A method for improving the minority carrier lifetime of silicon carbide epitaxial materials

Abstract

The present invention provides a method for improving the minority carrier lifetime of a silicon carbide epitaxial material. The steps include: Step 1, placing the SiC substrate into the reaction chamber and evacuating it; Step 2, introducing hydrogen into the reaction chamber, and introducing a carbon source, a silicon source, and a doping source for surface treatment; Step 3, introducing the carbon source, the silicon source, and the doping source into the reaction chamber for buffer layer growth; Step 4, performing epitaxial layer growth and epitaxial layer doping; Step 5, cooling in the first stage: closing the silicon source and the doping source, performing hydrogen atmosphere annealing treatment, and closing the carbon source after the annealing ends; Step 6, cooling in the second stage: performing hydrogen atmosphere annealing treatment; Step 7, repeating Step 6 several times until the temperature requirement is met; Step 8, reducing to the cavity opening temperature, opening the reaction chamber, and taking out the silicon carbide epitaxial material. The method provided by the present invention has a simple process, is suitable for industrial production; maximizes the carrier lifetime, and can avoid the damage to the material surface caused by long-term high-temperature annealing.

Description

Technical Field

[0001] The present invention belongs to the technical field of silicon carbide epitaxy, and particularly relates to a method for improving the minority carrier lifetime of silicon carbide epitaxial materials. Background Art

[0002] SiC materials have the advantages of high thermal stability, high breakdown electric field, high thermal conductivity, and good switching characteristics, etc. They are ideal materials for preparing high-voltage and high-power devices and play a crucial role in modern power transmission systems, especially in fields such as smart grids, new energy, and high-voltage direct current transmission systems. As the breakdown voltage of high-voltage and high-power devices continues to increase, the on-resistance and power consumption of the devices also continue to increase, and unipolar devices can no longer meet the requirements. Bipolar devices can effectively reduce the on-resistance through conductance modulation, so SiC bipolar devices have attracted extensive attention from scientific researchers. To enable bipolar devices to achieve effective conductance mechanisms, the material is required to have a sufficiently long minority carrier lifetime. However, there are a large number of deep-level defects in the SiC epitaxial layer, and these deep-level defects act as recombination centers, severely restricting the minority carrier lifetime of the material.

[0003] Currently, the methods for improving the minority carrier lifetime of SiC epitaxial materials mainly include thermal oxidation method, carbon implantation annealing method, carbon deposition annealing method, and hydrogen annealing method. However, these methods all use other equipment and processes to perform secondary treatment on the SiC epitaxial material after the material growth is completed, which increases the process complexity and is prone to contaminating the material. Summary of the Invention

[0004] To solve the technical problems in the prior art that the methods for improving the minority carrier lifetime of SiC epitaxial materials are complex in process and prone to contaminating the materials, the present invention provides a method for improving the minority carrier lifetime of silicon carbide epitaxial materials.

[0005] The present invention adopts the following technical solutions:

[0006] A method for improving the minority carrier lifetime of silicon carbide epitaxial materials, comprising the following steps:

[0007] Step 1, placing the SiC substrate into the reaction chamber of a chemical vapor deposition device and performing a vacuum pumping treatment on the reaction chamber;

[0008] Step 2, introducing hydrogen into the reaction chamber, adjusting the pressure of the reaction chamber to 60 - 110 mbar, raising the temperature to 1600 - 1680 °C, adjusting the flow rates of the carbon source, silicon source, and doping source to the flow rates required for growing the buffer layer and setting them as excluded, and performing surface treatment on the SiC substrate after the temperature is stable;

[0009] Step 3, keeping the temperature and pressure of the reaction chamber unchanged, and introducing the carbon source, silicon source, and doping source into the reaction chamber for buffer layer growth;

[0010] Step 4: Keeping the temperature and pressure of the reaction chamber unchanged, linearly adjust the flow rates of the carbon source and the silicon source to the flow rates required for growing the epitaxial layer for epitaxial layer growth, adjust the doping source to the flow rate required for the epitaxial layer and set it to be excluded. After the flow rate of the doping source is stable, introduce it into the reaction chamber for epitaxial layer doping;

[0011] Step 5: First-stage temperature reduction: Turn off the silicon source and the doping source, reduce the temperature to the preset temperature. After the temperature is stable, perform a hydrogen atmosphere annealing treatment for 3 - 10 min. After the annealing is completed, turn off the carbon source;

[0012] Step 6: Second-stage temperature reduction: Reduce the temperature. After the temperature is stable, perform a hydrogen atmosphere annealing treatment;

[0013] Step 7: Repeat Step 6 several times until the temperature requirement is met;

[0014] Step 8: Reduce the temperature to the cavity opening temperature, open the reaction chamber and take out the silicon carbide epitaxial material.

[0015] Preferably, in Step 1, the reaction chamber is evacuated so that the vacuum degree of the reaction chamber is below 2×10-3 mbar.

[0016] Preferably, when introducing the carbon source and the silicon source in Step 3, control 0.5 ≤ C / Si ratio ≤ 1; control the growth rate of the buffer layer ≤ 0.2 μm / min; doping concentration ≥ 1E18 cm -3 。

[0017] Preferably, the carbon source used in both Step 3 and Step 4 is propane or ethylene; the silicon source is silane or trichlorosilane; when the doping source is n-type, it is nitrogen, and when it is p-type, it is trimethylaluminum.

[0018] Preferably, in Step 4, control 0.8 ≤ C / Si ratio ≤ 1.1.

[0019] Preferably, when performing the first-stage temperature reduction in Step 5, keep the carbon source continuously introduced, reduce the temperature to below 1400 °C, and the carbon source flow rate is 5 - 100 ml / min.

[0020] Preferably, when performing the second-stage temperature reduction in Step 6, the temperature is reduced by 100 - 200 °C, and the annealing time is 3 - 10 min.

[0021] Preferably, in Step 7, repeat Step 6 several times until the temperature is below 800 °C.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] (1) Technologies such as thermal oxidation, carbon implantation annealing, and carbon deposition annealing are all used to process epitaxial materials with other equipment after the epitaxial process is completed. They involve two or more types of equipment and processes, which are relatively complex and not suitable for production. The technical solution provided by the present invention uses the cooling process after epitaxial growth to process the epitaxial material, and improves the carrier lifetime in the same process without involving multiple equipment and processes. The process is simple and suitable for industrial production.

[0024] (2) In the present invention, the epitaxial material is annealed in a hydrogen atmosphere using the cooling process after growth, further passivating the doping elements in the material, improving the carrier lifetime, and achieving multiple annealings by using a stepped cooling to make full use of the cooling process, maximizing the carrier lifetime and avoiding damage to the material surface caused by long-term high-temperature annealing.

[0025] (3) In the present invention, during the hydrogen atmosphere annealing process, a carbon source is introduced to create a carbon-rich environment. During the annealing process, carbon atoms diffuse into the epitaxial layer, thereby eliminating carbon vacancies in the material to a certain extent, reducing deep-level defect centers, further improving the carrier lifetime, and at the same time reducing the etching effect of hydrogen on the material surface. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a flowchart of the method for improving the minority carrier lifetime of silicon carbide epitaxial material in the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0027] The following further describes the present invention in conjunction with embodiments. The embodiments are only used to illustrate the present invention and do not constitute a limitation to the scope of the claims. Other alternative means that can be conceived by those skilled in the art are all within the scope of the claims of the present invention.

[0028] Embodiment 1

[0029] Improve the minority carrier lifetime of a 50-μm-thick SiC epitaxial material prepared on an N-type SiC substrate (using ethylene, trichlorosilane, and nitrogen as the carbon source, silicon source, and doping source respectively), as Figure 1 shown, including the following steps:

[0030] Step 1: Place the cleaned N-type SiC substrate into the reaction chamber of the SiC chemical vapor deposition equipment, and evacuate the reaction chamber to a vacuum degree of 2×10 -3 mbar;

[0031] Step 2: Introduce high-purity hydrogen gas into the reaction chamber, adjust the pressure of the reaction chamber to 80 mbar, slowly raise the temperature to 1650 °C, adjust the flow rates of ethylene, trichlorosilane, and nitrogen to 18 sccm, 75 sccm, and 250 sccm respectively and set them to be excluded. After the temperature stabilizes, maintain for 5 min to perform surface treatment on the SiC substrate.

[0032] Step 3: Keep the temperature and pressure of the reaction chamber unchanged, introduce ethylene, trichlorosilane, and nitrogen into the reaction chamber for buffer layer growth, and the growth time is 6 min.

[0033] Step 4: Keep the temperature and pressure of the reaction chamber unchanged, adjust the flow rates of ethylene and trichlorosilane to 150 sccm and 300 sccm respectively for epitaxial layer growth, set the flow rate of nitrogen to 80 sccm and set it to be excluded. After the flow rate of nitrogen remains stable, introduce it into the reaction chamber for epitaxial layer doping, and the epitaxial layer growth time is 48 min.

[0034] Step 5: Close trichlorosilane and nitrogen, keep the carbon source continuously introduced, lower the temperature to 1500 °C. After the temperature stabilizes, perform a 3-min annealing treatment. Then lower the temperature by 100 °C to 1400 °C. After the temperature stabilizes, perform a 3-min annealing treatment, and then close ethylene.

[0035] Step 6: Lower the temperature by 100 °C. After the temperature stabilizes, perform a 3-min annealing treatment.

[0036] Step 7: Repeat Step 6 six times until the temperature is lowered to 800 °C.

[0037] Step 8: Lower the temperature of the reaction chamber to the temperature at which it is allowed to be opened, pump the vacuum degree of the reaction chamber to 1×10 -1 mbar, then introduce argon gas and raise the pressure of the reaction chamber to one atmosphere, close the argon gas, and open the reaction chamber to take out the silicon carbide epitaxial material.

[0038] Example 2

[0039] Improve the minority carrier lifetime of a 50-μm-thick SiC epitaxial material prepared on an N-type SiC substrate, and use hydrogen chloride-assisted treatment of the substrate surface (using ethylene, trichlorosilane, and nitrogen as the carbon source, silicon source, and doping source respectively).

[0040] Step 1: Place the cleaned SiC substrate into the reaction chamber of the SiC chemical vapor deposition equipment, and perform a vacuum pumping treatment on the reaction chamber, pumping the vacuum degree to 2×10 -3 mbar;

[0041] Step 2: Introduce high-purity hydrogen into the reaction chamber, adjust the pressure of the reaction chamber to 80 mbar, slowly increase the temperature to 1650 °C, adjust the flow rates of ethylene, trichlorosilane, nitrogen, and hydrogen chloride to 18 sccm, 75 sccm, 250 sccm, and 10 sccm respectively and set them as exclusive. After the temperature stabilizes, introduce hydrogen chloride into the reaction chamber and keep it for 3 minutes to perform surface treatment on the SiC substrate.

[0042] Step 3: Keep the temperature and pressure of the reaction chamber unchanged, introduce ethylene, trichlorosilane, and nitrogen into the reaction chamber for buffer layer growth, and the growth time is 5 minutes.

[0043] Step 4: Keep the temperature and pressure of the reaction chamber unchanged, adjust the flow rates of ethylene and trichlorosilane to 150 sccm and 300 sccm respectively for epitaxial layer growth, set the flow rate of nitrogen to 80 sccm and set it as exclusive. After the flow rate of nitrogen stabilizes, introduce it into the reaction chamber for epitaxial layer doping. The epitaxial layer growth time is 48 minutes.

[0044] Step 5: Turn off trichlorosilane and nitrogen, lower the temperature to 1400 °C. After the temperature stabilizes, perform a 5-minute hydrogen atmosphere annealing treatment. After the annealing is completed, turn off ethylene.

[0045] Step 6: Lower the temperature by 100 °C. After the temperature stabilizes, perform a 5-minute hydrogen atmosphere annealing treatment.

[0046] Step 7: Repeat Step 6 six times until the temperature is lowered to 800 °C.

[0047] Step 8: Lower the temperature of the reaction chamber to the temperature at which it is allowed to be opened, evacuate the vacuum of the reaction chamber to 1×10 -1 mbar, then introduce argon and increase the pressure of the reaction chamber to one atmosphere. Turn off argon and open the reaction chamber to take out the silicon carbide epitaxial material.

[0048] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present invention, and they should all be covered within the scope of the claims of the present invention.

Claims

1. A method for improving the minority carrier lifetime of silicon carbide epitaxial materials, characterized in that, It includes the following steps: Step 1: Place the SiC substrate into the reaction chamber of the chemical vapor deposition equipment and evacuate the reaction chamber; Step 2: Introduce hydrogen into the reaction chamber, adjust the pressure of the reaction chamber to 60 - 110 mbar, raise the temperature to 1600 - 1680 °C, adjust the flow rates of the carbon source, silicon source, and doping source to the flow rates required for growing the buffer layer and set them as exclusive. After the temperature stabilizes, perform surface treatment on the SiC substrate; Step 3: Keep the temperature and pressure of the reaction chamber unchanged, and introduce the carbon source, silicon source, and doping source into the reaction chamber to grow the buffer layer; Step 4: Keep the temperature and pressure of the reaction chamber unchanged, linearly adjust the flow rates of the carbon source and silicon source to the flow rates required for growing the epitaxial layer to grow the epitaxial layer, adjust the doping source to the flow rate required for the epitaxial layer and set it as exclusive. After the flow rate of the doping source remains stable, introduce it into the reaction chamber for epitaxial layer doping; Step 5: First-stage cooling: Turn off the silicon source and doping source, lower the temperature to the preset temperature. After the temperature stabilizes, perform a hydrogen atmosphere annealing treatment for 3 - 10 min. After the annealing ends, turn off the carbon source. During the first-stage cooling, keep the carbon source continuously introduced and lower the temperature below 1400 °C, where the carbon source flow rate is 5 - 100 ml / min; Step 6: Second-stage cooling: Lower the temperature. After the temperature stabilizes, perform a hydrogen atmosphere annealing treatment. During the second-stage cooling, the temperature is lowered by 100 - 200 °C, and the annealing time is 3 - 10 min; Step 7: Repeat Step 6 several times until the temperature is lower than 800 °C; Step 8: Lower the temperature to the cavity opening temperature, open the reaction chamber and take out the silicon carbide epitaxial material.

2. The method for improving the minority carrier lifetime of silicon carbide epitaxial material according to claim 1, characterized in that, In step one, the reaction chamber is evacuated so that the vacuum degree of the reaction chamber is below 2×10 -3 mbar.

3. The method for improving the minority carrier lifetime of a silicon carbide epitaxial material according to claim 1, wherein In Step 3, when introducing the carbon source and silicon source, control the C / Si ratio to be 0.5 ≤ C / Si ratio ≤ 1; control the growth rate of the buffer layer ≤ 0.2 μm / min; the doping concentration ≥ 1E18 cm -3 .

4. The method for improving the minority carrier lifetime of a silicon carbide epitaxial material according to claim 1, wherein The carbon source used in Steps 3 and 4 is propane or ethylene; the silicon source is silane or trichlorosilane; when the doping source is n-type, it is nitrogen, and when it is p-type, it is trimethylaluminum.

5. The method for improving the minority carrier lifetime of a silicon carbide epitaxial material according to claim 1, wherein In Step 4, control 0.8 ≤ C / Si ratio ≤ 1.1.

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