A method for reducing the number of defects in silicon carbide epitaxial material

Abstract

The application discloses a method for reducing the number of defects of silicon carbide epitaxial material, selects a group of substrates with the same crystal direction, off-angle, surface roughness and resistivity as calibration pieces, etches a circle, a triangle, a quadrilateral or a polygon on the surface of the calibration pieces as a triangle defect nucleation point; adopts a process with a triangle defect density and a pit defect density less than half of a product qualified line to perform epitaxial growth on the calibration pieces and measures the size of the triangle defects at the pattern position and the length of the step flow in the vertical direction, which are taken as standard values; when the number of triangle defects or pit defects appears continuous fluctuation in the production process, the process conditions are kept unchanged, epitaxial growth is performed on the calibration pieces and the size of the triangle defects on the surface of the calibration pieces is measured, the difference between the size of the triangle defects and the standard values is compared, and the growth temperature is corrected according to the result, so that the method is simple and easy to implement, compatible with mainstream SiC epitaxial processes, suitable for industrial production and of great popularization value.

Description

TECHNICAL FIELD

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

[0002] SiC material is an excellent choice for preparing high-temperature, high-power and radiation-resistant devices due to its excellent performance, wide band gap, high thermal conductivity, high breakdown electric field and high saturation drift rate. The thin film material required for preparing silicon carbide devices is generally prepared by epitaxy, that is, a silicon carbide film of a certain doping type is grown on a silicon carbide single crystal substrate according to the design requirements of the device. The mainstream epitaxial material growth currently adopts the chemical vapor deposition (CVD) method, which is carried out at a high temperature 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 differs due to the replacement of consumables or improper installation, resulting in changes in the actual growth temperature and changes in the number of defects on the epitaxial material.

[0003] Excessive or insufficient growth temperature will increase the number of defects. It is difficult to determine 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. It needs to be tried many times, resulting in a large number of unqualified pieces.

[0004] Chinese patent CN202410883692.2 discloses a control method for the growth temperature of silicon carbide epitaxy, which comprises the following steps: obtaining a standard defect distribution map; controlling the growth of a sample in an epitaxial furnace cavity, and analyzing the defects of 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 during the growth of the sample deviates from the target temperature; and adjusting the actual temperature during the growth of the sample based on the determination result. The control method for the growth temperature of silicon carbide epitaxy can accurately obtain the deviation range of the growth temperature in the epitaxial furnace cavity from the standard temperature by comparing the defect distribution on the surface of the sample, so as to quickly and accurately adjust the actual temperature in the epitaxial furnace cavity to compensate the temperature in the chamber in real time.

[0005] US10020366B2 discloses removing basal plane dislocations from the surface of a silicon carbide substrate and preserving surface morphology by high temperature annealing, including adding a protective layer to 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; epitaxial layer on the substrate after removing the protective layer, wherein during growth of the first epitaxial layer, growth of the first epitaxial layer does not attempt to stop basal plane dislocations from propagating in the first epitaxial layer, and wherein the first epitaxial layer is free of basal plane dislocations; basal plane dislocations in silicon carbide (SiC) substrates can cause forward voltage drop in high power devices as they form stacking faults during device operation, and existing methods of reducing BPD density in SiC epitaxial layers are inefficient and can damage surface morphology; this method can produce BPD-free epitaxial layers of any desired thickness, preserving surface morphology and without the need for additional annealing steps, thereby enhancing the reliability and performance of high power SiC devices by reducing defects caused by BPD. SUMMARY

[0006] Technical problems 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, and the test temperature differs due to the replacement or improper installation of the consumables, thereby causing changes in the actual growth temperature, which in turn causes changes in the number of defects on the epitaxial material. High or low growth temperature will increase the number of defects, and it is difficult to determine whether the growth temperature is too high or too low only from the change in the number of defects, which cannot effectively correct the temperature and requires multiple attempts, resulting in a large number of unqualified wafers and other problems. A method for reducing the number of defects of silicon carbide epitaxial material is provided.

[0008] Technical solution:

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

[0010] Step one, prepare a calibration wafer for monitoring the change in the size of the triangle;

[0011] Step two, adjust the epitaxial growth process temperature to find the epitaxial material defect number minimum growth process temperature window;

[0012] Step three, use the calibration wafer prepared in step one and the process conditions adjusted in step two to grow epitaxial material, and measure the size of the triangular defect at the calibration point of the epitaxial material as a standard value for recording;

[0013] Step four, when the number of triangle defects of three wafers in succession exceeds 50 or the number of pit defects of three wafers in succession exceeds 3000, the epitaxial material growth is carried out by using a new calibration wafer and the current process condition, the size of triangle defects of the calibration point is measured and the value is recorded;

[0014] Step five, the size of triangle defects of the calibration wafer in step four is compared with the standard value in step three, if the size of triangle defects of the calibration wafer in step four is larger than the standard value, the growth temperature is lowered, if the size of triangle defects of the calibration wafer in step four is smaller than the standard value, the growth temperature is raised;

[0015] Step six, the epitaxial material is produced by using the growth temperature calibrated in step five.

[0016] As a preferred technical solution of the present application: the calibration wafer in step one is a group of silicon carbide substrates with the same crystal direction, angle, surface roughness and resistivity, and a circular, triangular, quadrilateral or polygonal pattern defect nucleation point is etched on the center or a position 10-30 mm away from the center of the surface of the calibration wafer, the maximum size of the pattern is 1-50 μm, and the pattern point and shape of all calibration wafers are the same.

[0017] As a preferred technical solution of the present application: in step two, the process debugging is carried out except that the growth temperature is changed.

[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 pattern etched on the calibration wafer in step one, and the measured size of the triangular defect is the length perpendicular to the flow direction of the step flow.

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

[0020] As a preferred technical solution of the present application: the size of the triangular defect of the calibration wafer recorded in step four is the same as the point of the standard value recorded in step three.

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

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

[0023] The original explanation: use the triangle defect size as the target of process temperature, judge the deviation of temperature through the change of triangle defect size, the result is intuitive and simple to operate; through the preparation of calibration sheet combined with the control of process conditions, ensure that other factors except growth temperature affect the triangle defect size, make the judgment result more accurate; according to the deviation of triangle defect size of calibration sheet and standard value, set the correction range of temperature, enhance the operability of temperature correction.

[0024] Beneficial effects:

[0025] The method for reducing the number of defects of silicon carbide epitaxial material provided by the present application has the following technical effects compared with the prior art:

[0026] 1. The technical solution provided by the present application uses the triangle defect size as the calibration of growth temperature, uses the change of triangle defect size at specific points on the calibration sheet to judge the deviation of actual growth temperature and optimal growth temperature, and corrects the temperature on this basis, which is compatible with the existing conventional epitaxial process and suitable for industrial production.

[0027] 2. In the present application, the change of triangle defect size is used as the basis for the change of 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 application, the triangle defect size at the optimal growth temperature is measured and recorded as a standard value, which provides a basis for subsequent temperature correction.

[0029] 4. In the present application, a batch of calibration sheets with specific patterns at the same point are prepared by selecting substrates of the same specification, and the growth process of the calibration sheet except temperature is kept unchanged, which eliminates the change of triangle defect size caused by other factors, and the result is more accurate.

[0030] 5. Compared with CN 202410883692 A, CN 202410883692 A uses changes in defect distribution to determine whether the growth temperature has deviated, while this invention uses changes in the size of triangular defects to determine whether the growth temperature has deviated; CN 202410883692 A directly uses the defect distribution map of the epitaxial material in production as the standard defect distribution map, while this invention first prepares a calibration wafer and uses the size of the triangular defects at fixed points on the calibration wafer as the standard value to eliminate the influence of the substrate and test points; CN 202410883692 A directly uses the process temperature of the epitaxial material in production as the standard process temperature, while this invention first optimizes the process temperature and uses the process temperature at which the epitaxial material quality reaches its best as the standard process temperature;

[0031] 6. Compared with US10020366 B2, which uses high-temperature annealing of the substrate to reduce the transformation of basal plane dislocations into the epitaxial layer, this invention reduces defects in the epitaxial material by temperature correction; US10020366 B2 does not involve the correction of growth temperature, while this invention provides a method for temperature correction using the size change of triangular defects; US10020366 B2 does not involve the preparation of calibration wafers, while this invention prepares calibration wafers to compare temperature changes at different times. Attached Figure Description

[0032] Figure 1 This is a process diagram illustrating the method for reducing the number of defects in silicon carbide epitaxial materials according to this application.

[0033] Figure 2 This is a schematic photograph illustrating the measurement of the triangular defect dimensions in this application. Detailed Implementation

[0034] The present invention will be further described below with reference to embodiments and process diagrams.

[0035] Example 1:

[0036] A method for reducing the number of defects in silicon carbide epitaxial materials is used for temperature correction after replacing the graphite consumables in the reaction chamber of the epitaxial equipment. The specific steps are as follows:

[0037] Step 1: Select 10 4° off-axis 150mm 4H-SiC substrates and etch a 5μm diameter circular groove at the center of each substrate to monitor changes in the size of the triangle.

[0038] Step 2: Keeping other process conditions unchanged, the growth temperature is adjusted. Based on the current growth temperature of 1620℃, the growth temperature is increased by 5℃ for epitaxial growth and surface testing is performed. The number of triangular defects and micro-pit defects has decreased.

[0039] Step three, after repeating step two four times, the growth temperature is 1645℃, the number of micro-pit defects starts to increase, and the number of triangular defects and micro-pit defects is less at 1635℃;

[0040] Step four, keeping other process conditions unchanged, epitaxial growth is carried out on the calibration wafer prepared in step one at a growth temperature of 1635℃, the thickness is 5.5μm, and after the growth is completed, the size of the triangular defects formed at the etched groove in the center of the calibration wafer is measured, which is 630μm in length, and is taken as a standard value;

[0041] Step five, after the graphite consumables in the reaction chamber of the epitaxial equipment reach the service life, the equipment is maintained and the graphite consumables are replaced;

[0042] Step six, after the equipment is restored, epitaxial material growth is carried out using the calibration in step one, the epitaxial layer thickness is 5.5μm, the growth temperature is the growth temperature used before the equipment maintenance, other process conditions are the same as those in step four, and after the growth is completed, the size of the triangular defects formed at the etched groove in the center of the calibration wafer is measured, which is 770μm in length;

[0043] Step seven, the length of the triangular defects in step six is 22% larger than the standard value, and the growth temperature is lowered by 10℃ for epitaxial growth.

[0044] Example 2:

[0045] A method for reducing the number of defects in silicon carbide epitaxial material, which is used to correct the growth temperature when the number of micro-pit defects fluctuates greatly without replacing the graphite parts of the epitaxial equipment, and the steps are as follows:

[0046] Step one, select 10 150mm 4H-SiC substrates with a 4° off-axis conduction, etch a circular groove with a diameter of 3μm in the center position, which is used to monitor the change of the triangular size;

[0047] Step two, keeping other process conditions unchanged, adjust the growth temperature, increase the growth temperature by 3℃ based on the current growth temperature of 1610℃ for epitaxial growth and surface testing, and the number of triangular defects and micro-pit defects increases;

[0048] Step three, keeping other process conditions unchanged, decrease the growth temperature by 3℃ based on the current 1610℃ for epitaxial growth and surface testing, and the number of triangular defects and micro-pit defects decreases;

[0049] Step four, after repeating step three four times, the number of micro-pit defects starts to increase at a growth temperature of 1585℃, and the number of triangular defects and micro-pit defects is less at 1600℃;

[0050] Step five, keeping other process conditions unchanged, epitaxial growth is carried out on the calibration wafer prepared in step one at a growth temperature of 1600 °C, the thickness is 10 μm, after the growth, the size of the triangle defect formed at the etched groove of the center point of the calibration wafer is measured, the length is 2800 μm, which is taken as the standard value;

[0051] Step six, during the production, the number of micro-pit defects of the epitaxial material is more than 3000 for three pieces in succession, epitaxial growth is carried out on the calibration wafer prepared in step one, the thickness of the epitaxial layer is 10 μm, the growth temperature is the current growth temperature, other process conditions are the same as those in step five, after the growth, the size of the triangle defect formed at the etched groove of the center point of the calibration wafer is measured, the length is 2650 μm;

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

[0053] It should be understood that the specific embodiments described herein are only for the purpose of illustrating and explaining the present application, and are not intended to limit the present application. There are many practical manufacturing schemes for the manufacturing method, and any equivalent changes and decorations made according to the claims of the present application are within the scope of the present application.

Claims

1. A method for reducing the number of defects in silicon carbide epitaxial materials, characterized in that, The steps are as follows: Step 1: Prepare a calibration plate to monitor changes in the size of the triangle; Step 2: Adjust the epitaxial growth process temperature to find the growth process temperature window with the fewest defects in the epitaxial material; Step 3: Using the calibration sheet prepared in Step 1 and the process conditions adjusted in Step 2, the epitaxial material is grown. The size of the triangular defects at the calibration points of the epitaxial material is measured and recorded as a standard value. Step 4: After replacing the graphite consumables in the reaction chamber, or when the number of triangular defects in the epitaxial material exceeds 50 for three consecutive wafers or the number of micro-pit defects exceeds 3000 for three consecutive wafers during production, use a new calibration wafer and the current process conditions to grow the epitaxial material. Measure and record the size of the triangular defects at the calibration points. The growth temperature of the calibration wafer 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 those of the calibration wafer in Step 3. Step 5: Compare the triangular defect size of the calibration piece in Step 4 with the standard value in Step 3. If the triangular defect size of the calibration piece in Step 4 is larger than the standard value, lower the growth temperature; if the triangular defect size of the calibration piece in Step 4 is smaller than the standard value, raise the growth temperature. Step six: Use the growth temperature calibrated in step five to produce epitaxial materials.

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

3. The method for reducing the number of defects in silicon carbide epitaxial materials according to claim 1, characterized in that: In step two, the process adjustment should keep all parameters unchanged except for the growth temperature.

4. The method for reducing the number of defects in silicon carbide epitaxial materials according to claim 2, characterized in that: In step three, the calibration points are the positions of the circular, triangular, quadrilateral, or polygonal shapes etched on the calibration plate in step one; the measured size of the triangular defect is the length in the direction perpendicular to the flow direction of the step flow.

5. The method for reducing the number of defects in silicon carbide epitaxial materials according to claim 1, characterized in that: The triangular defect size of the calibration piece recorded in step four should be at the same location as the standard value recorded in step three.

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

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

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

9. The method for reducing the number of defects in silicon carbide epitaxial materials according to claim 1, characterized in that: In step five, the size of the triangular defect in the calibration piece is 5% to 10% smaller than the standard value, and the temperature is increased by 1 to 5°C.

10. The method for reducing the number of defects in silicon carbide epitaxial materials according to claim 1, characterized in that: In step five, the size of the triangular defect in the calibration piece is 10% to 20% smaller than the standard value, and the temperature is increased by 5 to 10°C.

11. The method for reducing the number of defects in silicon carbide epitaxial materials according to claim 1, characterized in that: In step five, the size of the triangular defect in the calibration piece is 20% to 30% smaller than the standard value, and the temperature is increased by 10 to 15°C.

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