A method for reducing carbon vacancies in silicon carbide crystal material

Abstract

The application provides a method for reducing carbon vacancies of silicon carbide crystal material, which comprises the following steps: placing an initial silicon carbide sample after cleaning into an oxidation furnace; increasing the temperature in the oxidation furnace from an initial temperature to an intermediate temperature within a preset first oxidation time; continuously supplying a carrier gas into the oxidation furnace within a preset second oxidation time; immersing the silicon carbide sample after the second oxidation time into a preset buffer solution to remove the oxide layer on the surface of the silicon carbide sample; performing high-temperature annealing treatment on the silicon carbide sample after removing the oxide layer according to a preset target temperature within a preset annealing time, so as to obtain a target silicon carbide sample; and performing carbon vacancy testing on the target silicon carbide sample. The method can reduce the carbon vacancy density by using high-temperature oxidation and high-temperature annealing, so as to obtain a SiC epitaxial material with low carbon vacancy and high minority carrier lifetime, which is suitable for manufacturing high-voltage bipolar semiconductor power devices.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of wide band gap semiconductor material preparation, and particularly relates to a method for reducing carbon vacancies of silicon carbide crystal material. BACKGROUND

[0002] Silicon carbide (SiC) is the third generation semiconductor material, and has a series of characteristics such as high breakdown field, high electron saturation mobility, high thermal conductivity, corrosion resistance and the like, which are beneficial to preparation of high-power chips, and is the preferred material of high-voltage and high-power devices. SiC-based power semiconductor devices have high efficiency and energy saving advantages, and have great application potential. Compared with Si-based devices, SiC-based devices have the advantages of high efficiency and energy saving, high working frequency, good stability, small size and the like. With the research and development of SiC ultra-high voltage devices, related scientific problems also need to be solved.

[0003] High-performance ultra-high voltage power electronic devices (>10kV) are all bipolar devices, in order to realize low conduction loss of the ultra-high voltage SiC bipolar device, the carrier lifetime of the drift layer must be high enough to obtain the conductivity modulation, so it is very important to realize the regulation of the carrier lifetime. The regulation of the minority carrier lifetime of the thick epitaxial layer of SiC is mainly realized by intentionally reducing point defects, because many point defects will form a composite center. The carbon vacancy in the silicon carbide material is the main composite center affecting the carrier lifetime, and is also the most typical deep level defect. SUMMARY

[0004] (I) Technical problems to be solved

[0005] In view of the above problems, the main purpose of the present application is to provide a method for reducing carbon vacancies of silicon carbide crystal material, which can reduce the carbon vacancy density by high-temperature oxidation and high-temperature annealing, and obtain SiC epitaxial material with low carbon vacancy and high minority carrier lifetime, which is suitable for manufacturing high-voltage bipolar semiconductor power devices.

[0006] (II) Technical scheme

[0007] In order to achieve the above purpose, the present application provides a method for reducing carbon vacancies of silicon carbide crystal material, comprising: placing the cleaned initial silicon carbide sample into an oxidation furnace; in a preset first oxidation time, the temperature in the oxidation furnace is increased from an initial temperature to an intermediate temperature; in a preset second oxidation time, the carrier gas is continuously introduced into the oxidation furnace; the silicon carbide sample after the second oxidation time is soaked in a preset buffer solution to remove the oxide layer on the surface of the silicon carbide sample; in a preset annealing time, the silicon carbide sample after removing the oxide layer is subjected to high-temperature annealing treatment in an atmosphere according to a preset target temperature, so as to obtain a target silicon carbide sample; and the target silicon carbide sample is subjected to carbon vacancy test.

[0008] In the above scheme, the temperature in the oxidation furnace is increased from the initial temperature to the intermediate temperature within the preset first oxidation time, comprising: introducing oxygen into the oxidation furnace and gradually increasing to the preset first flow value within the preset first oxidation time; after the temperature in the oxidation furnace is increased from the initial temperature to the intermediate temperature, the intermediate temperature is kept unchanged.

[0009] In the above scheme, the carrier gas is continuously introduced into the oxidation furnace within the preset second oxidation time, wherein the carrier gas comprises NO or N2O gas, and the carrier gas is introduced at a preset second flow value.

[0010] In the above scheme, the silicon carbide sample after the second oxidation time is soaked in a preset buffer solution to remove the oxide layer on the surface of the silicon carbide sample, comprising: during the soaking process, the buffer solution is stirred to improve the removal efficiency and ensure that the active ingredients in the buffer solution can uniformly act on the surface of the sample; during the soaking process, a characterization means is used to monitor the surface state of the sample in real time to observe the removal effect of the oxide layer.

[0011] In the above scheme, the silicon carbide sample after the second oxidation time is soaked in a preset buffer solution to remove the oxide layer on the surface of the silicon carbide sample, wherein: the buffer solution comprises a hydrofluoric acid buffer solution, and the hydrofluoric acid buffer solution comprises a preset volume ratio of hydrofluoric acid and water.

[0012] In the above scheme, the silicon carbide sample after the second oxidation time is soaked in a preset buffer solution to remove the oxide layer on the surface of the silicon carbide sample, wherein: the buffer solution comprises a hydrofluoric acid buffer solution, and the hydrofluoric acid buffer solution comprises a preset volume ratio of hydrofluoric acid and water.

[0013] In the above scheme, the silicon carbide sample after the second oxidation time is soaked in a preset buffer solution to remove the oxide layer on the surface of the silicon carbide sample, wherein: the buffer solution comprises a hydrofluoric acid buffer solution, and the hydrofluoric acid buffer solution comprises a preset volume ratio of hydrofluoric acid and water.

[0014] In the above scheme, the carbon vacancy test of the target silicon carbide sample comprises: using a deep level transient spectroscopy (DLTS) method to test the carbon vacancy density distribution of the target silicon carbide sample.

[0015] (Three) beneficial effects

[0016] The technical scheme of the embodiment of the present application has at least the following beneficial effects:

[0017] (1) By the method for reducing carbon vacancies of silicon carbide crystal material, the carbon vacancy density can be reduced to 5E12cm-3 by high-temperature oxidation and high-temperature annealing -3 .

[0018] (2) The SiC epitaxial material with low carbon vacancies and high minority carrier lifetime is suitable for manufacturing high-voltage bipolar semiconductor power devices.

[0019] (3) In addition, the reduction of carbon vacancies of the SiC material is beneficial to the improvement of the material crystal quality, and is beneficial to the device to withstand higher power and reduce the conduction loss. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 A flowchart of the method for reducing carbon vacancies of silicon carbide crystal material according to an embodiment of the present application is shown;

[0021] Figure 2 A schematic diagram of carbon vacancy density distribution in a 4H-SiC epitaxial layer according to an embodiment of the present application is shown;

[0022] Figure 3 A schematic diagram of carbon vacancy density distribution in a 4H-SiC epitaxial layer according to an embodiment of the present application is shown. DETAILED DESCRIPTION

[0023] In order to make the purpose, technical scheme and advantages of the present application more clear, the present application is further described in detail below in combination with specific embodiments and with reference to the drawings.

[0024] Figure 1 A flowchart of the method for reducing carbon vacancies of silicon carbide crystal material according to an embodiment of the present application is shown.

[0025] As shown in Figure 1 , the method for reducing carbon vacancies of silicon carbide crystal material specifically includes operations S1-S6.

[0026] In operation S1, the cleaned initial silicon carbide sample is placed into an oxidation furnace.

[0027] In operation S2, the temperature in the oxidation furnace is increased from an initial temperature to an intermediate temperature within a preset first oxidation time.

[0028] In an embodiment of the present application, the temperature in the oxidation furnace is increased from the initial temperature to the intermediate temperature within the preset first oxidation time, including: within the preset first oxidation time, oxygen is introduced into the oxidation furnace and gradually increased to a preset first flow value; after the temperature in the oxidation furnace is increased from the initial temperature to the intermediate temperature, the intermediate temperature is kept unchanged.

[0029] For example, the obtained initial silicon carbide (SiC) sample is first cleaned, and then the initial SiC sample is placed in a high-temperature oxidation furnace. The temperature in the oxidation furnace is raised to an intermediate temperature, for example, the intermediate temperature can be 1250-1650°C, and O2 is introduced at a first flow rate, for example, the first flow rate of the introduced O2 can be 1-4 slm. Finally, the oxidation is carried out at a high temperature for a first oxidation time, for example, the first oxidation time can be 2-60 hours.

[0030] In operation S3, the carrier gas is continuously introduced into the oxidation furnace for a preset second oxidation time.

[0031] In an embodiment of the present application, the carrier gas is continuously introduced into the oxidation furnace for a preset second oxidation time, wherein the carrier gas comprises NO or N2O gas, and the carrier gas is introduced at a preset second flow rate.

[0032] For example, the NO or N2O gas is introduced at a preset second flow rate, for example, the second flow rate can be 300-1500 sccm, and then the oxidation is carried out for 10-90 minutes.

[0033] In operation S4, the silicon carbide sample after the second oxidation time is soaked in a preset buffer solution to remove the oxide layer on the surface of the silicon carbide sample.

[0034] In an embodiment of the present application, the buffer solution comprises a hydrofluoric acid buffer solution, wherein the hydrofluoric acid buffer solution comprises a preset volume ratio of hydrofluoric acid and water.

[0035] For example, the HF (hydrofluoric acid) buffer solution, for example, the volume ratio of HF:H2O is 1:4-1:10, is used to soak the sample for 2-10 minutes to remove the oxide layer on the surface of the sample.

[0036] During the soaking process, the buffer solution is stirred to improve the removal efficiency, to ensure that the active components in the buffer solution can uniformly act on the surface of the sample, and during the soaking process, a characterization means is used to monitor the surface state of the sample in real time, to observe the removal effect of the oxide layer.

[0037] In operation S5, the silicon carbide sample after the oxide layer is removed is subjected to an atmosphere high-temperature annealing treatment according to a preset target temperature for a preset annealing time, to obtain a target silicon carbide sample.

[0038] In an embodiment of the present application, the atmosphere gas comprises argon and hydrogen.

[0039] In the embodiment of the present application, the silicon carbide sample without the oxide layer is subjected to high-temperature annealing treatment in a protective atmosphere according to a preset target temperature and a preset target pressure within a preset annealing time; after the annealing is completed, the target silicon carbide sample is slowly cooled to avoid thermal stress damage caused by sudden temperature drop; and the protective atmosphere is continuously maintained during the cooling process to prevent re-oxidation.

[0040] For example, the silicon carbide sample without the oxide layer is subjected to high-temperature annealing treatment in a hydrogen (or Ar) atmosphere, wherein the preset target temperature can be 1200-1650°C, the preset target pressure can be 30-1000 mbar, and the annealing time can be 10-90 minutes.

[0041] In operation S6, the carbon vacancy of the target silicon carbide sample is tested.

[0042] In the embodiment of the present application, the Deep Level Transient Spectroscopy (DLTS) method is used to test the carbon vacancy density distribution of the target silicon carbide sample.

[0043] By the embodiment of the present application, the silicon carbide epitaxial material with low carbon vacancy density and meeting the preparation requirements of super-high-voltage bipolar devices can be prepared, which is suitable for super-high-voltage semiconductor high-power electronic power devices, can significantly reduce energy consumption, and improve the performance of SiC devices.

[0044] Figure 2 A schematic diagram of the carbon vacancy density distribution in a 4H-SiC epitaxial layer according to the embodiment of the present application is shown.

[0045] Figure 3 A schematic diagram of the carbon vacancy density distribution in a 4H-SiC epitaxial layer according to the embodiment of the present application is shown.

[0046] Based on the above method for reducing the carbon vacancy of the silicon carbide crystal material, the present embodiment takes a 126-micron-thick N-type 4H-SiC epitaxial wafer as an example for illustration.

[0047] Specifically, a 126-micron-thick N-type 4H-SiC epitaxial wafer (with a minority carrier lifetime of 1.26 μs before any treatment) is cleaned and then placed in a high-temperature oxidation furnace, oxygen is gradually introduced at a flow rate of 2 slm, the temperature is raised to 1300°C and maintained for 15 hours, then the oxygen atmosphere is replaced with NO while maintaining the temperature, and maintained for 30 minutes. Then the sample is immersed in an HF buffer solution (HF:H2O=1:6) for 5 minutes to remove the oxide layer, and finally placed in an annealing furnace, a hydrogen atmosphere is introduced, the pressure is 500 mbar, and annealing is performed at a temperature of 1600°C for 60 minutes. After the end of the annealing, the carbon vacancy is tested by the DLTS method.

[0048] As Figure 2 shown, the carbon vacancy density distribution in a 4-inch 100-µm-thick 4H-SiC epitaxial layer tested by the DLTS method, shows that long-time high-temperature oxidation effectively reduces the carbon vacancy density to less than 5E12 cm -3 , and improves the minority carrier lifetime of the silicon carbide thick epitaxial layer, as shown in Figure 3 , the minority carrier lifetime can be increased to 4 µs at the highest.

[0049] Through the embodiments of the present application, by the method for reducing the carbon vacancy of silicon carbide material of the embodiments of the present application, by using high-temperature oxidation and high-temperature annealing, the carbon vacancy density can be reduced to 5E12 cm -3 . Thus, a SiC epitaxial material with low carbon vacancy and high minority carrier lifetime is obtained, which is suitable for manufacturing high-voltage bipolar semiconductor power devices. In addition, the reduction of carbon vacancy of SiC material improves the crystal quality of the material, and is conducive to the device to withstand higher power and reduce the conduction loss.

[0050] Those skilled in the art can understand that, although the present application has been shown and described with reference to specific exemplary embodiments thereof, it should be understood that various changes in form and detail can be made thereto without departing from the spirit and scope of the application as defined by the appended claims and their equivalents. Therefore, the scope of the present application should not be limited to the above-described embodiments, but should be determined only by the appended claims, and should be limited by the equivalents of the appended claims.

[0051] The above specific embodiments further illustrate the purpose, technical solutions and beneficial effects of the present application, and it should be understood that the above are only specific embodiments of the present application and are not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application should be included in the protection scope of the present application.

Claims

1. A method for reducing carbon vacancies in silicon carbide crystalline materials, characterized in that, The method includes: The cleaned initial silicon carbide sample is placed in an oxidation furnace; Within a preset first oxidation time, the temperature inside the oxidation furnace is raised from the initial temperature to an intermediate temperature, the intermediate temperature being in the range of 1250℃~1650℃. During the preset second oxidation time, a carrier gas, including NO or N2O gas, is continuously introduced into the oxidation furnace. The carrier gas is introduced at a second flow rate value, which ranges from 300 sccm to 1500 sccm. The silicon carbide sample after the second oxidation time is immersed in a preset buffer solution to remove the oxide layer on the surface of the silicon carbide sample. Within a preset annealing time, the silicon carbide sample with the oxide layer removed is subjected to high-temperature annealing in an atmosphere according to a preset target temperature and a preset target pressure to obtain a target silicon carbide sample. The atmosphere gas includes argon and hydrogen. The target temperature ranges from 1200℃ to 1650℃, and the target pressure ranges from 30mbar to 1000mbar. Carbon vacancy testing was performed on the target silicon carbide sample.

2. The method for reducing carbon vacancies in silicon carbide crystal materials according to claim 1, characterized in that, The step of raising the temperature inside the oxidation furnace from the initial temperature to the intermediate temperature within a preset first oxidation time includes: During a preset first oxidation time, oxygen is introduced into the oxidation furnace and gradually increased to a preset first flow rate value; After raising the temperature inside the oxidation furnace from the initial temperature to the intermediate temperature, the intermediate temperature is kept constant.

3. The method for reducing carbon vacancies in silicon carbide crystal materials according to claim 1, characterized in that, The step of immersing the silicon carbide sample after the second oxidation time in a preset buffer solution to remove the oxide layer on the surface of the silicon carbide sample includes: During the soaking process, the buffer solution is stirred to improve the removal efficiency and ensure that the active ingredients in the buffer solution can act evenly on the sample surface; During the immersion process, characterization techniques were used to monitor the surface state of the samples in real time and observe the effect of oxide layer removal.

4. The method for reducing carbon vacancies in silicon carbide crystal materials according to claim 3, characterized in that, The step involves immersing the silicon carbide sample after the second oxidation time in a preset buffer solution to remove the oxide layer on the surface of the silicon carbide sample. The buffer solution includes a hydrofluoric acid buffer solution, wherein the hydrofluoric acid buffer solution comprises hydrofluoric acid and water in a predetermined volume ratio.

5. The method for reducing carbon vacancies in silicon carbide crystal materials according to claim 1, characterized in that, The step of performing high-temperature annealing treatment on the silicon carbide sample with the oxide layer removed, according to a preset target temperature and a preset target pressure within a preset annealing time, to obtain the target silicon carbide sample, further includes: After annealing, the target silicon carbide sample is slowly cooled to avoid thermal stress damage caused by a sudden drop in temperature. A protective atmosphere is maintained during the cooling process to prevent re-oxidation.

6. The method for reducing carbon vacancies in silicon carbide crystal materials according to claim 1, characterized in that, The carbon vacancy test on the target silicon carbide sample includes: The carbon vacancy density distribution in the target silicon carbide sample was tested using deep-level transient spectroscopy.

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