A method for effectively reducing triangle defects in silicon carbide epitaxial layers

Abstract

The present invention discloses a method for effectively reducing triangular defects in silicon carbide epitaxial layers, belonging to the field of semiconductor processing. The method comprises the following steps: growing a low-speed, low-carbon-to-silicon ratio buffer layer on a silicon carbide substrate using a first silicon source flow rate and a first carbon source flow rate; maintaining the silicon source flow rate constant, increasing the carbon source flow rate according to an S-shaped curve with respect to time to reach a second carbon source flow rate, during which a carbon-to-silicon ratio transition layer is formed; growing a low-speed, high-carbon-to-silicon ratio buffer layer using the first silicon source flow rate and the second carbon source flow rate; increasing the transition from the first silicon source flow rate to the second silicon source flow rate, and simultaneously increasing the transition from the second carbon source flow rate to the third carbon source flow rate, while maintaining the carbon-to-silicon ratio constant, to form a source flow transition layer; and growing a high-speed epitaxial layer using the second silicon source flow rate and the third carbon source flow rate. The method separates the carbon-to-silicon ratio change process from the growth rate change process, and achieves a smooth transition near the starting point and end point of the carbon-to-silicon ratio change process, which is conducive to reducing triangular defects.

Description

Technical Field

[0001] The invention relates to a method for effectively reducing triangle defects in a silicon carbide epitaxial layer, and belongs to the field of semiconductor processing. Background Art

[0002] Wide-bandgap semiconductor silicon carbide (SiC) is a high-performance semiconductor material with outstanding advantages, including a wide bandgap, high thermal conductivity, high breakdown field strength, high electron saturation drift rate, high temperature resistance, and radiation resistance. In recent years, it has been widely used in key fields such as new energy vehicles, photovoltaic power generation, 5G communications, smart grids, and national defense. Chemical vapor deposition is commonly used to grow SiC epitaxial layers and fabricate SiC power electronic devices. However, defects in epitaxial layers hinder product yield, increasing production costs.

[0003] Defects in silicon carbide epitaxial layers primarily arise from the extension of defects in the substrate (such as basal plane dislocations, screw dislocations, and edge dislocations), as well as defects formed during the epitaxial growth process (such as triangle defects, carrot defects, dropouts, and step clustering). Triangle defects are the most common and fatal epitaxial defects, easily leading to leakage failure in silicon carbide devices and reducing product yield. The industry typically incorporates a growth buffer layer between the substrate and epitaxial layer to effectively block substrate defects. Another function of the buffer layer is to reduce lattice stress caused by the lattice mismatch between the epitaxial layer and the substrate, thereby minimizing the formation of defect nucleation sites. The carbon-to-silicon ratio used in the buffer layer is generally lower than that used in the epitaxial layer. This lower carbon-to-silicon ratio helps reduce triangle defect nucleation sites and creates a well-defined surface step morphology. During the transition from the buffer layer to the epitaxial layer, the carbon-to-silicon ratio must be adjusted from that used in the buffer layer to that used in the epitaxial layer. The change of carbon-silicon ratio will cause the change of chemical potential, which in turn affects the change of adsorbed monomer type at the growth interface under different epitaxial rates, resulting in an increase in the nucleation probability of epitaxial defects such as triangle defects. [1] It can be seen that the change process of carbon-silicon ratio can easily produce defect nucleation points, which in turn induce the generation of epitaxial defects such as triangle defects. Summary of the Invention

[0004] In order to overcome the shortcomings of the prior art, the present invention provides a method for effectively reducing triangular defects in a silicon carbide epitaxial layer, which effectively reduces the triangular defect density by improving the buffer layer structure and the carbon-silicon ratio transition mode.

[0005] The technical solution adopted by the present invention to solve its technical problem is:

[0006] A method for effectively reducing triangular defects in a silicon carbide epitaxial layer, applied to a chemical vapor deposition process, comprises the following steps:

[0007] growing a low-speed, low-carbon-to-silicon ratio buffer layer on a silicon carbide substrate at a first silicon source flow rate and a first carbon source flow rate;

[0008] Keeping the silicon source flow rate constant, gradually increasing the flow rate of the first carbon source to the flow rate of the second carbon source, during which a carbon-silicon ratio transition layer is formed; the transition mode is that the carbon-silicon ratio is an S-shaped function with respect to time;

[0009] growing a low-speed high-carbon-to-silicon ratio buffer layer at the first silicon source flow rate and the second carbon source flow rate;

[0010] increasing the flow rate of the first silicon source to transition to the second silicon source flow rate, and simultaneously increasing the flow rate of the second carbon source to transition to the third carbon source flow rate, while keeping the carbon-silicon ratio unchanged, to form a source flow transition layer;

[0011] A high-speed epitaxial layer is grown with the second silicon source flow rate and the third carbon source flow rate.

[0012] The method provided by the present application for effectively reducing triangular defects in silicon carbide epitaxial layers, on the one hand, separates the carbon-silicon ratio change process and the growth rate change process, that is, a carbon-silicon ratio transition layer and a source flow transition layer are set, which is conducive to reducing triangular defects, and a buffer process of a stable growth atmosphere is added between the two processes, that is, a low-speed high carbon-silicon ratio buffer layer is grown to further reduce the formation of triangular defects; on the other hand, the change process of the carbon-silicon ratio is an S-shaped function of time. The applicant found that if the carbon-silicon ratio can achieve a smooth transition near the starting point and end point of the change process, the epitaxial defect density will be reduced.

[0013] The sigmoid function is a type of function that is similar in shape to the letter S, including the logistic function, the hyperbolic tangent function, the Goodman function, the error function, etc. Preferably, the form of the sigmoid function is:

[0014] Carbon-silicon ratio = Δr / (1+exp(-k*(t-t_mid) / Δt))+r1, formula 1;

[0015] Wherein, Δr=r2-r1, r1 is the carbon-to-silicon ratio of the first carbon source flow rate to the first silicon source flow rate, r2 is the carbon-to-silicon ratio of the second carbon source flow rate to the first silicon source flow rate; the independent variable t represents time, in minutes; t_mid=(t1+t2) / 2, Δt=t2-t1, t1 is the time point when the growth of the carbon-to-silicon ratio transition layer starts, and t2 is the time point when the growth of the low-speed high carbon-to-silicon ratio buffer layer starts, both in minutes; k is the adjustment parameter for controlling the steepness of the S-shaped function.

[0016] Furthermore, the r1 is 0.8, the r2 is 1.2, and the Δt is 2 min.

[0017] Since the change in chemical potential caused by the change in the carbon-silicon ratio will increase the nucleation probability of triangular defects, a long change time of the carbon-silicon ratio will lead to an increase in triangular defects. Controlling Δt, the carbon-silicon ratio change time, to 2 minutes is beneficial to reducing the total duration of the carbon-silicon ratio change, while ensuring a smooth transition of C / Si near the starting and end points of the C / Si change process. This will help reduce triangular defects and, to a certain extent, reduce the time consumed before growing the high-speed epitaxial layer.

[0018] Furthermore, the value range of k is 7 to 14.

[0019] The k value plays a crucial role in regulating the duration of the smooth transition portion of Equation 1, as well as the steepness of the curve in the middle section of the function. The middle section is the portion between the smooth transitions near the start and end of the carbon-silicon ratio change. A k value between 7 and 14 ensures sufficient time for a smooth transition near the start and end of the carbon-silicon ratio change, while also minimizing the drastic change in the carbon-silicon ratio in the middle section of Equation 1.

[0020] Furthermore, the ratio of nitrogen flow rate to silicon source flow rate is kept constant throughout the entire process from growing the low-speed and low-carbon-to-silicon ratio buffer layer to growing the high-speed epitaxial layer.

[0021] Carbon atoms compete with doped nitrogen atoms for position. During the growth of the carbon-to-silicon ratio transition layer, the present invention maintains the nitrogen and silicon source flow rates constant, adjusting only the carbon source flow rate. This reduces factors other than the carbon source flow rate that affect the actual deposited carbon-to-silicon ratio, ensuring that the actual deposited carbon-to-silicon ratio smoothly transitions between the starting and ending points of the carbon-to-silicon ratio change according to an S-shaped function. Furthermore, during the growth of the source flow transition layer, the nitrogen, silicon, and carbon source flow rates are simultaneously and proportionally increased, ensuring that the actual deposited carbon-to-silicon ratio does not significantly change compared to the low-speed, high-carbon-to-silicon ratio buffer layer, thereby reducing triangular defects.

[0022] Furthermore, the silicon source is trichlorosilane, and the carbon source is ethylene.

[0023] Furthermore, in the steps of increasing the flow rate of the first silicon source to transition to the second silicon source flow rate, and simultaneously increasing the flow rate of the second carbon source to transition to the third carbon source flow rate, the transition mode is a linear increase.

[0024] When trichlorosilane is selected as the silicon source, it is beneficial to avoid the generation of silicon droplets from high-concentration silicon sources. When growing the source flow transition layer, a linear increase method is used, which is also not easy to generate silicon droplets, which is beneficial to reducing the time consumed before growing the high-speed epitaxial layer.

[0025] Furthermore, the second silicon source flow rate is 10 times that of the first silicon source flow rate, and the third carbon source flow rate is 10 times that of the second carbon source flow rate. Since silicon droplets are less likely to be generated when trichlorosilane is used as the silicon source, the growth rate of the high-speed epitaxial layer can be greatly increased while ensuring product quality, thereby improving production efficiency.

[0026] Furthermore, before the step of growing a low-speed, low-carbon-to-silicon ratio buffer layer on the silicon carbide substrate at a first silicon source flow rate and a first carbon source flow rate, the method further includes the following steps:

[0027] A 4H-SiC substrate with a 4° off-angle was selected, and after cleaning the surface, it was placed in the reaction chamber.

[0028] Evacuate the chamber and heat it to 1400°C, the substrate etching temperature, at a rate not exceeding 20°C / min.

[0029] Set the hydrogen flow rate to 100 SLM, the HCl flow rate to 4 SLM, the reaction chamber pressure to 100 mbar, the temperature to 1410°C, and the etching time to 5 min;

[0030] Stop the HCl flow, maintain the hydrogen flow rate at 100 SLM, the reaction chamber pressure at 100 mbar, and raise the temperature to 1600°C;

[0031] After the step of growing a high-speed epitaxial layer with the second silicon source flow rate and the third carbon source flow rate, the method further includes the following steps:

[0032] Cool down at a rate not exceeding 15°C / min. When the temperature of the reaction chamber is lower than 500°C, take out the epitaxial wafer.

[0033] Furthermore, the thickness range of the low-speed low carbon-silicon ratio buffer layer is 0.3μm-2μm, the thickness range of the carbon-silicon ratio transition layer is 0.2μm-1μm, the thickness range of the low-speed high carbon-silicon ratio buffer layer is 0.3μm-2μm, and the thickness range of the source flow transition layer is 0.5μm-4μm.

[0034] The minimum thickness of the carbon-silicon ratio transition layer is limited by the shortest time required for the carbon-silicon ratio change process. When the carbon-silicon ratio change causes a change in chemical potential, the nucleation probability of triangular defects will increase. Therefore, the thickness of the carbon-silicon ratio transition layer should not be too large, and the carbon-silicon ratio change process should be completed in the shortest possible time. The minimum thickness of the source flow transition layer is limited by the shortest time required for the growth rate increase process. Prolonging the transition time appropriately can improve the quality of the layer, but it will reduce production efficiency. Therefore, the source flow transition layer should be less than 4μm. The minimum thickness of the low-speed low-carbon-silicon ratio buffer layer and the low-speed high-carbon-silicon ratio buffer layer is the minimum thickness at which they can play a buffering role. Excessive thickness of the buffer layer will also reduce production efficiency.

[0035] The beneficial effects of the present invention are as follows: in the method of the present invention for effectively reducing triangular defects in a silicon carbide epitaxial layer, the carbon-silicon ratio change process and the growth rate change process are separated, which is beneficial to reducing triangular defects, and a buffer process of a stable growth atmosphere is added between the two processes to further reduce the formation of triangular defects; in addition, the change process of the carbon-silicon ratio is made an S-shaped function with respect to time, so that the carbon-silicon ratio can achieve a smooth transition near the starting point and end point of the change process, which is beneficial to reducing the epitaxial defect density.

[0036] Other features and advantages of the present application will be described in the following description, and in part will become apparent from the description, or will be understood by practicing the present application. The purpose and other advantages of the present application can be realized and obtained through the written description. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 This is a schematic structural diagram of an epitaxial wafer produced by a method for effectively reducing triangular defects in a silicon carbide epitaxial layer provided in an embodiment of the present application.

[0038] Figure 2 This is the monitoring result of detecting the number of triangular defects on the silicon carbide epitaxial wafer obtained in Example 1 using a Lasertec defect analyzer.

[0039] Figure 3 It is an image of the curve obtained by formula 4 provided in the examples of this application.

[0040] Explanation of reference numerals: 10, substrate; 11, low-speed, low-carbon-silicon ratio buffer layer; 12, carbon-silicon ratio transition layer; 13, low-speed, high-carbon-silicon ratio buffer layer; 14, source flow transition layer; 15, high-speed epitaxial layer. DETAILED DESCRIPTION

[0041] The applicants discovered that if the carbon-silicon ratio can achieve a smooth transition near the start and end of the change process, the epitaxial defect density can be further reduced. In other words, the first-order derivative of the carbon-silicon ratio with time gradually increases near the start and decreases near the end, which is more conducive to reducing the epitaxial defect density than a discontinuous change in the first-order derivative of the carbon-silicon ratio with time. The applicants believe that near the start and end of the carbon-silicon ratio change process, the actual deposited carbon-silicon ratio is very sensitive to changes in chemical potential, which leads to the rapid formation of epitaxial defect nucleation sites such as triangular defects during these two periods when the chemical potential changes significantly.

[0042] Furthermore, the industry's commonly used linear transition method for source flow rate combines the carbon-silicon ratio change process and the rate switching process into a single process, which can easily induce epitaxial defects such as triangle defects. This is because when the rate or source flow rate increases, the effect of the carbon-silicon ratio change on the chemical potential change becomes very significant, which in turn increases the probability of defect nucleation points forming.

[0043] Reference Figure 1 To address the above problems, the present application provides a method for effectively reducing triangular defects in a silicon carbide epitaxial layer, which is applied to a chemical vapor deposition process and includes the following steps:

[0044] S1: growing a low-speed, low-carbon-to-silicon ratio buffer layer 11 on a silicon carbide substrate at a first silicon source flow rate and a first carbon source flow rate.

[0045] S2: Keeping the silicon source flow constant, gradually increase the carbon source flow from the first to the second carbon source flow, during which a carbon-silicon ratio transition layer 12 is formed. In this transition mode, the carbon-silicon ratio is an S-shaped function with respect to time.

[0046] S3: growing a low-speed high-carbon-to-silicon ratio buffer layer 13 at a first silicon source flow rate and a second carbon source flow rate.

[0047] S4: increasing the flow rate from the first silicon source to the second silicon source, and at the same time increasing the flow rate from the second carbon source to the third carbon source, while keeping the carbon-silicon ratio unchanged, to form a source flow transition layer 14 .

[0048] S5: growing a high-speed epitaxial layer 15 with a second silicon source flow rate and a third carbon source flow rate.

[0049] On the one hand, the embodiments of the present application separate the carbon-silicon ratio change process from the growth rate change process, namely, providing a carbon-silicon ratio transition layer 12 and a source flow rate transition layer 14, which is beneficial for reducing triangular defects. A buffer process for stabilizing the growth atmosphere is added between these two processes, namely, growing a low-speed, high-carbon-silicon ratio buffer layer 13, further reducing the formation of triangular defects. On the other hand, the change in the carbon-silicon ratio is an S-shaped function with respect to time, which allows the carbon-silicon ratio to achieve a smooth transition near the starting and end points of the change process, which is beneficial for reducing the epitaxial defect density. This may be due to the relative lag in the change of the growth atmosphere state on the substrate surface. The carbon-silicon ratio actually deposited on the surface is not completely consistent with the supply gas ratio. For example, if the carbon-silicon ratio is changed linearly, the period of low carbon-silicon ratio at the beginning of the carbon-silicon ratio change is relatively short. The growth atmosphere on the substrate surface lags and fails to change simultaneously with the source gas. After the precursors originally adsorbed on the substrate surface undergo surface reactions, the newly adsorbed precursor components are already carbon-rich, resulting in a large difference and prone to defect formation. In the embodiment of the present application, there is a sufficient period of time in which the carbon-silicon ratio slowly increases, which is beneficial for the growth atmosphere on the substrate surface to keep up with the changes in the gas source, thereby gradually adapting to the carbon-rich atmosphere.

[0050] The sigmoid function is a type of function that is similar in shape to the letter S, including the logistic function, the hyperbolic tangent function, the Goodman function, the error function, etc. Preferably, the form of the sigmoid function is:

[0051] Carbon-silicon ratio = Δr / (1+exp(-k*(t-t_mid) / Δt))+r1, formula 1; that is

[0052] .

[0053] Among them, Δr=r2-r1, r1 is the carbon-silicon ratio of the first carbon source flow rate to the first silicon source flow rate, that is, the carbon-silicon ratio used when growing the low-speed and low-carbon-silicon ratio buffer layer 11; r2 is the carbon-silicon ratio of the second carbon source flow rate to the first silicon source flow rate, that is, the carbon-silicon ratio used when growing the low-speed and high-carbon-silicon ratio buffer layer 13; the independent variable t represents time, and the unit is minute; t_mid=(t1+t2) / 2, Δt=t2-t1, t1 is the time point when the growth of the carbon-silicon ratio transition layer starts, and t2 is the time point when the growth of the low-speed and high-carbon-silicon ratio buffer layer starts, both in minutes. For example, after the substrate is placed, the reaction chamber is started at 0 min, the growth of the carbon-silicon ratio transition layer starts at 77 min, and the growth of the carbon-silicon ratio transition layer ends at 79 min, then t2=79 min, t1=77 min; k is the adjustment parameter for controlling the steepness of the S-type function; e is a natural constant.

[0054] In some embodiments, a low-speed, low-carbon-silicon ratio buffer layer 11 is grown in a silicon-rich atmosphere at a carbon-silicon ratio of 0.8. This lower carbon-silicon ratio helps reduce nucleation sites for triangular defects and forms a good surface step morphology, facilitating the healing of defects on the substrate 10 during their transfer to the low-speed, low-carbon-silicon ratio buffer layer 11. A carbon-silicon ratio of 1.2 is used when growing the high-speed epitaxial layer, and after the carbon-silicon ratio transition layer is grown, the carbon-silicon ratio remains unchanged, i.e., in the S-shaped function, r1 = 0.8 and r2 = 1.2. Because changes in the carbon-silicon ratio cause changes in chemical potential, which increases the nucleation probability of triangular defects, prolonged carbon-silicon ratio changes can lead to an increase in triangular defects. Controlling Δt, the carbon-silicon ratio change time, to 2 minutes, while ensuring a smooth C / Si transition near the start and end of the C / Si change process, helps reduce the total duration of the carbon-silicon ratio change, thereby reducing triangular defects and, to a certain extent, reducing the time consumed before growing the high-speed epitaxial layer. The k value plays an important role in regulating the time taken for the smooth transition part of the function in Formula 1 and the steepness of the curve in the middle section of the function in Formula 1. The so-called middle section is the section between the two smooth transition sections near the starting point and the end point of the carbon-silicon ratio change process. When the k value is 7 to 14, it is ensured that the carbon-silicon ratio has enough time to achieve a smooth transition near the starting point and the end point of the change process, and the carbon-silicon ratio corresponding to the middle section of the function in Formula 1 does not change too drastically. Based on this, as an example, the S-shaped function can be expressed as:

[0055] .

[0056] In the art, nitrogen atoms in nitrogen gas are typically used to perform N-type doping on wafers. These nitrogen atoms compete with carbon atoms for lattice positions, meaning that the N-doped nitrogen atoms occupy carbon vacancies in the 4H-SiC lattice. In the embodiments of the present application, throughout the entire process of growing the low-speed, low-carbon-to-silicon ratio buffer layer 11, the carbon-to-silicon ratio transition layer 12, the low-speed, high-carbon-to-silicon ratio buffer layer 13, the source flow transition layer 14, and the high-speed epitaxial layer 15, the ratio of the nitrogen flow rate to the silicon source flow rate is maintained constant (the actual nitrogen concentration is related to the preset doping concentration; this application does not discuss doping concentration; the only requirement here is that the nitrogen flow rate is always proportional to the silicon source flow rate). During the growth of the carbon-to-silicon ratio transition layer 12, the nitrogen flow rate and the silicon source flow rate are maintained constant, while only the carbon source flow rate is adjusted. This reduces factors other than the carbon source flow rate that affect the actual deposited carbon-to-silicon ratio, thereby ensuring that the actual deposited carbon-to-silicon ratio smoothly transitions between the starting point and the end point of the carbon-to-silicon ratio variation according to an S-shaped function. When growing the source flow transition layer 14, the nitrogen flow, silicon source flow and carbon source flow are increased in equal proportion at the same time, which is beneficial to ensure that the actual deposited carbon-silicon ratio does not change significantly compared with the low-speed high carbon-silicon ratio buffer layer, and is beneficial to reducing triangular defects.

[0057] The applicant discovered that the growth atmosphere is actually unstable just after the carbon-silicon ratio change process ends. If the source flow transition layer 14 is grown directly on the carbon-silicon ratio transition layer 12 at this time, the carbon source flow, nitrogen flow, and silicon source flow will be increased simultaneously when the growth atmosphere is unstable, making the carbon-silicon ratio actually deposited on the surface unstable, which can easily lead to the generation of epitaxial defects. This is partly due to the relative lag in the change of the growth atmosphere state on the substrate surface, and partly due to the limitations of the equipment PID adjustment control process. Therefore, the applicant believes that it is necessary to add a buffer process to stabilize the growth atmosphere between the carbon-silicon ratio change process and the rate switching process, that is, to grow a low-speed, high-carbon-silicon ratio buffer layer 13, which is very beneficial to reducing the epitaxial defect density.

[0058] Preferably, the thickness range of the low-speed low-carbon-silicon ratio buffer layer is 0.3μm-2μm, the thickness range of the carbon-silicon ratio transition layer is 0.2μm-1μm, the thickness range of the low-speed high-carbon-silicon ratio buffer layer is 0.3μm-2μm, and the thickness range of the source flow transition layer is 0.5μm-4μm.

[0059] The minimum thickness of the carbon-silicon ratio transition layer 12 is limited by the shortest time required for the carbon-silicon ratio change process. When the carbon-silicon ratio change causes a change in chemical potential, the nucleation probability of triangular defects will increase. Therefore, the thickness of the carbon-silicon ratio transition layer 12 should not be too large, and the carbon-silicon ratio change process should be completed in the shortest possible time. The minimum thickness of the source flow transition layer 14 is limited by the shortest time required for the growth rate increase process. Prolonging the transition time appropriately can improve the quality of this layer, but it will reduce production efficiency. Therefore, the source flow transition layer 14 is preferably less than 4μm. The minimum thickness of the low-speed low-carbon-silicon ratio buffer layer 11 and the low-speed high-carbon-silicon ratio buffer layer 13 is the minimum thickness at which they can play a buffering role. Excessive thickness of the buffer layer will also reduce production efficiency.

[0060] Example 1

[0061] A method for effectively reducing triangular defects in a silicon carbide epitaxial layer comprises the following steps:

[0062] 1) Cleaning: Select a 4H-SiC substrate with a 4° off-angle and clean the surface of the 4H-SiC substrate using a standard RCA cleaning process.

[0063] 2) Heating to etching temperature: Place the 4H-SiC substrate in the reaction chamber, evacuate the chamber, and heat it to the substrate etching temperature of 1400°C at a heating rate not exceeding 20°C / min.

[0064] 3) Etching: Set the H2 flow rate to 100 SLM, the HCl flow rate to 4 SLM, the reaction chamber pressure to 100 mbar, the temperature to 1410°C, and the etching time to 5 min.

[0065] 4) Raise the temperature to the growth temperature: Turn off the HCl flowmeter, maintain the H2 flow rate at 100 SLM, the reaction chamber pressure at 100 mbar, and raise the temperature to 1600°C.

[0066] 5) Growth of a low-speed, low-carbon-to-silicon ratio buffer layer: Set the TCS (SiHCl3) flow rate to 50 sccm, the C2H4 flow rate to 20 sccm, the carbon-to-silicon ratio to 0.8, the N2 flow rate to 45 sccm, the growth time to 3 min, and the growth thickness to approximately 0.6 μm.

[0067] 6) Growth of carbon-silicon ratio transition layer: Set TCS flow rate to 50sccm, N2 flow rate to 45sccm, and C2H4 flow rate from 20sccm to 30sccm. The transition method is according to formula 4. The function graph of formula 4 is as follows: Figure 3 As shown, the transition time is 2 minutes. During this process, the carbon-silicon ratio gradually transitions from 0.8 to 1.2, and the thickness of the carbon-silicon ratio transition layer is about 0.4 μm.

[0068] .

[0069] 7) Growth of a low-speed high carbon-silicon ratio buffer layer: Set the TCS flow rate to 50 sccm, the C2H4 flow rate to 30 sccm, the carbon-silicon ratio to 1.2, the N2 flow rate to 45 sccm, the growth time to 2.5 min, and the growth thickness to about 0.5 μm.

[0070] 8) Growth source flow transition layer: Set the TCS flow rate to transition from 50 sccm to 500 sccm, the C2H4 flow rate to transition from 30 sccm to 300 sccm, and the N2 flow rate to transition from 45 sccm to 450 sccm. The transition method is a linear function and the transition time is 2 minutes. The carbon-silicon ratio in this process remains unchanged at 1.2, and the growth thickness is about 2 μm.

[0071] 9) Growth of high-speed epitaxial layer: Set the TCS flow rate to 500 sccm, the C2H4 flow rate to 300 sccm, the N2 flow rate to 450 sccm, the growth time to 1 hour, and the growth thickness to about 100 μm.

[0072] 10) Cooling: After the growth is completed, cool down slowly with a cooling rate not exceeding 15°C / min. When the reaction chamber temperature is lower than 500°C, take out the epitaxial wafer.

[0073] like Figure 2 As shown in the figure (due to a problem with the software of the Lasertec defect analyzer, "composite" is still displayed when only one defect is selected. In this experiment, the triangle defect was actually selected). The Lasertec defect analyzer was used to detect the number of triangle defects on the silicon carbide epitaxial wafer. The detection area was 160.7 cm 2 , the number of triangle defects detected is 29.

[0074] Comparative Example 1

[0075] 1) Cleaning: Select a 4H-SiC substrate with a 4° off-angle and clean the surface of the 4H-SiC substrate using a standard RCA cleaning process.

[0076] 2) Heating to etching temperature: Place the 4H-SiC substrate in the reaction chamber, evacuate the chamber, and heat it to the substrate etching temperature of 1400°C at a heating rate not exceeding 20°C / min.

[0077] 3) Etching: Set the H2 flow rate to 100 SLM, the HCl flow rate to 4 SLM, the reaction chamber pressure to 100 mbar, the temperature to 1410°C, and the etching time to 5 min.

[0078] 4) Raise the temperature to the growth temperature: Turn off the HCl flowmeter, maintain the H2 flow rate at 100 SLM, the reaction chamber pressure at 100 mbar, and raise the temperature to 1600°C.

[0079] 5) Growth of a low-speed, low-carbon-to-silicon ratio buffer layer: Set the TCS flow rate to 50 sccm, the C2H4 flow rate to 20 sccm, the carbon-to-silicon ratio to 0.8, the N2 flow rate to 45 sccm, the growth time to 3 min, and the growth thickness to approximately 0.6 μm.

[0080] 6) Growth of transition layer (changing source flow rate and carbon-silicon ratio to target values at the same time): Set the TCS flow rate to transition from 50 sccm to 500 sccm, the C2H4 flow rate to transition from 20 sccm to 300 sccm, and the N2 flow rate to transition from 45 sccm to 450 sccm. The transition method is a linear function with a transition time of 2 min. During this process, the carbon-silicon ratio gradually increases from 0.8 to 1.2, and the growth thickness is about 2 μm.

[0081] 7) Growth of high-speed epitaxial layer: Set the TCS flow rate to 500 sccm, the C2H4 flow rate to 300 sccm, the N2 flow rate to 450 sccm, the growth time to 1 hour, and the growth thickness to about 100 μm.

[0082] 8) Cooling: After the growth is completed, cool down slowly with a cooling rate not exceeding 15°C / min. When the reaction chamber temperature is lower than 500°C, take out the epitaxial wafer.

[0083] The number of triangular defects on a silicon carbide epitaxial wafer was detected using a Lasertec defect analyzer, with an inspection area of 160.7 cm 2 , the number of triangle defects detected is 105.

[0084] Comparative Example 2

[0085] 1) Cleaning: Select a 4H-SiC substrate with a 4° off-angle and clean the surface of the 4H-SiC substrate using a standard RCA cleaning process.

[0086] 2) Heating to etching temperature: Place the 4H-SiC substrate in the reaction chamber, evacuate the chamber, and heat it to the substrate etching temperature of 1400°C at a heating rate not exceeding 20°C / min.

[0087] 3) Etching: Set the H2 flow rate to 100 SLM, the HCl flow rate to 4 SLM, the reaction chamber pressure to 100 mbar, the temperature to 1410°C, and the etching time to 5 min.

[0088] 4) Raise the temperature to the growth temperature: Turn off the HCl flowmeter, maintain the H2 flow rate at 100 SLM, the reaction chamber pressure at 100 mbar, and raise the temperature to 1600°C.

[0089] 5) Growth of a low-speed, low-carbon-to-silicon ratio buffer layer: Set the TCS flow rate to 50 sccm, the C2H4 flow rate to 20 sccm, the carbon-to-silicon ratio to 0.8, the N2 flow rate to 45 sccm, the growth time to 3 min, and the growth thickness to approximately 0.6 μm.

[0090] 6) Growth of a carbon-silicon ratio transition layer: Set the TCS flow rate to 50 sccm, the N2 flow rate to 45 sccm, and the C2H4 flow rate from 20 sccm to 30 sccm. The transition method is a linear function and the transition time is 2 minutes. During this process, the carbon-silicon ratio gradually transitions from 0.8 to 1.2, and the growth thickness is about 0.4 μm.

[0091] 7) Growth source flow transition layer: Set the TCS flow rate to transition from 50 sccm to 500 sccm, the C2H4 flow rate to transition from 30 sccm to 300 sccm, and the N2 flow rate to transition from 45 sccm to 450 sccm. The transition method is a linear function and the transition time is 2 minutes. The carbon-silicon ratio in this process remains unchanged at 1.2, and the growth thickness is about 2 μm.

[0092] 8) Growth of high-speed epitaxial layer: Set the TCS flow rate to 500 sccm, the C2H4 flow rate to 300 sccm, the N2 flow rate to 450 sccm, the growth time to 1 hour, and the growth thickness to about 100 μm.

[0093] 9) Cooling: After the growth is completed, cool down slowly with a cooling rate not exceeding 15°C / min. When the reaction chamber temperature is lower than 500°C, take out the epitaxial wafer.

[0094] The number of triangular defects on a silicon carbide epitaxial wafer was detected using a Lasertec defect analyzer, with an inspection area of 160.7 cm 2 , the number of triangle defects detected is 63.

[0095] Comparative Example 3

[0096] 1) Cleaning: Select a 4H-SiC substrate with a 4° off-angle and clean the surface of the 4H-SiC substrate using a standard RCA cleaning process.

[0097] 2) Heating to etching temperature: Place the 4H-SiC substrate in the reaction chamber, evacuate the chamber, and heat it to the substrate etching temperature of 1400°C at a heating rate not exceeding 20°C / min.

[0098] 3) Etching: Set the H2 flow rate to 100 SLM, the HCl flow rate to 4 SLM, the reaction chamber pressure to 100 mbar, the temperature to 1410°C, and the etching time to 5 min.

[0099] 4) Raise the temperature to the growth temperature: Turn off the HCl flowmeter, maintain the H2 flow rate at 100 SLM, the reaction chamber pressure at 100 mbar, and raise the temperature to 1600°C.

[0100] 5) Growth of a low-speed, low-carbon-to-silicon ratio buffer layer: Set the TCS (SiHCl3) flow rate to 50 sccm, the C2H4 flow rate to 20 sccm, the carbon-to-silicon ratio to 0.8, the N2 flow rate to 45 sccm, the growth time to 3 min, and the growth thickness to approximately 0.6 μm.

[0101] 6) Growth of a carbon-silicon ratio transition layer: Set the TCS flow rate to 50 sccm, the N2 flow rate to 45 sccm, and the C2H4 flow rate from 20 sccm to 30 sccm. The transition method is according to Formula 5, and the transition time is 10 minutes. During this process, the carbon-silicon ratio gradually transitions from 0.8 to 1.2, and the growth thickness is about 2 μm.

[0102] .

[0103] 7) Growth of a low-speed high carbon-silicon ratio buffer layer: Set the TCS flow rate to 50 sccm, the C2H4 flow rate to 30 sccm, the carbon-silicon ratio to 1.2, the N2 flow rate to 45 sccm, the growth time to 2.5 min, and the growth thickness to about 0.5 μm.

[0104] 8) Growth source flow transition layer: Set the TCS flow rate to transition from 50 sccm to 500 sccm, the C2H4 flow rate to transition from 30 sccm to 300 sccm, and the N2 flow rate to transition from 45 sccm to 450 sccm. The transition method is a linear function and the transition time is 2 minutes. The carbon-silicon ratio in this process remains unchanged at 1.2, and the growth thickness is about 2 μm.

[0105] 9) Growth of high-speed epitaxial layer: Set the TCS flow rate to 500 sccm, the C2H4 flow rate to 300 sccm, the N2 flow rate to 450 sccm, the growth time to 1 hour, and the growth thickness to about 100 μm.

[0106] 10) Cooling: After the growth is completed, cool down slowly with a cooling rate not exceeding 15°C / min. When the reaction chamber temperature is lower than 500°C, take out the epitaxial wafer.

[0107] The number of triangular defects on a silicon carbide epitaxial wafer was detected using a Lasertec defect analyzer, with an inspection area of 160.7 cm 2 , the number of triangle defects detected is 84.

[0108] Comparative Example 4

[0109] 1) Cleaning: Select a 4H-SiC substrate with a 4° off-angle and clean the surface of the 4H-SiC substrate using a standard RCA cleaning process.

[0110] 2) Heating to etching temperature: Place the 4H-SiC substrate in the reaction chamber, evacuate the chamber, and heat it to the substrate etching temperature of 1400°C at a heating rate not exceeding 20°C / min.

[0111] 3) Etching: Set the H2 flow rate to 100 SLM, the HCl flow rate to 4 SLM, the reaction chamber pressure to 100 mbar, the temperature to 1410°C, and the etching time to 5 min.

[0112] 4) Raise the temperature to the growth temperature: Turn off the HCl flowmeter, maintain the H2 flow rate at 100 SLM, the reaction chamber pressure at 100 mbar, and raise the temperature to 1600°C.

[0113] 5) Growth of a low-speed, low-carbon-to-silicon ratio buffer layer: Set the TCS (SiHCl3) flow rate to 50 sccm, the C2H4 flow rate to 20 sccm, the carbon-to-silicon ratio to 0.8, the N2 flow rate to 45 sccm, the growth time to 3 min, and the growth thickness to approximately 0.6 μm.

[0114] 6) Growth of a carbon-silicon ratio transition layer: Set the TCS flow rate to 50 sccm, the N2 flow rate to 45 sccm, and the C2H4 flow rate from 20 sccm to 30 sccm. The transition method is a linear function and the transition time is 2 minutes. During this process, the carbon-silicon ratio gradually transitions from 0.8 to 1.2, and the growth thickness is about 0.4 μm.

[0115] 7) Growth of a low-speed high carbon-silicon ratio buffer layer: Set the TCS flow rate to 50 sccm, the C2H4 flow rate to 30 sccm, the carbon-silicon ratio to 1.2, the N2 flow rate to 45 sccm, the growth time to 2.5 min, and the growth thickness to about 0.5 μm.

[0116] 8) Growth source flow transition layer: Set the TCS flow rate to transition from 50 sccm to 500 sccm, the C2H4 flow rate to transition from 30 sccm to 300 sccm, and the N2 flow rate to transition from 45 sccm to 450 sccm. The transition method is a linear function and the transition time is 2 minutes. The carbon-silicon ratio in this process remains unchanged at 1.2, and the growth thickness is about 2 μm.

[0117] 9) Growth of high-speed epitaxial layer: Set the TCS flow rate to 500 sccm, the C2H4 flow rate to 300 sccm, the N2 flow rate to 450 sccm, the growth time to 1 hour, and the growth thickness to about 100 μm.

[0118] 10) Cooling: After the growth is completed, cool down slowly with a cooling rate not exceeding 15°C / min. When the reaction chamber temperature is lower than 500°C, take out the epitaxial wafer.

[0119] The number of triangular defects on a silicon carbide epitaxial wafer was detected using a Lasertec defect analyzer, with an inspection area of 160.7 cm 2 , the number of triangle defects detected is 57.

[0120] Comparative Example 5

[0121] 1) Cleaning: Select a 4H-SiC substrate with a 4° off-angle and clean the surface of the 4H-SiC substrate using a standard RCA cleaning process.

[0122] 2) Heating to etching temperature: Place the 4H-SiC substrate in the reaction chamber, evacuate the chamber, and heat it to the substrate etching temperature of 1400°C at a heating rate not exceeding 20°C / min.

[0123] 3) Etching: Set the H2 flow rate to 100 SLM, the HCl flow rate to 4 SLM, the reaction chamber pressure to 100 mbar, the temperature to 1410°C, and the etching time to 5 min.

[0124] 4) Raise the temperature to the growth temperature: Turn off the HCl flowmeter, maintain the H2 flow rate at 100 SLM, the reaction chamber pressure at 100 mbar, and raise the temperature to 1600°C.

[0125] 5) Growth of a low-speed, low-carbon-to-silicon ratio buffer layer: Set the TCS (SiHCl3) flow rate to 50 sccm, the C2H4 flow rate to 20 sccm, the carbon-to-silicon ratio to 0.8, the N2 flow rate to 45 sccm, the growth time to 3 min, and the growth thickness to approximately 0.6 μm.

[0126] 6) Growth of a carbon-silicon ratio transition layer: Set the TCS flow rate to 50 sccm, the N2 flow rate to 45 sccm, and the C2H4 flow rate from 20 sccm to 30 sccm. The transition method is according to Formula 4, and the transition time is 2 minutes. During this process, the carbon-silicon ratio gradually transitions from 0.8 to 1.2, and the growth thickness is about 0.4 μm.

[0127] 7) Growth source flow transition layer: Set the TCS flow rate to transition from 50 sccm to 500 sccm, the C2H4 flow rate to transition from 30 sccm to 300 sccm, and the N2 flow rate to transition from 45 sccm to 450 sccm. The transition method is a linear function and the transition time is 2 minutes. The carbon-silicon ratio in this process remains unchanged at 1.2, and the growth thickness is about 2 μm.

[0128] 8) Growth of high-speed epitaxial layer: Set the TCS flow rate to 500 sccm, the C2H4 flow rate to 300 sccm, the N2 flow rate to 450 sccm, the growth time to 1 hour, and the growth thickness to about 100 μm.

[0129] 9) Cooling: After the growth is completed, cool down slowly with a cooling rate not exceeding 15°C / min. When the reaction chamber temperature is lower than 500°C, take out the epitaxial wafer.

[0130] The number of triangular defects on a silicon carbide epitaxial wafer was detected using a Lasertec defect analyzer, with an inspection area of 160.7 cm 2 , the number of triangle defects detected is 41.

[0131] Comparative Example 1 is a source flow linear transition method and a carbon-silicon ratio change method commonly used in the industry. Changing the source flow and the carbon-silicon ratio to the target value at the same time will cause more defects to be transferred to the surface of the high-speed epitaxial layer, and there will be many triangular defects. Comparative Example 2 separates the carbon-silicon ratio change process and the rate switching process, but performs the rate switching process immediately after the carbon-silicon ratio change process. There is a lack of a buffer process for a stable growth atmosphere between the two, which is not conducive to controlling the epitaxial defect density. Comparative Example 3 has a long duration of the carbon-silicon ratio change process, so the probability of defects is large, which easily induces an increase in defect density. Comparative Example 4 has a stable growth process with a high carbon-silicon ratio and a low growth rate, but the carbon-silicon ratio changes linearly, resulting in a still high number of defects. The carbon-silicon ratio of Comparative Example 5 also changes according to an S-shaped function, but there is no buffer process afterwards to directly increase the growth rate, and the number of defects is slightly higher than that of Example 1. It is proved that the embodiments of the present application effectively improve the yield of silicon carbide epitaxial products, which is conducive to reducing production costs.

[0132] Throughout this specification, references to terms such as "one embodiment," "certain embodiments," "illustrative embodiments," "examples," "specific examples," or "some examples" indicate that a specific feature, structure, material, or characteristic described in conjunction with the embodiment or example is included in at least one embodiment or example of the present invention. In this specification, illustrative uses of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0133] The above is a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications are also considered to be within the scope of protection of the present invention.

[0134] References:

[0135] [1] Sun Yongqiang. 150mm 4H-SiC thick film epitaxial growth of growth monomer regulated by chemical potential[D]. Xiamen University, 2019.

Claims

1. A method for effectively reducing triangular defects in silicon carbide epitaxial layers, applied to a chemical vapor deposition process, characterized in that: The following steps are involved: growing a low-speed, low-carbon-to-silicon ratio buffer layer on a silicon carbide substrate at a first silicon source flow rate and a first carbon source flow rate; Keeping the silicon source flow rate constant, gradually increasing the flow rate of the first carbon source to the flow rate of the second carbon source, during which a carbon-silicon ratio transition layer is formed; the transition mode is that the carbon-silicon ratio is an S-shaped function with respect to time; growing a low-speed high-carbon-to-silicon ratio buffer layer at the first silicon source flow rate and the second carbon source flow rate; increasing the flow rate of the first silicon source to transition to the second silicon source flow rate, and simultaneously increasing the flow rate of the second carbon source to transition to the third carbon source flow rate, while maintaining the carbon-silicon ratio unchanged, to form a source flow transition layer; growing a high-speed epitaxial layer with the second silicon source flow rate and the third carbon source flow rate; The form of the sigmoid function is: Carbon-silicon ratio = Δr / (1+exp(-k*(t-t_mid) / Δt))+r1; Wherein, Δr=r2-r1, r1 is the carbon-to-silicon ratio of the first carbon source flow rate to the first silicon source flow rate, r2 is the carbon-to-silicon ratio of the second carbon source flow rate to the first silicon source flow rate; the independent variable t represents time, in minutes; t_mid=(t1+t2) / 2,Δt=t2-t1,t1 is the time point when the carbon-to-silicon ratio transition layer starts to grow, t2 is the time point when the low-speed high-carbon-to-silicon ratio buffer layer starts to grow, both in minutes; k is the adjustment parameter for controlling the steepness of the S-shaped function; The r1 is 0.8, the r2 is 1.2, and the Δt is 2 min; The value range of k is 7 to 14.

2. The method for effectively reducing triangular defects in silicon carbide epitaxial layers according to claim 1, characterized in that: The ratio of nitrogen flow rate to silicon source flow rate is kept unchanged throughout the entire process from growing the low-speed and low-carbon-to-silicon ratio buffer layer to growing the high-speed epitaxial layer.

3. The method for effectively reducing triangular defects in silicon carbide epitaxial layers according to claim 1, characterized in that: The silicon source is trichlorosilane and the carbon source is ethylene.

4. The method for effectively reducing triangular defects in a silicon carbide epitaxial layer according to claim 3, characterized in that: In the steps of increasing the flow rate of the first silicon source to transition to the second silicon source flow rate, and simultaneously increasing the flow rate of the second carbon source to transition to the third carbon source flow rate, the transition modes are both linear increases.

5. The method for effectively reducing triangular defects in a silicon carbide epitaxial layer according to claim 4, characterized in that: The flow rate of the second silicon source is 10 times that of the first silicon source, and the flow rate of the third carbon source is 10 times that of the second carbon source.

6. The method for effectively reducing triangular defects in a silicon carbide epitaxial layer according to claim 1, characterized in that: Before the step of growing a low-speed, low-carbon-to-silicon ratio buffer layer on the silicon carbide substrate with a first silicon source flow rate and a first carbon source flow rate, the method further includes the following steps: A 4H-SiC substrate with a 4° off-angle was selected, and after cleaning the surface, it was placed in the reaction chamber. Evacuate the chamber and heat it to 1400°C, the substrate etching temperature, at a rate not exceeding 20°C / min. Set the hydrogen flow rate to 100 SLM, the HCl flow rate to 4 SLM, the reaction chamber pressure to 100 mbar, the temperature to 1410°C, and the etching time to 5 min; Stop the HCl flow, maintain the hydrogen flow rate at 100 SLM, the reaction chamber pressure at 100 mbar, and raise the temperature to 1600°C; After the step of growing a high-speed epitaxial layer with the second silicon source flow rate and the third carbon source flow rate, the method further includes the following steps: Cool down at a rate not exceeding 15°C / min. When the temperature of the reaction chamber is lower than 500°C, take out the epitaxial wafer.

7. The method for effectively reducing triangular defects in a silicon carbide epitaxial layer according to claim 1, characterized in that: The thickness range of the low-speed low-carbon-silicon ratio buffer layer is 0.3μm-2μm, the thickness range of the carbon-silicon ratio transition layer is 0.2μm-1μm, the thickness range of the low-speed high-carbon-silicon ratio buffer layer is 0.3μm-2μm, and the thickness range of the source flow transition layer is 0.5μm-4μm.

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