Silicon carbide wafer with improved surface crystallization quality and application

Abstract

The invention relates to a silicon carbide wafer with improved surface crystallization quality and application, and belongs to the technical field of silicon carbide wafer surface treatment. According to the scheme, the silicon surface of the silicon carbide wafer is processed through the hydrogen-oxygen plasmas in a certain proportion, dangling bonds are broken through plasma processing, stress is effectively released through temperature control, the problem that the wafer surface crystallization quality is poor due to the dangling bonds is effectively solved, and when the epitaxial layer grows on the processed wafer, the wafer surface quality is improved. And the lattice adaptability of the epitaxial layer and the wafer is better, so that the quality of the epitaxial layer is better. The IF1 value and the IF2 value of the treated silicon carbide wafer are increased, the curvature change is smaller than or equal to 1%, the unit cell volume change rate is smaller than or equal to 0.01%, the damage to the surface is small in the treatment process, the surface of the wafer is not prone to being damaged, and dislocation slippage is not prone to being caused.

Description

Technical Field

[0001] This application relates to a silicon carbide wafer with improved surface crystallization quality and its application, belonging to the technical field of silicon carbide wafer surface treatment. Background Art

[0002] Silicon carbide is a wide-bandgap semiconductor widely used in power devices, radio frequency devices, etc. Silicon carbide has extremely rich physical properties, with high electron mobility, high thermal conductivity, and high temperature resistance. Since silicon carbide is a polar crystal, its front and back sides, namely the silicon-carbon planes, exhibit different physical properties. Different from traditional silicon materials, both the silicon-carbon planes of silicon carbide are prone to reconstruction, which generally occurs during the annealing process. Reconstruction will affect the lattice matching between the single-crystal substrate and the epitaxial layer, and at the same time, it will also affect the on-state current of the device. Reconstruction is manifested as a change in the surface crystallization quality at the crystal end. Therefore, the reconstruction situation on the surface can be intuitively observed by studying the surface crystallization quality.

[0003] Currently, the conventional treatments for silicon carbide wafers, including chemical mechanical polishing, cleaning with acid-base solutions, and annealing in a protective atmosphere, will all affect the surface crystallization quality. Under normal circumstances, high temperature and chemical treatments will change the state of dangling bonds on the wafer surface. Although these treatment methods can remove the damaged layer to a certain extent, the surface crystallization quality will not be effectively improved.

[0004] In order to improve the surface crystallization quality of silicon carbide wafers and reduce the influence of reconstruction on the epitaxial layer and even the device, it is necessary to provide a method for improving the surface crystallization quality of silicon carbide wafers. Summary of the Invention

[0005] To solve the above problems, this application provides a silicon carbide wafer with improved surface crystallization quality and its application. In the solution of this application, the silicon surface of the silicon carbide wafer is treated with a certain proportion of hydrogen-oxygen plasma, effectively improving the crystallization quality of the wafer surface without damaging the wafer surface, and being able to reduce the influence of reconstruction on the epitaxial layer and even the device.

[0006] According to one aspect of this application, a silicon carbide wafer with improved surface crystallization quality is provided, and the IF 1 value of the silicon carbide wafer ≥ 3, and the IF 2 value ≥ 3; The IF 1 value = Peak (1-16) / (10000 * FWHM (1-16) ); The IF 2 value = Peak (118) / (10000 * FWHM (118) ); Among them, Peak(1-16) and FWHM (1-16) are respectively the diffraction peak intensity and the full width at half maximum (FWHM) of the (1-16) crystal plane in X-ray diffraction analysis, Peak (118) and FWHM (118) are respectively the diffraction peak intensity and the full width at half maximum (FWHM) of the (118) crystal plane in X-ray diffraction analysis.

[0007] The silicon carbide wafer with improved surface crystallization quality provided by this application has a higher IF 1 value and IF 2 value compared with the prior art products. The problem of poor crystallization quality caused by dangling bonds on the wafer surface is less. When growing an epitaxial layer, the lattice matching between the epitaxial layer and the wafer will be better, resulting in a better quality of the epitaxial layer and better quality of the components prepared from the epitaxial layer.

[0008] The reason for choosing the two planes of (1-16) and (118) for detection is that their diffraction angles are small and the penetration depth is shallow, which can represent the information of the wafer surface. The incident directions during the diffraction of these two planes are 1-100 and 11-20 respectively, and these two characteristic directions represent the characteristic physical properties of the silicon carbide wafer. By performing diffraction tests in these two directions, physical information representing the silicon carbide wafer surface can be obtained.

[0009] Both the diffraction peak intensity and the full width at half maximum are indicators that can measure the crystallization quality of the wafer. The reason for using the diffraction peak intensity divided by the full width at half maximum in this application is that different devices, different X-ray diffractometer powers, selected X-rays, and test environments will all cause differences in the test results of the diffraction peak intensity and the full width at half maximum. By defining the IF value, not only can the factors of the diffraction peak intensity and the full width at half maximum be considered simultaneously, but also the factors that cause differences in measuring the diffraction peak intensity or the full width at half maximum separately due to the test environment can be excluded.

[0010] Optionally, the IF 1 value of the silicon carbide wafer is 3 to 10, and the IF 2 value is 3 to 10. The above two IF values are used to characterize the crystallization quality of the wafer surface and the situation of surface reconstruction. When growing an epitaxial layer on a silicon carbide wafer within the above range, higher-quality products can be obtained.

[0011] Optionally, within the 2 / 3 diameter range of the silicon carbide wafer, the IF 1 value is 5 to 10, and the IF 2 value is 5 to 10; within the remaining ring range after removing the circle within the 2 / 3 diameter range of the silicon carbide wafer, the IF 1 value is 3 to 10, and the IF 2 value is 3 to 10.

[0012] It should be noted that the 2 / 3 diameter range of the silicon carbide wafer is based on the center point of the wafer. Due to the structure of the silicon carbide crystal growth and the heating method, there are certain differences in the curvature within the 2 / 3 diameter range and outside the 2 / 3 diameter. At the same time, the crystallization quality is also different. This difference will lead to uneven doping concentration across the entire surface after homoepitaxy, affecting the uniformity of the device.

[0013] In this application, this problem can be avoided by processing the silicon carbide wafer. Especially during the heteroepitaxy process, the crystallinity of the processed wafer is more uniform, significantly improving the uneven lattice matching on the wafer.

[0014] Optionally, within the 2 / 3 diameter range of the silicon carbide wafer, the absolute value of the difference between any two IF 1 values is ≤ 1, and the absolute value of the difference between any two IF 2 values is ≤ 2; Within the remaining ring range after removing the circle within the 2 / 3 diameter range of the silicon carbide wafer, the absolute value of the difference between any two IF 1 values is ≤ 1, and the absolute value of the difference between any two IF 2 values is ≤ 2.

[0015] Optionally, the cell volume change rate of the silicon carbide wafer is ≤ 0.01%. The calculation formula for the cell volume change rate is: (|V - 82.82| / 82.82) * 100%, where V is the cell volume.

[0016] According to the basic principles of crystallography, there are differences in the cell size on the surface of the material and the cell size within the material body. Moreover, due to the presence of the processing damage layer, this difference will be further amplified, and this difference directly leads to an increase in the lattice mismatch degree during the growth of the epitaxial layer. Through the processing method of this application, the surface can be directly modified, reducing the cell volume change rate while reducing the influence of lattice mismatch, and obtaining a silicon carbide wafer with improved surface crystallization quality.

[0017] According to another aspect of this application, there is provided the use of the above-mentioned silicon carbide wafer with improved surface crystallization quality in the growth of an epitaxial layer. The silicon carbide wafer provided by this application can significantly improve the quality of the epitaxial layer during both homoepitaxy and heteroepitaxy processes.

[0018] According to another aspect of this application, there is provided a method for improving the surface crystallization quality of a silicon carbide wafer. The method includes the following steps: 1) Place the silicon carbide wafer to be processed in a reaction furnace, heat it to 940 - 960K, and stabilize for 3 - 7 minutes; 2) Heat it to 1030 - 1070K at a rate of 1 - 5K / min; 3) Maintain for 1 to 5 minutes, during which hydrogen and oxygen are introduced alternately; 4) Cooling to room temperature within 15 minutes to obtain the silicon carbide wafer with improved surface crystallization quality.

[0019] In step 2), the temperature is pre-increased so that in step 3), the temperature can be quickly and stably raised to the processing temperature without causing drastic changes in the wafer surface. Alternating the introduction of hydrogen and oxygen during the treatment process is beneficial to the removal of dangling bonds, wherein hydrogen plasma passivates the dangling bonds on the surface of the wafer and increases their energy, and then the introduction of oxygen plasma can further increase the energy of the dangling bonds and cause bond breakage, and this can be repeated to remove the surface dangling bonds.

[0020] If the temperature after step 2) is too high, it will easily lead to excessive proliferation of basal plane dislocations. If the high temperature is maintained for too long in step 3), it will also cause an increase in the change in the curvature of the wafer. If the heating speed in step 2) is too fast, it will easily cause permanent changes to the surface shape of the wafer.

[0021] When the temperature is in the range of 940K~960K, it is not close to the plastic transition temperature of the wafer, so the temperature can be raised quickly to reduce the impact of the slow heating thermal history on stress; the temperature continues to rise to 1030~1070K, which is already close to the plastic transition temperature, and needs to be raised slowly to prevent excessive deformation of the wafer; cooling in about 15 minutes can control the cooling time not to be too long, so as to try to maintain the surface shape at high temperature.

[0022] Optionally, in step 3), the flow ratio of hydrogen to oxygen is (7-13): 1. Since oxygen has a stronger ability to remove surface dangling bonds, a higher oxygen flow rate than hydrogen ensures better removal efficiency, but too high an oxygen flow rate can easily cause large-area oxidation of the surface, which is not conducive to the removal of dangling bonds and crystal surface recrystallization.

[0023] Optionally, in step 3), the oxygen flow rate is 5-10 sccm.

[0024] Optionally, in step 3), hydrogen and oxygen are introduced alternately at intervals of 10 to 60 seconds.

[0025] It should be noted that the above range is only one of the feasible operating conditions. Those skilled in the art can adjust the oxygen flow rate and the alternating introduction method based on the technical ideas of the present application, which can achieve the removal of surface dangling bonds and does not impose any necessary limitations on the present application scheme.

[0026] Optionally, a change in the number of basal plane dislocations of the silicon carbide wafer before and after processing is ≤0.1%.

[0027] Optionally, the change in the bow of the silicon carbide wafer before and after processing is ≤ 1%.

[0028] The beneficial effects of this application include but are not limited to: 1. The silicon carbide wafer with improved surface crystallization quality according to this application has a relatively high IF 1 value and IF 2 value. The problem of poor crystallization quality caused by dangling bonds on the wafer surface is relatively small. When growing an epitaxial layer, the lattice matching between the epitaxial layer and the wafer will be better, resulting in a better quality of the epitaxial layer and better quality of the components prepared from the epitaxial layer.

[0029] 2. The silicon carbide wafer with improved surface crystallization quality according to this application effectively improves the crystallization quality of the wafer surface by treating the silicon surface of the silicon carbide wafer with a certain proportion of hydrogen-oxygen plasma, effectively improves the surface crystallization quality, and effectively solves the problem of dangling bonds.

[0030] 3. The silicon carbide wafer with improved surface crystallization quality according to this application has a rapid temperature rise, little damage to the surface shape, and a short processing time that will not damage the wafer surface. After processing, the crystallization quality of the surface is improved, and dislocation slip will not occur.

[0031] 4. For the silicon carbide wafer with improved surface crystallization quality according to this application, high-temperature annealing or acid-base solution cleaning of the wafer in the prior art cannot effectively improve the surface crystallization quality of the wafer. Acid / alkali cleaning can remove some dangling bonds, but this improvement in crystallization quality is mainly affected by reducing roughness, which is only applicable to the case where the surface state is relatively rough. On the one hand, this application's solution breaks the dangling bonds through hydrogen-oxygen plasma, and on the other hand, specific temperature conditions can promote the release of stress in the wafer, thereby effectively improving the surface crystallization quality of the wafer. Description of the Drawings

[0032] The drawings described herein are used to provide a further understanding of this application and form a part of this application. The schematic embodiments of this application and their descriptions are used to explain this application and do not constitute an improper limitation of this application. In the drawings: Figure 1 It is a diagram showing the diffraction peak intensity and Gaussian function fitting results of the crystal plane of the processed wafer (118) involved in Embodiment 1 of this application; Figure 2 It is a schematic diagram of the two-dimensional plane and the three-dimensional crystal cell structure of the wafer involved in the embodiments of this application. Detailed Embodiments

[0033] The following describes this application in detail with reference to the embodiments. However, this application is not limited to these embodiments. Unless otherwise specified, the raw materials and reagents in the embodiments of this application are purchased through commercial channels.

[0034] The solution of the present application will be described below through specific embodiments.

[0035] Embodiment 1 1) Place the mechanically polished wafer in a reaction furnace and expose the silicon surface for treatment. Select a wafer with a roughness of 1 nm and a curvature of about 50 μm. 2) Heat up to 950 K within 5 min and stabilize for 5 min. 3) Heat up to 1050 K at a rate of 3 K / min. 4) Hold for 3 min. During this period, hydrogen and oxygen are alternately introduced at intervals of 30 s. The flow rate ratio of hydrogen to oxygen is 10:1, and the flow rate of oxygen introduced is 7.5 sccm. 5) Introduce Ar to cool down. Cool down to room temperature within 10 min to complete the treatment and obtain a silicon carbide wafer with improved surface crystallization quality.

[0036] Embodiment 2 1) Place the mechanically polished wafer in a reaction furnace and expose the silicon surface for treatment. Select a wafer with a roughness of 1 nm and a curvature of about 50 μm. 2) Heat up to 940 K within 5 min and stabilize for 7 min. 3) Heat up to 1070 K at a rate of 5 K / min. 4) Hold for 1 min. During this period, hydrogen and oxygen are alternately introduced at intervals of 10 s. The flow rate ratio of hydrogen to oxygen is 7:1, and the flow rate of oxygen introduced is 5 sccm. 4) Introduce Ar to cool down. Cool down to room temperature within 15 min to complete the treatment and obtain a silicon carbide wafer with improved surface crystallization quality.

[0037] Embodiment 3 1) Place the mechanically polished wafer in a reaction furnace and expose the silicon surface for treatment. Select a wafer with a roughness of 1 nm and a curvature of about 50 μm. 2) Heat up to 960 K within 5 min and stabilize for 3 min. 3) Heat up to 1030 K at a rate of 1 K / min. 4) Hold for 5 min. During this period, hydrogen and oxygen are alternately introduced at intervals of 60 s. The flow rate ratio of hydrogen to oxygen is 13:1, and the flow rate of oxygen introduced is 10 sccm. 5) Introduce Ar to cool down. Cool down to room temperature within 12 min to complete the treatment and obtain a silicon carbide wafer with improved surface crystallization quality.

[0038] Embodiment 4 This embodiment is basically the same as Embodiment 1, except that in step 3), the temperature is raised to 1300 K.

[0039] Embodiment 5 This example is basically the same as Example 1, except that in step 4), it is maintained for 15 minutes.

[0040] Example 6 This example is basically the same as Example 1, except that in step 4), only hydrogen is introduced.

[0041] Example 7 This example is basically the same as Example 1, except that in step 4), only oxygen is introduced.

[0042] Example 8 This example is basically the same as Example 1, except that in step 4), the hydrogen:oxygen flow rate ratio is 5:1.

[0043] Example 9 This example is basically the same as Example 1, except that in step 4), the hydrogen:oxygen flow rate ratio is 15:1.

[0044] Example 10 This example is basically the same as Example 1, except that in step 3), the heating rate is 10 K / min.

[0045] Example 11 This example is basically the same as Example 1, except that in step 5), it is cooled to room temperature in 50 minutes.

[0046] Comparative Example 1 This comparative example is the high-temperature annealing treatment step of silicon carbide wafers in the prior art. Specifically, it is heated to 1800 K, and the annealing time is 2 h. During this period, nitrogen or argon is introduced as a protective gas, and the pressure is 40 torr.

[0047] Test Example 1 The silicon carbide wafers prepared in the examples and comparative examples were detected, and the performance before and after treatment was compared.

[0048] The IF value is the ratio of the diffraction peak intensity of the (1-16) or (118) crystal plane in the X-ray diffraction analysis to 10000 * the full width at half maximum. If the IF value is greater than 3, it is considered that the surface crystallization quality has improved. As Figure 1 shown, the diffraction peak intensity and the full width at half maximum can be obtained by fitting and calculating the X-ray diffraction analysis results.

[0049] The cell volume change rate is the relative change rate of the cell volume V to the standard value of 82.82. The calculation formula is: (|V - 82.82| / 82.82) * 100%. The cell volume V can be measured by transmission electron microscopy or X-ray diffraction. As Figure 2As shown, the left figure is a two-dimensional plane schematic diagram of a partial wafer, and the right figure is a three-dimensional schematic diagram of a unit cell. The calculation formula for the volume V of the unit cell is: V = 3 ½ / 2 * a 2 * c.

[0050] The curvature change rate characterizes the change in the curvature of the wafer before and after processing. The calculation formula is: (curvature after processing - curvature before processing) / curvature before processing * 100%. The curvature is detected using a laser interferometer.

[0051] The change in the number of basal plane dislocations characterizes the change in the number of basal plane dislocations before and after processing. The calculation formula is: (number of basal plane dislocations after processing - number of basal plane dislocations before processing) / number of basal plane dislocations before processing * 100%. The number of basal plane dislocations is detected using KOH etching.

[0052] Among them, the absolute value of the difference between any two IF 1 values and the absolute value of the difference between any two IF 2 values are calculated after detecting two samples randomly selected in the sampling area. The test results are shown in Table 1 below.

[0053] Table 1 Detection Results of the Performance of Silicon Carbide Wafers

[0054] Table 1 Continued Table 1

[0055] Table 1 Continued Table 2

[0056] According to the results in Table 1, it can be seen that the silicon carbide wafers prepared in Examples 1 to 3 of this application have relatively high IF 1 values and IF 2 values. The problem of poor crystal quality caused by dangling bonds on the wafer surface is relatively small. When growing an epitaxial layer, the lattice compatibility between the epitaxial layer and the wafer will be better, resulting in better quality of the epitaxial layer. In contrast, the conventional high-temperature annealing method in Comparative Example 1 basically does not show the effect of surface reconstruction and cannot solve the problem of poor crystal quality caused by dangling bonds.

[0057] Comparing Example 1 and Example 4, it can be seen that if the heating temperature is too high, it will cause excessive proliferation of basal plane dislocations and too large a change in the curvature rate.

[0058] Comparing Example 1 and Example 5, it can be seen that too long a holding time means a longer processing time for surface reconstruction, which will result in lower IF values outside the 2 / 3 diameter range and a worse surface reconstruction effect.

[0059] Comparing Comparative Example 1 with Example 6 shows that when only hydrogen is introduced, the surface reconstruction treatment has little effect.

[0060] Comparing Comparative Example 1 with Example 7 shows that when only oxygen is introduced, the surface reconstruction treatment has little effect and at the same time causes an increase in the change amount of the curvature.

[0061] Comparing Comparative Example 1 with Example 8 shows that if the proportion of oxygen introduced is too high, it will lead to poor surface reconstruction effect and is likely to cause an increase in the change amount of the curvature, but has little impact on the surface shape.

[0062] Comparing Comparative Example 1 with Example 9 shows that if the proportion of oxygen introduced is too low, the surface reconstruction effect is poor.

[0063] Comparing Comparative Example 1 with Example 10 shows that too large a heating rate will cause an increase in the change amount of the basal plane dislocation of the silicon carbide wafer and an increase in the change amount of the curvature.

[0064] Comparing Comparative Example 1 with Example 11 shows that too small a cooling rate in the cooling step results in an increase in the change amount of the basal plane dislocation of the silicon carbide wafer, an increase in the change amount of the curvature, and a deterioration in the surface reconstruction effect.

[0065] As described above, only the embodiments of the present application are mentioned. The protection scope of the present application is not limited by these specific embodiments, but is determined by the claims of the present application. For those skilled in the art, various changes and modifications can be made to the present application. Any modification, equivalent replacement, improvement, etc. made within the technical idea and principle of the present application shall be included within the protection scope of the present application.

Claims

1. A silicon carbide wafer with improved surface crystal quality, characterized in that: The IF1 value of the silicon carbide wafer is ≥3, and the IF2 value is ≥3; IF1 value = Peak (1-16) / (10000*FWHM (1-16) ); IF2 value = Peak (118) / (10000*FWHM (118) ); Among them, Peak (1-16) and FWHM (1-16) The diffraction peak intensity and half-height width of the (1-16) crystal plane analyzed by X-ray diffraction, Peak (118) and FWHM (118) They are the diffraction peak intensity and half-height width of the (118) crystal plane analyzed by X-ray diffraction.

2. The silicon carbide wafer with improved surface crystal quality according to claim 1, characterized in that: The IF1 value of the silicon carbide wafer is 3-10, and the IF2 value is 3-10.

3. The silicon carbide wafer with improved surface crystal quality according to claim 1, characterized in that: Within the 2 / 3 diameter range of the silicon carbide wafer, the IF1 value is 5-10, and the IF2 value is 5-10; After removing the circle within the 2 / 3 diameter range of the silicon carbide wafer, within the remaining circular ring range, the IF1 value is 3-10, and the IF2 value is 3-10.

4. The silicon carbide wafer with improved surface crystal quality according to claim 1, characterized in that: Within a 2 / 3 diameter range of the silicon carbide wafer, the absolute value of the difference between any two IF1 values ​​is ≤1, and the absolute value of the difference between any two IF2 values ​​is ≤2. In the remaining circular ring range after removing the circle within the 2 / 3 diameter range of the silicon carbide wafer, the absolute value of the difference between any two IF1 values ​​is ≤1, and the absolute value of the difference between any two IF2 values ​​is ≤2.

5. The silicon carbide wafer with improved surface crystal quality according to claim 1, characterized in that: The unit cell volume change rate of the silicon carbide wafer is ≤0.01%, wherein the calculation formula of the unit cell volume change rate is: (|V-82.82| / 82.82)*100%, where V is the unit cell volume.

6. Use of the silicon carbide wafer with improved surface crystallization quality as claimed in any one of claims 1 to 5 in growing an epitaxial layer.

7. A method for improving the surface crystal quality of a silicon carbide wafer, characterized in that: The method comprises the following steps: 1) Place the silicon carbide wafer to be processed in the reactor, heat it to 940~960K, and stabilize it for 3~7 minutes; 2) Raise the temperature to 1030~1070K at 1~5K / min; 3) Maintain for 1 to 5 minutes, during which hydrogen and oxygen are introduced alternately; 4) Cooling to room temperature within 15 minutes to obtain the silicon carbide wafer with improved surface crystallization quality.

8. The method for improving the surface crystal quality of silicon carbide wafer according to claim 7, characterized in that: In the step 3), the flow ratio of hydrogen to oxygen is (7-13):

1.

9. The method for improving the surface crystal quality of silicon carbide wafer according to claim 7, characterized in that: The change in the number of basal plane dislocations of the silicon carbide wafer before and after processing is ≤0.1%.

10. The method for improving the surface crystal quality of silicon carbide wafer according to claim 7, characterized in that: The change in curvature of the silicon carbide wafer before and after processing is ≤1%.

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