A method for epitaxial growth of silicon carbide

Abstract

The application discloses a silicon carbide epitaxial growth method. The method comprises the following steps: placing a substrate into a reaction cavity; increasing the temperature of the reaction cavity to a first preset temperature based on a first heater, and introducing HCl gas and hydrogen into the reaction cavity based on a spraying component, maintaining the pressure of the reaction cavity to a first preset pressure and lasting for a first preset time, so as to perform in-situ etching on the surface of the substrate; introducing process gas, doping gas and HCl gas into the reaction cavity based on the spraying component, so as to grow a silicon carbide buffer layer on the surface of the etched silicon carbide substrate, and the growth of the silicon carbide buffer layer comprises a high C / Si stage and a low C / Si stage; introducing process gas, doping gas and HCl gas into the reaction cavity based on the spraying component, so as to grow a silicon carbide drift layer on the surface of the buffer layer. In the growth stage of the buffer layer, the high C / Si and low C / Si combination mode is adopted and cyclic growth is performed, the dislocation penetration path is changed for multiple times, and the probability of dislocation penetration is reduced.

Description

Technical Field

[0001] This application relates to the field of epitaxial technology, specifically to a method for silicon carbide epitaxial growth. Background Technology

[0002] As a very important member of the third generation of semiconductors, SiC material has shown broad application prospects and huge market development potential in fields such as 5G communication, ultra-high voltage long-distance power transmission, fast charging of new energy vehicles, and aerospace due to its excellent material physical properties such as high bandgap, high thermal conductivity, high electron mobility, and high radiation resistance. Compared with Si, SiC is more suitable for making high-voltage and high-temperature high-power devices.

[0003] However, as the withstand voltage of devices increases, the thickness of the epitaxial layer also increases. For example, for medium voltage (1200V-1700V), the SiC epitaxial layer thickness only needs to be 10-15µm. But for high voltage (10KV and above), the SiC epitaxial layer thickness needs to reach more than 100µm.

[0004] Currently, the domestic process for growing thick SiC films mainly involves increasing the growth time of the drift layer for a one-time forming. This method, due to continuous epitaxial growth, results in significant surface defects and wafer deformation in the grown silicon carbide. The uniformity of concentration and thickness is difficult to control, with film thickness STD around 4% and concentration STD around 8%. The surface defect density of the product is also above 50 cm⁻², which is far from sufficient for product performance. To further improve product performance and yield, there is an urgent need to develop new products with better uniformity.

[0005] Some manufacturers have tried to adjust the uniformity of epitaxial wafers by simply adjusting the airflow distribution, but this is difficult to promote due to the fact that the current level of machine hardware and epitaxial structure has basically reached its limit. Summary of the Invention

[0006] To overcome the above-mentioned shortcomings, the purpose of this application is to provide a silicon carbide epitaxial growth method, which provides a high-quality silicon carbide homoepitaxial growth method.

[0007] To achieve the above objectives, this application adopts the following technical solution:

[0008] A method for silicon carbide epitaxial growth, the method comprising the following steps:

[0009] Place the substrate into the reaction chamber;

[0010] The temperature of the reaction chamber is raised to a first preset temperature based on the first heater or a combination of the first heater and the second heater. At the same time, HCl gas and hydrogen gas are introduced into the reaction chamber based on the spray component, the pressure of the reaction chamber is maintained at the first preset pressure and continued for a first preset time, so as to perform in-situ etching on the substrate surface.

[0011] Process gas, doping gas, and HCl gas are introduced into the reaction chamber through a spraying component to grow a silicon carbide buffer layer on the surface of the etched silicon carbide substrate. The growth stage of the silicon carbide buffer layer includes a high C / Si (carbon-silicon ratio) stage and a low C / Si (carbon-silicon ratio) stage in the introduced process gas.

[0012] The process gas, dopant gas, and HCl gas are introduced into the reaction chamber through a spray component, and a silicon carbide drift layer is grown on the surface of the buffer layer. This design utilizes ultra-low pressure and high temperature growth during the buffer layer growth process. The high temperature reduces step accumulation during the step flow growth process, improving surface roughness, while the low pressure reduces the generation of triangular defects.

[0013] In one embodiment, the stage of growing a silicon carbide drift layer on the surface of the buffer layer includes: a first stage, a second stage, and a third stage.

[0014] In the first stage, the growth pressure in the reaction chamber is maintained between 50-150 mbar, the rotation speed is 400-600 rpm, and a process gas with a C / Si ratio between 0.9-1.2 is introduced. The growth time T1 is...

[0015] In the second stage, the growth pressure in the reaction chamber is maintained between 50-150 mbar, the rotation speed is 400-600 rpm, and a process gas with a C / Si ratio between 0.9-1.2 is introduced. The growth time T2 is...

[0016] In the third stage, the growth pressure in the reaction chamber is maintained between 50-150 mbar, the rotation speed is 400-600 rpm, and a process gas with a C / Si ratio between 0.7-0.9 is introduced, with a growth time of T3. In this method, a low C / Si ratio is used in the third stage, which reduces the C flow rate while slightly increasing the doping concentration, providing a good contact layer for subsequent Schottky or ohmic contacts in the device. Reducing the C flow rate lowers the growth rate, resulting in denser surface growth and preventing dislocation penetration.

[0017] In one embodiment, after the first stage is completed and before the second stage begins, the method further includes:

[0018] During the cooling and annealing stage, hydrogen gas is introduced into the reaction chamber only through the spray component. The temperature of the reaction chamber is lowered to 1400-1450℃, and then raised to 1630-1680℃ for intermittent growth. During the intermittent growth, only 1000 sccm of HCl gas and H2 are introduced.

[0019] In one embodiment, the process includes, after the second stage is completed and before the third stage begins:

[0020] The spray component only introduces hydrogen into the reaction chamber. After the temperature of the reaction chamber drops to 1400-1450℃, it is then raised to 1630-1680℃ for intermittent growth. During the intermittent growth, only 1000 sccm of HCl gas and H2 are introduced.

[0021] In one embodiment, the high C / Si stage includes introducing a process gas with a C / Si ratio between 1.0 and 1.2.

[0022] In one embodiment, the low C / Si stage includes introducing a process gas with a C / Si ratio between 0.7 and 0.9.

[0023] In one embodiment, the stage of growing the silicon carbide buffer layer includes:

[0024] First, a process gas with a C / Si ratio between 0.7 and 0.9 is introduced, and growth is carried out for a first preset time, followed by a second preset time interruption. During the interruption, only HCl gas and H2 are introduced.

[0025] Then, a process gas with a C / Si ratio between 1.0 and 1.2 is introduced, and growth is performed for a third preset time, followed by a fourth preset time of interruption. During the interruption, HCl, H2, and N2 are introduced, constituting one cycle (e.g., 10 cycles). In this method, interrupted growth is performed after each growth segment, and HCl cleaning is carried out. This can effectively reduce surface defects, reduce triangular problems caused by scratches and dot loss, alleviate step accumulation, and reduce surface roughness. At the same time, introducing N2 during the interrupted growth can increase the doping concentration of the buffer layer.

[0026] In one embodiment, after growing the silicon carbide drift layer, the method further includes:

[0027] Based on the fact that the spray component stops introducing process gas into the reaction chamber and only introduces hydrogen, the temperature is cooled to the pick-up temperature only in the hydrogen atmosphere, and then it is transferred out by the robot arm.

[0028] In one embodiment, the process further includes: before performing in-situ etching on the substrate surface.

[0029] The spray component switches the gas introduced into the reaction chamber from argon to hydrogen, and gradually increases the hydrogen flow rate to a target value, which is between 90-130 slm.

[0030] In one embodiment, a first preset pressure of 50-150 mbar is applied for 5-10 min to perform in-situ etching on the substrate surface.

[0031] Beneficial effects

[0032] The epitaxial growth method of this application employs a high / low C / Si ratio combination during the growth of the buffer layer. Since thick films are more prone to defects such as dislocation penetration than thin films, different C / Si ratios are used to adjust the lattice size, and cyclic growth is performed to repeatedly change the dislocation penetration path, thereby reducing the probability of dislocation penetration. Furthermore, the different growth rates of high and low C / Si ratios effectively mitigate the probability of dislocation penetration, improve the surface defects of the epitaxial wafer, and reduce the concentration and thickness uniformity of the thick film epitaxial wafer. Attached Figure Description

[0033] The accompanying drawings are provided to illustrate the technical solutions of this disclosure and form part of the specification. They are used together with the embodiments of this disclosure to explain the technical solutions of this disclosure and do not constitute a limitation on the technical solutions of this disclosure. The shapes and sizes of the components in the drawings do not reflect actual proportions and are only intended to illustrate the content of this application.

[0034] Figure 1 This is a schematic flowchart of the silicon carbide epitaxial growth method according to an embodiment of this application.

[0035] Figure 2 This is a schematic diagram of the process for growing a silicon carbide buffer layer according to an embodiment of this application.

[0036] Figure 3 This is a schematic diagram of the process for growing a silicon carbide drift layer according to an embodiment of this application. Detailed Implementation

[0037] The above-described solution will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of this application. The implementation conditions used in the embodiments may be further adjusted according to the conditions of specific manufacturers, and the implementation conditions not specified are generally those in routine experiments.

[0038] The silicon carbide epitaxial growth method proposed in this application will now be described with reference to the accompanying drawings. This method is used to grow homogeneous silicon carbide epitaxy.

[0039] This application discloses an epitaxial device including a film forming apparatus, a transfer cavity, and a loading cavity. A robotic arm is provided in the transfer cavity. The robotic arm is used to transfer the substrate to be epitaxially grown from the loading cavity to the film forming apparatus, where epitaxial growth is performed. After the growth is completed, the substrate is picked up by the robotic arm and placed into the loading cavity. This process is repeated to perform epitaxial growth.

[0040] The film-forming apparatus includes a main body with a spraying component at its top. This spraying component is connected to a gas source via a pipeline, through which process gases (trichlorosilane (SiHCl3) and ethylene (C2H4)) are introduced into the main body (also called the reaction chamber). A support component is disposed within the main body, with a tray placed on its top. The support component faces the spraying component. Preferably, a first heater, which may be a graphite heater, is disposed within the support component. Preferably, the main body is cylindrical, and at least one second heater, also a graphite heater, extends axially within the main body. The support component is connected to a drive component at the bottom of the main body, and the drive component rotates the support component, causing the tray on it to rotate. The rotational speed of the tray may vary at different stages. Epitaxial growth is performed using this film-forming apparatus.

[0041] Next, combine Figures 1-3 This application describes a method for silicon carbide epitaxial growth (hereinafter referred to as the "method"). The method includes the following steps:

[0042] S1. Place the (silicon carbide) substrate into the reaction chamber. This step includes using a robotic arm to place the silicon carbide substrate (along with a tray) into the reaction chamber, evacuating the chamber, and rotating the tray to a first rotational speed (e.g., 400-600 rpm) using a drive unit. The chamber pressure of the reaction chamber is set between 150 mbar and 300 mbar.

[0043] S2. Based on the first heater or the first heater and the second heater, the temperature of the reaction chamber is gradually increased to a first preset temperature (e.g., 1650-1700℃), the reaction pressure of the chamber is reduced, and HCl gas and hydrogen gas are introduced into the reaction chamber through the spray component. Pure hydrogen gas and HCl gas are used to perform in-situ etching on the substrate surface. In this step, the pressure of the reaction chamber (first preset pressure) is maintained between 50-150 mbar and lasted for 5-10 minutes (first preset time) to perform in-situ etching on the substrate surface.

[0044] S3. Process gas, dopant gas, and HCl gas are introduced into the reaction chamber via a spray system to grow a silicon carbide buffer layer on the surface of the etched silicon carbide substrate. In this step, a gas containing a Si source (such as trichlorosilane (SiHCl3)), a gas containing a C source (such as ethylene (C2H4)), a dopant gas (such as high-purity nitrogen (N2) as the N source), and HCl gas are introduced into the reaction chamber via the spray system. The flow rate of the HCl gas is between 600-1200 sccm, the pressure in the reaction chamber is maintained between 50-150 mbar, the tray rotation speed is between 400-600 rpm, and the growth temperature is between 1630-1680℃. In this stage, the silicon carbide buffer layer adopts an alternating growth mode (alternating growth mode refers to low-C mode and high-C mode; in low-C mode, C / Si ratio less than 1 is preferred, with a C / Si ratio between 0.7 and 0.9; in high-C mode, C / Si ratio greater than 1 is preferred, with a C / Si ratio between 1.0 and 1.2). In this embodiment, during the growth of the silicon carbide buffer layer, a process gas with a C / Si ratio between 0.7 and 0.9 is first introduced for a first preset time (30s), followed by a second preset time interruption (e.g., 10s), during which only HCl and H2 gases are introduced. Then, a process gas with a C / Si ratio between 1.0 and 1.2 is introduced for a third preset time (e.g., 45s), followed by a fourth preset time interruption (e.g., 10s), during which HCl, H2, and N2 gases are introduced. This constitutes one cycle, and this process is repeated 5-20 times. Ten cycles were performed to grow a 1.5 μm thick buffer layer (alternating growth mode: growing a low-C layer (C / Si between 0.7 and 0.9) for 30 seconds, followed by a 10-second pause during which only HCl and H2 gases were introduced; then growing a high-C layer (C / Si between 1.0 and 1.2) for 45 seconds, followed by a 10-second pause during which HCl, H2, and N2 gases were introduced; this constituted one cycle, and a total of 10 cycles were performed, for a total of 950 seconds, resulting in a growth thickness of 1.5 μm. The tested doping concentration was 2E15 / cm². 3 The doping concentration was tested at 2E15 / cm3. In this embodiment, a 10-second intermittent growth method was adopted between cycles. During the growth process, the gas was switched to ensure that the gas flow rate was stable after the switch before the gas was introduced into the cavity for growth. The MFC currently in use was tested and observed. After the gas was switched, the flow rate could reach the set flow rate within 1-2 seconds and the flow rate was kept stable for several seconds. Therefore, a 10-second switching time was set, and the intermittent growth was also for short-term stress release.

[0045] Table 1 shows the statistics for different cycles during the buffer layer growth stage, assuming other conditions remain unchanged.

[0046] Table 1

[0047]

[0048] As can be seen from Table 1, the thickness uniformity and concentration uniformity are basically similar under different cycles, and the roughness is also basically the same. However, in terms of surface defects, the variable defects after 10 cycles are significantly better than the experimental results after 8 cycles and 12 cycles. Finally, 10 cycles were selected as the standard condition.

[0049] S4. Process gas, dopant gas, and HCl gas are introduced into the reaction chamber via a spray system to grow a silicon carbide drift layer on the surface of the buffer layer. In this step, trichlorosilane (SiHCl3), ethylene (C2H4), and high-purity nitrogen (N2) are introduced into the reaction chamber via the spray system.

[0050] Preferably, the drift layer growth includes three stages, also known as three-stage growth. In the first and second stages, the C / Si ratio is between 0.9 and 1.2, the growth pressure in the reaction chamber is between 50 and 150 mbar, and the rotation speed is between 400 and 600 rpm. The growth times are T1 and T2, respectively. In one embodiment, T1 is 1500 s with a growth thickness of 20 μm, and T2 is 2200 s with a growth thickness of 30 μm. After the first stage is completed, a cooling annealing process is performed for 200 seconds, cooling to 1400-1450℃, during which only H2 is introduced. Then, the temperature is raised to 1630-1680℃ for intermittent growth for 300 seconds, with only 1000 sccm of HCl gas and H2 introduced, and no other source gases introduced. The third stage uses a C / Si ratio of 0.7-0.9, a growth pressure of 50-150 mbar, a rotation speed of 400-600 rpm, a growth time T3 (e.g., 2700 s), and a growth thickness of approximately 30 μm. Preferably, between the second and third stages, a cooling annealing process is performed for 200 seconds, cooling to 1400-1450℃, during which only H2 is introduced, followed by an intermittent growth process at 1630-1680℃ for 300 seconds, with only 1000 sccm of HCl gas and H2 introduced, and no other source gases introduced. The N-doping concentration of the three segments is 8.04E15 / cm3, with a total thickness of 92.06 μm. The concentration uniformity and thickness uniformity are 2.53% and 1.63%, respectively, which fully meets the requirements for high-quality thick-film silicon carbide power devices. This method is best suited for growing epitaxial thicknesses greater than 15 μm (e.g., devices with a breakdown voltage of 1200V and above can be fabricated when the epitaxial thickness is greater than 100 μm).

[0051] Preferably, during the growth of the drift layer, a long annealing process is performed, with other conditions remaining unchanged, only the annealing temperature is varied. Table 2 shows the data results when the annealing temperatures are selected as 1300-1350℃, 1350-1400℃, 1400-1450℃, and 1450-1500℃:

[0052]

[0053] Table 2

[0054] As shown in Table 2, as the annealing temperature decreases, the thickness uniformity decreases with the deepening of annealing conditions, but the concentration uniformity increases. The higher the annealing temperature, the greater the defect density, and the most significant changes occur in the 1400-1450℃ range. The roughness remains basically unchanged. Considering the annealing time and the insignificant changes after 1400-1450℃, the annealing temperature is selected in the 1400-1450℃ range. Considering the heating wire power change rate, the temperature change rate, and the flow rate change between the two drift layers during the heating and cooling stages, the next stage of growth can only proceed after the temperature and flow rate have stabilized. Therefore, the annealing time is set to 200s.

[0055] S5. Based on the spray component, stop introducing process gas into the reaction chamber and only introduce hydrogen. In this step, after the reaction is completed, cool down to the removal temperature (e.g., 800℃, 850℃, 900℃) only in a hydrogen atmosphere, and then transfer it out by a robotic arm. This method can obtain high-quality silicon carbide homoepitaxial wafers. In this method, a combination of high C / Si and low C / Si is used in the buffer layer growth stage. Because growing thick films is more prone to defects such as dislocation penetration than thin films, using high C / Si and low C / Si can adjust the lattice size and perform cyclic growth, changing the dislocation penetration path multiple times to reduce the probability of dislocation penetration. At the same time, the growth rates of high C / Si and low C / Si (also known as high-low C / Si) are different, which can also effectively slow down the probability of dislocation penetration. In this embodiment, a short single-growth time and cyclic growth mode are adopted during buffer layer growth. This reduces the increase in epitaxial layer stress caused by N atom substitution for C atom doping. Because the single-layer growth time is short and there is intermittent growth between layers, stress can be effectively released, reducing stress accumulation (stress accumulation is one of the main causes of surface defects and roughness; excessive stress may also cause epitaxial wafer breakage, a phenomenon more pronounced in thick film growth). During buffer layer growth, intermittent growth and HCl cleaning are performed after each growth segment, effectively reducing surface defects, minimizing triangular defects caused by scratches and dopant defects, alleviating step accumulation, and reducing surface roughness. Simultaneously, introducing N2 during intermittent growth increases the doping concentration of the buffer layer, as N atoms in high C / Si layers are less prone to doping. The use of ultra-low pressure and high temperature growth in the buffer layer aims to reduce step accumulation and improve surface roughness during step flow growth through high temperature, while low pressure reduces the generation of triangular defects.

[0056] In this embodiment, the drift layer is grown in three stages, with HCl gas used for etching between stages to reduce surface roughness and address scratches and chipping. A cooling annealing process is also performed to reduce stress accumulation during thick film growth, releasing stress layer by layer and reducing dislocation generation. In the third stage of drift layer growth, a low C / Si ratio is used to reduce C flow and improve (slightly increase) doping concentration, providing a good contact layer for subsequent Schottky or ohmic contacts. Simultaneously, the growth rate is reduced to achieve a denser surface and prevent dislocation penetration. The epitaxial layer grown using this method exhibits reduced concentration uniformity and thickness uniformity of 2.53% and 1.63%, respectively. The on-wafer kill density (the sum of MP, Carrot, Downfall, and Triangle densities) is less than 0.5 particles / cm², effectively improving product yield; the epitaxial layer surface is smooth with a surface roughness of only 0.09 nm.

[0057] In one embodiment, prior to step S2, the gas introduced into the reaction chamber is switched from argon to hydrogen based on the spray component, and the hydrogen flow rate is gradually increased to a target value, and then the hydrogen flow rate is kept constant. Preferably, the target hydrogen flow rate is between 90-130 slm (standard litre per minute).

[0058] The above embodiments are only for illustrating the technical concept and features of this application, and are intended to enable those skilled in the art to understand the content of this application and implement it accordingly. They should not be used to limit the scope of protection of this application. All equivalent changes or modifications made in accordance with the spirit and essence of this application should be included within the scope of protection of this application.

Claims

1. A method for silicon carbide epitaxial growth, characterized in that, The method includes the following steps: Place the substrate into the reaction chamber; In-situ etching is performed on the substrate surface. The temperature of the reaction chamber is raised to a first preset temperature based on the first heater or a combination of the first heater and the second heater. At the same time, HCl gas and hydrogen gas are introduced into the reaction chamber based on the spray component, the pressure of the reaction chamber is maintained at the first preset pressure and continued for a first preset time, so as to perform in-situ etching on the substrate surface. The process gas, doping gas, and HCl gas with high C / Si and low C / Si ratios are introduced into the reaction chamber by a spray component to grow silicon carbide buffer layers with different carbon concentrations on the surface of the etched silicon carbide substrate. The growth stage of the silicon carbide buffer layer includes: first, introducing a process gas with a C / Si ratio between 0.7 and 0.9, growing for a first preset time, then interrupting for a second preset time, during which only HCl gas and H2 are introduced, then introducing a process gas with a C / Si ratio between 1.0 and 1.2, growing for a third preset time, then interrupting for a fourth preset time, during which HCl gas, H2, and N2 are introduced, and this constitutes one cycle. Based on the process gas, dopant gas, and HCl gas introduced into the reaction chamber by the spray component, a silicon carbide drift layer is grown on the surface of the buffer layer. The stage of growing the silicon carbide drift layer on the surface of the buffer layer includes: a first stage, a second stage, and a third stage. In the first stage, the growth pressure in the reaction chamber is maintained between 50-150 mbar, the rotation speed is 400-600 rpm, and the process gas with a C / Si ratio between 0.9-1.2 is introduced, with a growth time of T1. In the second stage, the growth pressure in the reaction chamber is maintained between 50-150 mbar, the rotation speed is 400-600 rpm, and the process gas with a C / Si ratio between 0.9-1.2 is introduced, with a growth time of T2. In the third stage, the growth pressure in the reaction chamber is maintained between 50-150 mbar, the rotation speed is 400-600 rpm, and the process gas with a C / Si ratio between 0.7-0.9 is introduced, with a growth time of T3.

2. The silicon carbide epitaxial growth method as described in claim 1, characterized in that, The process includes the following steps after the first phase is completed and before the second phase begins: During the cooling and annealing stage, hydrogen gas is introduced into the reaction chamber only through the spray component. The temperature of the reaction chamber is lowered to 1400-1450℃, and then raised to 1630-1680℃ for intermittent growth. During the intermittent growth, only 1000 sccm of HCl gas and H2 are introduced.

3. The silicon carbide epitaxial growth method as described in claim 2, characterized in that, The process includes, after the completion of the second phase and before the commencement of the third phase: The spray component only introduces hydrogen into the reaction chamber. After the temperature of the reaction chamber drops to 1400-1450℃, it is then raised to 1630-1680℃ for intermittent growth. During the intermittent growth, only 1000 sccm of HCl gas and H2 are introduced.

4. The silicon carbide epitaxial growth method as described in claim 1, characterized in that, The high C / Si stage includes introducing process gas with a C / Si ratio between 1.0 and 1.

2.

5. The silicon carbide epitaxial growth method as described in claim 4, characterized in that, The low C / Si stage includes introducing process gas with a C / Si ratio between 0.7 and 0.

9.

6. The silicon carbide epitaxial growth method as described in claim 1, characterized in that, The process after growing the silicon carbide drift layer also includes: Based on the fact that the spray component stops introducing process gas into the reaction chamber and only introduces hydrogen, the temperature is cooled to the pick-up temperature only in the hydrogen atmosphere and then transferred out by the robot arm.

7. The silicon carbide epitaxial growth method as described in claim 1, characterized in that, The process before in-situ etching of the substrate surface also includes: The spray component switches the gas introduced into the reaction chamber from argon to hydrogen, and gradually increases the hydrogen flow rate to a target value, which is between 90-130 slm.

8. The silicon carbide epitaxial growth method as described in claim 1, characterized in that, The first preset pressure is between 50-150 mbar and is maintained for 5-10 min to perform in-situ etching on the substrate surface.

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