Growth method for improving surface defect density of silicon carbide epitaxial layer

Abstract

The present invention discloses a growth method for improving the surface defect density of a silicon carbide epitaxial layer, the growth method comprising the following steps: S1, cleaning the silicon carbide substrate, using a solution of a specific mixing ratio to clean the substrate twice; S2, loading the substrate into a reaction chamber; S3, performing the first etching; S4, performing the second etching; S5, growing the first buffer layer; S6, growing the second buffer layer; S7, growing the main epitaxial layer; S8, epitaxial growth is completed, and the epitaxial wafer is taken out. The present invention uses a cleaning solution to clean the silicon carbide substrate twice, eliminates particles and metal ions on the surface of the substrate, improves the surface quality of the substrate, and thereby reduces the number of shallow triangle defects generated during the epitaxy process.

Description

Technical Field

[0001] The invention relates to the technical field of semiconductor materials, and in particular to a growth method for improving the surface defect density of a silicon carbide epitaxial layer. Background Art

[0002] SiC is a typical third-generation semiconductor material, represented by 4H-SiC, which has a bandgap width three times that of Si and a critical breakdown electric field 10 times that of Si, and can achieve higher voltage, higher power, and higher frequency device performance. At the same time, 4H-SiC material has a higher electron saturation drift velocity and thermal conductivity, making SiC power devices more advantageous in the field of high temperature and high power. Many excellent properties such as large bandgap, high critical breakdown electric field strength, high electron saturation drift velocity, high thermal conductivity, strong radiation resistance, and good physical and chemical stability give 4H-SiC power devices greater room for optimization, including device size, quality, operating temperature, and switching loss. Therefore, 4H-SiC has become the next generation of semiconductor materials that are the focus of research worldwide and is known as "a future material."

[0003] As an important processing link in the industrial chain, SiC epitaxy is currently mainly grown through CVD-based homoepitaxial technology to grow high-quality 4H-SiC epitaxial wafers with different doping concentrations and thicknesses, and then prepare electronic devices that meet different electrical properties.

[0004] During the epitaxial growth of SiC, due to foreign particles, surface scratches or crystal defects such as TSD affecting the flow of atomic steps, epitaxial morphological defects with triangular shapes or patterns are formed on the surface of the 4H-SiC epitaxial layer. The triangular defect is a fatal defect of power devices and is the main defect that limits the performance and yield of SiC power devices. Under extremely low reverse bias, the triangular defect will cause a large reverse leakage current; under forward low-voltage bias conditions, new conductive channels will appear, which will also cause the current to increase rapidly. Therefore, a method is needed to effectively improve the surface quality of the substrate and eliminate shallow triangular defects on the surface of the epitaxial layer. Summary of the invention

[0005] Purpose of the invention: In view of the above shortcomings, the present invention provides a growth method for improving the surface defect density of a silicon carbide epitaxial layer.

[0006] Technical solution: To solve the above problems, the present invention adopts a growth method for improving the surface defect density of a silicon carbide epitaxial layer, comprising the following steps:

[0007] S1, first use a mixed solution of ammonia, hydrogen peroxide and pure water to rinse the substrate for the first time, rinse with pure water after rinsing, then use a mixed solution of hydrochloric acid, hydrogen peroxide and pure water to rinse the substrate for the second time, rinse with pure water after rinsing, and spin dry the substrate for standby use;

[0008] S2, placing the substrate on a carrier and transferring it to a reaction chamber, and setting the temperature and pressure parameters of the reaction chamber to preset values;

[0009] S3, introducing hydrogen and HCl into the reaction chamber, introducing Ar gas to rotate the air flotation tray, keeping the gas flow of hydrogen, HCl and Ar gas stable and continuing for a preset time, and performing the first etching on the substrate surface;

[0010] S4, raising the temperature in the reaction chamber, introducing hydrogen into the reaction chamber, and then cooling the reaction chamber to the buffer layer reaction temperature, and performing a second etching on the substrate surface;

[0011] S5, introducing a silicon source, a central carbon source, a side carbon source, a doping source N2 and hydrogen for diluting the doping source N2 into the reaction chamber to grow a first buffer layer;

[0012] S6, increasing the flow rate of the silicon source and the central carbon source introduced into the reaction chamber, closing the side carbon source, and growing the second buffer layer;

[0013] S7, continue to increase the flow rate of silicon source and central carbon source to grow the main epitaxial layer;

[0014] S8. After the epitaxial growth is completed, the reaction gas is turned off and the epitaxial wafer is taken out.

[0015] Furthermore, in step S1, the volume mixing ratio of ammonia water, hydrogen peroxide and pure water is 2:(3-4):5, and the volume mixing ratio of hydrochloric acid, hydrogen peroxide and pure water is 1:(1-2):20.

[0016] Furthermore, in step S2, the temperature of the reaction chamber is increased from 900°C to 1550°C-1700°C, with a ramp-up time of 8-15 minutes, and the pressure of the reaction chamber is reduced to 80-200 mbar.

[0017] Furthermore, in step S3, the hydrogen flow rate is 50-150 slm, the HCl gas flow rate is 150-300 sccm, and the Ar gas flow rate is 1.2-3 slm, and the hydrogen, HCl, and Ar gas flows are kept stable for 3-8 minutes.

[0018] Furthermore, in step S4, the reaction chamber is heated to 1650°C-1800°C, the hydrogen flow rate is 50-150slm, and the gas flow is kept stable for 3-8mins; then the reaction chamber is cooled to 1550°C-1680°C, and the cooling time is 3-5mins.

[0019] Furthermore, in step S5, trichlorosilane is used as the silicon source, ethylene is used as the central carbon source and the side carbon source, and high-purity N2 is used as the doping source N2; the doping concentration of the first buffer layer is 3 to 7E18 cm-3, the doping concentration of the second buffer layer is 8E17 to 3E18 cm-3, and the doping concentration of the main epitaxial layer is 7 to 9E15 cm-3.

[0020] Furthermore, in step S5, the C / Si ratio in the central area of ​​the reaction chamber is 0.4~0.6, the C / Si ratio in the side area is 0.5~0.7, the flow rate of the doping source N2 is 200~300sccm, the flow rate of the hydrogen is 500~2000sccm, the flow rate of the diluted N2 in the central area is 220~300sccm, and the flow rate of the diluted N2 in the side area is controlled at 50~100sccm, and the gas flow is kept stable for 2~5mins.

[0021] Furthermore, in step S6, the C / Si ratio in the central area of ​​the reaction chamber is 0.6~0.8, the flow rate of the doping source N2 is 150~250sccm, the flow rate of the hydrogen is 500~2000sccm, the flow rate of the diluted N2 in the central area is 150~220sccm, and the flow rate of the diluted N2 in the side area is controlled at 20~50sccm, and the gas flow is kept stable for 2~5mins.

[0022] Furthermore, in step S7, the C / Si ratio in the central area of ​​the reaction chamber is 0.8-1.

[0023] Furthermore, in step S8, the temperature in the reaction chamber is lowered to 700°C-1000°C for 8-15 minutes, and after the pressure in the reaction chamber is increased to normal pressure, the epitaxial wafer is taken out after being purged to room temperature in the load lock chamber.

[0024] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: (1) by using a cleaning solution to clean the silicon carbide substrate twice, particles and metal ions on the substrate surface are eliminated, the surface quality of the substrate is improved, and the number of shallow triangular defects generated during the epitaxial growth process is reduced; (2) in the first etching process, by adding an appropriate amount of HCl gas, the hydrogen etching efficiency is improved, the surface quality of the silicon carbide substrate and the role of the cavity environment are further improved, and the hydrogen etching time is shortened, thereby improving the process growth efficiency; (3) the present invention grows two buffer layers, and by adjusting the carbon-silicon ratio and doping concentration of the two buffer layers, the conversion of dislocations in the substrate into shallow triangular defects during the epitaxial growth process can be effectively improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a schematic diagram of the overall process of the growth method of the present invention;

[0026] Figure 2 A comparison diagram of the number of particles on the surface of the silicon carbide substrate before and after cleaning according to Examples 1-3 of the present invention;

[0027] Figure 3 It is a comparison chart of defect density after epitaxy of Examples 1-3 of the present invention and the traditional process. DETAILED DESCRIPTION

[0028] Embodiment 1

[0029] like Figure 1 As shown, a growth method for improving the surface defect density of a silicon carbide epitaxial layer in this embodiment includes the following steps:

[0030] S1. Cleaning of silicon carbide substrate. First, rinse the substrate for the first time with a mixed solution of ammonia water, hydrogen peroxide and pure water in a volume ratio of 2:3:5, and rinse with pure water after rinsing. Then, rinse the substrate for the second time with a mixed solution of hydrochloric acid, hydrogen peroxide and pure water in a volume ratio of 1:1:20, and rinse with pure water after rinsing. Use a spin dryer to spin dry the substrate for standby use.

[0031] S2. Load the substrate into the reaction chamber. Place the substrate in a graphite carrier and transfer it to the reaction chamber. The pressure in the reaction chamber is slowly reduced to 80 mbar by the process pump, and the pressure reduction time is 8 minutes. The temperature in the reaction chamber is increased from 900°C to 1550°C, and the ramp-up time is 8 minutes.

[0032] S3, perform the first etching. Introduce hydrogen and HCl into the reaction chamber, introduce Ar gas to rotate the air flotation tray, the hydrogen flow rate is 50 slm, the HCl gas flow rate is 150 sccm, and the Ar gas flow rate of the air flotation tray is 1.2 slm. Keep the gas flow stable for 3 minutes to perform the first etching on the substrate surface.

[0033] S4, perform the second etching. Rapidly raise the temperature in the reaction chamber to 1650°C, introduce only hydrogen gas, the hydrogen flow rate is 50slm, and keep the gas flow stable for 3mins; then slowly cool the reaction chamber to 1550°C, the cooling time is 3mins, and perform the second etching on the substrate surface.

[0034] S5, growing the first buffer layer. Introduce trichlorosilane, ethylene, side ethylene, doping source N2 and hydrogen for diluting doping source N2 into the reaction chamber, control the C / Si ratio in the center area of ​​the reaction chamber to 0.4, control the C / Si ratio in the side area to 0.5, the doping source N2 flow rate to 200sccm, the hydrogen flow rate to 500sccm, the flow rate of diluted N2 in the center area to 220sccm, the flow rate of diluted N2 in the side area to 50sccm, keep the gas flow stable for 2mins, and grow the first buffer layer.

[0035] S6, grow the second buffer layer. Gradually increase the flow of trichlorosilane and ethylene into the reaction chamber, close the flow of ethylene gas on the side, set the C / Si ratio in the center area of ​​the reaction chamber to 0.6, the flow of doping source N2 to 150sccm, the flow of hydrogen to 500sccm, the flow of diluted N2 in the center area to 150sccm, and the flow of diluted N2 in the side area to 20sccm, keep the gas flow stable for 2mins, and grow the second buffer layer.

[0036] S7, growing the main epitaxial layer. Continue to increase the flow rate of trichlorosilane and ethylene, the ramp time is 1 min, and the C / Si ratio in the center area of ​​the reaction chamber is controlled to 0.8 to grow the main epitaxial layer.

[0037] S8. After the epitaxial growth is completed, the reaction gas is turned off, the temperature in the reaction chamber is cooled to 700°C for 8 minutes, and the pressure in the reaction chamber is increased to normal pressure. After the pressure is purged to room temperature in the load lock chamber, the epitaxial wafer is taken out.

[0038] Embodiment 2

[0039] A growth method for improving the surface defect density of a silicon carbide epitaxial layer in this embodiment includes the following steps:

[0040] S1. Cleaning of silicon carbide substrate. First, rinse the substrate for the first time with a mixed solution of ammonia water, hydrogen peroxide and pure water in a volume ratio of 2:3.5:5, and rinse with pure water after rinsing. Then, rinse the substrate for the second time with a mixed solution of hydrochloric acid, hydrogen peroxide and pure water in a volume ratio of 1:1.5:20, and rinse with pure water after rinsing. Use a spin dryer to spin dry the substrate for standby use.

[0041] S2. Load the substrate into the reaction chamber. Place the substrate in a graphite carrier and transfer it to the reaction chamber. The pressure in the reaction chamber is slowly reduced to 140 mbar by the process pump, and the pressure reduction time is 12 minutes. The temperature in the reaction chamber is increased from 900°C to 1620°C, and the ramp-up time is 12 minutes.

[0042] S3, perform the first etching. Introduce hydrogen and HCl into the reaction chamber, introduce Ar gas to rotate the air flotation tray, the hydrogen flow rate is 100 slm, the HCl gas flow rate is 220 sccm, and the Ar gas flow rate of the air flotation tray is 2 slm. Keep the gas flow stable for 5 minutes to perform the first etching on the substrate surface.

[0043] S4, perform the second etching. Rapidly raise the temperature in the reaction chamber to 1730°C, introduce only hydrogen gas, the hydrogen flow rate is 100 slm, and keep the gas flow stable for 5 minutes; then cool the reaction chamber to 1600°C, the cooling time is 4 minutes, and perform the second etching on the substrate surface.

[0044] S5, growing the first buffer layer. Introduce trichlorosilane, ethylene, side ethylene, doping source N2 and hydrogen for diluting doping source N2 into the reaction chamber, control the C / Si ratio in the center area of ​​the reaction chamber to 0.5, control the C / Si ratio in the side area to 0.6, the doping source N2 flow rate to 250sccm, the hydrogen flow rate to 1300sccm, the flow rate of diluted N2 in the center area to 260sccm, the flow rate of diluted N2 in the side area to 75sccm, keep the gas flow stable for 3mins, and grow the first buffer layer.

[0045] S6, grow the second buffer layer. Gradually increase the flow of trichlorosilane and ethylene into the reaction chamber, close the flow of ethylene gas on the side, set the C / Si ratio in the center area of ​​the reaction chamber to 0.7, the flow of doping source N2 to 200 sccm, the flow of hydrogen to 1300 sccm, the flow of diluted N2 in the center area to 180 sccm, and the flow of diluted N2 in the side area to 35 sccm, keep the gas flow stable for 3 minutes, and grow the second buffer layer.

[0046] S7, growing the main epitaxial layer. Continue to increase the flow rate of trichlorosilane and ethylene, the ramp time is 2 minutes, and the C / Si ratio in the center area of ​​the reaction chamber is controlled to 0.9 to grow the main epitaxial layer.

[0047] S8. After the epitaxial growth is completed, the reaction gas is turned off, the temperature in the reaction chamber is cooled to 900°C for 12 minutes, and the pressure in the reaction chamber is increased to normal pressure. After the pressure is purged to room temperature in the load lock chamber, the epitaxial wafer is taken out.

[0048] Embodiment 3

[0049] A growth method for improving the surface defect density of a silicon carbide epitaxial layer in this embodiment includes the following steps:

[0050] S1. Cleaning of silicon carbide substrate. First, rinse the substrate for the first time with a mixed solution of ammonia water, hydrogen peroxide and pure water in a volume ratio of 2:4:5, and rinse with pure water after rinsing. Then, rinse the substrate for the second time with a mixed solution of hydrochloric acid, hydrogen peroxide and pure water in a volume ratio of 1:2:20, and rinse with pure water after rinsing. Use a spin dryer to spin dry the substrate for standby use.

[0051] S2. Load the substrate into the reaction chamber. Place the substrate in a graphite carrier and transfer it to the reaction chamber. The pressure in the reaction chamber is slowly reduced to 200 mbar by the process pump, and the pressure reduction time is 15 minutes. The temperature in the reaction chamber is increased from 900°C to 1700°C, and the ramp-up time is 15 minutes.

[0052] S3, perform the first etching. Introduce hydrogen and HCl into the reaction chamber, introduce Ar gas to rotate the air flotation tray, the hydrogen flow rate is 150 slm, the HCl gas flow rate is 300 sccm, the Ar gas flow rate of the air flotation tray is 3 slm, keep the gas flow stable for 8 minutes, and perform the first etching on the substrate surface.

[0053] S4, perform the second etching. Rapidly raise the temperature in the reaction chamber to 1800°C, introduce only hydrogen gas, the hydrogen flow rate is 150slm, and keep the gas flow stable for 8mins; then cool the reaction chamber to 1680°C, the cooling time is 5mins, and perform the second etching on the substrate surface.

[0054] S5, growing the first buffer layer. Introduce trichlorosilane, ethylene, side ethylene, doping source N2 and hydrogen for diluting doping source N2 into the reaction chamber, control the C / Si ratio in the center area of ​​the reaction chamber to 0.6, control the C / Si ratio in the side area to 0.7, the doping source N2 flow rate to 300sccm, the hydrogen flow rate to 2000sccm, the flow rate of diluted N2 in the center area to 300sccm, and the flow rate of diluted N2 in the side area to 100sccm, keep the gas flow stable for 5mins, and grow the first buffer layer.

[0055] S6, grow the second buffer layer. Gradually increase the flow of trichlorosilane and ethylene into the reaction chamber, close the flow of ethylene gas on the side, set the C / Si ratio in the center area of ​​the reaction chamber to 0.8, the flow of doping source N2 to 250sccm, the flow of hydrogen to 2000sccm, the flow of diluted N2 in the center area to 220sccm, and the flow of diluted N2 in the side area to 50sccm, keep the gas flow stable for 5mins, and grow the second buffer layer.

[0056] S7, growing the main epitaxial layer. Continue to increase the flow rate of trichlorosilane and ethylene, the ramp time is 3 minutes, and the C / Si ratio in the center area of ​​the reaction chamber is controlled to 1 to grow the main epitaxial layer.

[0057] S8. After the epitaxial growth is completed, the reaction gas is turned off, the temperature in the reaction chamber is cooled to 1000°C for 15 minutes, and the pressure in the reaction chamber is increased to normal pressure. After the pressure is purged to room temperature in the load lock chamber, the epitaxial wafer is taken out.

[0058] like Figure 2 As shown in the table, substrates 1 to 3 are silicon carbide substrates corresponding to embodiments 1 to 3, respectively. The number of surface particles (particals) before and after two cleanings is compared. It can be seen from the table that the number of surface particles on the substrates is significantly reduced after cleaning, and the surface quality of the substrates is improved, thereby reducing the number of shallow triangle defects generated during the epitaxy process. Figure 3The figures show the comparison of the number of shallow triangles, triangles, and obtuse triangles, as well as the comparison of the density of triangle defects, in Examples 1-3 of the present invention compared with two conventional processes. It can be seen from the data that after using the growth method of the present invention, the number of triangle defects on the epitaxial wafer is reduced, especially the number of shallow triangles is significantly reduced, and the density of triangle defects is significantly reduced, achieving a good effect of improving the density of triangle defects on the surface of the silicon carbide epitaxial layer and the effect is stable.

Claims

1. A growth method for improving the surface defect density of a silicon carbide epitaxial layer, characterized in that: The following steps are involved: S1, first use a mixed solution of ammonia, hydrogen peroxide and pure water to rinse the substrate for the first time, rinse with pure water after rinsing, then use a mixed solution of hydrochloric acid, hydrogen peroxide and pure water to rinse the substrate for the second time, rinse with pure water after rinsing, and spin dry the substrate for standby use; S2, placing the substrate on a carrier and transferring it to a reaction chamber, and setting the temperature and pressure parameters of the reaction chamber to preset values; S3, introducing hydrogen and HCl into the reaction chamber, introducing Ar gas to rotate the air flotation tray, keeping the gas flow of hydrogen, HCl and Ar gas stable and continuing for a preset time, and performing the first etching on the substrate surface; S4, raising the temperature in the reaction chamber, introducing hydrogen into the reaction chamber, and then cooling the reaction chamber to the buffer layer reaction temperature, and performing a second etching on the substrate surface; S5. Introduce a silicon source, a central carbon source, a side carbon source, a doping source N2, and hydrogen for diluting the doping source N2 into the reaction chamber to grow a first buffer layer; specifically, the C / Si ratio in the central area of ​​the reaction chamber is 0.4-0.6, the C / Si ratio in the side area is 0.5-0.7, the flow rate of the doping source N2 is 200-300 sccm, the flow rate of the hydrogen is 500-2000 sccm, the flow rate of the diluted N2 in the central area is 220-300 sccm, the flow rate of the diluted N2 in the side area is controlled at 50-100 sccm, and the gas flow is kept stable for 2-5 minutes; S6, increase the flow rate of silicon source and central carbon source introduced into the reaction chamber, close the side carbon source, and grow the second buffer layer; specifically, the C / Si ratio in the central area of ​​the reaction chamber is 0.6-0.8, the flow rate of doping source N2 is 150-250sccm, the flow rate of hydrogen is 500-2000sccm, the flow rate of diluted N2 in the central area is 150-220sccm, the flow rate of diluted N2 in the side area is controlled at 20-50sccm, and the gas flow is kept stable for 2-5mins; S7, continue to increase the flow rate of silicon source and central carbon source, the C / Si ratio in the central area of ​​the reaction chamber is 0.8~1, and the main epitaxial layer is grown; S8. After the epitaxial growth is completed, the reaction gas is turned off and the epitaxial wafer is taken out.

2. The growth method according to claim 1, characterized in that In step S1, the volume mixing ratio of ammonia water, hydrogen peroxide and pure water is 2:(3-4):5, and the volume mixing ratio of hydrochloric acid, hydrogen peroxide and pure water is 1:(1-2):

20.

3. The growth method according to claim 1, characterized in that In step S2, the temperature of the reaction chamber is increased from 900°C to 1550°C-1700°C, with a ramp-up time of 8-15 minutes, and the pressure of the reaction chamber is reduced to 80-200 mbar.

4. The growth method according to claim 1, characterized in that In step S3, the hydrogen flow rate is 50-150 slm, the HCl gas flow rate is 150-300 sccm, and the Ar gas flow rate is 1.2-3 slm, and the hydrogen, HCl, and Ar gas flows are kept stable for 3-8 minutes.

5. The growth method according to claim 1, characterized in that In step S4, the reaction chamber is heated to 1650°C-1800°C, the hydrogen flow rate is 50-150slm, and the gas flow is kept stable for 3-8mins; then the reaction chamber is cooled to 1550°C-1680°C, and the cooling time is 3-5mins.

6. The growth method according to claim 1, characterized in that In step S5, trichlorosilane is used as the silicon source, ethylene is used as the central carbon source and the side carbon source, and high-purity N2 is used as the doping source N2; the doping concentration of the first buffer layer is 3 to 7E18 cm-3, the doping concentration of the second buffer layer is 8E17 to 3E18 cm-3, and the doping concentration of the main epitaxial layer is 7 to 9E15 cm-3.

7. The growth method according to claim 1, characterized in that In step S8, the temperature in the reaction chamber is lowered to 700°C-1000°C for 8-15 minutes, and the pressure in the reaction chamber is increased to normal pressure. The epitaxial wafer is then taken out after being purged to room temperature in the load lock chamber.

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