Silicon carbide epitaxial equipment and epitaxial wafer manufacturing method

Abstract

The invention discloses silicon carbide epitaxy equipment and an epitaxial wafer manufacturing method, a groove is formed in the middle of the upper surface of an air floatation tray of the equipment, an air inlet system comprises five air inlet channels arranged in parallel, and the air inlet directions of the air inlet channels are parallel to the upper surface of the air floatation tray; the five air inlet channels comprise a central air channel located in the middle, two secondary edge air channels located on the two sides of the central air channel and two edge air channels located on the outer sides of the secondary edge air channels; the center line of the center gas circuit is right opposite to the center of the preset placing position of the wafer, the center line of the secondary edge gas circuit is right opposite to the R / 2 position of the preset placing position of the wafer, R is the radius of the wafer, and the center line of the edge gas circuit is right opposite to the outer edge of the preset placing position of the wafer. By means of the five gas paths and the air floating tray slotting structure, the uniformity of the gas flow field and the temperature field of the epitaxial furnace is improved, a foundation is laid for uniform growth of epitaxial wafers, the defect of uneven doping of the prepared epitaxial wafers is overcome, and the number of surface defects of the epitaxial wafers can be reduced.

Description

Technical Field

[0001] This invention relates to the field of semiconductor epitaxial growth technology, and in particular to a silicon carbide epitaxial equipment and a method for manufacturing epitaxial wafers. Background Technology

[0002] In the field of silicon carbide (SiC) epitaxy, the uniformity of the gas flow and temperature field in an eight-inch epitaxial furnace is a crucial factor affecting the growth quality of epitaxial wafers. Regarding the gas flow, most existing eight-inch epitaxial furnaces employ a three-way gas inlet, with one inlet channel in the middle and one on each side. Figure 1 As shown, due to the depletion of gas flow, the reactive gas cannot uniformly cover the entire wafer area, leaving dead zones in the R / 2 and edge regions. This results in low and uncontrollable doping efficiency and poor concentration uniformity. Regarding the temperature field, existing eight-inch epitaxial furnaces use a single induction heating source, leading to high temperatures at the center and low temperatures at the edges. Due to the combined effects of heat radiation loss and convection within the cavity, the temperature gradient between the center and edges of the eight-inch wafer reaches 10-20°C, causing uneven doping concentration and increased defects in the epitaxial wafer. How to effectively optimize the gas flow and temperature field within the epitaxial furnace is a pressing issue that needs to be addressed. Summary of the Invention

[0003] Purpose of the invention: To address the shortcomings of existing epitaxial equipment, such as uneven airflow and temperature fields leading to uneven doping concentration and numerous surface defects in epitaxial wafers, this invention provides a silicon carbide epitaxial equipment and an epitaxial wafer manufacturing method.

[0004] Technical Solution: To solve the above problems, the present invention employs a silicon carbide epitaxial device, comprising a loading chamber, a transfer chamber, and a reaction chamber connected in sequence. An air-floating tray is provided within the reaction chamber, and an air intake system is provided on one side of the reaction chamber. The air-floating tray has a groove in the center of its upper surface. The air intake system includes five parallel air intake channels, with the air intake direction parallel to the upper surface of the air-floating tray. The upper surface of the air-floating tray has a preset wafer placement position for placing a wafer. The five air intake channels include a central air path located in the center, two secondary edge air paths located on either side of the central air path, and two edge air paths located outside the secondary edge air paths. The centerline of the central air path is aligned with the center of the preset wafer placement position, the centerlines of the secondary edge air paths are aligned with R / 2 of the preset wafer placement position (where R is the wafer radius), and the centerlines of the edge air paths are aligned with the outer edge of the preset wafer placement position.

[0005] Furthermore, the groove has a circular cross-section and a rectangular, V-shaped, or arc-shaped longitudinal section.

[0006] Furthermore, the radius of the groove on the air-floating tray is R / 4 to R / 2, where R is the wafer radius.

[0007] Furthermore, the five air intake channels are symmetrically arranged along the centerline of the central air path.

[0008] This invention also provides a method for manufacturing epitaxial wafers using the aforementioned silicon carbide epitaxial equipment, comprising the following steps: S1. Initialize the reaction chamber: Place the silicon carbide substrate into the reaction chamber, introduce air flotation gas to make the air flotation tray rotate, set the initial temperature and pressure of the reaction chamber, then introduce hydrogen gas into the reaction chamber and heat up and depressurize the reaction chamber. S2. High-temperature in-situ etching: HCl and hydrogen are introduced into the reaction chamber to keep the temperature and pressure of the reaction chamber constant, and the silicon carbide substrate is etched in-situ at high temperature. S3. Low-temperature in-situ etching: HCl and hydrogen are introduced into the reaction chamber, the flow rate of HCl and the temperature of the reaction chamber are reduced, and the pressure of the reaction chamber is kept constant to perform low-temperature in-situ etching on the silicon carbide substrate. S4. Epitaxial growth of the buffer layer; keeping the temperature and pressure of the reaction chamber constant, carbon source, silicon source, hydrogen gas and dopant source are introduced into the reaction chamber. The flow rate ratio of the carbon source, silicon source and hydrogen gas mixture in the five inlet channels is: center gas path: secondary edge gas path: edge gas path = 3:2:4; the flow rate ratio of the dopant source in the five inlet channels is: center gas path: secondary edge gas path: edge gas path = 3:2:1. S5. Growth of the main epitaxial layer; keeping the temperature and pressure of the reaction chamber constant, carbon source, silicon source, hydrogen gas and dopant source are introduced into the reaction chamber, increasing the flow rate of carbon source and silicon source and the concentration of dopant source gas. The flow rate ratio of the carbon source, silicon source and hydrogen gas mixture in the five inlet channels is: center gas path: secondary edge gas path: edge gas path = 3:2:4; the flow rate ratio of the dopant source in the five inlet channels is: center gas path: secondary edge gas path: edge gas path = 5:6:1. S6. Cool and pressurize the reaction chamber, shut down the air flotation system, and remove the epitaxial wafer.

[0009] Furthermore, in step S1, the initial temperature is 600-1000℃, the initial pressure is 900-1200mbar, the hydrogen flow rate is 100-200slm, the reaction chamber temperature is raised to 1500-1700℃, and the reaction chamber pressure is reduced to 50-200mbar.

[0010] Furthermore, in step S2, the HCl flow rate is 50-200 sccm, the hydrogen flow rate is 100-200 slm, and the etching time is 5-10 min.

[0011] Furthermore, in step S3, the HCl flow rate is 30-200 sccm, the hydrogen flow rate is 100-200 slm, the reaction chamber temperature is 1500-1650℃, and the etching time is 5-10 min.

[0012] Furthermore, in step S4, the carbon source flow rate is 10-100 sccm, the silicon source flow rate is 50-200 sccm, the hydrogen flow rate is 100-200 slm, the doping source is a mixture of doping gas and diluted hydrogen, the doping gas flow rate is 100-400 sccm, the diluted hydrogen flow rate is 1000-2000 sccm, and the doping gas pipeline pressure is 1500-2500 mbar.

[0013] Furthermore, in step S5, the carbon source flow rate is 50-300 sccm, the silicon source flow rate is 50-800 sccm, the hydrogen flow rate is 100-200 slm, the doping source is a mixture of doping gas and hydrogen, the doping gas flow rate is 200-500 sccm, the dilution hydrogen flow rate is 1000-2000 sccm, and the doping gas pipeline pressure is 1500-2500 mbar.

[0014] Beneficial effects: Compared with the prior art, the significant advantage of this invention is that it improves the uniformity of the airflow and temperature field of the epitaxial furnace through the five-way air path and the slotted structure of the air-floating tray, laying the foundation for the uniform growth of epitaxial wafers, improving the defects of uneven doping of the epitaxial wafers, and reducing the number of surface defects of the epitaxial wafers. Attached Figure Description

[0015] Figure 1 A schematic diagram of the three-way air intake system of an existing silicon carbide epitaxial equipment; Figure 2 This is a schematic diagram of the overall structure of the silicon carbide epitaxial device of the present invention; Figure 3 This is a schematic diagram of the five-way air intake system of the silicon carbide epitaxial device of the present invention; Figure 4 This is a schematic diagram of the epitaxial wafer manufacturing method of the present invention. Detailed Implementation

[0016] Example 1

[0017] like Figure 2 and Figure 3As shown, a silicon carbide epitaxial device in this embodiment includes a loading chamber 1, a transfer chamber 2, and a reaction chamber 3 connected in sequence. An air flotation tray 4 is provided inside the reaction chamber 3. An air intake system 5 is provided on one side of the reaction chamber 3, and the air intake system 5 is connected to a gas pipeline 6 to introduce reaction gas into the reaction chamber. The air intake system 5 includes five parallel air intake channels, with the air intake direction parallel to the upper surface of the air flotation tray, employing a horizontal air intake. The five air intake channels include a central air path 51 located in the middle, two secondary edge air paths 52 located on both sides of the central air path, and two edge air paths 53 located outside the secondary edge air paths. The five air intake channels are symmetrically arranged along the centerline of the central air path. The centerline of the central air path 51 is directly opposite the center of the preset placement position of the wafer 7. The centerline of the secondary edge air paths 51 is directly opposite to R / 2 of the preset placement position of the wafer 7, where R is the wafer radius. The centerline of the edge air paths 53 is directly opposite the outer edge of the preset placement position of the wafer 7. Two new edge gas paths are added, which allows the gas range to cover from the center of the wafer to the edge of the wafer, eliminating gas flow dead zones, improving the uniformity of the reaction gas distribution, and laying the foundation for uniform growth of epitaxial wafers.

[0018] A groove 41 is formed in the middle of the upper surface of the air-floating tray 4. The groove has a circular cross-section and a rectangular, V-shaped, or arc-shaped longitudinal section. In this embodiment, the longitudinal section of the groove is rectangular, the groove radius is 50 mm, and the depth is 0.8 mm. After the groove is formed, the central contact area between the graphite carrier and the air-floating tray is reduced, the heat conduction is reduced, the central temperature is reduced, and the radial temperature difference of the temperature field of the epitaxial wafer is reduced.

[0019] like Figure 4 As shown, the fabrication of an eight-inch epitaxial wafer using the aforementioned silicon carbide epitaxial equipment specifically includes the following steps: S1. Initialization of the reaction chamber. The silicon carbide substrate is placed into the reaction chamber, and a floating gas is introduced to rotate the floating tray. The floating gas can be argon, hydrogen, or other inert gases; in this embodiment, hydrogen is used. The initial temperature of the reaction chamber is set to 900°C, and the initial pressure to 1000 mbar. Then, 160 slm of hydrogen is introduced into the reaction chamber as a carrier gas, and the temperature is raised to 1620°C and the pressure is reduced to 100 mbar over a 10-minute ramp-up period.

[0020] S2. High-temperature in-situ etching. HCl at 120 sccm and hydrogen at 160 slm are introduced into the reaction chamber. While maintaining constant temperature and pressure in the reaction chamber, high-temperature in-situ etching is performed on the silicon carbide substrate for 5 minutes.

[0021] S3. Low-temperature in-situ etching. Introduce 30 sccm of HCl and 160 slm of hydrogen into the reaction chamber to lower the temperature to 1590°C. Keep the pressure in the reaction chamber constant and perform low-temperature in-situ etching on the silicon carbide substrate for 5 minutes.

[0022] S4. Epitaxial growth of the buffer layer. Maintaining constant temperature and pressure in the reaction chamber, introduce a carbon source, a silicon source, hydrogen gas, and a dopant source into the reaction chamber. The silicon source can be dichlorosilane, trichlorosilane, or silane; the carbon source can be ethylene, propylene, methane, ethane, or propane; and the dopant source gas can be nitrogen or ammonia. Specifically, in this embodiment, the silicon source is trichlorosilane (SiHCl3), the carbon source is ethylene, and the dopant source gas is ammonia.

[0023] A mixture of TCS (SiHCl3) at a flow rate of 80 sccm, ethylene (C2H4) at a flow rate of 20 sccm, and hydrogen at a flow rate of 160 slm was introduced into the chamber for epitaxial growth. The gas flow ratio of the central gas path: secondary edge gas path: edge gas path was 3:2:4. The dopant gas was a mixture of ammonia (NH3) at a flow rate of 100 sccm and carrier hydrogen at a flow rate of 1000 sccm. The dopant gas was distributed in a 3:2:1 ratio across the central, secondary, and edge gas paths. The epitaxial buffer layer growth time was 480 s.

[0024] S5. Main Epitaxial Layer Growth. Maintaining constant temperature and pressure in the reaction chamber, introduce TCS (SiHCl3) at a flow rate of 300 sccm, ethylene (C2H4) at 120 sccm, and hydrogen at 160 sccm. After mixing, the gases are divided into three groups and introduced into the chamber for epitaxial growth. The gas flow ratio of the central gas path: secondary edge gas path: edge gas path is 3:2:4. The dopant gas is a mixture of ammonia (NH3) at 200 sccm and carrier hydrogen at 1000 sccm. The dopant gas distribution ratio in the central gas path: secondary edge gas path: edge gas path is 5:6:1. The main epitaxial layer growth time is 600 s.

[0025] S6. Adjust the hydrogen flow rate to 50 slm, allow it to cool naturally to 900℃ and pressurize it to 1000 mbar, turn off the air flotation system, and remove the epitaxial wafer.

[0026] The gas flow rate and ratio in each step can be flexibly adjusted according to the actual epitaxial wafer growth requirements. The specific values ​​given are parameters commonly used in actual production and have good epitaxial wafer growth effects.

[0027] Example 2

[0028] The groove dimensions of the air-floating tray in the silicon carbide epitaxial equipment of this embodiment differ from those in Embodiment 1, but the other structures are the same. The longitudinal section of the groove is rectangular, with a radius of 100 mm and a depth of 1 mm. The epitaxial wafer is prepared using this equipment, and the specific steps are the same as in Embodiment 1.

[0029] Comparative Example 1

[0030] This comparative example retains the three-way air intake of traditional epitaxial equipment, and only grooves are made on the upper surface of the air flotation tray. The longitudinal section of the groove is rectangular, the groove radius is 100mm, and the depth is 1mm.

[0031] The epitaxial color code was used for epitaxial wafer preparation. Steps S1, S3, and S6 were the same as in Example 1. Steps S4 and S5 are as follows: S4. Epitaxial Growth of the Buffer Layer. Maintaining constant temperature and pressure in the reaction chamber, introduce TCS (SiHCl3) at a flow rate of 80 sccm, ethylene (C2H4) at 20 sccm, and hydrogen at 160 sccm. After mixing, the gases are divided into two groups and introduced into the chamber for epitaxial growth, with a central-to-edge gas flow ratio of 2:3. The doping gas is a mixture of ammonia (NH3) at 100 sccm and hydrogen as the carrier gas at 1000 sccm, with a central-to-edge gas flow ratio of 2:1. The epitaxial buffer layer growth time is 480 s.

[0032] S5. Main Epitaxial Layer Growth. Maintaining constant temperature and pressure in the reaction chamber, introduce TCS (SiHCl3) at a flow rate of 300 sccm, ethylene (C2H4) at 120 sccm, and hydrogen at 160 slm. After mixing, the gases are divided into two groups and introduced into the chamber for epitaxial growth, with a central-to-edge gas flow ratio of 2:3. The doping gas is a mixture of ammonia (NH3) at 200 sccm and carrier hydrogen at 1000 sccm, with a central-to-edge gas flow ratio of 3:4. The main epitaxial layer growth time is 600 s.

[0033] Comparative Example 2

[0034] The epitaxial equipment used in this comparative example is a traditional epitaxial equipment with three air inlets and no slotted air flotation tray. The epitaxial wafer was prepared using this equipment, and the specific steps were the same as those in Comparative Example 1.

[0035] The uniformity tests of the epitaxial wafers prepared in each embodiment and comparative example are shown in Table 1 below: Concentration inhomogeneity Thickness non-uniformity Example 1 1.7% 1.2% Example 2 1.1% 0.9% Comparative Example 1 2.5% 1.8% Comparative Example 2 3% 1.8% Table 1 Concentration uniformity is mainly determined by the distribution ratio of each gas inlet channel of the doping gas, and thickness uniformity is mainly determined by the distribution ratio of each gas inlet channel of the carbon source, silicon source, and hydrogen mixed gas. As can be seen from Table 1, the concentration non-uniformity and thickness non-uniformity of Examples 1 and 2 with five gas channels are lower than those of Comparative Examples 1 and 2 with three gas channels, indicating that five gas channels can improve the concentration uniformity and thickness uniformity of the epitaxial wafer.

[0036] The number of three types of surface defects in the epitaxial wafers prepared in each embodiment and comparative example was tested, and the results are shown in Table 2 below: Triangular defects Base plane dislocation Stacking fault Example 1 48 77 69 Example 2 23 26 18 Comparative Example 1 25 30 25 Comparative Example 2 77 89 249 Table 2 The number of surface defects is related to the temperature uniformity during epitaxy. As can be seen from the table above, compared with Comparative Example 3 without grooves, the number of three types of surface defects in Examples 1, 2 and Comparative Example 1 with air-floating tray grooves decreased. Moreover, Examples 2 and Comparative Example 1 with groove radius of 100 mm and depth of 1 mm were better than Examples 1 with groove radius of 50 mm and depth of 0.8 mm. This indicates that when the groove radius is larger, which is half the wafer radius, it can have a better effect on adjusting temperature uniformity.

[0037] Regarding the airflow field, this invention adds an independently controlled airflow channel to the outer edges of the wafer's R / 2 region and the edge region, based on the three-way airflow system. This results in a more uniform distribution of reactant gases, and effectively eliminates the airflow dead zones present in the R / 2 and edge regions of traditional three-way airflow systems. By independently adjusting the flow rate of each airflow channel, precise gas supply to different regions of the wafer is achieved, significantly improving the uniformity of reactant gas distribution and laying the foundation for uniform epitaxial layer growth.

[0038] Regarding the temperature field, the slotted structure of the air-floating tray of this invention creates a controllable thermal resistance region between the tray and the graphite carrier. This design effectively reduces direct heat conduction in the central region, resulting in a more balanced heat distribution and successfully suppressing the radial temperature gradient caused by overheating in the center. It achieves a uniform distribution of the thermal field, solving the problem of uneven growth rate caused by excessively high central temperatures in traditional trays.

[0039] The simultaneous optimization of the airflow and temperature fields ensured uniform growth of the epitaxial layer thickness, stabilized the radial distribution of doping concentration, and significantly reduced the defect density during thick film growth. The coordinated control of the temperature and airflow fields also enhanced the reliability of process monitoring signals, providing a foundation for precise control of the growth rate.

Claims

1. A silicon carbide epitaxial device, comprising a loading chamber (1), a transfer chamber (2), and a reaction chamber (3) connected in sequence, wherein an air flotation tray (4) is provided inside the reaction chamber, and an air intake system (5) is provided on one side of the reaction chamber, characterized in that, The upper surface of the air-float tray has a groove (41) in the middle. The air intake system includes five parallel air intake channels with the air intake direction parallel to the upper surface of the air-float tray. The upper surface of the air-float tray is provided with a preset wafer placement position for placing wafers. The five air intake channels include a central air path (51) in the middle, two secondary edge air paths (52) on both sides of the central air path, and two edge air paths (53) on the outside of the secondary edge air paths. The center line of the central air path is directly opposite the center of the preset wafer placement position, the center line of the secondary edge air path is directly opposite R / 2 of the preset wafer placement position, where R is the wafer radius, and the center line of the edge air path is directly opposite the outer edge of the preset wafer placement position.

2. The silicon carbide epitaxial apparatus as described in claim 1, characterized in that, The groove (41) has a circular cross-section and a rectangular, V-shaped or arc-shaped longitudinal section.

3. The silicon carbide epitaxial apparatus as described in claim 2, characterized in that, The groove is located on the air-float tray with a circular radius of R / 4 to R / 2, where R is the wafer radius.

4. The silicon carbide epitaxial apparatus as described in claim 2, characterized in that, The five air intake channels are symmetrically arranged along the centerline of the central air path.

5. A method for manufacturing an epitaxial wafer using the silicon carbide epitaxial apparatus according to any one of claims 1-4, characterized in that, Includes the following steps: S1. Initialize the reaction chamber: Place the silicon carbide substrate into the reaction chamber, introduce air flotation gas to make the air flotation tray rotate, set the initial temperature and pressure of the reaction chamber, then introduce hydrogen gas into the reaction chamber and heat up and depressurize the reaction chamber. S2. High-temperature in-situ etching: HCl and hydrogen are introduced into the reaction chamber to keep the temperature and pressure of the reaction chamber constant, and the silicon carbide substrate is etched in-situ at high temperature. S3. Low-temperature in-situ etching: HCl and hydrogen are introduced into the reaction chamber, the flow rate of HCl and the temperature of the reaction chamber are reduced, and the pressure of the reaction chamber is kept constant to perform low-temperature in-situ etching on the silicon carbide substrate. S4. Epitaxial growth of the buffer layer; keeping the temperature and pressure of the reaction chamber constant, carbon source, silicon source, hydrogen gas and dopant source are introduced into the reaction chamber. The flow rate ratio of the carbon source, silicon source and hydrogen gas mixture in the five inlet channels is: center gas path: secondary edge gas path: edge gas path = 3:2:4; the flow rate ratio of the dopant source in the five inlet channels is: center gas path: secondary edge gas path: edge gas path = 3:2:

1. S5. Growth of the main epitaxial layer; keeping the temperature and pressure of the reaction chamber constant, carbon source, silicon source, hydrogen gas and dopant source are introduced into the reaction chamber, increasing the flow rate of carbon source and silicon source and the concentration of dopant source gas. The flow rate ratio of the carbon source, silicon source and hydrogen gas mixture in the five inlet channels is: center gas path: secondary edge gas path: edge gas path = 3:2:4; the flow rate ratio of the dopant source in the five inlet channels is: center gas path: secondary edge gas path: edge gas path = 5:6:

1. S6. Cool and pressurize the reaction chamber, shut down the air flotation system, and remove the epitaxial wafer.

6. The epitaxial wafer manufacturing method as described in claim 5, characterized in that, In step S1, the initial temperature is 600-1000℃, the initial pressure is 900-1200mbar, the hydrogen flow rate is 100-200slm, the reaction chamber temperature is raised to 1500-1700℃, and the reaction chamber pressure is reduced to 50-200mbar.

7. The epitaxial wafer manufacturing method as described in claim 5, characterized in that, In step S2, the HCl flow rate is 50-200 sccm, the hydrogen flow rate is 100-200 slm, and the etching time is 5-10 min.

8. The epitaxial wafer manufacturing method as described in claim 5, characterized in that, In step S3, the HCl flow rate is 30-200 sccm, the hydrogen flow rate is 100-200 slm, the reaction chamber temperature is 1500-1650℃, and the etching time is 5-10 min.

9. The epitaxial wafer manufacturing method as described in claim 5, characterized in that, In step S4, the carbon source flow rate is 10-100 sccm, the silicon source flow rate is 50-200 sccm, the hydrogen flow rate is 100-200 slm, the doping source is a mixture of doping gas and diluted hydrogen, the doping gas flow rate is 100-400 sccm, the diluted hydrogen flow rate is 1000-2000 sccm, and the doping gas pipeline pressure is 1500-2500 mbar.

10. The epitaxial wafer manufacturing method as described in claim 5, characterized in that, In step S5, the carbon source flow rate is 50-300 sccm, the silicon source flow rate is 50-800 sccm, the hydrogen flow rate is 100-200 slm, the doping source is a mixture of doping gas and hydrogen, the doping gas flow rate is 200-500 sccm, the dilution hydrogen flow rate is 1000-2000 sccm, and the doping gas pipeline pressure is 1500-2500 mbar.

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