A method for reducing pit defects on the surface of a silicon carbide epitaxial layer

Abstract

The application discloses a growth method for reducing pit defects on a silicon carbide epitaxial surface, and after epitaxial growth is completed, the flow of gas floating of a base is increased, the temperature in a reaction chamber is increased, the pressure in the reaction chamber is reduced, and the flow of hydrogen is increased, and then an etching stage is entered; in the etching stage, hydrogen chloride gas is continuously fed, including at least one feeding period and a pause period after the feeding period; by using the thermal instability of SiC at high temperature / low pressure, H2 / HCl is used to cooperatively etch the system to realize efficient decomposition, the etching rate is increased, the generation of sub-damage and dislocation is reduced, the thickness of the removed epitaxial layer can be accurately controlled, the pit defects on the surface of the epitaxial layer are reduced, and the crystallization quality of the epitaxial layer is maintained, so that the preparation requirements of subsequent power devices are met.

Description

Technical Field

[0001] This invention belongs to the field of silicon carbide epitaxial technology, specifically relating to a growth method for reducing pit defects on the surface of silicon carbide epitaxy. Background Technology

[0002] Compared to traditional Si devices, 4H-SiC, with its superior material properties such as wide bandgap, high breakdown electric field, and high thermal conductivity, has demonstrated revolutionary advantages in high-voltage, high-power applications such as new energy vehicles, rail transportation, and smart grids. Especially in the high-voltage field above 1200V, it has gradually replaced silicon-based IGBT devices. However, the superior performance of these devices is highly dependent on the fabrication of high-quality epitaxial layers. During the SiC epitaxial growth process (usually using chemical vapor deposition, CVD), various crystal defects are inevitably generated. The presence of these defects severely degrades the electrical performance and long-term reliability of the devices.

[0003] Early research and technological breakthroughs primarily focused on fatal defects that directly cause device failure. For example, triangular defects can lead to short circuits or premature breakdown; carrot defects severely affect carrier transport and blocking characteristics; and stacking fault defects reduce carrier mobility, increase conduction losses, and may cause degradation of the forward voltage in bipolar devices. In recent years, with the continuous development of epitaxial technology, the control technologies for these fatal defects have developed rapidly and gradually matured. Meanwhile, the impact of non-fatal defects such as pit defects on device performance has become increasingly apparent, posing a new challenge to device performance and reliability.

[0004] Pit defects are small depressions or pits on the surface of SiC epitaxial layers, with morphology as follows: Figure 1 As shown, these pits are typically in the micrometer or submicrometer range in size, with a depth usually less than 20 nm, and exhibit diverse morphologies. The presence of pit defects can increase device leakage current, thereby affecting the long-term reliability of the device. Therefore, optimizing the process and effectively reducing pit defects on the epitaxial surface is of positive significance for the development of silicon carbide. Summary of the Invention

[0005] This invention addresses the shortcomings of existing technologies by providing a growth method for reducing pit defects on the surface of silicon carbide epitaxial layers.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows:

[0007] A growth method for reducing pit defects on the surface of silicon carbide epitaxial epitaxial material includes the following steps:

[0008] 1) Silicon carbide epitaxial growth is completed in the reaction chamber, and the epitaxial thickness is greater than the target thickness; during epitaxial growth, the substrate is placed on the base of the reaction chamber, and the base is kept in an air-floating state;

[0009] 2) After the epitaxial growth is completed, the growth source is turned off, the air flotation flow rate of the substrate is increased, the temperature in the reaction chamber is increased, the pressure in the reaction chamber is decreased, and the hydrogen flow rate is increased before entering the etching stage; during the etching stage, hydrogen chloride gas is introduced discontinuously, including at least one introduction period and an interruption period after the introduction period; during the etching stage, the epitaxial layer is etched to the target thickness.

[0010] 3) After etching is completed, turn off the hydrogen chloride source, reduce the air flotation flow rate of the substrate and the hydrogen flow rate, increase the pressure of the reaction chamber to atmospheric pressure, and reduce the temperature of the reaction chamber to room temperature in a hydrogen atmosphere.

[0011] 4) Turn off the hydrogen flow and flotation flow, fill the reaction chamber with inert gas, open the reaction chamber and take out the epitaxial wafer.

[0012] Optionally, in step 2), the temperature in the reaction chamber of the etching stage is 1700℃~1750℃, and the pressure in the reaction chamber is 30mbar~80mbar.

[0013] Optionally, in step 2), the hydrogen flow rate during the etching stage is 250 slm to 350 slm.

[0014] Optionally, in step 2), the air flotation flow rate during the etching stage is 2000 sccm to 2500 sccm.

[0015] Optionally, in step 2), one of the access periods and one of the interruption periods constitute a cycle, and the etching stage includes multiple cycles.

[0016] Optionally, the hydrogen chloride flow rate during the inlet period is 1500-2000 sccm, and the duration is 10s-1min; the hydrogen chloride flow rate during the interruption period is 0, and the duration is 30s-2min.

[0017] Optionally, the thickness of the surface layer of the epitaxial layer removed during the etching stage is 0.1 μm to 0.2 μm.

[0018] Optionally, the conditions for epitaxial growth described in step 1) include: hydrogen flow rate of 80 slm to 200 slm, air flotation flow rate of 500 scmm to 1000 scmm, reaction chamber temperature of 1600℃ to 1650℃, and reaction chamber pressure of 150 mbar to 250 mbar.

[0019] Optionally, in step 3), the temperature of the reaction chamber is reduced to 1000℃ to 1200℃ within 5 min to 15 min, while the air flotation flow rate of the base is reduced to 50 sccm to 150 sccm, the hydrogen flow rate is reduced to 50 slm to 150 slm, the pressure of the reaction chamber is increased to atmospheric pressure, and then the temperature of the reaction chamber is reduced to room temperature.

[0020] A silicon carbide epitaxial wafer, obtained by the above-described growth method for reducing pit defects on the silicon carbide epitaxial surface, wherein the distribution density of pit defects on the surface of the epitaxial wafer is <0.1 defects / cm². 2 .

[0021] The beneficial effects of this invention are as follows:

[0022] After epitaxial growth is completed, an etching stage is introduced. Taking advantage of the thermal instability of SiC under high temperature / low pressure, an efficient decomposition is achieved through an H2 / HCl synergistic etching system. Through the dynamic bonding weakening-repair mechanism of HCl, the strong etching effect of HCl can destroy the Si-C bonds on the epitaxial layer surface. Subsequently, a pure H2 stage achieves selective etching, which increases the etching rate while reducing the generation of sub-damage and dislocations. The introduction of HCl also reduces the probability of silicon droplet generation during the etching process. At the same time, the small disk is lifted by air flotation, and the etching uniformity is enhanced by a higher rotation speed. By controlling the synergistic process of H2 / HCl, the thickness of the epitaxial layer removed can be precisely controlled, and the surface roughness of the epitaxial layer after processing can be guaranteed. Without CMP (chemical mechanical polishing) treatment, pit defects on the surface of the epitaxial layer can be reduced, and the crystal quality of the epitaxial layer can be maintained to meet the requirements of subsequent power device fabrication.

[0023] Other features and advantages of the invention will be set forth in the following description, and will be apparent in part from the description, or may be learned by practicing the invention. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the morphology of pit defects in the prior art;

[0025] Figure 2 This is a schematic diagram of the process conditions for the growth method in Example 1;

[0026] Figure 3 The image shows the pits defect distribution of three epitaxial wafers obtained by the growth method in Example 1 (SICA detection).

[0027] Figure 4 The images show the surface roughness of three epitaxial wafers obtained by the growth method in Example 1.

[0028] Figure 5 The image shows the distribution of pits defects in the epitaxial wafer obtained by the growth method in Comparative Example 1 (SICA detection).

[0029] Figure 6 The image shows the pits defect distribution of the epitaxial wafer obtained by the growth method in Example 2 (SICA detection).

[0030] Figure 7The images show the surface roughness of three epitaxial wafers obtained by the growth method in Example 2.

[0031] Figure 8 The image shows the pits defect distribution of the epitaxial wafer obtained by the growth method in Example 3 (SICA detection).

[0032] Figure 9 The images show the surface roughness of three epitaxial wafers obtained by the growth method in Example 3.

[0033] Figure 10 The image shows the pits defect distribution of the epitaxial wafer obtained by the growth method in Example 4 (SICA detection).

[0034] Figure 11 The images show the surface roughness of three epitaxial wafers obtained by the growth method in Example 4.

[0035] Figure 12 The image shows the pits defect distribution of the epitaxial wafer obtained by the growth method in Example 5 (SICA detection).

[0036] Figure 13 The images show the surface roughness of three epitaxial wafers obtained by the growth method in Example 5. Detailed Implementation

[0037] The present invention will be further explained below with reference to the accompanying drawings and specific embodiments. While preferred embodiments of the invention are described below, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Where specific techniques or conditions are not specified in the embodiments, they should be performed in accordance with the techniques or conditions described in the literature in the art or in accordance with the product manual.

[0038] The growth method for reducing pit defects on the silicon carbide epitaxial surface in this embodiment involves performing precise micro-etching on the epitaxial layer surface in situ within a reaction chamber after silicon carbide epitaxial growth, followed by cooling and wafer unloading. The etching process employed uses alternating HCl / H2 etching under high temperature and low pressure conditions, combined with high-flow-rate air flotation, which effectively eliminates pit defects on the epitaxial layer surface while maintaining the crystal quality of the epitaxial layer.

[0039] Silicon carbide epitaxial growth can be performed using known growth processes, including substrate cleaning, etching, and the growth of buffer and epitaxial layers. For example, after standard cleaning, the silicon carbide substrate is placed on a pedestal (i.e., a small disk for supporting the substrate) in the reaction chamber. The reaction chamber is evacuated to a vacuum, then hydrogen gas is introduced, and the temperature is raised. For example, argon gas is used to float the disk, keeping it in a floating state, while the substrate is etched. Then, growth sources and doping sources are introduced, and the buffer and epitaxial layers are grown sequentially under suitable growth conditions.

[0040] The growth source includes carbon and silicon sources, and common silicon carbide growth materials can be used. The silicon source includes, but is not limited to, TCS (SiHCl3), and the carbon source includes, but is not limited to, ethylene (C2H4). The doping source can be common silicon carbide growth materials, including, but not limited to, high-purity nitrogen (N2) or trimethylaluminum.

[0041] To reduce pit defects during epitaxial growth, based on the formation mechanism of pit defects, optimization of epitaxial process parameters can be achieved by lowering the growth temperature or the C / Si ratio, thereby reducing pit defects. For example, epitaxial growth conditions include: hydrogen flow rate of 80 slm–200 slm, air flotation flow rate of 500 scmm–1000 scmm, reaction chamber temperature of 1600℃–1650℃, and reaction chamber pressure of 150 mbar–250 mbar. The epitaxial thickness is greater than the target thickness to allow for removal in subsequent etching stages.

[0042] After epitaxial growth is completed, the growth source and doping source are shut off. The substrate air flotation flow rate is increased, the reaction chamber temperature is raised, the reaction chamber pressure is lowered, and the hydrogen flow rate is increased before entering the etching stage. During the etching stage, hydrogen chloride gas is introduced discontinuously. Specifically, hydrogen gas is continuously introduced into the reaction chamber, and within 2–3 minutes, the hydrogen flow rate is increased from 80–200 slm during the epitaxial stage to 250–350 slm. Simultaneously, the small disk air flotation (argon) flow rate is increased from 500–1000 scmm during the epitaxial stage to 2000–2500 sccm; the pressure is reduced from 150–250 mbar during the epitaxial stage to 30–80 mbar; and the temperature is increased from 1600–1650 °C during the epitaxial stage to 1700–1750 °C. After keeping the above conditions constant, hydrogen chloride gas is introduced. The discontinuity mentioned here refers to the intermittent introduction of hydrogen chloride gas during the etching stage, with at least one introduction period and an interruption period following it. Furthermore, by using one introduction period and one interruption period as a cycle, the etching stage can be similar to a pulse, including multiple consecutive cycles, forming a periodic pulse etching environment. The hydrogen chloride flow rate during the introduction period is 1500–2000 sccm, lasting 10 s–1 min; the hydrogen chloride flow rate during the interruption period is 0, lasting 30 s–2 min. The number of cycles can be adjusted according to the actual etching thickness requirements to precisely control the thickness of the removed epitaxial layer, ultimately achieving the target thickness of the epitaxial wafer. Based on the goal of effectively eliminating pits defects at a depth of 3–20 nm, the number of cycles can be, for example, 3–8, removing 0.1–0.2 μm of epitaxial surface layer.

[0043] In SiC epitaxial processes, SiC exhibits very stable physicochemical properties, resulting in a slow decomposition rate. However, it decomposes more readily under high temperature and low pressure conditions. Consequently, compared to the epitaxial stage, the etching stage increases the temperature and decreases the pressure within the reaction chamber. Since H2 reacts with C to readily generate CxHx, and HCl reacts with Si to produce SiCl, both of which accelerate SiC decomposition, the etching effect of introducing H2+HCl is more significant. During the HCl introduction stage, the strong etching effect rapidly disrupts the Si-C bond lattice structure on the epitaxial wafer surface, making the epitaxial layer surface easier to etch. However, this strong etching effect may damage the lattice structure of the epitaxial layer surface, leading to dislocations or sub-damage. Therefore, intermittent HCl introduction helps to achieve micro-etching of the epitaxial layer surface without creating new dislocations or damage by alternating small amounts of HCl to disrupt the surface structure and subsequently assisting H2 in selective etching. Furthermore, the introduction of HCl reduces the probability of "silicon droplet" formation on the epitaxial wafer surface, improving the quality of the epitaxial layer.

[0044] During the etching stage, increasing the air flotation flow rate of the small disk to 1.5-2 times that of conventional processes accelerates the rotation speed of the epitaxial wafer on the small disk, which is beneficial for uniform etching of the epitaxial wafer surface. Overall, this process is similar to chemical mechanical polishing of the epitaxial wafer surface. By controlling the etching stage time and etching efficiency, a certain thickness of epitaxial layer is reduced on the epitaxial wafer surface, thereby reducing pit defects on the epitaxial wafer surface and maintaining excellent surface roughness.

[0045] After etching is complete, the hydrogen chloride source is shut off. Within 5-15 minutes, the temperature of the reaction chamber is lowered to 1000-1200°C. Simultaneously, the gas flow rate of the substrate is reduced to 50-150 sccm, and the hydrogen flow rate is reduced to 50-150 slm. The pressure in the reaction chamber is increased to atmospheric pressure, and the temperature is lowered to room temperature in a hydrogen atmosphere. Then, the hydrogen and gas flow rates of the small disk are shut off. Inert gas is introduced to displace the hydrogen in the reaction chamber, and the chamber is evacuated and maintained for 3-10 minutes. Afterward, inert gas is introduced into the reaction chamber to atmospheric pressure, the chamber is opened, and the epitaxial wafer is removed. The inert gas referred to here is the gas corresponding to a Group 0 element in the periodic table, such as argon.

[0046] Example 1

[0047] The silicon carbide thin film growth method using TCS+ethylene involves the following main parameter changes: Figure 2 As shown, the steps are explained in detail below.

[0048] Step 1: Select an 8-inch silicon carbide substrate with a 4° offset in the <11-20> direction, perform standard cleaning, and place the substrate on a small tray in the reaction chamber.

[0049] Step 2: Evacuate the reaction chamber to a vacuum, then introduce hydrogen gas, maintaining a hydrogen flow rate of 200 slm and a reaction chamber pressure of 200 mbar. Raise the reaction chamber temperature from room temperature to 1650°C, with the small disk argon flow rate at 800 slm, and maintain this temperature for 10 minutes. Change the hydrogen flow rate to 200 slm, maintain the temperature at 1650°C, and after the pressure stabilizes, introduce TCS (SiHCl3) gas + ethylene (C2H4) gas into the reaction chamber. Set the TCS flow rate to 40 slm, C / Si ratio to 1, high-purity nitrogen as the doping source, a growth thickness of ~0.5 μm, and a doping concentration of ~1E18 / cm². 3 A buffer layer was used; temperature, pressure, and hydrogen flow rate were kept constant, and the TCS flow rate was controlled at 280 slm, C / Si ratio at 1.2, and doping concentration at 1E16 / cm³. 3 An epitaxial layer is grown to the target thickness +0.1µm with the target doping concentration.

[0050] Step 3: After the epitaxial layer growth is complete, shut off the growth source gas and doping source. Continuously purge hydrogen into the reaction chamber, and within 2 minutes, increase the hydrogen flow rate to 300 slm, while simultaneously increasing the flow rate of the small disk air flotation (argon) to 2000 sccm; reduce the pressure to 50 mbar; and raise the temperature to 1700℃ and maintain it constant. Subsequently, intermittently purge hydrogen chloride (HCl) in a pulse-like manner, with an HCl flow rate of 1500 sccm. HCl is purged instantaneously and maintained constant for 30 seconds (the purging period), then the HCl is shut off. After 1 minute (the interruption period), HCl is purged instantaneously again and maintained constant for 30 seconds (the purging period). This process is repeated four times to create a periodic pulse etching environment for etching the epitaxial layer surface.

[0051] Step 4: Turn off the HCl source, and within 10 minutes, reduce the temperature to 1000-1200℃, while reducing the gas flotation flow rate of the small disk to 100 sccm and the hydrogen flow rate to 100 slm. Increase the pressure in the reaction chamber to atmospheric pressure, and then reduce the temperature of the reaction chamber to room temperature in a hydrogen atmosphere.

[0052] Step 5: Turn off the hydrogen flow and the small disk air flotation flow, introduce argon to replace the hydrogen in the reaction chamber, evacuate the reaction chamber and maintain it for 5 minutes, then fill the reaction chamber with argon to atmospheric pressure, open the reaction chamber and take out the epitaxial wafer.

[0053] Three 8-inch epitaxial wafers were grown consecutively using the above growth method. Their pit defect distribution (SICA inspection) is shown below. Figure 3 As shown, the surface roughness is as follows Figure 4 As shown.

[0054] Comparative Example 1

[0055] Comparative Example 1 uses a silicon carbide epitaxial growth method based on TCS and ethylene, with the following steps:

[0056] Steps 1 and 2 are the same as in Example 1, growing an epitaxial layer to the target thickness and doping concentration.

[0057] Step 3: After the epitaxial layer growth is completed, turn off the growth source gas and doping source. Within 10 minutes, reduce the temperature to 1000-1200℃, reduce the gas flow rate of the small disk to 100 sccm, reduce the hydrogen flow rate to 100 slm, increase the pressure of the reaction chamber to atmospheric pressure, and then reduce the temperature of the reaction chamber to room temperature in a hydrogen atmosphere.

[0058] Step 4: Turn off the hydrogen flow and the small disk air flotation flow, introduce argon to replace the hydrogen in the reaction chamber, evacuate the reaction chamber and maintain it for 5 minutes, then fill the reaction chamber with argon to atmospheric pressure, open the reaction chamber and take out the epitaxial wafer.

[0059] The pits defect distribution map (SICA inspection) of an 8-inch epitaxial wafer grown using the above method is shown below. Figure 5 As shown.

[0060] Depend on Figure 5 As can be seen, the epitaxial wafer in Comparative Example 1, which did not undergo the etching stage after epitaxial layer growth, had 656 pit defects. Figure 3 As can be seen, in Example 1, the etching process after epitaxial layer growth resulted in 20, 26, and 26 pit defects on three consecutive epitaxial wafers, respectively, all less than 30. Converted to distribution density, the pit defect distribution density is 0.068 pcs / cm². 2 0.088pcs / cm 2 0.088pcs / cm 2 All were less than 0.1 pcs / cm 2 This significantly reduces surface defects in silicon carbide epitaxial films.

[0061] Depend on Figure 4 As can be seen, in Example 1, through the etching process after epitaxial layer growth, the surface roughness Rq of three consecutive epitaxial wafers are 0.179nm, 0.172nm and 0.149nm respectively, all less than 0.2nm, and the surface of the epitaxial wafers maintains excellent roughness.

[0062] Example 2

[0063] The silicon carbide thin film growth method using TCS+ethylene comprises the following steps:

[0064] Steps 1 and 2 are the same as in Example 1. An epitaxial layer is grown to the target thickness + 0.15 μm with the target doping concentration.

[0065] Step 3: After the epitaxial layer growth is complete, shut off the growth source gas and doping source. Continuously purge hydrogen into the reaction chamber, and within 2 minutes, increase the hydrogen flow rate to 300 slm, while simultaneously increasing the flow rate of the small disk air flotation (argon) to 2000 sccm; reduce the pressure to 60 mbar; and raise the temperature to 1720℃ and maintain it constant. Subsequently, intermittently purge hydrogen chloride (HCl) in a pulse-like manner, with an HCl flow rate of 1500 sccm. HCl is purged instantaneously and maintained constant for 1 minute (the purging period), then shut off for 1 minute (the interruption period), followed by another instantaneous HCl purging and maintenance for 1 minute (the purging period). This process is repeated five times to create a periodic pulse etching environment for etching the epitaxial layer surface.

[0066] Steps 4 and 5 are the same as in Example 1.

[0067] Three 8-inch epitaxial wafers were grown consecutively using the above growth method. Their pit defect distribution (SICA inspection) is shown below. Figure 6 As shown in the figure, in Example 2, the etching process after epitaxial layer growth resulted in 25, 19, and 23 pit defects on three consecutive epitaxial wafers, respectively. Converted to distribution density, the pit defect distribution density is 0.084 pcs / cm². 2 0.064pcs / cm 2 0.078pcs / cm 2 This significantly reduces surface defects in silicon carbide epitaxial films.

[0068] Depend on Figure 7 As can be seen, in Example 2, through the etching process after epitaxial layer growth, the surface roughness Rq of three consecutive epitaxial wafers are 0.146nm, 0.151nm and 0.148nm, respectively, all less than 0.2nm, and the surface of the epitaxial wafers maintains excellent roughness.

[0069] Example 3

[0070] The silicon carbide thin film growth method using TCS+ethylene comprises the following steps:

[0071] Steps 1 and 2 are the same as in Example 1. An epitaxial layer is grown to the target thickness + 0.10 μm with the target doping concentration.

[0072] Step 3: After the epitaxial layer growth is complete, shut off the growth source gas and doping source. Continuously purge hydrogen into the reaction chamber, and within 2 minutes, increase the hydrogen flow rate to 300 slm, while simultaneously increasing the flow rate of the small disk air flotation (argon) to 2500 sccm; reduce the pressure to 80 mbar; and raise the temperature to 1750℃ and maintain it constant. Subsequently, intermittently purge hydrogen chloride (HCl) in a pulse-like manner, with an HCl flow rate of 1500 sccm. HCl is purged instantaneously and maintained constant for 10 seconds (the purging period), then shut off, and after 30 seconds (the interruption period), purge again instantaneously and maintain constant flow for 10 seconds (the purging period). This process is repeated for three cycles to create a periodic pulse etching environment for etching the epitaxial layer surface.

[0073] Steps 4 and 5 are the same as in Example 1.

[0074] Three 8-inch epitaxial wafers were grown consecutively using the above growth method. Their pit defect distribution (SICA inspection) is shown below. Figure 8 As shown in the figure, in Example 3, the etching process after epitaxial layer growth resulted in 25, 17, and 26 pit defects on three consecutive epitaxial wafers, respectively. Converted to a distribution density, the pit defect density is 0.085 pcs / cm². 2 0.058pcs / cm 2 0.088pcs / cm 2 This significantly reduces surface defects in silicon carbide epitaxial films.

[0075] Depend on Figure 9 As can be seen, in Example 3, through the etching process after epitaxial layer growth, the surface roughness Rq of three consecutive epitaxial wafers are 0.148nm, 0.153nm and 0.155nm, respectively, all less than 0.2nm, and the surface of the epitaxial wafers maintains excellent roughness.

[0076] Example 4

[0077] The silicon carbide thin film growth method using TCS+ethylene comprises the following steps:

[0078] Steps 1 and 2 are the same as in Example 1. An epitaxial layer is grown to the target thickness + 0.12 μm with the target doping concentration.

[0079] Step 3: After the epitaxial layer growth is complete, shut off the growth source gas and doping source. Continuously purge hydrogen into the reaction chamber, and within 2 minutes, increase the hydrogen flow rate to 350 slm, while simultaneously increasing the flow rate of the small disk air flotation (argon) to 2000 sccm; reduce the pressure to 40 mbar; and raise the temperature to 1700℃ and maintain it constant. Subsequently, intermittently purge hydrogen chloride (HCl) in a pulse-like manner, with an HCl flow rate of 1600 sccm. HCl is purged instantaneously and maintained constant for 1 minute (the purging period), then the HCl is shut off for 2 minutes (the interruption period), followed by another instantaneous HCl purging and maintenance of 1 minute (the purging period). This process is repeated four times to create a periodic pulse etching environment for etching the epitaxial layer surface.

[0080] Steps 4 and 5 are the same as in Example 1.

[0081] Three 8-inch epitaxial wafers were grown consecutively using the above growth method. Their pit defect distribution (SICA inspection) is shown below. Figure 10 As shown in the figure, in Example 4, the etching process after epitaxial layer growth resulted in 15, 17, and 24 pit defects on three consecutive epitaxial wafers, respectively. Converted to a distribution density, the pit defect density is 0.051 pcs / cm². 2 0.058pcs / cm 2 0.081pcs / cm 2 This significantly reduces surface defects in silicon carbide epitaxial films.

[0082] Depend on Figure 11 As can be seen, in Example 4, through the etching process after epitaxial layer growth, the surface roughness Rq of three consecutive epitaxial wafers are 0.158nm, 0.152nm and 0.153nm, respectively, all less than 0.2nm, and the surface of the epitaxial wafers maintains excellent roughness.

[0083] Example 5

[0084] The silicon carbide thin film growth method using TCS+ethylene comprises the following steps:

[0085] Steps 1 and 2 are the same as in Example 1. An epitaxial layer is grown to the target thickness + 0.10 μm with the target doping concentration.

[0086] Step 3: After the epitaxial layer growth is complete, shut off the growth source gas and doping source. Continuously purge hydrogen into the reaction chamber, and within 2 minutes, increase the hydrogen flow rate to 250 slm, while simultaneously increasing the flow rate of the small disk air flotation (argon) to 2000 sccm; reduce the pressure to 30 mbar; and raise the temperature to 1750℃ and maintain it constant. Subsequently, intermittently purge hydrogen chloride (HCl) in a pulse-like manner, with an HCl flow rate of 2000 sccm. HCl is purged instantaneously and maintained constant for 30 seconds (the purging period), then shut off, and after 1 minute (the interruption period), purge again instantaneously and maintain constant for 30 seconds (the purging period). This process is repeated for two cycles to create a periodic pulse etching environment for etching the epitaxial layer surface.

[0087] Steps 4 and 5 are the same as in Example 1.

[0088] Three 8-inch epitaxial wafers were grown consecutively using the above growth method. Their pit defect distribution (SICA inspection) is shown below. Figure 12 As shown in the figure, in Example 5, the etching process after epitaxial layer growth resulted in 21, 15, and 23 pit defects on three consecutive epitaxial wafers, respectively. Converted to distribution density, the pit defect distribution density is 0.071 pcs / cm². 2 0.051 pcs / cm 2 0.071 pcs / cm 2 This significantly reduces surface defects in silicon carbide epitaxial films.

[0089] Depend on Figure 13 As can be seen, in Example 5, through the etching process after epitaxial layer growth, the surface roughness Rq of three consecutive epitaxial wafers are 0.136nm, 0.157nm and 0.158nm, respectively, all less than 0.2nm, and the surface of the epitaxial wafers maintains excellent roughness.

[0090] The above embodiments are only used to further illustrate a growth method for reducing pit defects on the surface of silicon carbide epitaxial layer according to the present invention. However, the present invention is not limited to the embodiments. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention shall fall within the protection scope of the technical solution of the present invention.

Claims

1. A growth method for reducing pit defects on the surface of silicon carbide epitaxial wafers, characterized in that, Includes the following steps: 1) Silicon carbide epitaxial growth is completed in the reaction chamber, and the epitaxial thickness is greater than the target thickness; during epitaxial growth, the substrate is placed on the base of the reaction chamber, and the base is kept in an air-floating state; 2) After the epitaxial growth is completed, the growth source is turned off, the air flotation flow rate of the substrate is increased, the temperature in the reaction chamber is increased, the pressure in the reaction chamber is decreased, and the hydrogen flow rate is increased before entering the etching stage. The etching stage involves discontinuous introduction of hydrogen chloride gas, including at least one introduction period and an interruption period following the introduction period; one introduction period and one interruption period constitute one cycle, and the etching stage includes multiple cycles; the hydrogen chloride flow rate during the introduction period is 1500~2000 sccm, and the duration is 10s~1min; the hydrogen chloride flow rate during the interruption period is 0, and the duration is 30s~2min; the etching stage etches the epitaxial layer to the target thickness; 3) After etching is completed, turn off the hydrogen chloride source, reduce the air flotation flow rate of the substrate and the hydrogen flow rate, increase the pressure of the reaction chamber to atmospheric pressure, and reduce the temperature of the reaction chamber to room temperature in a hydrogen atmosphere. 4) Turn off the hydrogen flow and flotation flow, fill the reaction chamber with inert gas, open the reaction chamber and take out the epitaxial wafer.

2. The growth method for reducing pit defects on the surface of silicon carbide epitaxial wafers according to claim 1, characterized in that: In step 2), the temperature in the reaction chamber of the etching stage is 1700℃~1750℃, and the pressure in the reaction chamber is 30 mbar~80 mbar.

3. The growth method for reducing pit defects on the surface of silicon carbide epitaxial wafers according to claim 1, characterized in that: In step 2), the hydrogen flow rate during the etching stage is 250 slm to 350 slm.

4. The growth method for reducing pit defects on the surface of silicon carbide epitaxial wafers according to claim 1, characterized in that: In step 2), the air flotation flow rate during the etching stage is 2000 sccm to 2500 sccm.

5. The growth method for reducing pit defects on the surface of silicon carbide epitaxial wafers according to claim 1, characterized in that: The thickness of the surface layer removed during the etching stage is 0.1 μm to 0.2 μm.

6. The growth method for reducing pit defects on the surface of silicon carbide epitaxial wafers according to claim 1, characterized in that: The conditions for epitaxial growth described in step 1) include: hydrogen flow rate of 80 slm~200 slm, air flotation flow rate of 500 sccm~1000 sccm, reaction chamber temperature of 1600℃~1650℃, and reaction chamber pressure of 150 mbar~250 mbar.

7. The growth method for reducing pit defects on the surface of silicon carbide epitaxial wafers according to claim 1, characterized in that: In step 3), the temperature of the reaction chamber is reduced to 1000℃~1200℃ within 5min~15min, while the air flotation flow rate of the base is reduced to 50 sccm~150 sccm, the hydrogen flow rate is reduced to 50 slm~150 slm, the pressure of the reaction chamber is increased to atmospheric pressure, and then the temperature of the reaction chamber is reduced to room temperature.

8. A silicon carbide epitaxial wafer, characterized in that: The silicon carbide epitaxial wafer is obtained by the growth method for reducing pit defects on the surface of the silicon carbide epitaxial wafer as described in any one of claims 1 to 7, wherein the distribution density of pit defects on the surface of the epitaxial wafer is <0.1 pcs / cm². 2 .

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