High-uniformity silicon carbide substrate, preparation method thereof and semiconductor device
By controlling the movement trend of the growth characteristic surface during the growth process of the silicon carbide substrate and fixing it to the crystal edge, the doping and carrier uniformity problems caused by the growth characteristic surface are solved, and a high uniform silicon carbide liner is achieved The preparation of the bottom improves the performance and reliability of the device and is suitable for the large-scale production of silicon carbide substrates.
Patent Information
- Application Number
- CN202411279473.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Priority Date
- 2023-10-09
- Filing Date
- 2024-05-11
- Publication Date
- 2024-12-13
AI Technical Summary
The growth characteristic surface of the silicon carbide substrate during the growth process leads to uneven doping and poor carrier uniformity, which limits the performance and reliability of the device, especially in large-scale production and application.
By setting a discontinuous temperature gradient distribution during the growth process of the silicon carbide substrate, the movement trend of the growth characteristic surface is controlled, so that it moves toward the edge of the crystal, thereby eliminating the growth characteristic surface after cutting and processing, achieving a full area range High uniformity within.
It realizes high uniformity of silicon carbide substrates, improves doping uniformity, carrier uniformity and resistivity uniformity, improves the yield and reliability of the device, reduces production costs, and is suitable for large-scale industrialization. application.
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Figure CN119121404A_ABST
Abstract
Description
[0001] This application is a divisional application with application number CN202410579039.7. The application date of the original application is May 11, 2024, the priority date is October 9, 2023, and the name of the invention is a highly uniform silicon carbide substrate, a preparation method thereof, and a semiconductor device. Technical Field
[0002] The present invention relates to the technical field of silicon carbide wafers, and in particular to a silicon carbide substrate with high uniformity, a preparation method thereof, and a semiconductor device. Background Art
[0003] Silicon carbide semiconductors have attracted much attention due to their excellent physical properties such as large bandgap, high breakdown field strength, and high thermal conductivity. Power devices based on silicon carbide single crystal substrates have excellent properties such as high voltage resistance, high temperature resistance, and low loss, and are therefore widely used in new energy vehicles, photovoltaics, and power grid industries. After years of technological and industrial development, silicon carbide single crystal substrate preparation technology has made great progress, but it still faces some problems, including: 1. Substrate quality issues, which affect the yield, performance, and reliability of silicon carbide devices; 2. Substrate cost issues, which affect the application of silicon carbide at the terminal. Among them, the loss of material and device yield caused by material quality is also the main reason for the current high cost and difficulty in application of silicon carbide.
[0004] Furthermore, the quality problems of silicon carbide substrates include two categories: one is the explicit quality problems such as material quality and yield caused by defects, which can be better reflected in the substrate material indicators; the other is the material yield and device performance reliability problems caused by quality consistency problems, which are often difficult to reflect in the substrate material indicators, thus bringing greater risks to the reliability of subsequent device applications.
[0005] Such "facets" will exist on SiC crystals and substrates prepared by conventional physical vapor transport methods. This "facet" refers to the growth characteristic surface, which is collectively referred to as the growth characteristic surface in the present invention. There are many names for the growth characteristic surface, among which the growth characteristic surface is commonly known as "small face", "growth small face", "characteristic growth surface" and the like in the field. Due to the existence of the growth characteristic surface, defects will be concentrated in this area, and the elements will be induced to gather and increase at the growth characteristic surface during the element doping process, which will manifest as uneven doping, making the resistivity at the growth characteristic surface higher than other areas. The overall substrate has poor carrier uniformity, which will limit the large-scale use of silicon carbide substrates. In addition, the growth characteristic surface in the present invention does not refer to the growth interface.
[0006] Furthermore, the growth feature surface is an inherent property of SiC crystals prepared by the sublimation method. Such growth feature surfaces exist on SiC crystals and substrates prepared by conventional physical vapor transport (PVT). The growth feature surface area has a higher doping concentration than other areas. Therefore, the carrier concentration and resistivity in the growth feature surface area are significantly different from those in other areas, resulting in abnormal quality problems in the electrical properties and defect states of the growth feature surface area.
[0007] Therefore, improving substrate quality and reducing substrate costs are the goals of the sustainable development of silicon carbide crystal materials. Especially at the stage where the silicon carbide industry is rapidly entering large-scale production and application, the stability, consistency and reliability of the performance of silicon carbide materials will play a vital role in the development of the industry. The present invention focuses on the problem of consistency of electrical properties during the preparation of silicon carbide single crystals, with the aim of solving the problem of inconsistent electrical properties caused by the intrinsic characteristics of silicon carbide during growth and the potential performance and reliability risks of the device end caused by this. Summary of the invention
[0008] In order to solve the above problems, the first aspect of the present invention provides a high-uniformity silicon carbide substrate, which is conductive and does not contain any one or more of the growth feature surface, high-doping area and defect aggregation area within its entire area. The properties of the silicon carbide substrate within the entire area satisfy any one or two of the following a to b;
[0009] a. Doping concentration change rate <10%;
[0010] b. Carrier concentration change rate is less than 5%.
[0011] Optionally, the silicon carbide substrate is n-type doped, and the n-type element doping concentration is ≥ 1E 18 cm -3 , and does not contain any one or both of a high-doping region and a defect aggregation region within its entire area; the silicon carbide substrate is prepared by a PVT method.
[0012] The growth characteristic surface is an inherent property of SiC crystals prepared by the PVT method. The high-uniformity silicon carbide substrate in this application can change the movement trend of the growth characteristic surface during PVT growth, so that it moves to the edge of the crystal and is fixed within 5 mm from the edge of the crystal. When the crystal is actually used, the edge is cut. Therefore, after the crystal is cut, ground, polished and other processes, a silicon carbide substrate without a growth characteristic surface can be obtained.
[0013] Due to the existence of the growth feature surface in the original substrate, defects will be concentrated in this area. The element doping process will induce the elements to gather and increase at the growth feature surface, thus showing uneven doping. The resistivity at the growth feature surface is also higher than that in other areas, and the carrier uniformity of the overall substrate is poor. The above limits the large-scale use of silicon carbide substrates.
[0014] The high-uniformity silicon carbide substrate in the present application has no growth feature surface, and the substrate as a whole is uniformly distributed in both radial and axial directions. Therefore, it is possible to fundamentally curb the generation and aggregation of defects, avoid element aggregation during the doping process, and achieve uniform element doping, thereby improving the doping uniformity, resistivity uniformity and carrier uniformity of the substrate. Therefore, the devices produced using the silicon carbide substrate not only have good performance themselves, but also have good consistency in mass production, which is conducive to industrial promotion and use.
[0015] Optionally, the main doping element in the n-type doping is N element, and in addition to N element, other elements may be co-doped, such as V group elements phosphorus, arsenic, etc.; IV group elements Ge, Sn, etc.; III group elements B, Al, etc.
[0016] Optionally, the doping concentration change rate may be less than 8%; or the doping concentration change rate may be less than 5%; or the doping concentration change rate may be less than 3%.
[0017] Optionally, the carrier concentration change rate is less than 3%; or the carrier concentration change rate is less than 2%; or the carrier concentration change rate is less than 1%.
[0018] Optional, doping concentration not higher than 5E 19 cm -3 , the carrier concentration change rate is less than 5%.
[0019] Optionally, the n-type element doping is N2 doping, the doping concentration change rate is less than 3%, and the carrier concentration change rate is less than 1%.
[0020] The doping concentration change rate is "the maximum doping concentration in the silicon carbide substrate surface - the minimum doping concentration in the silicon carbide substrate surface"; the carrier concentration change rate is "the maximum carrier concentration in the silicon carbide substrate surface - the minimum carrier concentration in the silicon carbide substrate surface".
[0021] The above N-type element doping concentration is greater than 1e 18 cm -3 , which belongs to medium to high nitrogen doping. For those skilled in the art, the higher the doping concentration, the more likely it is that there will be uneven doping. In the process of controlling the movement trend of the growth feature surface, the present application fixes the growth feature surface at the edge of the crystal, thereby improving the doping uniformity during the doping process and making the resistivity of the substrate more uniform.
[0022] The carriers are related to the doping concentration and uniformity in the crystal. The carrier concentration change rate of the silicon carbide substrate of the present application is less than 5%, which can represent the uniformity of the carriers of the silicon carbide substrate, thereby helping to improve the quality of the downstream device-end lithography process and thus improve device performance.
[0023] Optionally, the TDV density of the silicon carbide substrate is less than 100 cm -2 Preferably, the TDV density of the silicon carbide substrate is less than 50cm -2 More preferably, the TDV density of the silicon carbide substrate is less than 10cm -2 .
[0024] The total density variation (TDV) is defined as: a number of squares with specific areas are divided in the substrate, such as n squares with areas of 1mmx1mm, 2mmx2mm, 5mmx5mm, and 10mmx10mm, and the density of edge dislocations (TED) or screw dislocations (TSD) in the squares is d1, d2, d3...dn. TDV is the difference between the maximum TED / TSD density and the minimum TED / TSD density dmax-dmin.
[0025] Optionally, the total TED density variation of the silicon carbide substrate is less than 100 cm -2 Preferably, the total TED density variation of the silicon carbide substrate is less than 50 cm -2 More preferably, the total TED density variation of the silicon carbide substrate is less than 10 cm -2 .
[0026] Since the growth feature surface is eliminated in the silicon carbide substrate of the present application, the TED and TSD distribution can be made more uniform, so the TDV value is relatively low, which means that the dislocation distribution of the entire substrate is relatively uniform, eliminating the problem of low overall defect density but high local density in the current substrate.
[0027] Optionally, the total density variation of the silicon carbide substrate basal plane dislocation (BPD) is less than 50 cm -2 Preferably, the total BPD density variation of the silicon carbide substrate is less than 20 cm -2 More preferably, the total BPD density variation of the silicon carbide substrate is less than 10 cm -2 .
[0028] When the above substrate is used to prepare power electronic devices, due to the characteristics of low doping concentration change rate and low carrier concentration change rate, the device can be guaranteed to have excellent electrical performance and reliability during the device production process.
[0029] Optionally, the size of the silicon carbide substrate may be 4 inches, 6 inches, 8 inches, 10 inches or 12 inches.
[0030] A second aspect of the present invention provides a method for preparing a high-uniformity silicon carbide substrate, wherein the silicon carbide substrate is obtained by at least cutting a crystal, and the preparation method includes a crystal stable growth stage, and the growth process conditions of the crystal stable growth stage include the following steps:
[0031] S1: A discontinuous temperature gradient distribution is set in the radial direction of the crystal growth surface, there is a limiting edge near the crystal growth edge, the distance between the limiting edge and the crystal growth edge is not more than 6mm, and a continuous and positive temperature gradient is set from the limiting edge to the crystal center; the temperature gradient within the range between the limiting edge and the crystal growth edge is ≥2℃ / cm, and the temperature gradient value within the range between the limiting edge and the crystal growth edge is greater than the temperature gradient value from the limiting edge to the crystal center.
[0032] S2: Set the seed crystal to have a deviation angle of >0° along <11-20> or <1-100> or any other crystal direction parallel to the c-plane direction.
[0033] S3: Setting the angle α of the crystal growth graphite ring parallel to the crystal growth direction to be greater than 0°.
[0034] S4: Sufficient silicon carbide powder is arranged between the inner wall of the crystal growth chamber and the crystal growth graphite ring, so as to ensure that the SiC crystal has sufficient reaction atmosphere for lateral growth and a chemical environment for continuous lateral growth of the SiC crystal. The highly uniform silicon carbide substrate is obtained by processing the SiC crystal.
[0035] Optionally, the temperature gradient within the range between the defined edge and the crystal growth edge in step S1 is ≥5°C / cm;
[0036] and / or the seed crystal has a deflection angle of >2° along the <11-20> crystal direction in step S2;
[0037] And / or in step S3, the angle α of the crystal growing graphite ring parallel to the crystal growth direction is ≥8°.
[0038] Optionally, the distance between the limiting edge and the crystal growth edge is no more than 5 mm.
[0039] Optionally, in step S1: with 5 mm from the crystal growth edge as the boundary, a continuous and positive temperature gradient is set within a range greater than 5 mm from the crystal growth edge, the continuous and positive temperature gradient value is ≤3°C / cm, and the temperature gradient within a range less than 5 mm from the crystal growth edge is ≥5°C / cm. For example, refer to Figure 6As shown, the origin of the coordinate axis represents the center of the wafer, and a discontinuous temperature gradient distribution is set in the radial direction of the crystal growth surface. The positive temperature gradient within the range greater than 5 mm from the crystal growth edge is a continuous smooth curve, and the temperature gradient within the range less than 5 mm from the crystal growth edge is greater than the temperature gradient within the range greater than 5 mm from the crystal growth edge.
[0040] The radial temperature gradient is calculated as the ratio of the temperature difference (T2-T1) between the temperature T1 at a point closer to the center of the wafer and the temperature T2 at a point farther from the center of the wafer, and the distance d between the two points in the radial direction radiating outward from the center of the wafer. The positive (positive) temperature gradient ΔT = (T2-T1) / d; otherwise, it is a negative temperature gradient, ΔT = (T1-T2) / d.
[0041] The preparation method adopted in the present application is that under the setting of step S1, during the crystal growth process, the edge is also constantly growing and expanding in diameter. During the crystal growth process, the present invention controls the temperature gradient value within a range of less than 6 mm from the crystal growth edge to be greater than the temperature gradient value within a range of more than 6 mm from the crystal growth edge, thereby ensuring that the crystal edge has sufficient lateral growth driving force and the continuous expansion growth ability of the crystal edge. The growth feature surface is driven to move toward the edge of the crystal by expansion growth and fixed within 5 mm of the edge of the crystal to obtain a highly uniform silicon carbide substrate. However, it can be understood by those skilled in the art that the movement trend of the growth feature surface may also be controlled by other means to obtain the silicon carbide substrate of the present application, so the present application only illustrates the preparation method of the high uniformity silicon carbide substrate prepared this time, and other methods for controlling the trend of the growth feature surface are not within the scope of the present application.
[0042] The radial temperature gradient of crystal growth in step S1 can be set by conventional technical means in the industry, such as adjusting the temperature or pressure in the growth chamber or the thickness of the insulation layer material for overall adjustment. The discontinuous temperature gradient setting can be achieved by structurally improving the crystal growth chamber and optimizing the temperature distribution of the crystal growth interface, so as to achieve controllable adjustment of the temperature gradient, such as placing a material with lower thermal conductivity than the central area at the edge of the crystal growth chamber to reduce the heat loss at the edge, thereby achieving a temperature distribution jump at the crystal growth interface; conversely, such as placing a material with higher thermal conductivity at the edge of the crystal growth or reducing the thickness of the edge insulation layer, etc., a reverse temperature gradient distribution can be set; in addition, different thermal field structures or new materials can be set in the growth chamber to adjust the temperature distribution, such as setting a TaC coating material coated with high reflectivity on the graphite ring at the edge of the crystal growth, so that the heat radiation in the growth chamber is concentrated to the edge of the crystal growth, thereby achieving a temperature gradient jump. Through the above more common technical means used in the industry, the scheme can be configured according to actual needs to achieve the purpose of adjusting the temperature gradient in the crystal growth chamber.
[0043] Optionally, during the stable crystal growth stage, the temperature in the growth chamber is first raised to above 2200°C at a rate of 10-50°C / min, and the pressure in the growth chamber is simultaneously reduced to 1-100 mbar, and then the crystal growth is carried out under the settings of steps S1-S4 and maintained for more than 50 hours.
[0044] Optionally, in the stable crystal growth stage, the temperature in the growth chamber is first increased to above 2200°C at a rate of 10-30°C / min, while the pressure is reduced to 5-50 mbar, and then maintained for more than 50 hours under the settings of steps S1-S4 for crystal growth.
[0045] In the present invention, the PVT method is used to prepare silicon carbide crystals, isostatic graphite is used as the raw material of the growth chamber (crucible) for crystal growth, and SiC powder is used as the raw material for crystal growth. In order to ensure the excellent and stable electrical properties of silicon carbide, the present invention preferably uses a silicon carbide synthetic powder with a certain purity, and the total impurity content of the silicon carbide powder is not higher than 1E 19 cm -3 More preferably, the total impurity content in the silicon carbide powder is not higher than 1E 17 cm -3 .
[0046] In the present invention, when silicon carbide crystals grow, SiC powder is loaded into a graphite crucible chamber and a SiC seed crystal is placed on the top of the growth chamber, the crucible is sealed, the crucible is wrapped in a thermal insulation material made of graphite soft felt or hard felt, and then moved into the chamber of a crystal growth device for crystal growth.
[0047] In the present invention, reference Figure 3 As shown, by arranging a graphite support component on the upper part of the SiC crucible, SiC powder is loaded between the graphite support component and the wall of the SiC crucible as a source of material for lateral growth, thereby ensuring that the radial growth caused by the lateral growth of the crystal has sufficient diameter expansion space. However, the present invention is not limited to this, and other design methods can also be used.
[0048] Optionally, before the crystal stable growth stage, a crystal nucleation stage is also included, and the growth process conditions of the crystal nucleation stage include the following steps:
[0049] After the crystal growth chamber is sealed, the growth chamber is evacuated to 10 -3 Pa, after the vacuum stage is stable for a period of time, inert gas is introduced to gradually increase the pressure in the growth chamber to 100-1000mbar and then stabilize it. At the same time, nitrogen is introduced into the chamber at 1ml / min-100ml / min.
[0050] Optionally, while the pressure in the growth chamber is increased during the crystal nucleation stage, the temperature in the growth chamber is gradually increased from room temperature to 1600-2100°C and then kept constant, and then the crystal stable growth stage is carried out after maintaining the constant temperature and pressure for 5-50 hours.
[0051] Optionally, during the crystal nucleation stage, the temperature in the growth chamber is kept constant at 1800-2100° C., and the pressure in the growth chamber is kept constant at 300-800 mbar. After maintaining the constant temperature and pressure for 30-50 hours, the crystal stable growth stage is performed.
[0052] In the crystal nucleation stage, the silicon carbide powder sublimates to form a crystal nucleus. In the subsequent stable crystal growth stage, the silicon carbide powder can fully sublimate and be transferred to the seed crystal for stable growth, and finally obtain a silicon carbide crystal. Since the seed crystal diameter is at least 5mm larger than the target crystal and the substrate diameter, the prepared SiC crystal has an edge processing allowance, and a highly uniform silicon carbide crystal can be obtained by cutting the edge. At the same time, it can ensure the smooth preparation of large-size silicon carbide substrates and improve the quality of the prepared silicon carbide substrates.
[0053] A third aspect of the present invention provides a semiconductor device including the above-mentioned silicon carbide substrate.
[0054] Compared with the prior art, the present invention achieves at least one of the following beneficial effects:
[0055] (1) The silicon carbide substrate prepared by the present invention has no growth feature surface visible to the naked eye, and the doping concentration change rate in the entire area is less than 10%, and the carrier concentration change rate is less than 5%, which means that the silicon carbide substrate has a high degree of uniformity. The semiconductor device prepared using the silicon carbide substrate has higher yield, performance and reliability.
[0056] (2) The TDV density of the silicon carbide substrate prepared by the present invention is less than 100 cm -2 , which eliminates the problem of low overall defect density but high local density in the current substrate, and there are almost no defects such as dislocations and stacking faults, so it is more suitable for large-scale promotion and use.
[0057] (3) The preparation method of the present invention can control the movement trend of the growth feature surface by regulating step S1 during the growth of the crystal, and lock it within 5 mm of the crystal edge area. After the crystal is cut, ground, polished, etc., the target silicon carbide substrate can be obtained.
[0058] (4) The silicon carbide substrate prepared by the present invention has a high degree of uniformity, for example, doping uniformity, carrier uniformity, etc. When the substrate is cut for use in preparing semiconductor devices, the effective area utilization rate can be improved. Compared with other substrates of the same area, the semiconductor devices prepared by the substrate not only have good performance, but also are larger in number, which can reduce the production cost of semiconductor devices. BRIEF DESCRIPTION OF THE DRAWINGS
[0059] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:
[0060] Figure 1 An exemplary embodiment of a schematic diagram of a silicon carbide substrate structure containing a growth feature surface visible to the naked eye is shown;
[0061] Figure 2 An exemplary embodiment of a schematic diagram of a growth process of a growth feature surface of the present invention is shown;
[0062] Figure 3 An exemplary embodiment of a schematic diagram of a silicon carbide crystal growth structure of the present invention is shown;
[0063] Figure 4 A comparison diagram of the carrier concentration of the silicon carbide substrate of Example 2 and the carrier concentration of the silicon carbide substrate of Comparative Example 1 is shown;
[0064] Figure 5 An exemplary embodiment of a schematic diagram of a silicon carbide substrate structure without growth feature surfaces is shown;
[0065] Figure 6 An exemplary embodiment of a schematic diagram showing a discontinuous temperature gradient radially arranged on a crystal growth surface of the present invention is shown. DETAILED DESCRIPTION
[0066] In order to more clearly illustrate the overall concept of the present invention, a detailed description is given below in an exemplary manner in conjunction with the accompanying drawings.
[0067] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention can also be implemented in other ways different from those described herein, and therefore, the scope of protection of the present invention is not limited by the specific embodiments disclosed below. In the description of this specification, the description of reference terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily have to be directed to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.
[0068] In the process of preparing the silicon carbide substrate in the following embodiments 1-6, the growth feature surface can be locked at the edge of the silicon carbide crystal. As the edge of the crystal is cut, a silicon carbide substrate without a growth feature surface is obtained. Due to the disappearance of the inherent structural attribute of the growth feature surface, the number of defects in the silicon carbide substrate itself is reduced and no aggregation will occur. At the same time, the aggregation of elements in doping can be avoided, that is, the existence of high-doping areas can be avoided, thereby improving the doping uniformity and carrier uniformity of the silicon carbide substrate with a structure without a growth feature surface.
[0069] Example 1
[0070] This embodiment relates to a method for preparing a 6-inch high-uniformity silicon carbide substrate, which specifically includes the following steps:
[0071] (1) Crystal nucleation stage
[0072] The silicon carbide powder and seed crystal were placed in the crucible, and then the growth chamber was sealed and evacuated to 10°C by a mechanical pump and a vacuum pump. -3 Pa, inert gas was introduced after a period of stabilization in the vacuum stage, and the pressure in the growth chamber was gradually increased to 100mbar, while nitrogen was introduced into the chamber at 10ml / min. During the crystal nucleation stage, while the pressure in the growth chamber was increased, the temperature in the furnace was gradually increased from room temperature to 1600℃ through power setting and maintained for 10h.
[0073] (2) Crystal stable growth stage
[0074] After the crystal nucleation stage, the temperature was raised to 2300°C at a rate of 20°C / min, and the pressure in the growth chamber was reduced to 3 mbar by adjusting the pressure controller and maintained for 60 hours.
[0075] S1: A discontinuous temperature gradient distribution is set in the radial direction of the crystal growth surface, with 3mm from the crystal growth edge as the boundary, and a continuous and positive temperature gradient is set within a range greater than 3mm from the crystal growth edge, and the continuous and positive temperature gradient value is 5℃ / cm; the temperature gradient within a range less than 3mm from the crystal growth edge is 10℃ / cm, so as to ensure that the crystal edge has sufficient lateral growth driving force and the crystal edge has the ability to continuously expand its diameter.
[0076] S2: setting the seed crystal's deflection angle along the <11-20> crystal direction to 1.5°;
[0077] S3: The angle α of the crystal growth graphite ring parallel to the crystal growth direction is set to 10°, so as to ensure that the radial growth caused by the lateral growth of the crystal has sufficient expansion space.
[0078] S4: Sufficient silicon carbide powder is placed between the inner wall of the crystal growth chamber and the crystal growth graphite ring to ensure that the SiC crystal has sufficient reaction atmosphere for lateral growth and a chemical environment for continuous lateral growth of the SiC crystal. The grown crystal is cut, ground, polished, etc. to obtain the target silicon carbide substrate.
[0079] Example 2
[0080] This embodiment relates to a method for preparing a 6-inch high-uniformity silicon carbide substrate, which specifically includes the following steps:
[0081] (1) Crystal nucleation stage
[0082] The silicon carbide powder and seed crystal were placed in the crucible, and then the growth chamber was sealed and evacuated to 10°C by a mechanical pump and a vacuum pump. -3 Pa, inert gas was introduced after a period of stabilization in the vacuum stage, and the pressure in the growth chamber was gradually increased to 400mbar, while nitrogen was introduced into the chamber at 40ml / min. During the crystal nucleation stage, while the pressure in the growth chamber was increased, the temperature in the furnace was gradually increased from room temperature to 1900℃ through power setting and maintained for 40h.
[0083] (2) Crystal stable growth stage
[0084] After the crystal nucleation stage, the temperature was raised to 2500°C at a rate of 30°C / min, and the pressure in the growth chamber was reduced to 20 mbar by adjusting the pressure controller and maintained for 60 hours.
[0085] S1: A discontinuous temperature gradient distribution is set in the radial direction of the crystal growth surface, with 5 mm from the crystal growth edge as the boundary, and a continuous and positive temperature gradient is set within a range greater than 5 mm from the crystal growth edge, with a continuous and positive temperature gradient value of 2°C / cm; the temperature gradient within a range less than 5 mm from the crystal growth edge is 8°C / cm, thereby ensuring that the crystal edge has sufficient lateral growth driving force and the crystal edge has the ability to continuously expand its diameter.
[0086] S2: Set the seed crystal's deflection angle along the <11-20> crystal direction to 1°;
[0087] S3: The angle α of the crystal growth graphite ring parallel to the crystal growth direction is set to 8°, so as to ensure that the radial growth caused by the lateral growth of the crystal has sufficient expansion space.
[0088] S4: Sufficient silicon carbide powder is placed between the inner wall of the crystal growth chamber and the crystal growth graphite ring to ensure that the SiC crystal has sufficient reaction atmosphere for lateral growth and a chemical environment for continuous lateral growth of the SiC crystal. The grown crystal is cut, ground, polished, etc. to obtain the target silicon carbide substrate.
[0089] Example 3
[0090] This embodiment relates to a method for preparing a 6-inch high-uniformity silicon carbide substrate, which specifically includes the following steps:
[0091] (1) Crystal nucleation stage
[0092] The silicon carbide powder and seed crystal were placed in the crucible, and then the growth chamber was sealed and evacuated to 10°C by a mechanical pump and a vacuum pump. -3 Pa, inert gas was introduced after a period of stabilization in the vacuum stage, and the pressure in the growth chamber was gradually increased to 900mbar, while nitrogen was introduced into the chamber at 60ml / min. During the crystal nucleation stage, while the pressure in the growth chamber was increased, the temperature in the furnace was gradually increased from room temperature to 2000℃ through power setting and maintained for 40h.
[0093] (2) Crystal stable growth stage
[0094] After the crystal nucleation stage, the temperature was raised to 2700°C at a rate of 40°C / min, and the pressure in the growth chamber was reduced to 40 mbar by adjusting the pressure controller and maintained for 60 hours.
[0095] S1: A discontinuous temperature gradient distribution is set in the radial direction of the crystal growth surface, with 2 mm from the crystal growth edge as the boundary, and a continuous and positive temperature gradient is set within a range greater than 2 mm from the crystal growth edge, and the continuous and positive temperature gradient value is 3°C / cm; the temperature gradient within a range less than 2 mm from the crystal growth edge is 12°C / cm, thereby ensuring that the crystal edge has sufficient lateral growth driving force and the crystal edge has the ability to continue to expand its diameter.
[0096] S2: setting the seed crystal's deflection angle along the <11-20> crystal direction to 3°;
[0097] S3: The angle α of the crystal growth graphite ring parallel to the crystal growth direction is set to 10°, so as to ensure that the radial growth caused by the lateral growth of the crystal has sufficient expansion space.
[0098] S4: Sufficient silicon carbide powder is placed between the inner wall of the crystal growth chamber and the crystal growth graphite ring to ensure that the SiC crystal has sufficient reaction atmosphere for lateral growth and a chemical environment for continuous lateral growth of the SiC crystal. The grown crystal is cut, ground, polished, etc. to obtain the target silicon carbide substrate.
[0099] Example 4
[0100] This embodiment relates to a method for preparing a 6-inch high-uniformity silicon carbide substrate, which specifically includes the following steps:
[0101] (1) Crystal nucleation stage
[0102] The silicon carbide powder and seed crystal were placed in the crucible, and then the growth chamber was sealed and evacuated to 10°C by a mechanical pump and a vacuum pump. -3 Pa, inert gas was introduced after a period of stabilization in the vacuum stage, and the pressure in the growth chamber was gradually increased to 300mbar, while nitrogen was introduced into the chamber at 40ml / min. During the crystal nucleation stage, while the pressure in the growth chamber was increased, the temperature in the furnace was gradually increased from room temperature to 1800℃ through power setting and maintained for 30h.
[0103] (2) Crystal stable growth stage
[0104] After the crystal nucleation stage, the temperature was raised to 2400°C at a rate of 30°C / min, and the pressure in the growth chamber was reduced to 10 mbar by adjusting the pressure controller and maintained for 70 hours.
[0105] S1: A discontinuous temperature gradient distribution is set in the radial direction of the crystal growth surface, with 1 mm from the crystal growth edge as the boundary, and a continuous and positive temperature gradient is set within a range greater than 1 mm from the crystal growth edge, and the continuous and positive temperature gradient value is 2°C / cm; the temperature gradient within a range less than 1 mm from the crystal growth edge is 4°C / cm, thereby ensuring that the crystal edge has sufficient lateral growth driving force and the crystal edge has the ability to continue to expand its diameter.
[0106] S2: Set the seed crystal's deflection angle along the <11-20> crystal direction to 0.5°;
[0107] S3: The angle α of the crystal growth graphite ring parallel to the crystal growth direction is set to 20°, so as to ensure that the radial growth caused by the lateral growth of the crystal has sufficient expansion space.
[0108] S4: Sufficient silicon carbide powder is placed between the inner wall of the crystal growth chamber and the crystal growth graphite ring to ensure that the SiC crystal has sufficient reaction atmosphere for lateral growth and a chemical environment for continuous lateral growth of the SiC crystal. The grown crystal is cut, ground, polished, etc. to obtain the target silicon carbide substrate.
[0109] Example 5
[0110] The main difference between this embodiment and embodiment 2 is that in step S1, the temperature gradient is 6°C / cm within a range less than 5 mm from the crystal growth edge, and an 8-inch silicon carbide substrate is prepared in this embodiment. The remaining steps are the same as those in embodiment 2.
[0111] Example 6
[0112] The main difference between this embodiment and embodiment 2 is that in step S1, a continuous and positive temperature gradient is set within a range greater than 5 mm from the crystal growth edge, and the continuous and positive temperature gradient value is 7°C / cm; and an 8-inch silicon carbide substrate is prepared in this embodiment, and the remaining steps are the same as in embodiment 2.
[0113] Comparative Example 1
[0114] The difference between this comparative example and Example 2 is that in step S1, a continuous positive temperature gradient is set from the center to the edge of the crystal, and the continuous positive temperature gradient is 3°C / cm. The remaining steps are the same as in Example 2.
[0115] Comparative Example 2
[0116] The difference between this comparative example and Example 2 is that in step S1, the temperature gradient is 1°C / cm within a range less than 5 mm from the crystal growth edge, and the remaining steps are the same as in Example 2.
[0117] The above embodiments and comparative examples all adopt the PVT crystal growth method to prepare silicon carbide crystals, and the embodiments and comparative examples all adopt the same edge cutting (removal of 5 mm), radial cutting, grinding and polishing processes to obtain silicon carbide substrates. The performance of the obtained silicon carbide substrate samples is tested, and the results are shown in Table 1.
[0118] Table 1 Silicon carbide substrate performance test table
[0119]
[0120] The present application sets a discontinuous temperature gradient distribution in the radial direction of the crystal growth surface to ensure that the crystal edge has sufficient lateral growth driving force and the crystal edge has the ability to continuously expand and grow. The crystals of the embodiment and the comparative example undergo the same conventional edge cutting, radial cutting, grinding, and polishing processes without changing the quality of the substrate. Therefore, according to the data in Table 1, the preparation method of the present application can control the movement trend of the growth feature surface and lock it at the edge of the crystal. The movement trend control reference Figure 2 The growth feature surface at the edge of the crystal can be removed as the crystal edge is cut, so the substrates of Examples 1-6 do not have a growth feature surface, and the existing positive temperature gradient in Comparative Example 1 and the 1°C / mm temperature gradient at the edge in Comparative Example 2 cannot cause the growth feature surface to move toward the edge and be fixed at the edge.
[0121] The silicon carbide substrates of Comparative Examples 1 and 2 both contain growth feature surfaces visible to the naked eye, and their structures are as follows: Figure 1 As shown, it can be seen that the silicon carbide substrate without growth feature surface does not contain any black spots similar to "birthmarks" in the entire area. The silicon carbide substrates prepared in Examples 1-6 do not contain any growth feature surface visible to the naked eye. Figure 5 As shown. From the above embodiments and comparative examples and Figure 1 , Figure 5 It can be seen that the silicon carbide substrate without growth feature surface is prepared by the preparation method of the present application. Combined with other parameters disclosed in Table 1, it can be seen that due to the absence of the growth feature surface structure, the in-plane doping concentration variation rate of the silicon carbide substrate is less than 10%, the carrier concentration variation rate is less than 5%, and the TDV density is less than 200 cm -2 , indicating that the overall performance of the silicon carbide substrate has been improved. In Comparative Examples 1 and 2, the silicon carbide substrate with growth feature surface has an intra-plane doping concentration variation rate greater than 15%, a carrier concentration variation rate greater than 50%, and a TDV greater than 450cm -2 , which means the overall performance of the silicon carbide substrate is poor.
[0122] refer to Figure 4 As shown, the abscissa represents the test points along the diameter direction of the substrate, and the ordinate represents the carrier concentration. Figure 4The curve without black dots is a curve of carrier concentration variation along the diameter direction of the silicon carbide substrate without growth feature surface in Example 2 of the present invention; the curve with black dots is a curve of carrier concentration variation along the diameter direction of the conventional substrate in Comparative Example 1. Figure 4 It can be seen that for conventional silicon carbide substrates with growth feature surfaces, obvious high-concentration nitrogen-doped regions and high-carrier concentration regions will appear in the growth feature surface area along the diameter direction. The resistivity in this area is significantly lower than that in other areas, resulting in uneven resistivity distribution within the substrate surface. In addition, the high-nitrogen-doped area is likely to be the area with the highest crystal growth rate, and is prone to defects such as edge dislocations. The high-concentration carrier area will also cause basal plane dislocations to transform and expand into stacking faults during epitaxy and device use, thereby affecting the device yield, performance and ultimate reliability.
[0123] Since the growth feature surface is eliminated in the present application, the doping uniformity and carrier uniformity inside the substrate are greatly improved. There are no inclusions or aggregations of defects such as dislocations and micropipes at the growth feature surface that exist in normal substrates inside the substrate, so the substrate quality and yield are greatly improved; the performance and reliability of the substrate in subsequent device processes and use will be greatly improved.
[0124] Since the elimination of the growth characteristic surface is completed in the crystal growth stage, the subsequent substrate processing technology will not affect the above-mentioned electrical properties. Therefore, the present invention has no special restrictions on the substrate processing method, which is a routine operation for those skilled in the art. Such a growth scheme is simple and easy to implement, and can ensure the stress and defect control under the continuous and small temperature gradient in the central area of the crystal. Through the above innovation, the growth characteristic surface can be fixed at the edge of the crystal and removed in the subsequent crystal processing process, so that there is no growth characteristic surface on the entire crystal rod and the substrate processed therefrom, so as to achieve the purpose of eliminating the defect aggregation area and ensure the device end yield and reliability.
[0125] However, the preparation method of the silicon carbide substrate without growth characteristic surface of the present invention includes but is not limited to this. Those skilled in the art may also prepare the silicon carbide substrate by other methods capable of controlling the characteristic growth surface, so the preparation method disclosed in this application is only for illustration and does not constitute a limitation on the performance of the silicon carbide substrate itself. Those skilled in the art may also study new preparation methods to obtain the silicon carbide substrate of this application through existing technical reserves and creative labor. Other preparation methods are not within the research scope of this application and will not be studied further.
[0126] The above description is only an embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent substitution, improvement, etc. made within the spirit and principle of the present invention should be included in the scope of the claims of the present invention.
Claims
1. A method for preparing a high-uniformity silicon carbide substrate, characterized in that: The preparation method includes a crystal stable growth stage, a growth process condition of the crystal stable growth stage The following steps are involved: S1: a discontinuous temperature gradient distribution is set in the radial direction of the crystal growth surface, there is a limiting edge near the crystal growth edge, the distance between the limiting edge and the crystal growth edge is not more than 6mm, and a continuous and positive temperature gradient is set from the limiting edge to the crystal center; the temperature gradient within the range between the limiting edge and the crystal growth edge is ≥2°C / cm, and the temperature gradient value within the range between the limiting edge and the crystal growth edge is greater than the temperature gradient value from the limiting edge to the crystal center; S2: setting the seed crystal to have a deflection angle of >0° along <11-20> or <1-100> or any other crystal direction parallel to the c-plane direction; S3: setting the angle α of the crystal growth graphite ring parallel to the crystal growth direction to be greater than 0°; S4: Sufficient silicon carbide powder is arranged between the inner wall of the crystal growth chamber and the crystal growth graphite ring, so as to ensure that the SiC crystal has sufficient reaction atmosphere for lateral growth and a chemical environment for continuous lateral growth of the SiC crystal. The highly uniform silicon carbide substrate is obtained by processing the SiC crystal.
2. The preparation method according to claim 1, characterized in that: The temperature gradient between the limiting edge and the crystal growth edge in step S1 is ≥5°C / cm; and / or the seed crystal has a deflection angle of >2° along the <11-20> crystal direction in step S2; And / or in step S3, the angle α of the crystal growing graphite ring parallel to the crystal growth direction is ≥8°.
3. The preparation method according to claim 1, characterized in that: In step S1: taking 5 mm from the crystal growth edge as the boundary, a continuous and positive temperature gradient is set within a range greater than 5 mm from the crystal growth edge, the continuous and positive temperature gradient value is ≤3°C / cm, and the temperature gradient within a range less than 5 mm from the crystal growth edge is ≥5°C / cm.
4. The preparation method according to claim 1, characterized in that: During the stable crystal growth stage, the temperature in the growth chamber is first raised to above 2200°C at a rate of 10-50°C / min, and the pressure in the growth chamber is reduced to 1-100 mbar. Then, the crystal growth is maintained for more than 50 hours under the settings of steps S1-S4.
5. The preparation method according to claim 4, characterized in that: In the stable crystal growth stage, the temperature in the growth chamber is first increased to above 2200°C at a rate of 10-30°C / min, while the pressure is reduced to 5-50 mbar, and then maintained for more than 50 hours under the settings of steps S1-S4 for crystal growth.
6. The preparation method according to any one of claims 1 to 5, characterized in that: Before the stable crystal growth stage, it also includes the crystal nucleation stage. The growth process conditions of the crystal nucleation stage are The following steps are involved: After the crystal growth chamber is sealed, the growth chamber is evacuated to 10 -3 Pa, after the vacuum stage is stable for a period of time, inert gas is introduced to gradually increase the pressure in the growth chamber to 100-1000mbar and then stabilize it. At the same time, nitrogen is introduced into the chamber at 1ml / min-100ml / min.
7. The preparation method according to claim 6, characterized in that: During the crystal nucleation stage, while the pressure in the growth chamber is increased, the temperature in the growth chamber is gradually increased from room temperature to 1600-2100°C and then kept constant. After maintaining the constant temperature and pressure for 5-50 hours, the crystal stable growth stage is carried out.
8. The preparation method according to claim 7, characterized in that: The temperature in the growth chamber is gradually increased from room temperature to 1800-2100°C, and the pressure in the growth chamber is gradually increased to 300-800mbar and then kept constant. After maintaining the constant temperature and pressure for 30-50h, the crystal stable growth stage is carried out.
9. A high uniformity silicon carbide substrate, characterized in that: The high-uniformity silicon carbide substrate is conductive, and does not contain any one or more of a growth feature surface, a high-doping area, and a defect aggregation area within its entire area.
10. A semiconductor device, characterized in that: The semiconductor device comprises the highly uniform silicon carbide substrate according to claim 9.