 ).

[0066] Example 3

[0067] The difference between Example 3 and Example 1 lies only in the use of a graphite substrate with a diameter of 250 mm. During the deposition process, the MTS delivery flow rate was controlled at 1.0 L / min, the H2 delivery flow rate at 50 L / min, and the N2 delivery flow rate at 50 L / min, i.e., H2:MTS = 50:1 and N2:MTS = 50:1. The total gas flow rate of H2, MTS, and N2 was Q = 101 L / min. The substrate diameter was 250 mm, and the substrate surface area was A ≈ 0.049 m². 2 Gas flow rate per unit area q = Q / A ≈ 2061 L / (min·m 2 The rotational speed of the stage is N = 300 rpm, then (Q / A) × N = 2061 × 300 = 6.18 × 10⁻⁶. 5 L·rpm / (min·m 2 ).

[0068] Example 4

[0069] Example 4 is essentially the same as Example 1. During the deposition process, the MTS delivery flow rate is controlled at 1.0 L / min, the H2 delivery flow rate at 30 L / min, and the N2 delivery flow rate at 30 L / min, i.e., H2:MTS = 30:1, N2:MTS = 30:1. The total gas flow rate of H2, MTS, and N2 is Q = 61 L / min. The substrate diameter is 320 mm, and the substrate surface area is A ≈ 0.080 m². 2 The gas flow rate per unit area is q = Q / A ≈ 762 L / (min·m²). 2 The rotational speed of the stage is N = 700 rpm, then (Q / A) × N = 762 × 700 = 5.33 × 10⁻⁶. 5 L·rpm / (min·m 2 ).

[0070] Comparative Example 1

[0071] The only difference between Comparative Example 1 and Example 1 is the rotational speed. A 320mm diameter graphite substrate was used, and the rotational speed N = 200 rpm. During deposition, the MTS delivery flow rate was controlled at 1.0 L / min, the H2 delivery flow rate at 50 L / min, and the N2 delivery flow rate at 50 L / min, i.e., H2:MTS = 50:1, N2:MTS = 50:1. The total gas flow rate of H2, MTS, and N2 was Q = 101 L / min. The substrate diameter was 320mm, and the substrate surface area was A ≈ 0.0804 m². 2 Gas flow rate per unit area q = Q / A ≈ 1256 L / (min·m 2 ). (Q / A)×N=1256×200=2.5×10 5 L·rpm / (min·m 2Due to the low rotational speed, the product of the gas flow rate per unit area and the rotational speed is less than 5 × 10⁻⁶. 5 L·rpm / (min·m 2 Insufficient mass transfer rate leads to high resistivity of the wafer.

[0072] Comparative Example 2

[0073] The only difference between Comparative Example 2 and Example 1 is that during the deposition process, the MTS delivery flow rate was controlled at 0.2 L / min, the H2 delivery flow rate at 10 L / min, and the N2 delivery flow rate at 10 L / min, i.e., H2:MTS = 50:1 and N2:MTS = 50:1. The total gas flow rate Q of H2, MTS, and N2 was 20.2 L / min. The substrate diameter was 320 mm, and the substrate surface area A ≈ 0.0804 m². 2 Gas flow rate per unit area q = Q / A ≈ 251 L / (min·m 2 ). (Q / A)×N=251×500=1.25×10 5 L·rpm / (min·m 2 Due to the low total gas flow rate, the product of the gas flow rate per unit area and the rotational speed is less than 5 × 10⁻⁶. 5 L·rpm / (min·m 2 Insufficient mass transfer rate leads to high resistivity of the wafer.

[0074] Comparative Example 3

[0075] The only difference between Comparative Example 3 and Example 1 is that during the deposition process, the MTS delivery flow rate was controlled at 1.0 L / min, the H2 delivery flow rate at 50 L / min, and the N2 delivery flow rate at 50 L / min, i.e., H2:MTS = 50:1 and N2:MTS = 50:1. The total gas flow rate of H2, MTS, and N2 was Q = 101 L / min. The substrate diameter was 320 mm, and the substrate surface area was A ≈ 0.0804 m². 2 Gas flow rate per unit area q = Q / A ≈ 1256 L / (min·m 2 If the rotational speed of the stage is N = 1000 rpm, then (Q / A) × N = 1256 × 1000 = 1.25 × 10⁻⁶. 6 L·rpm / (min·m 2 Although the nitrogen doping efficiency meets the requirements, the large value of (Q / A)×N prevents the MTS from reacting sufficiently, resulting in a slow growth rate. Furthermore, the spherical microstructure of the wafer leads to excessive stress and SiC wafer cracking during slicing.

[0076] Comparative Example 4

[0077] The only difference between Comparative Example 4 and Example 1 is that during the deposition process, the MTS delivery flow rate was controlled at 1.0 L / min, the H2 delivery flow rate at 10 L / min, and the N2 delivery flow rate at 10 L / min, i.e., H2:MTS = 10:1 and N2:MTS = 10:1. The total gas flow rate Q of H2, MTS, and N2 was 21 L / min. The substrate diameter was 320 mm, and the substrate surface area A ≈ 0.0804 m². 2 Gas flow rate per unit area q = Q / A ≈ 261 L / (min·m 2 If the rotational speed of the stage is N = 2000 rpm, then (Q / A) × N = 261 × 2000 = 5.2 × 10⁻⁶. 5 L·rpm / (min·m 2 Although reducing the H2 / MTS and N2 / MTS ratios and increasing the rotary table speed can ensure that the product of gas flow rate and rotation speed per single surface area is greater than 5 × 10⁻⁶, this can be achieved. 5 L·rpm / (min·m 2 However, due to the high rotation speed, the strength of graphite at high temperatures is insufficient to support the edge stress, resulting in problems such as the graphite substrate detaching from the sample stage, or excessive stress on the SiC wafer causing edge chipping during cutting.

[0078] Comparative Example 5

[0079] The only difference between Comparative Example 5 and Example 1 is that the reaction device without dual inlets is not used; N2, H2, and MTS all enter the chamber through an inlet 100 mm in front of the sample. Because the mean free path of N ions generated after nitrogen ionization at high temperature is short, they easily recombine and lose reactivity during transport to the wafer surface, resulting in a higher final resistivity.

[0080] The polycrystalline silicon carbide wafers obtained in the above embodiments and comparative examples were subjected to room temperature resistivity tests. The test results for Example 1 are as follows: Figure 3 As shown in Table 1, the results are as follows.

[0081] Table 1

[0082]

[0083] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0084] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for preparing a polycrystalline silicon carbide wafer, characterized in that, Includes the following steps: A mixture of methyltrichlorosilane and hydrogen is introduced into the reaction chamber of the chemical vapor deposition equipment through the first feed port, and nitrogen is introduced into the reaction chamber through the second feed port. Chemical vapor deposition is performed on the substrate surface, and polycrystalline silicon carbide wafers are obtained after the deposition is completed. Wherein, the shortest distance between the second feed inlet and the substrate is less than the shortest distance between the first feed inlet and the substrate; the flow rate ratio of hydrogen to methyltrichlorosilane is greater than 10:1; the flow rate ratio of nitrogen to methyltrichlorosilane is greater than 10:1; the total flow rate of hydrogen, methyltrichlorosilane, and nitrogen is Q; the substrate is placed on the rotating stage of the chemical vapor deposition apparatus; the rotating stage is controlled to rotate at a speed N; and the speed N of the rotating stage and the total flow rate Q of the gas entering the reaction chamber satisfy 5 × 10⁻⁶. 5 L·rpm / (min·m 2 )≤(Q / A)×N≤1×10 6 L·rpm / (min·m 2 A is the surface area of ​​the substrate.

2. The method for preparing polycrystalline silicon carbide wafers according to claim 1, characterized in that, The ratio of the flow rate of hydrogen to that of methyltrichlorosilane is 15:1 to 50:

1.

3. The method for preparing polycrystalline silicon carbide wafers according to claim 1, characterized in that, The ratio of nitrogen flow rate to methyltrichlorosilane flow rate is 15:1 to 100:

1.

4. The method for preparing polycrystalline silicon carbide wafers according to claim 1, characterized in that, The flow rate of the methyltrichlorosilane is 0.5 L / min to 3 L / min; And / or, the hydrogen delivery flow rate is 25 L / min to 200 L / min; And / or, the nitrogen flow rate is 10L / min to 200L / min.

5. The method for preparing polycrystalline silicon carbide wafers according to claim 1, characterized in that, The rotational speed N of the rotating stage is 500 rpm to 5000 rpm.

6. The method for preparing a polycrystalline silicon carbide wafer according to claim 1, characterized in that, The chemical vapor deposition temperature is 1200℃~1600℃, and the pressure is 10kPa~30kPa.

7. The method for preparing a polycrystalline silicon carbide wafer according to claim 6, characterized in that, During the heating process, when the temperature reaches 800℃~1200℃, nitrogen gas is first introduced into the reaction chamber. When the temperature reaches 1200℃~1600℃, hydrogen gas is then introduced into the reaction chamber. After the temperature and pressure stabilize, methyltrichlorosilane is mixed with hydrogen gas to form a mixed gas and then introduced.

8. The method for preparing a polycrystalline silicon carbide wafer according to claim 1, characterized in that, The axis of the first feed port is parallel to the surface of the substrate, and the axis of the second feed port is perpendicular to the surface of the substrate.

9. The method for preparing a polycrystalline silicon carbide wafer according to claim 1, characterized in that, The shortest distance between the first feed inlet and the substrate is 10mm~100mm; And / or, the shortest distance between the second feed port and the substrate is 5mm to 50mm.

10. The method for preparing a polycrystalline silicon carbide wafer according to claim 1, characterized in that, The diameter of the substrate is greater than or equal to 12 inches.

Images