Method for reducing carbon vacancy of silicon carbide crystal material

Abstract

The invention provides a method for reducing carbon vacancies of a silicon carbide crystal material. The method comprises the following steps: putting a cleaned initial silicon carbide sample into an oxidizing furnace; within the preset first oxidation time, the temperature in the oxidation furnace is increased to the intermediate temperature from the initial temperature; within a preset second oxidation time, continuously introducing a carrier gas into the oxidation furnace; soaking the silicon carbide sample after the second oxidation time in a preset buffer solution to remove an oxide layer on the surface of the silicon carbide sample; carrying out atmosphere high-temperature annealing treatment on the silicon carbide sample without the oxide layer according to a preset target temperature within a preset annealing time to obtain a target silicon carbide sample; and performing carbon vacancy test on the target silicon carbide sample. According to the method, high-temperature oxidation and high-temperature annealing are utilized, the carbon vacancy density can be reduced, the SiC epitaxial material with low carbon vacancy and long minority carrier lifetime is obtained, and the method is suitable for manufacturing high-voltage bipolar semiconductor power devices.

Description

Technical Field

[0001] The invention relates to the technical field of wide bandgap semiconductor material preparation, and in particular to a method for reducing carbon vacancies in silicon carbide crystal materials. Background Art

[0002] As a third-generation semiconductor material, silicon carbide (SiC) has a series of properties that are conducive to the preparation of high-power chips, such as high breakdown field strength, high electron saturation mobility, high thermal conductivity, and corrosion resistance. It is the preferred material for high-voltage and high-power devices. SiC-based power semiconductor devices have the advantages of high efficiency and energy saving, and have huge application potential. Compared with similar Si-based devices, SiC-based devices have the advantages of high efficiency and energy saving, high operating frequency, good stability, and small size. With the development of SiC ultra-high voltage devices, related scientific problems also need to be solved urgently.

[0003] High-performance ultra-high voltage power electronic devices (>10kV) are all bipolar devices. In order to achieve low conduction loss of ultra-high voltage SiC bipolar devices, the carrier lifetime of the drift layer must be high enough to obtain conductivity modulation, so it is crucial to achieve the regulation of carrier lifetime. The minority carrier lifetime of SiC thick epitaxial layer is mainly regulated by intentionally reducing point defects, because many point defects will constitute recombination centers. The carbon vacancies in silicon carbide materials are the main recombination centers that affect the carrier lifetime and are also the most typical deep energy level defects. Summary of the invention

[0004] 1. Technical issues to be resolved

[0005] In view of the above-mentioned deficiencies, the main purpose of the present invention is to provide a method for reducing carbon vacancies in silicon carbide crystal materials. By utilizing high-temperature oxidation and high-temperature annealing, the carbon vacancy density can be reduced to obtain SiC epitaxial materials with low carbon vacancies and high minority carrier lifetime, which are suitable for the manufacture of high-voltage bipolar semiconductor power devices.

[0006] (II) Technical solution

[0007] In order to achieve the above-mentioned purpose, the present invention provides a method for reducing carbon vacancies in silicon carbide crystalline materials, comprising: placing a cleaned initial silicon carbide sample into an oxidation furnace; within a preset first oxidation time, raising the temperature in the oxidation furnace from the initial temperature to an intermediate temperature; within a preset second oxidation time, continuously introducing a carrier gas into the oxidation furnace; immersing the silicon carbide sample after the second oxidation time in a preset buffer solution to remove an oxide layer on the surface of the silicon carbide sample; within a preset annealing time, performing an atmosphere high-temperature annealing treatment on the silicon carbide sample with the oxide layer removed according to a preset target temperature to obtain a target silicon carbide sample; and performing a carbon vacancy test on the target silicon carbide sample.

[0008] In the above scheme, the temperature in the oxidation furnace is raised 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 raised from the initial temperature to the intermediate temperature, the intermediate temperature is kept unchanged.

[0009] In the above scheme, during the preset second oxidation time, a carrier gas is continuously introduced into the oxidation furnace, wherein the carrier gas includes NO or N 2 O gas and carrier gas are introduced at a preset second flow value.

[0010] In the above scheme, 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, including: during the immersion process, stirring the buffer solution 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, using characterization means to monitor the surface state of the sample in real time and observe the removal effect of the oxide layer.

[0011] In the above scheme, 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, wherein the buffer solution includes a hydrofluoric acid buffer solution, wherein the hydrofluoric acid buffer solution includes hydrofluoric acid and water in a preset volume ratio.

[0012] In the above scheme, the silicon carbide sample with the oxide layer removed is subjected to atmosphere high temperature annealing treatment at a preset target temperature within a preset annealing time to obtain a target silicon carbide sample, wherein the atmosphere gas includes argon and hydrogen.

[0013] In the above scheme, the silicon carbide sample with the oxide layer removed is subjected to atmosphere high-temperature annealing treatment according to a preset target temperature within a preset annealing time to obtain a target silicon carbide sample, and also includes: within a preset annealing time, according to a preset target temperature and a preset target pressure, the silicon carbide sample with the oxide layer removed is subjected to atmosphere high-temperature annealing treatment; after the annealing is completed, the target silicon carbide sample is slowly cooled to avoid thermal stress damage caused by a sudden drop in temperature; and the protective atmosphere is continued to be maintained during the cooling process to prevent re-oxidation.

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

[0015] (III) Beneficial effects

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

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

[0018] (2) Obtain SiC epitaxial materials with low carbon vacancies and high minority carrier lifetime, which are suitable for the manufacture of high-voltage bipolar semiconductor power devices.

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

[0020] Figure 1 A flow chart of a method for reducing carbon vacancies in silicon carbide crystal material according to an embodiment of the present invention is shown;

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

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

[0023] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings.

[0024] Figure 1 A flow chart of a method for reducing carbon vacancies in a silicon carbide crystal material according to an embodiment of the present invention is shown.

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

[0026] In operation S1, the cleaned initial silicon carbide sample is placed in 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 invention, the temperature in the oxidation furnace is raised from the initial temperature to the intermediate temperature within a 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 raised 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. When the temperature in the oxidation furnace is raised to an intermediate temperature, for example, the intermediate temperature may be 1250°C-1650°C, O is introduced. 2 , where the O 2 The first flow rate may range from 1 slm to 4 slm. Finally, during the first oxidation time, the oxidation is performed at a high temperature. For example, the first oxidation time may range from 2 hours to 60 hours.

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

[0031] In an embodiment of the present invention, during the preset second oxidation time, a carrier gas is continuously introduced into the oxidation furnace, wherein the carrier gas includes NO or N 2 O gas and carrier gas are introduced at a preset second flow value.

[0032] For example, NO or N is then introduced 2 O gas is used at a preset second flow rate, for example, the second flow rate may range from 300 sccm to 1500 sccm, and then the oxidation is performed for 10 minutes to 90 minutes.

[0033] In operation S4, 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.

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

[0035] For example, a HF (hydrofluoric acid) buffer, such as HF:H 2 The range of O (volume ratio) is 1:4 to 1:10, and the oxide layer on the surface of the material is removed by immersion for 2 to 10 minutes.

[0036] During the immersion 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 methods are 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 with the oxide layer removed is subjected to an atmosphere high temperature annealing treatment within a preset annealing time and according to a preset target temperature to obtain a target silicon carbide sample.

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

[0039] In an embodiment of the present invention, within a preset annealing time, the silicon carbide sample with the oxide layer removed is subjected to atmosphere high temperature annealing treatment according to a preset target temperature and a preset target pressure; after the annealing is completed, the target silicon carbide sample is slowly cooled to avoid thermal stress damage caused by a sudden drop in temperature; and the protective atmosphere is continued to be maintained during the cooling process to prevent re-oxidation.

[0040] Exemplarily, the silicon carbide sample with the oxide layer removed is subjected to high temperature annealing in a hydrogen (or Ar) atmosphere, wherein the preset target temperature may range from 1200°C to 1650°C, the preset target pressure may range from 30mbar to 1000mbar, and the annealing time may be, for example, 10 minutes to 90 minutes.

[0041] In operation S6 , a carbon vacancy test is performed on the target silicon carbide sample.

[0042] In an embodiment of the present invention, a deep level transient spectroscopy (DLTS) method is used to test the carbon vacancy density distribution in a target silicon carbide sample.

[0043] Through the embodiments of the present invention, the method can prepare silicon carbide epitaxial material with low carbon vacancy density that meets the preparation requirements of ultra-high voltage bipolar devices, is suitable for ultra-high voltage semiconductor high-power electronic power devices, can significantly reduce energy consumption, and improve SiC device performance.

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

[0045] Figure 3 A schematic diagram showing the distribution of carbon vacancy density corresponding to minority carrier lifetime in a 4H-SiC epitaxial layer according to an embodiment of the present invention is shown.

[0046] Based on the above method for reducing carbon vacancies in silicon carbide crystal materials, this embodiment is described by taking a 126 micron thick N-type 4H-SiC epitaxial wafer as an example.

[0047] Specifically, a 126-micron thick N-type 4H-SiC epitaxial wafer (with a minority carrier lifetime of 1.26μs before any treatment) was used, cleaned and placed in a high-temperature oxidation furnace, and oxygen was introduced gradually to 2slm. The temperature was raised to 1300°C and kept constant for 15 hours. Then, the oxygen atmosphere was replaced with NO and kept constant for 30 minutes. Then, in an HF buffer (HF:H 2 O=1:6) for 5 minutes to remove the oxide layer, and finally put it into an annealing furnace, pass hydrogen atmosphere, pressure 500 mbar, and anneal at 1600℃ for 60 minutes. After completion, the carbon vacancies were tested by DLTS method.

[0048] like Figure 2 The figure shows the carbon vacancy density distribution in a 4-inch diameter 100µm thick 4H-SiC epitaxial layer tested by the DLTS method, indicating that long-term high-temperature oxidation effectively reduces the carbon vacancy density to less than 5E12cm -3 , which increases the minority carrier lifetime in thick SiC epitaxial layers, such as Figure 3 As shown, the minority carrier lifetime can be increased to 4μs at most.

[0049] According to the embodiment of the present invention, the method for reducing carbon vacancies in silicon carbide materials according to the embodiment of the present invention can reduce the carbon vacancy density to 5E12cm by high temperature oxidation and high temperature annealing. -3 . Thus, SiC epitaxial materials with low carbon vacancies and high minority carrier lifetime are obtained, which are suitable for making high-voltage bipolar semiconductor power devices. In addition, the reduction and improvement of carbon vacancies in SiC materials are conducive to improving the quality of material crystals, helping devices to withstand higher power and reduce conduction losses.

[0050] It will be appreciated by those skilled in the art that, although the present invention has been shown and described with reference to specific exemplary embodiments of the present invention, it will be appreciated by those skilled in the art that, without departing from the spirit and scope of the present invention as defined by the appended claims and their equivalents, various changes in form and detail may be made to the present invention. Therefore, the scope of the present invention should not be limited to the above-described embodiments, but should be determined not only by the appended claims, but also by the equivalents of the appended claims.

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

Claims

1. A method for reducing carbon vacancies in silicon carbide crystal material, characterized in that: The method comprises: The cleaned initial silicon carbide sample is placed in an oxidation furnace; During a preset first oxidation time, the temperature in the oxidation furnace is raised from an initial temperature to an intermediate temperature; During a preset second oxidation time, continuously introducing a carrier gas into the oxidation furnace; Soaking the silicon carbide sample after the second oxidation time in a preset buffer solution to remove an oxide layer on the surface of the silicon carbide sample; Performing an atmosphere high temperature annealing treatment on the silicon carbide sample with the oxide layer removed according to a preset target temperature within a preset annealing time to obtain a target silicon carbide sample; A carbon vacancy test is performed on the target silicon carbide sample.

2. The method for reducing carbon vacancies in silicon carbide crystal material according to claim 1, characterized in that: The step of increasing the temperature in the oxidation furnace from the initial temperature to the intermediate temperature within the preset first oxidation time comprises: During a 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 raised from the initial temperature to the intermediate temperature, the intermediate temperature is kept unchanged.

3. The method for reducing carbon vacancies in silicon carbide crystal material according to claim 1, characterized in that: During the preset second oxidation time, a carrier gas is continuously introduced into the oxidation furnace, wherein the carrier gas includes NO or N2O gas, and the carrier gas is introduced at a preset second flow value.

4. The method for reducing carbon vacancies in silicon carbide crystal material 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 comprises: During the immersion process, the buffer solution was stirred to improve the removal efficiency and ensure that the active ingredients in the buffer solution could act evenly on the sample surface; During the immersion process, characterization methods were used to monitor the surface state of the samples in real time and observe the removal effect of the oxide layer.

5. The method for reducing carbon vacancies in silicon carbide crystal material according to claim 4, characterized in that: 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, wherein; The buffer comprises a hydrofluoric acid buffer, wherein the hydrofluoric acid buffer comprises hydrofluoric acid and water in a preset volume ratio.

6. The method for reducing carbon vacancies in silicon carbide crystal material according to claim 1, characterized in that: The silicon carbide sample with the oxide layer removed is subjected to atmosphere high temperature annealing treatment according to a preset target temperature within a preset annealing time to obtain a target silicon carbide sample, wherein the atmosphere gas includes argon and hydrogen.

7. The method for reducing carbon vacancies in silicon carbide crystal material according to claim 1 or 6, characterized in that: The method further comprises: performing an atmosphere high temperature annealing treatment on the silicon carbide sample with the oxide layer removed according to a preset target temperature within a preset annealing time to obtain a target silicon carbide sample. Performing an atmosphere 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; After the annealing is completed, the target silicon carbide sample is slowly cooled to avoid thermal stress damage caused by a sudden drop in temperature; The protective atmosphere is maintained during the cooling process to prevent re-oxidation.

8. The method for reducing carbon vacancies in silicon carbide crystal material according to claim 1, characterized in that: The step of performing a carbon vacancy test on the target silicon carbide sample comprises: The deep level transient spectroscopy method is used to test the carbon vacancy density distribution in the target silicon carbide sample.

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