Method for reducing number of defects of silicon carbide epitaxial material

Abstract

The invention discloses a method for reducing the number of defects of a silicon carbide epitaxial material, which comprises the following steps of: selecting a group of substrates with the same crystal orientation, deflection angle, surface roughness and resistivity as calibration sheets, and etching circles, triangles, quadrangles or polygons on the surfaces of the substrates as triangular defect nucleation points; carrying out epitaxial growth on the calibration sheet by adopting a process that the triangular defect density and the micro-pit defect density are both smaller than half of a product qualified line, and measuring the triangular defect size of a pattern position and the length of a step flowing direction in the vertical direction, and taking the measured values as standard values; when the number of the triangular defects or the micro-pit defects continuously fluctuates in the production process, the process conditions are kept unchanged, a calibration sheet is adopted for epitaxial growth, the sizes of the triangular defects on the surface of the calibration sheet are measured, the difference between the sizes of the triangular defects and a standard value is compared, and the growth temperature is corrected according to the result. And the method is compatible with a mainstream SiC epitaxial process, is suitable for industrial production, and has great popularization value.

Description

Technical Field

[0001] The present application relates to the technical field of silicon carbide epitaxy, and in particular to a method for reducing the number of defects in silicon carbide epitaxial materials. Background Art

[0002] SiC materials have become an excellent choice for the preparation of high-temperature, high-power and radiation-resistant devices due to their excellent performance, wide bandgap, high thermal conductivity, high breakdown electric field, high saturation drift rate, etc. The thin film materials required for the preparation of silicon carbide devices are generally prepared by epitaxial method, that is, a certain type of doped silicon carbide film is grown on a silicon carbide single crystal substrate according to the device design requirements. At present, the mainstream epitaxial material growth adopts the chemical vapor deposition (CVD) method, which is carried out under high temperature conditions of about 1600℃~1650℃, and the number of defects in the epitaxial material is closely related to the temperature, especially the triangular defects and micro-pit defects. The temperature measurement system of the mainstream epitaxial equipment tests the temperature of the graphite consumables in the reaction chamber rather than the temperature on the epitaxial material. The test temperature varies due to the replacement or improper installation of the consumables, which leads to changes in the actual growth temperature, and then causes changes in the number of defects on the epitaxial material.

[0003] Growth temperatures that are too high or too low will lead to an increase in defects. It is difficult to determine whether the growth temperature is too high or too low simply by looking at the change in the number of defects. Temperature correction cannot be performed effectively and multiple attempts are required, resulting in a large number of unqualified wafers.

[0004] Chinese patent CN202410883692.2 discloses a method for controlling the epitaxial growth temperature of silicon carbide, the steps comprising: obtaining a standard defect distribution map; controlling the growth of a sample in an epitaxial furnace chamber, and performing defect analysis on the grown sample to obtain an actual defect distribution map; comparing the actual defect distribution map with the standard defect distribution map to determine whether the actual temperature of the sample during growth deviates from the target temperature; based on the determination result, adjusting the actual temperature during sheet growth. The present application discloses a method for controlling the epitaxial growth temperature of silicon carbide. By comparing the defect distribution on the surface of the sample, the deviation range of the growth temperature in the epitaxial furnace chamber and the standard temperature can be accurately obtained, so that the actual temperature in the epitaxial furnace chamber can be quickly and accurately adjusted to compensate the chamber temperature in real time.

[0005] U.S. Patent US10020366B2 discloses removing basal plane dislocations on the surface of a silicon carbide substrate by high temperature annealing and maintaining the surface morphology, including adding a protective layer on the surface of the substrate, annealing the substrate at a temperature of about greater than or equal to 1850°C, removing the protective layer from the surface of the substrate after annealing, and growing a first layer; an epitaxial layer on the substrate after removing the protective layer, wherein when growing the first epitaxial layer, the growth of the first epitaxial layer does not attempt to prevent basal plane dislocations from propagating in the first epitaxial layer, and wherein the first epitaxial layer has no basal plane dislocations; basal plane dislocations in silicon carbide (SiC) substrates can cause a drop in forward voltage in high-power devices because they form stacking faults during device operation, and existing methods for reducing BPD density in SiC epitaxial layers are inefficient and may damage the surface morphology; this method can produce a BPD-free epitaxial layer of any desired thickness, retain the surface morphology and do not require an additional annealing step, thereby enhancing the reliability and performance of high-power SiC devices by reducing defects caused by BPDs. Summary of the invention

[0006] Technical issues solved:

[0007] The technical problem to be solved by the present application is that the temperature measurement system of the existing mainstream epitaxial equipment tests the temperature of the graphite consumables in the reaction chamber rather than the temperature on the epitaxial material. The test temperature varies due to the replacement or improper installation of the consumables, which leads to changes in the actual growth temperature, and then causes changes in the number of defects on the epitaxial material. Too high or too low growth temperature will lead to an increase in defects. It is difficult to judge whether the growth temperature is too high or too low only from the change in the number of defects, and the temperature cannot be effectively corrected. Multiple attempts are required, resulting in a large number of unqualified wafers, etc. A method for reducing the number of defects in silicon carbide epitaxial materials is provided.

[0008] Technical solution:

[0009] A method for reducing the number of defects in silicon carbide epitaxial material comprises the following steps:

[0010] Step 1: prepare a calibration sheet for monitoring the change of triangle size;

[0011] Step 2: Adjust the epitaxial growth process temperature to find the growth process temperature window with the least number of epitaxial material defects;

[0012] Step 3, using the calibration piece prepared in step 1 and the process conditions debugged in step 2 to grow the epitaxial material, measuring the size of the triangular defect at the calibration point of the epitaxial material, and recording it as the standard value;

[0013] Step 4: After the equipment replaces the graphite consumables in the reaction chamber or when the number of triangular defects in the epitaxial material exceeds 50 for three consecutive pieces or the number of micro-pit defects exceeds 3000 for three consecutive pieces during the production process, a new calibration piece and the current process conditions are used to grow the epitaxial material, and the size of the triangular defects at the calibration point is measured and its value is recorded;

[0014] Step 5, comparing the size of the triangular defect of the calibration piece in step 4 with the standard value in step 3, if the size of the triangular defect of the calibration piece in step 4 is larger than the standard value, then lowering the growth temperature; if the size of the triangular defect of the calibration piece in step 4 is smaller than the standard value, then increasing the growth temperature;

[0015] Step six, using the growth temperature calibrated in step five to produce epitaxial material.

[0016] As a preferred technical solution of the present application: in the step one, the calibration piece is a group of silicon carbide substrates with the same crystal orientation, deflection angle, surface roughness and resistivity. A circular, triangular, quadrilateral or polygonal graphic defect nucleation point is etched at the center of the calibration piece surface or at a position 10-30 mm away from the center. The maximum size of the graphic is 1 to 50 μm, and the graphic points and shapes of all calibration pieces are the same.

[0017] As a preferred technical solution of the present application: in the process debugging in step 2, except for the growth temperature, other parameter conditions should remain unchanged.

[0018] As a preferred technical solution of the present application: the calibration point in step three is the position of the circular, triangular, quadrilateral or polygonal figure etched on the calibration wafer in step one; the measured triangular defect size is the length in the direction perpendicular to the step flow direction.

[0019] As a preferred technical solution of the present application: the growth temperature of the calibration piece in step four should be consistent with the growth temperature of the epitaxial material in production, and other process conditions and epitaxial layer thickness should be consistent with the calibration piece in step three.

[0020] As a preferred technical solution of the present application: the triangle defect size of the calibration piece recorded in step four should be the same as the point position of the standard value recorded in step three.

[0021] As a preferred technical solution of the present application: in the step five, the size of the triangular defect of the calibration piece is 5% to 10%, 10% to 20%, 20% to 30% larger than the standard value, and the temperature is lowered by 1 to 5°C, 5 to 10°C, and 10 to 15°C respectively.

[0022] As a preferred technical solution of the present application: in the step five, the size of the triangular defect of the calibration piece is 5% to 10%, 10% to 20%, 20% to 30% smaller than the standard value, and the temperature is increased by 1 to 5°C, 5 to 10°C, and 10 to 15°C respectively.

[0023] Principle explanation: The triangle defect size is used as the standard of process temperature. The temperature deviation is judged by the change of the triangle defect size. The result is intuitive and the operation is simple. By preparing the calibration piece and controlling the process conditions, the influence of other factors besides the growth temperature on the triangle defect size is ensured, making the judgment result more accurate. The temperature correction range is set according to the deviation between the triangle defect size of the calibration piece and the standard value to enhance the operability of temperature correction.

[0024] Beneficial effects:

[0025] The method for reducing the number of defects in silicon carbide epitaxial materials described in the present application adopts the above technical solution and has the following technical effects compared with the prior art:

[0026] 1. The technical solution provided by the present invention uses the size of the triangular defect as the calibration of the growth temperature, and uses the change of the size of the triangular defect at a specific point on the calibration wafer to judge the deviation between the actual growth temperature and the optimal growth temperature, and uses this as a basis for temperature correction. The process is compatible with the existing conventional epitaxial process and is suitable for industrial production;

[0027] 2. In the present invention, the change in the size of the triangular defect is used as the basis for the change in the growth temperature. The result is intuitive and the operation process is simple, which greatly improves the accuracy of the judgment result;

[0028] 3. In the present invention, the size of the triangular defect at the optimal growth temperature is measured and recorded as a standard value, so that subsequent temperature correction has a basis to rely on;

[0029] 4. In the present invention, a batch of calibration pieces with specific patterns at the same points are prepared by selecting substrate pieces of the same specifications, and the growth process of the calibration pieces is kept unchanged except for the temperature, so as to eliminate the change of the size of the triangular defect caused by other factors, and the result is more accurate;

[0030] 5. Compared with CN 202410883692 A, CN 202410883692 A uses the change of defect distribution to determine whether the growth temperature deviates, while the present invention uses the change of triangular defect size to determine whether the growth temperature deviates; CN 202410883692 A directly uses the defect distribution map of the epitaxial material in production as the standard defect distribution map, while the present invention first prepares a calibration piece, and uses the size of the triangular defect at a fixed point of the calibration piece as the standard value, eliminating the influence caused by the substrate and the test point; CN 202410883692 A directly uses the process temperature of the epitaxial material in production as the standard process temperature, while the present invention first optimizes the process temperature, and uses the process temperature when the quality of the epitaxial material reaches the best as the standard process temperature;

[0031] 6. Compared with US10020366 B2, US10020366 B2 adopts high-temperature annealing of the substrate to reduce the transformation of basal plane dislocations into epitaxial layers, while the present invention reduces the defects of epitaxial materials by temperature correction; US10020366 B2 does not involve the correction of growth temperature, while the present invention provides a method for temperature correction using the change in the size of triangular defects; US10020366 B2 does not involve the preparation of calibration plates, while the present invention compares the changes in temperature at different periods by preparing calibration plates. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 A process diagram of a method for reducing the number of defects in silicon carbide epitaxial materials according to the present application;

[0033] Figure 2 This is a schematic photo showing the measurement of triangle defect size for this application. DETAILED DESCRIPTION

[0034] The present invention is further described below in conjunction with embodiments and process diagrams.

[0035] Embodiment 1:

[0036] A method for reducing the number of defects in silicon carbide epitaxial materials, wherein the method is used to perform temperature correction after replacing graphite consumables in a reaction chamber of an epitaxial device, and the specific steps are as follows:

[0037] Step 1: Select 10 4° off-axis conductive 150 mm 4H-SiC substrates and etch a circular groove with a diameter of 5 μm at the center to monitor the change of triangle size;

[0038] Step 2: Keep other process conditions unchanged and adjust the growth temperature. Based on the current growth temperature of 1620°C, the growth temperature is increased by 5°C for epitaxial growth and surface testing. The number of triangle defects and micro-pit defects has decreased.

[0039] Step 3, after repeating step 2 four times, the growth temperature is 1645°C, and the number of micro-pit defects begins to increase. At 1635°C, the number of triangle defects and micro-pit defects are both small;

[0040] Step 4: Keeping other process conditions unchanged, epitaxial growth is performed on the calibration piece made in step 1 at a growth temperature of 1635°C, with a thickness of 5.5 μm. After the growth is completed, the size of the triangular defect formed at the etching groove at the center of the calibration piece is measured, and the length is 630 μm, which is used as the standard value;

[0041] Step 5: After the graphite consumables in the reaction chamber of the epitaxial equipment reach the end of their service life, the equipment is maintained and the graphite consumables are replaced;

[0042] Step 6: Restore the equipment and grow epitaxial material using the calibration done in step 1. The thickness of the epitaxial layer is 5.5 μm. The growth temperature is the growth temperature used before the equipment maintenance. Other process conditions are the same as step 4. After the growth is completed, the size of the triangular defect formed at the center of the calibration plate etched groove is measured, and its length is 770 μm.

[0043] Step seven: In step six, the length of the triangle defect is 22% greater than the standard value, and the growth temperature is lowered by 10° C. for epitaxial growth.

[0044] Embodiment 2:

[0045] A method for reducing the number of defects in silicon carbide epitaxial materials, when the epitaxial equipment has not replaced the graphite parts but the number of micro-pit defects fluctuates greatly, the method is used to correct the growth temperature, the steps are as follows:

[0046] Step 1: select 10 4° off-axis conductive 150 mm 4H-SiC substrates and etch a circular groove with a diameter of 3 μm at the center to monitor the change of triangle size;

[0047] Step 2: Keep other process conditions unchanged and adjust the growth temperature. Based on the current growth temperature of 1610°C, the growth temperature is increased by 3°C for epitaxial growth and surface testing. The number of triangle defects and micro-pit defects increases.

[0048] Step 3: Keeping other process conditions unchanged, the growth temperature is lowered by 3°C from the current 1610°C for epitaxial growth and surface testing. The number of triangle defects and micro-pit defects has decreased.

[0049] Step 4: After repeating step 3 four times, the number of micro-pit defects begins to increase at a growth temperature of 1585°C, and the number of triangle defects and micro-pit defects are both small at 1600°C;

[0050] Step 5: Keeping other process conditions unchanged, epitaxial growth is performed on the calibration piece made in step 1 at a growth temperature of 1600°C, with a thickness of 10 μm. After the growth is completed, the size of the triangular defect formed at the etching groove at the center of the calibration piece is measured, and the length is 2800 μm, which is used as the standard value;

[0051] Step 6: During the production process, if the number of micro-pit defects in the epitaxial material exceeds 3000 for three consecutive pieces, the epitaxial material is grown using the calibration made in step 1. The thickness of the epitaxial layer is 10 μm, the growth temperature is the current growth temperature, and the other process conditions are the same as step 5. After the growth is completed, the size of the triangular defect formed at the etching groove at the center of the calibration piece is measured, and its length is 2650 μm.

[0052] Step seven: In step six, the length of the triangle defect is 5.3% smaller than the standard value, and the growth temperature is increased by 3° C. for epitaxial growth.

[0053] It should be understood that the specific embodiments described herein are limited to explaining the present invention and are not intended to limit the present invention. There are many practical production schemes that can be adopted in the production method, and all equivalent changes and decorations made according to the claims of the present invention are within the scope of the present invention.

Claims

1. A method for reducing the number of defects in silicon carbide epitaxial material, characterized in that: Here are the steps: Step 1: prepare a calibration sheet for monitoring the change of triangle size; Step 2: Adjust the epitaxial growth process temperature to find the growth process temperature window with the least number of epitaxial material defects; Step 3, using the calibration piece prepared in step 1 and the process conditions debugged in step 2 to grow the epitaxial material, measuring the size of the triangular defect at the calibration point of the epitaxial material, and recording it as the standard value; Step 4: After the equipment replaces the graphite consumables in the reaction chamber or when the number of triangular defects in the epitaxial material exceeds 50 for three consecutive pieces or the number of micro-pit defects exceeds 3000 for three consecutive pieces during the production process, a new calibration piece and the current process conditions are used to grow the epitaxial material, and the size of the triangular defects at the calibration point is measured and its value is recorded; Step 5, comparing the size of the triangular defect of the calibration piece in step 4 with the standard value in step 3, if the size of the triangular defect of the calibration piece in step 4 is larger than the standard value, then lowering the growth temperature; if the size of the triangular defect of the calibration piece in step 4 is smaller than the standard value, then increasing the growth temperature; Step six, using the growth temperature calibrated in step five to produce epitaxial material.

2. The method for reducing the number of defects in silicon carbide epitaxial material according to claim 1, characterized in that: In the step 1, the calibration piece is a group of silicon carbide substrates with the same crystal orientation, deflection angle, surface roughness and resistivity. A circular, triangular, quadrilateral or polygonal defect nucleation point is etched at the center of the calibration piece surface or at a position 10-30 mm away from the center. The maximum size of the pattern is 1 to 50 μm, and the pattern points and shapes of all calibration pieces are the same.

3. The method for reducing the number of defects in silicon carbide epitaxial material according to claim 1, characterized in that: In the process debugging in step 2, except for the growth temperature, other parameter conditions should remain unchanged.

4. A method for reducing the number of defects in silicon carbide epitaxial materials according to claim 2, characterized in that: The calibration point in step three is the position of the circular, triangular, quadrilateral or polygonal figure etched on the calibration wafer in step one; the measured triangle defect size is the length in the direction perpendicular to the step flow direction.

5. The method for reducing the number of defects in silicon carbide epitaxial material according to claim 1, characterized in that: The growth temperature of the calibration piece in step 4 should be consistent with the growth temperature of the epitaxial material in production, and other process conditions and epitaxial layer thickness should be consistent with the calibration piece in step 3.

6. The method for reducing the number of defects in silicon carbide epitaxial material according to claim 1, characterized in that: The triangular defect size of the calibration piece recorded in step 4 should be the same as the point position of the standard value recorded in step 3.

7. The method for reducing the number of defects in silicon carbide epitaxial material according to claim 1, characterized in that: In the step 5, if the size of the triangular defect of the calibration piece is 5% to 10%, 10% to 20%, 20% to 30% larger than the standard value, the temperature is lowered by 1 to 5°C, 5 to 10°C, and 10 to 15°C, respectively.

8. The method for reducing the number of defects in silicon carbide epitaxial material according to claim 1, characterized in that: Step 5 Winning the bid If the size of the triangle defect of the fixed piece is 5% to 10%, 10% to 20%, 20% to 30% smaller than the standard value, the temperature shall be increased by 1 to 5℃, 5 to 10℃ respectively. 10～15℃。

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