A process for epitaxial growth of n-type doped silicon carbide

Abstract

The present invention discloses an epitaxial growth process of n-type doped silicon carbide, which comprises placing a silicon carbide substrate in a reaction chamber, pre-etching the substrate in a hydrogen atmosphere, introducing a carbon source and a silicon source as growth source gases, using hexamethyldisilazane as an n-type doping source, and carrying the hexamethyldisilazane into the reaction chamber by hydrogen to grow an n-type doped silicon carbide epitaxial wafer. The present invention can effectively dope N elements into SiC lattices, improve doping efficiency, reduce the residual N elements in the cavity environment, effectively reduce the influence of background concentration on doping concentration during silicon carbide epitaxial growth, and realize accurate control of doping concentration; in the continuous epitaxial growth process, the stability of doping concentration is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of silicon carbide epitaxial growth, and in particular relates to an epitaxial growth process of n-type doped silicon carbide. Background Art

[0002] The production of 4H-SiC devices has specific requirements for epitaxial doping concentration. For the design of 600V~10kV 4H-SiC devices, the general control range of epitaxial doping concentration is: n-type is 1×10 14 ~2×10 16 cm -3 , p-type is 2×10 14 ~5×10 16 cm -3 For CVD epitaxial doping of 4H-SiC, nitrogen (N 2 ) is often used as an n-type dopant, while trimethylaluminum (TMA) is often used as a p-type dopant. Under the condition that other growth conditions remain unchanged, the doping concentration of 4H-SiC epitaxy can be linearly adjusted by adjusting the flow rate of the dopant. The doping mechanism of N and Al can be explained by the site competition effect: there is a certain relationship between the lattice position occupied by each dopant atom and the radius of the dopant atom. The radius of the carbon atom is The radius of a silicon atom is The radius of the nitrogen atom is The radius of an aluminum atom is Therefore, during doped epitaxial growth, nitrogen atoms replace carbon atoms in the SiC lattice, and aluminum atoms replace silicon atoms in the SiC lattice.

[0003] In the prior art, nitrogen (N 2 ) is used as an n-type dopant. Due to the low efficiency of nitrogen incorporation, a large amount of N element is likely to remain in the cavity environment, which leads to the doping concentration in the epitaxial layer being easily affected by the background concentration of N element in the cavity environment during continuous epitaxial growth. The actual doping concentration deviates from the target value, making it difficult to accurately control the doping concentration and having low stability. Summary of the invention

[0004] The present invention aims at the deficiencies in the prior art and provides an epitaxial growth process for n-type doped silicon carbide.

[0005] In order to achieve the above purpose, the technical solution of the present invention is:

[0006] An epitaxial growth process of n-type doped silicon carbide comprises the following steps:

[0007] 1) placing a silicon carbide substrate in a reaction chamber and performing a pre-etching treatment on the substrate in a hydrogen atmosphere;

[0008] 2) performing epitaxial growth, maintaining the temperature of the reaction chamber at 1500° C. to 1700° C., introducing a carbon source and a silicon source as growth source gases, and having a C / Si molar ratio of 0.9 to 1.3; using hexamethyldisilazane as an n-type doping source, and carrying the hexamethyldisilazane into the reaction chamber by hydrogen gas, and growing an n-type doped silicon carbide epitaxial film to a target thickness;

[0009] 3) Turn off the carbon source, silicon source and doping source, and obtain an n-type doped silicon carbide epitaxial wafer after cooling.

[0010] Optionally, in step 1), the silicon carbide substrate is placed in a reaction chamber in a hydrogen atmosphere, the initial pressure of the reaction chamber is 800-1200 mbar, and the initial temperature is 500°C-700°C; hydrogen 1 is kept flowing into the reaction chamber, the flow rate of hydrogen 1 is 50-150 slm, the temperature of the reaction chamber is 1500°C-1700°C, the pressure of the reaction chamber is 50-300 mbar, and the etching time is 5-20 min.

[0011] Optionally, in step 2), hydrogen 1 is kept introduced into the reaction chamber, the flow rate of hydrogen 1 is 50-150 slm, and the pressure of the reaction chamber is 50-300 mbar. During the epitaxial growth process, the reaction chamber temperature, hydrogen 1 flow rate and reaction chamber pressure are kept constant.

[0012] Optionally, the gas flow rate of the carbon source is 50-200 sccm.

[0013] Optionally, the flow rate of the mixed gas formed by hydrogen carrying hexamethyldisilazane into the reaction chamber is 20-400 sccm.

[0014] Optionally, liquid hexamethyldisilazane is placed in a bubbler, and hydrogen 2 is introduced into the bubbler to form a first mixed gas of hexamethyldisilazane and hydrogen 2. The first mixed gas is mixed with hydrogen 3 to form a second mixed gas, which is then introduced into the reaction chamber.

[0015] Optionally, the amount of hexamethyldisilazane introduced is controlled by controlling the flow rate of hydrogen 2, the flow rate of hydrogen 3 and the flow rate of the second mixed gas introduced into the reaction chamber to control the n-type doping concentration.

[0016] Optionally, the flow rate of the hydrogen gas 2 is 50 to 200 sccm, and the flow rate of the hydrogen gas 3 is 10 to 500 slm.

[0017] Optionally, in step 3), after the reaction chamber is cooled to 600-1000° C. and the reaction chamber pressure is restored to 800-1200 mbar, the n-type doped silicon carbide epitaxial wafer is transferred to an inert gas atmosphere and cooled to room temperature.

[0018] N-type doped silicon carbide prepared by the above epitaxial growth process.

[0019] The beneficial effects of the present invention are:

[0020] Hexamethyldisilazane is used as the doping source for n-type silicon carbide epitaxial growth, which can effectively dope N elements into the SiC lattice, reduce the residue in the cavity environment, effectively reduce the influence of background concentration on the doping concentration during the silicon carbide epitaxial growth process, and achieve precise control of the doping concentration; in the continuous epitaxial growth process, the stability of the doping concentration is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a schematic diagram of doping concentration of the epitaxial growth process of n-type doped silicon carbide in Example 1 when growing 10 furnaces continuously;

[0022] Figure 2 A schematic diagram of doping concentration of n-type doped silicon carbide in comparative example 1 during continuous growth of 10 furnaces of epitaxial growth process;

[0023] Figure 3 for Figure 1 and Figure 2 Coordinate diagram of the locations of medium concentration detection. DETAILED DESCRIPTION

[0024] The present invention is further explained below in conjunction with the accompanying drawings and specific embodiments. The accompanying drawings of the present invention are only for illustration to make the present invention easier to understand.

[0025] An epitaxial growth process of n-type doped silicon carbide, comprising the following steps:

[0026] Step 1: placing the silicon carbide substrate in a transfer chamber filled with inert gas, and transferring it to a silicon carbide CVD reaction chamber in a hydrogen atmosphere by a robotic arm, wherein the reaction chamber has an initial pressure and an initial temperature;

[0027] Step 2: Keep introducing hydrogen 1 into the reaction chamber, set the temperature and pressure of the reaction chamber to a first temperature and a first pressure, and maintain the temperature and pressure of the reaction chamber for a period of time after the temperature and pressure gradually reach the set value and stabilize, so as to perform a pre-etching process on the substrate;

[0028] Step 3: Perform epitaxial growth, and the growth conditions are as follows:

[0029] a. During the epitaxial growth process, the temperature and pressure of the reaction chamber are maintained at a first temperature and a first pressure, and hydrogen 1 is introduced at a constant flow rate;

[0030] b. Using a carbon source and a silicon source as growth source gases, if the silicon source is liquid, the liquid silicon source is stored in a bubbler 1, hydrogen is introduced into the bubbler 1, and the silicon source is carried into the reaction chamber by the hydrogen;

[0031] c. Hexamethyldisilazane is used as an n-type doping source, liquid hexamethyldisilazane is stored in a bubbler 2, hydrogen 2 is introduced into the bubbler 2, and hexamethyldisilazane is carried by the hydrogen 2 into the reaction chamber. Before the first mixed gas formed by the hydrogen 2 and the hexamethyldisilazane is introduced into the reaction chamber, a diluting hydrogen gas, hydrogen 3, can be used again to mix with the first mixed gas to form a second mixed gas, so as to reduce the concentration of hexamethyldisilazane in the second mixed gas introduced into the reaction chamber;

[0032] d. The epitaxial growth time is determined by the designed epitaxial thickness;

[0033] Step 4: After the epitaxial growth is completed, the process gases such as the carbon source, silicon source, and doping source are turned off, the temperature is gradually reduced to above the initial temperature, and after the pressure is gradually restored to the initial pressure, the epitaxial wafer is taken out of the CVD reaction chamber to a transfer chamber filled with inert gas. The epitaxial wafer is cooled to room temperature in the transfer chamber. After the air pressure in the transfer chamber is restored to atmospheric pressure, the silicon carbide epitaxial wafer is taken out.

[0034] The amount of hexamethyldisilazane introduced is determined by the flow rate of hydrogen 2, the flow rate of hydrogen 3 and the flow rate of the second mixed gas introduced into the reaction chamber. The n-type doping concentration can be regulated by adjusting the amount of hexamethyldisilazane introduced.

[0035] The gas flow rate of the carbon source is 50-200 sccm, and the amount of carbon source and silicon source introduced maintains a C / Si molar ratio of 0.9-1.3; the flow rate of hydrogen 2 is 50-200 sccm, the flow rate of hydrogen 3 is 10-500 slm, and the flow rate of the second mixed gas into the reaction chamber is 20-400 sccm.

[0036] Conventional carbon sources and silicon sources can be applied to the epitaxial growth process of the present invention. For example, the carbon sources include methane, ethane, ethylene, etc.; the silicon source is preferably trichlorosilane, dichlorosilane, etc. The C / Si molar ratio refers to the molar ratio of C atoms in the C-based raw material gas relative to the Si atoms in the Si-based raw material gas. In n-type doping, N atoms replace C atoms in the SiC lattice, and the C / Si molar ratio will affect the doping process, and the C / Si molar ratio is controlled to be 0.9 to 1.3. The C / Si molar ratio in silicon carbide crystals is 1. When the C / Si molar ratio in the growth source gas is too high or too low, it will cause a large number of defects in the epitaxial growth layer.

[0037] Under the growth conditions of the present invention, the amount of carbon and silicon provided by hexamethyldisilazane during the epitaxial growth process is less than one thousandth of the amount provided by the carbon source and the silicon source, and therefore is not included in the calculation of the carbon-silicon ratio. The calculation of the carbon-silicon ratio only considers the amount provided by the carbon source and the silicon source.

[0038] Hexamethyldisilazane is used as the doping source, and its N is easier to enter the SiC lattice. 2 Other doping sources such as N-doping source have higher doping efficiency, reduce the residue in the cavity environment, reduce the interference of the formed N element background concentration on the doping concentration, and improve the stability and controllability of the doping concentration.

[0039] Hexamethyldisilazane is used as a doping source, the epitaxial growth temperature of n-type doped SiC is 1500° C. to 1700° C., and the pressure of the reaction chamber is 50 to 300 mbar.

[0040] The silicon carbide substrate is first placed in a transfer chamber filled with inert gas, and then transferred to a silicon carbide CVD reaction chamber in a hydrogen atmosphere by a robotic arm. After the growth is completed, it is taken out of the CVD reaction chamber and transferred to a transfer chamber filled with inert gas. The epitaxial wafer is cooled to room temperature in the transfer chamber, which will facilitate the realization of a continuous growth process. The inert gas refers to at least one of the zero group element gases of the periodic table, such as argon.

[0041] The continuous growth mentioned here means that after the growth of steps 1 to 4 is completed, steps 1 to 4 are repeated.

[0042] Example 1

[0043] The epitaxial growth process of n-type doped silicon carbide of Example 1 is described in detail below.

[0044] Step 1: Place the silicon carbide substrate in a transfer chamber filled with argon gas, and use a robotic arm to transfer it to a silicon carbide CVD reaction chamber in a hydrogen atmosphere. The initial pressure of the reaction chamber is 1000 mbar and the initial temperature is 600°C.

[0045] Step 2: Keep introducing hydrogen 1 into the reaction chamber at a flow rate of 100 slm, set the temperature of the reaction chamber to 1600°C and the pressure to 150 mbar, and maintain for 10 minutes after the temperature and pressure of the reaction chamber gradually reach the set values ​​and stabilize, so as to pre-etch the substrate.

[0046] Step 3: Perform epitaxial growth, and the growth conditions are as follows:

[0047] a. The reaction chamber temperature is 1600°C, the hydrogen 1 flow rate is 100 slm, and the reaction chamber pressure is 150 mbar; at the same time, the reaction chamber temperature, hydrogen 1 flow rate and reaction chamber pressure are kept constant during the epitaxial growth process;

[0048] b. Ethylene (carbon source) and trichlorosilane (silicon source) were used as growth source gases, the carbon source gas flow rate was 100 sccm, and the carbon source and silicon source were introduced in such amounts that the carbon-silicon molar ratio was 1.2;

[0049] c. Hexamethyldisilazane is used as an n-type doping source. Liquid hexamethyldisilazane is stored in a bubbler. 50 sccm of hydrogen 2 is introduced into the bubbler. Hexamethyldisilazane is carried by hydrogen 2 into the reaction chamber. Before the first mixed gas formed by hydrogen 2 and hexamethyldisilazane is introduced into the reaction chamber, a diluent hydrogen 3 (with a flow rate of 20 slm) is used again to mix with the mixed gas to reduce the concentration of hexamethyldisilazane in the mixed gas. The flow rate of the diluted second mixed gas introduced into the reaction chamber is 60 sccm.

[0050] d. The epitaxial growth time is determined by the designed epitaxial thickness.

[0051] Step 4: After the epitaxial growth is completed, the process gases such as carbon source, silicon source, and doping source are turned off, and the temperature is gradually reduced to 800°C. After the pressure is gradually restored to 1000mbar, the epitaxial wafer is taken out of the CVD reaction chamber to the transfer chamber filled with argon. The epitaxial wafer is cooled to room temperature in the transfer chamber, and the pressure in the transfer chamber is restored to atmospheric pressure before the silicon carbide epitaxial wafer is taken out.

[0052] Repeat the epitaxial growth process of steps 1 to 4 of Example 1, and use the same process parameters to continuously grow 10 batches of n-type doped silicon carbide epitaxial wafers. The doping concentration is as follows: Figure 1 shown.

[0053] Example 2

[0054] Step 1: Place the silicon carbide substrate in a transfer chamber filled with argon gas, and use a robotic arm to transfer it to a silicon carbide CVD reaction chamber in a hydrogen atmosphere. The initial pressure of the reaction chamber is 1000 mbar and the initial temperature is 600°C.

[0055] Step 2: Keep introducing hydrogen 1 into the reaction chamber at a flow rate of 100 slm, set the temperature of the reaction chamber to 1600°C and the pressure to 150 mbar, and maintain for 10 minutes after the temperature and pressure of the reaction chamber gradually reach the set values ​​and stabilize, so as to pre-etch the substrate.

[0056] Step 3: Perform epitaxial growth, and the growth conditions are as follows:

[0057] a. The reaction chamber temperature is 1600°C, the hydrogen 1 flow rate is 100 slm, and the reaction chamber pressure is 150 mbar; at the same time, the reaction chamber temperature, hydrogen 1 flow rate and reaction chamber pressure are kept constant during the epitaxial growth process;

[0058] b. Ethylene (carbon source) and trichlorosilane (silicon source) were used as growth source gases, the carbon source gas flow rate was 100 sccm, and the carbon source and silicon source were introduced in such amounts that the carbon-silicon molar ratio was 1.2;

[0059] c. Hexamethyldisilazane is used as an n-type doping source. Liquid hexamethyldisilazane is stored in a bubbler. 100 sccm of hydrogen 2 is introduced into the bubbler. The hexamethyldisilazane is carried by the hydrogen 2 into the reaction chamber. Before the first mixed gas of hydrogen 2 and hexamethyldisilazane is introduced into the reaction chamber, a diluent hydrogen 3 (with a flow rate of 300 slm) is used again to mix with the mixed gas to reduce the concentration of hexamethyldisilazane in the mixed gas. The flow rate of the diluted second mixed gas introduced into the reaction chamber is 200 sccm.

[0060] d. The epitaxial growth time is determined by the designed epitaxial thickness.

[0061] Step 4: After the epitaxial growth is completed, the process gases such as carbon source, silicon source, and doping source are turned off, and the temperature is gradually reduced to 800°C. After the pressure is gradually restored to 1000mbar, the epitaxial wafer is taken out of the CVD reaction chamber to the transfer chamber filled with argon. The epitaxial wafer is cooled to room temperature in the transfer chamber, and the pressure in the transfer chamber is restored to atmospheric pressure before the silicon carbide epitaxial wafer is taken out.

[0062] Comparative Example 1

[0063] Step 1: Place the silicon carbide substrate in a transfer chamber filled with argon gas, and use a robotic arm to transfer it to a silicon carbide CVD reaction chamber in a hydrogen atmosphere. The initial pressure of the reaction chamber is 1000 mbar and the initial temperature is 600°C.

[0064] Step 2: Keep introducing hydrogen 1 into the reaction chamber at a flow rate of 100 slm, set the temperature of the reaction chamber to 1600°C and the pressure to 150 mbar, and maintain for 10 minutes after the temperature and pressure of the reaction chamber gradually reach the set values ​​and stabilize, so as to pre-etch the substrate.

[0065] Step 3: Perform epitaxial growth, and the growth conditions are as follows:

[0066] a. The reaction chamber temperature is 1600°C, the hydrogen 1 flow rate is 100 slm, and the reaction chamber pressure is 150 mbar; at the same time, the reaction chamber temperature, hydrogen 1 flow rate and reaction chamber pressure are kept constant during the epitaxial growth process;

[0067] b. Ethylene (carbon source) and trichlorosilane (silicon source) were used as growth source gases, the carbon source gas flow rate was 100 sccm, and the carbon source and silicon source were introduced in such amounts that the carbon-silicon molar ratio was 1.2;

[0068] c. Use nitrogen as the n-type doping source with a nitrogen flow rate of 400 sccm, use a dilution hydrogen gas (flow rate of 400 sccm) to mix with the nitrogen; the flow rate of the mixed gas into the reaction chamber is 200 sccm;

[0069] d. The epitaxial growth time is the same as that in Example 1.

[0070] Step 4: After the epitaxial growth is completed, the process gases such as carbon source, silicon source, and doping source are turned off, and the temperature is gradually reduced to 800°C. After the pressure is gradually restored to 1000mbar, the epitaxial wafer is taken out of the CVD reaction chamber to the transfer chamber filled with argon. The epitaxial wafer is cooled to room temperature in the transfer chamber, and the pressure in the transfer chamber is restored to atmospheric pressure before the silicon carbide epitaxial wafer is taken out.

[0071] Repeat the epitaxial growth process of steps 1 to 4 of the comparative example, and use the same process parameters to continuously grow 10 batches of n-type doped silicon carbide epitaxial wafers. The doping concentration is as follows: Figure 2 shown.

[0072] Figure 1 , Figure 2 The horizontal axis refers to the surface position coordinate of the epitaxial wafer, such as Figure 3 The position of the point shown is the test position; the ordinate is the doping concentration (E15 / cm 3 ).Depend on Figure 1 and Figure 2 It can be seen that the doping concentration curves of the n-type doped silicon carbide epitaxial wafers obtained in Example 1 are highly overlapped under the same parameter process and are between 8.5 and 9.5 E15 / cm 3 The actual doping concentration is close to the target value within the range, indicating that it is less affected by the background concentration and has high stability of the doping concentration. However, the doping concentration curve of the 10 furnaces of n-type doped silicon carbide epitaxial wafers obtained in Comparative Example 1 has a large floating change, and the range is expanded to 7-11E15 / cm 3 , the actual doping concentration deviates from the target value, indicating that it is greatly affected by the background concentration and the stability of the doping concentration is low.

[0073] The above embodiments are only used to further illustrate an epitaxial growth process of n-type doped silicon carbide of the present invention, but the present invention is not limited to the embodiments. Any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention fall within the protection scope of the technical solution of the present invention.

Claims

1. A process for epitaxial growth of n-type doped silicon carbide, characterized in that: The following steps are involved: 1) Placing the silicon carbide substrate in a reaction chamber and pre-etching the substrate in a hydrogen atmosphere; 2) performing epitaxial growth, maintaining the temperature of the reaction chamber at 1500°C to 1700°C, introducing a carbon source and a silicon source as growth source gases, the C / Si molar ratio being 0.9 to 1.3, the carbon source comprising methane, ethane and ethylene, and the silicon source comprising trichlorosilane and dichlorosilane; using hexamethyldisilazane as an n-type doping source, carrying hexamethyldisilazane into the reaction chamber by hydrogen, and growing an n-type doped silicon carbide epitaxial film to a target thickness; wherein the gas flow rate of the carbon source is 50 to 200 sccm; placing liquid hexamethyldisilazane in a bubbler, introducing hydrogen 2 into the bubbler to form a first mixed gas of hexamethyldisilazane and hydrogen 2, the first mixed gas is mixed with hydrogen 3 to form a second mixed gas, and then introduced into the reaction chamber, the flow rate being 20 to 400 sccm. sccm; controlling the amount of hexamethyldisilazane introduced by controlling the flow rate of hydrogen 2, the flow rate of hydrogen 3 and the flow rate of the second mixed gas introduced into the reaction chamber to control the n-type doping concentration; 3) Turn off the carbon source, silicon source and doping source, and obtain an n-type doped silicon carbide epitaxial wafer after cooling.

2. The epitaxial growth process of n-type doped silicon carbide according to claim 1, characterized in that: In step 1), the silicon carbide substrate is placed in a reaction chamber with a hydrogen atmosphere, the initial pressure of the reaction chamber is 800-1200 mbar, and the initial temperature is 500°C-700°C; hydrogen 1 is kept introduced into the reaction chamber, the flow rate of hydrogen 1 is 50-150 slm, the temperature of the reaction chamber is 1500°C-1700°C, the pressure of the reaction chamber is 50-300 mbar, and the etching time is 5-20 min.

3. The epitaxial growth process of n-type doped silicon carbide according to claim 1, characterized in that: In step 2), hydrogen 1 is continuously introduced into the reaction chamber, the flow rate of hydrogen 1 is 50-150 slm, and the pressure of the reaction chamber is 50-300 mbar. During the epitaxial growth process, the temperature of the reaction chamber, the flow rate of hydrogen 1 and the pressure of the reaction chamber are kept constant.

4. The epitaxial growth process of n-type doped silicon carbide according to claim 1, characterized in that: The flow rate of the hydrogen gas 2 is 50-200 sccm, and the flow rate of the hydrogen gas 3 is 10-500 slm.

5. The epitaxial growth process of n-type doped silicon carbide according to claim 1, characterized in that: In step 3), the reaction chamber is cooled to 600-1000°C, and after the reaction chamber pressure is restored to 800-1200 mbar, the n-type doped silicon carbide epitaxial wafer is transferred to an inert gas atmosphere and cooled to room temperature.

6. N-type doped silicon carbide prepared by the epitaxial growth process according to any one of claims 1 to 5.

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