Method for controlling surface flatness of large-size epitaxial wafer

Abstract

The invention provides a method for controlling the surface flatness of a large-size epitaxial wafer, and the method comprises the steps: detecting the film thickness of a grown sample wafer, and obtaining the uniformity of the film thickness; if the film thickness uniformity is greater than or equal to the standard value, obtaining a radial film thickness linear graph of the sample; obtaining a radial film thickness linear relation based on the radial film thickness linear graph; based on the radial film thickness linear relation of the sample wafer, determining the area where the minimum or maximum film thickness of the sample wafer is located; based on the area where the minimum film thickness or the maximum film thickness is located, the corresponding technology during sheet growth is adjusted, and a qualified sheet is obtained. According to the control method for the surface flatness of the large-size epitaxial wafer, the positions of different film thicknesses can be adjusted in a targeted mode through different control methods, the problem that the surface flatness difference is large or abnormal can be effectively solved, the accurate and qualified surface flatness is obtained, the surface quality of the epitaxial wafer is improved, the production cost is reduced, and the production efficiency is improved. The control method is effective, safe and reliable.

Description

Technical Field

[0001] The present application belongs to the technical field of epitaxial wafer processing, and in particular, relates to a method for controlling the surface flatness of a large-size epitaxial wafer. Background Art

[0002] At present, the monitoring method for large-size thick epitaxial wafers is mainly to evaluate related parameters such as film thickness and resistance, but there is relatively little research on surface flatness. With the improvement of the advanced process capabilities of back-end chips and the higher demand for terminal products, the increase in the size and thickness of epitaxial wafers is an inevitable trend, such as 200mm IGBT epitaxial wafers. However, with the increase in the size and thickness of epitaxial wafers, the back-end chip process has more stringent requirements on the surface flatness of epitaxial wafers. For example, in areas such as near the V-groove of the epitaxial wafer and the edge of the wafer, poor surface flatness often causes chip yield loss. A more serious situation occurs during the photolithography stage, where the overall surface flatness of the epitaxial wafer is poor, so it is impossible to focus and the entire wafer is scrapped.

[0003] As the size of the epitaxial wafer increases (e.g. 125mm→150mm→200mm), the temperature field and gas flow field during the crystal growth process become more complex, and the local epitaxial growth rate becomes more difficult to control, so the surface flatness after epitaxy becomes more difficult to optimize. When the thickness of the epitaxial wafer increases from 60um to 130um, the difference in the local growth rate of the epitaxial wafer will cause a sharp increase in the cumulative difference in the local film thickness after epitaxy, and the surface flatness of the epitaxial wafer will increase synchronously.

[0004] With existing epitaxial wafer growth equipment, when growing large-size, thick epitaxial wafers, it is not only found that the abnormal location of the epitaxial wafer surface flatness generally appears near the V-groove; it is also found that the inner film thickness of the epitaxial wafer is uneven; it is also found that the surface flatness of the epitaxial wafer is poor. Summary of the invention

[0005] The present application provides a method for controlling the surface flatness of a large-sized epitaxial wafer, which is particularly suitable for the growth of large-sized and thick epitaxial wafers, and solves the technical problem of poor epitaxial wafer flatness caused by unreasonable existing production processes.

[0006] In order to solve at least one of the above technical problems, the technical solution adopted in this application is:

[0007] A method for controlling the surface flatness of a large-size epitaxial wafer, comprising the following steps:

[0008] Detect the film thickness of the grown sample and obtain its film thickness uniformity;

[0009] If the film thickness uniformity is greater than or equal to the standard value, obtain the radial film thickness linear graph of the sample;

[0010] Based on the radial film thickness linear diagram, the radial film thickness linear relationship is obtained;

[0011] Based on the linear relationship of radial film thickness of the sample, the area where the minimum or maximum film thickness of the sample is located is determined;

[0012] Based on the area of ​​minimum or maximum film thickness, the corresponding process during sheet growth is adjusted to obtain qualified sheets.

[0013] Furthermore, the film thickness of the sample after growth is detected by:

[0014] The diameter of the V-groove in the selected sample is the film thickness measurement path;

[0015] Taking the end of the measuring path away from the V-groove as the starting point, n test points are selected in a preset range on the measuring path, and all the test points are symmetrical with respect to the center of the sample, where n is an odd number;

[0016] The outermost edge of the preset range is 3 mm from the edge of the sample.

[0017] Furthermore, the obtaining of the uniformity of the film thickness is specifically as follows:

[0018] Based on the film thickness results of each test point, select the maximum film thickness value Tmax and the minimum film thickness value Tmin;

[0019] Then, based on the formula, the film thickness uniformity Tuni of the sample is calculated;

[0020] The formula is:

[0021] Tuni=(Tmax-Tmin) / (Tmax+Tmin).

[0022] Furthermore, the standard value of the film thickness uniformity is 2%;

[0023] If the film thickness uniformity of the sample is measured to be less than 2%, the surface flatness of the sample is qualified and the sample can be directly produced into a sheet.

[0024] Furthermore, the obtained sample radial film thickness linear graph is a linear graph formed by taking the position of each test point in the test path as the X-axis and the film thickness corresponding to each test point as the Y-axis, which is the radial film thickness linear graph;

[0025] The radial film thickness linear diagram includes a linear relationship and a nonlinear relationship.

[0026] Furthermore, when the radial film thickness line graph is linearly related, it can be determined that the area where the minimum film thickness of the sample is located is located at the edge of the sample, and its film thickness changes gradually from high to low or from low to high along the measurement path; the flow rate of the middle air inlet pipe in the growth furnace is adjusted during growth.

[0027] Furthermore, when the radial film thickness line graph is nonlinear, it can be determined that the area where the minimum film thickness of the sample is located includes the non-V-groove position at the edge of the sample, the inside of the sample, and the V-groove position.

[0028] Furthermore, when the area where the minimum film thickness of the sample is located is at the non-V-groove position at the edge of the sample, it indicates that the edge film thickness is low, and the process temperature during its growth is adjusted, that is, the original growth temperature is increased by 1-10°C.

[0029] Furthermore, when the area where the minimum film thickness of the sample is located is inside the sample, the position of the coil used to heat the temperature inside the sample is adjusted to shorten the vertical distance between the coil and the sample.

[0030] Furthermore, when the area where the minimum film thickness of the sample is located is in the V-groove, it indicates that the film thickness of the V-groove is relatively high, and the matching relationship between the needle valve corresponding to the V-groove position and the corresponding air inlet hole is changed.

[0031] A method for controlling the surface flatness of a large-size epitaxial wafer designed in this application can be used to adjust the positions of different film thicknesses in a targeted manner through different control methods, which can effectively solve the problem of large or abnormal surface flatness differences, obtain accurate and qualified surface flatness, improve the surface quality of epitaxial wafers, and reduce production costs. The control method is effective, safe and reliable. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a flow chart of a method for controlling the surface flatness of a large-size epitaxial wafer in the present application;

[0033] Figure 2 It is a schematic diagram of the layout of the epitaxial wafer in the present application when it is grown in a growth furnace;

[0034] Figure 3 It is the film thickness test fitting diagram when the minimum film thickness of the sample is at the non-V-groove position of the sample edge (V-groove facing downward);

[0035] Figure 4 It is the film thickness test fitting diagram when the minimum film thickness of the sample is inside the sample (V groove facing downward);

[0036] Figure 5 This is the film thickness test fitting diagram when the minimum film thickness of the sample is in the V-groove (V-groove facing downward).

[0037] In the figure:

[0038] 10. epitaxial wafer 20. placement tray 30. air intake system

[0039] 31. Intake pipe 1 32. Intake pipe 2 33. Distribution pipe

[0040] 34. Air inlet 35. Needle valve 36. Control valve

[0041] 40. Test path 41. Test point DETAILED DESCRIPTION

[0042] The present application is described in detail below with reference to the accompanying drawings and specific embodiments.

[0043] This embodiment proposes a method for controlling the surface flatness of a large-size epitaxial wafer, such as Figure 1 As shown, the steps include:

[0044] S1. Obtain the grown sample, detect the film thickness of the grown sample, and obtain the uniformity of the film thickness.

[0045] like Figure 2 As shown, it is a simplified diagram of the epitaxial wafer 10 when it is grown in the epitaxial furnace, that is, the epitaxial wafer 10 is placed in the same placing tray 20, and 5 epitaxial wafers 10 are placed in each placing tray 20. A V-groove is provided on each epitaxial wafer 10 (the figure is omitted, which is common knowledge in this field), and the openings of the V-grooves of all epitaxial wafers 10 are arranged outward, and during the entire growth process, the placing tray 20 always rotates continuously in the same direction, and accordingly, the V-groove is always facing the outermost side of the placing tray 20.

[0046] At the top of the furnace body, and just above the center diameter position of the placing tray 20 in the horizontal direction, an air intake system 30 is provided, which includes three air intake pipes interconnected with the same air inlet, and the three air intake pipes are respectively an air intake pipe 1 31 located in the middle position and air intake pipes 2 32 located at the left and right sides. The air intake pipe 1 31 and the air intake pipes 2 32 on both sides are provided with control valves 36 for controlling their flow rates. Since the air intake pipe 1 31 in the middle position is mainly used to ventilate the middle most area of ​​the placing tray 20, its flow rate and distribution area are greater than the flow rate and radiated area of ​​the air intake pipes 2 32 on both sides.

[0047] Accordingly, in order to improve the uniformity of the distribution of the intake gas, a transversely arranged distribution pipe 33 is provided below the intake pipe 1 31 and the intake pipe 2 32, and each distribution pipe 33 is provided with a plurality of intake holes 34, and each intake hole 34 is provided with a needle valve 35 that matches the intake hole 34. In the actual working process, these needle valves 35 are in an open state, that is, they are not inserted into the intake hole 34, and the growth gas enters the growth furnace through all the intake holes 34.

[0048] In this embodiment, the distribution pipe 33 connected to the air inlet pipe 1 31 is provided with 16 air inlet holes 34, and correspondingly, 16 needle valves 35 are also provided. For the air inlet pipes 2 32 on the left and right sides, there is also a distribution pipe 33, and each distribution pipe 33 is provided with 6 air inlet holes 34 and 6 needle valves 35. For all the air inlet holes 34 connected to the air inlet pipe 2 32 on both sides, they are mainly aimed at the film thickness growth on the edge of the epitaxial wafer, and all the air inlet holes 34 in the middle position connected to the air inlet pipe 1 31 are mainly aimed at the film thickness growth on the inside of the epitaxial wafer.

[0049] However, before the finished product is processed, the sample needs to be tested. All samples in this application refer to the single epitaxial wafer 10; but when the finished product is grown, the adjustment process is to adjust the components in the structure of the entire furnace body, which will be described in detail when each specific embodiment is used.

[0050] In this embodiment, an epitaxial wafer sample is first obtained, wherein the growth process of the epitaxial wafer sample is:

[0051] On a substrate with a diameter of 200mm, an epitaxial wafer 10 with a film thickness of 90-130um is introduced into the furnace chamber. Among them, the growth gas is introduced into the furnace chamber through gas channel 1 31 and gas channel 2 32, wherein the flow rate of the main hydrogen gas is preset to 150-200SLM, and the growth temperature is set to 1020-1120℃; the flow rate of trichlorosilane is set to 5-20SLM. The first step of heating is from room temperature to 970-1070℃, and the heating time is 1000-1500s; the second step of heating is from the temperature of the first step to 1020-1120℃, the heating time is 300-360s, and the growth time is 1000-5000s; wherein, the dilution hydrogen flow rate is set to 0-30SLM, and the doping flow rate is set to 0-300Sccm.

[0052] Then select any epitaxial wafer sample and test its film thickness after growth using a film thickness meter. The specific operation is as follows:

[0053] like Figure 3 As shown, the diameter of the V-groove in the sample is first selected as the film thickness measurement path 40; and the end of the measurement path 40 away from the V-groove is selected as the starting point, and n test points 41 are selected in the preset range area on the measurement path 40, where n is an odd number. And all the test points 41 are symmetrical with respect to the center of the sample, that is, at least one test point 41 is located at the center of the sample. On the measurement path 40, the preset range area where all the test points 41 are located is Figure 3 The dotted circle in the figure has a distance of 3mm from the outermost edge of the dotted circle to the edge of the sample. Avoid the thickness test results within the range of 3mm from the edge to vary too much, which is not enough to represent the wide range of the film thickness of the sample.

[0054] In this embodiment, when calculating the uniformity of the film thickness, at least 49 test points 41 need to be selected on the measurement path 40 for calculation, so that the calculated value of the uniformity of the film thickness of the sample is universal. Therefore, after measuring these 49 test points 41, 49 film thickness test values ​​can be obtained. Based on these 49 film thickness test values, the maximum film thickness value Tmax and the minimum film thickness value Tmin of this sample, as well as the position range corresponding to the maximum film thickness value and the minimum film thickness value can be obtained.

[0055] Based on the maximum film thickness value Tmax and the minimum film thickness value Tmin, the film thickness uniformity Tuni of the sample is calculated using the film thickness uniformity formula.

[0056] Among them, the Tuni formula for film thickness uniformity is:

[0057] Tuni=(Tmax-Tmin) / (Tmax+Tmin).

[0058] Since the units of the maximum film thickness value Tmax and the minimum film thickness value Tmin are both um, the calculated value of the film thickness uniformity is a percentage.

[0059] S2. If the film thickness uniformity is greater than or equal to the standard value, obtain the radial film thickness linear graph of the sample.

[0060] The test value calculated based on the Tuni formula for film thickness uniformity is compared with the standard value for film thickness uniformity, where the standard value for film thickness uniformity is 2%.

[0061] If the measured film thickness uniformity of the sample is less than 2% of the standard value, it means that the surface flatness of the sample is qualified. Accordingly, its production process can be directly used to produce finished sheets without adjustment.

[0062] If the measured film thickness uniformity of the sample is greater than or equal to the standard value of 2%, it means that the surface flatness of the sample is unqualified. Accordingly, it is necessary to further determine the linear relationship of the line graph of its radial film thickness.

[0063] When drawing a line graph of radial film thickness, it is only necessary to select any five test points 41 from the 49 test points just measured to complete a line connection, so as to observe the linear relationship of the line graph.

[0064] The positions of the five test points 41 are selected as follows: Figure 2The example in the sample in the upper right corner. That is, it is necessary to first obtain the test values ​​of the sample based on these test points 41 to draw a graph and obtain a linear graph of its radial position and film thickness. The linear graph of radial film thickness of the sample is obtained by taking the position of each test point in the test path as the X-axis and the film thickness corresponding to each test point as the Y-axis. The linear graph formed is the radial film thickness linear graph. Among them, the intersection point between the X-axis and the Y-axis is the starting point in the test path 40, and its end point is the point close to one side of the V-groove.

[0065] S3. Based on the radial film thickness linear diagram, the radial film thickness linear relationship is obtained.

[0066] The radial film thickness linear graph includes linear and nonlinear relationships, that is, for each group of radial film thickness linear graphs, based on its graph, it can be intuitively observed whether the film thickness values ​​of these test points 41 are in a linear relationship of gradual increase or decrease, or a fluctuating nonlinear relationship (figure omitted).

[0067] S4. Based on the linear relationship of the radial film thickness of the sample, determine the area where the minimum or maximum film thickness of the sample is located.

[0068] For the obtained radial film thickness line graph, when the relationship between the position of the test point 41 and its film thickness value is a linear relationship, it means that the film thickness changes from the starting point to the end point along the measurement path, gradually from high to low or from low to high. In this way, it can be determined that the film thickness change of the sample is across its surface, but the area where the minimum or maximum film thickness is located is mainly located at the edge of the sample.

[0069] When the position of the test point 41 in the radial film thickness line graph and its film thickness value are in a nonlinear relationship, it can be determined that the area where the minimum or maximum film thickness of the sample is located includes the non-V-groove position at the edge of the sample, the inside of the sample and the V-groove position.

[0070] S5. Based on the area where the minimum or maximum film thickness is located, the corresponding process during the sheet growth is adjusted to obtain a qualified sheet.

[0071] When the position of the test point 41 in the radial film thickness line graph is linearly related to its film thickness value, it can be determined that the area where the minimum film thickness of the sample is located is located at the edge of the sample, and its film thickness changes gradually from high to low or from low to high along the measurement path. At this time, it is necessary to adjust the air flow rate on the left and right sides of the air intake pipe 2 32 during growth, or only adjust the air flow rate on the air intake pipe 1 31 in the middle position, so as to change the circulation intensity of the growth gas on both sides. The purpose is to increase the gas flow rate on both sides to change the gas flow intensity at this position, thereby increasing the growth film thickness value at this position.

[0072] When the radial film thickness line graph presents a nonlinear relationship, if the area where the minimum film thickness of the sample is located is at the non-V-groove position at the edge of the sample, it indicates that the film thickness at the edge is relatively low, indicating that when growing in the growth furnace, the temperature at the edge of the placement plate 20 is lower than the standard temperature when it rotates, so it is necessary to adjust the process temperature during growth, that is, to increase the original growth temperature by 1-10°C.

[0073] When the area where the minimum film thickness of the sample is located is inside the sample, it indicates that the film thickness inside the sample is low, and the position of the coil used to heat the temperature inside the sample is adjusted; this is because during growth, the sample body needs to be heated by the heating coil placed under the placement plate 20, and the vertical distance between the coil and the sample is shortened to increase the growth temperature time.

[0074] When the area with the maximum film thickness of the sample is in the V-groove, it indicates that the film thickness of the V-groove is thicker, and the airflow state corresponding to the V-groove position is changed, that is, the coordination state of some needle valves 34 on the distribution pipes 33 on both sides and the corresponding air inlet holes 34 is controlled to close the air inlet holes 34, that is, the needle valve 34 is controlled to be inserted into the corresponding inlet hole 34, so as to adjust the growth film thickness value at this position.

[0075] In order to enable those skilled in the art to further understand the method of the present invention, the technical solution of the present invention will be explained in detail below in conjunction with specific embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments.

[0076] The following takes an 8-inch substrate epitaxial wafer as an example, and the details are as follows:

[0077] Embodiment 1:

[0078] When the relationship between the position of the test point 41 and its film thickness value is linear, and the film thickness changes from high to low along the measurement path from the starting point to the end point, at this time, the film thickness at the location of the V-groove is the lowest. In this way, it can be determined that the film thickness change of the sample is across its surface, but the area with the minimum film thickness is mainly located at the edge of the sample.

[0079] An 8-inch substrate was introduced into the growth furnace chamber to grow 90um thick epitaxial growth. The main hydrogen was set to 180SLM, the growth temperature was set to 1050°C, the trichlorosilane flow rate was set to 11SLM, the first step of heating to 1000°C took 1200s, the second step of heating to 1050°C took 360s, the growth time was set to 2990s, the doping dilution hydrogen flow rate was set to 25SLM, the doping flow rate was set to 45Sccm, and the grown epitaxial wafer was obtained.

[0080] Five test points 41 are set in a preset area in the epitaxial wafer, and the film thickness uniformity Tuni=2.1% is obtained, which is greater than the standard value of 2%, and its radial film thickness line graph is linear, and the lowest point of the film thickness is located at the V groove.

[0081] The specific adjustment process is:

[0082] Increase the air flow on the left and right intake ducts 32 or only reduce the air flow on the middle intake duct 1 31. Figure 2 The control valves 36 in the left and right air intake pipes 32 are used to adjust the gas flow entering the two air intake pipes 32 so that the air flow in the left and right air intake pipes is adjusted from 28 SLM to 29.2 SLM.

[0083] Based on the adjusted process, the film thickness uniformity of the epitaxial wafer finally obtained is Tuni=1.42%, which is less than the standard value of 2%. The surface flatness test of the epitaxial wafer results in TIR=2.3, which meets the card control standard.

[0084] When the relationship between the position of the test point 41 and its film thickness value is a nonlinear relationship, such as in the following embodiments, specifically:

[0085] Embodiment 2:

[0086] like Figure 3 The fitting diagram of the film thickness test shown in the figure shows that the V groove is set downward, that is, it is at the lowest point of the figure. It can be seen from the figure that the area where the minimum film thickness of the sample is located is at the non-V groove position at the edge of the sample, indicating that the film thickness at the edge is low. The process temperature during growth is adjusted, that is, the original growth temperature is increased by 1-10℃.

[0087] The 8-inch substrate was introduced into the growth furnace chamber to grow 130um thick epitaxial growth. The main hydrogen was set to 180SLM, the growth temperature was set to 1050°C, the trichlorosilane flow rate was set to 11SLM, the first step of heating to 1000°C took 1200s, the second step of heating to 1050°C took 360s, the growth time was set to 4230s, the doping dilution hydrogen flow rate was set to 28SLM, the doping flow rate was set to 32.5Sccm, and the epitaxial wafer was obtained.

[0088] Then, 49 test points 41 are set in a preset area in the epitaxial wafer, and the film thickness uniformity Tuni=2.26% is obtained, which is greater than the standard value of 2%; and the radial film thickness line graph thereof shows a nonlinear relationship.

[0089] The specific adjustment process is:

[0090] The process temperature is increased by 5°C, that is, in the first step of heating, the temperature remains unchanged; but in the second step of heating, the original temperature of 1050°C is increased to 1055°C, and the growth temperature is increased from the original 1050°C to 1055°C.

[0091] Based on the adjusted process, the film thickness uniformity of the epitaxial wafer finally obtained is Tuni=1.57%, which is less than the standard value of 2%. The surface flatness test of the epitaxial wafer is carried out, and TIR=2.7 is obtained, which meets the card control standard.

[0092] Embodiment three:

[0093] like Figure 4 The fitting diagram of the film thickness test shown in the figure shows that the V-groove is set downward, that is, it is at the lowest point of the diagram. It can be seen from the figure that the area where the minimum film thickness of the sample is located is inside the sample, indicating that the film thickness inside the sample is low; the position of the coil used to heat the temperature inside the sample is adjusted to shorten the vertical distance between the coil and the sample.

[0094] The 8-inch substrate was introduced into the growth furnace chamber to grow 90um thick epitaxial growth. The main hydrogen was set to 180SLM, the growth temperature was set to 1050°C, the trichlorosilane flow rate was set to 11SLM, the first step of heating to 1000°C took 1200s, the second step of heating to 1050°C took 360s, the growth time was set to 2990s, the doping dilution hydrogen flow rate was set to 25SLM, the doping flow rate was set to 45Sccm, and the epitaxial wafer was obtained.

[0095] Then 49 test points 41 are set in a preset area in the epitaxial wafer, and the film thickness uniformity Tuni=2.38% is obtained, which is 2% greater than the standard value, and its radial film thickness line graph is nonlinear, and the lowest point of the film thickness limit is located inside the epitaxial wafer.

[0096] The specific adjustment process is:

[0097] The coil below the lowest point of the film thickness is adjusted from 18 mm to 16 mm from the base, that is, the height of the coil below the lowest point of the epitaxial wafer film thickness is increased by 2 mm.

[0098] Based on the adjusted process, the film thickness uniformity of the epitaxial wafer finally obtained is Tuni=1.7%, which is less than the standard value of 2%. The surface flatness test of the epitaxial wafer is performed and TIR=4.2 is obtained, which meets the card control standard.

[0099] Embodiment 4:

[0100] like Figure 5The fitting diagram of the film thickness test is shown in the figure. At this time, the V groove is set downward, that is, it is at the lowest point of the figure. It can be seen from the figure that the area where the maximum film thickness of the sample is located is at the V groove position of the sample, indicating that the V groove film thickness is high, and the working state of the regulating valve on the intake pipe corresponding to the V groove position is changed.

[0101] The 8-inch substrate was introduced into the growth furnace chamber to grow 130um thick epitaxial growth. The main hydrogen gas was set to 180SLM, the growth temperature was set to 1050°C, the trichlorosilane flow rate was set to 11SLM, the first step of heating to 1000°C took 1200s, the second step of heating to 1050°C took 360s, the growth time was set to 4230s, the doping dilution gas flow rate was set to 28SLM, the doping flow rate was set to 32.5Sccm, and the epitaxial wafer was obtained.

[0102] Then 49 test points 41 are set in a preset area in the epitaxial wafer, and the film thickness uniformity Tuni=2.5% is obtained, which is greater than the standard value of 2%, and its radial film thickness line graph is nonlinear, and the highest point of the film thickness is located at the V-groove position in the epitaxial wafer.

[0103] The specific adjustment process is:

[0104] Adjust as Figure 2 The coordination state of the individual needle valve 35 and the air inlet hole 32 on the distribution pipe 33 connected to the second air inlet pipe 32 is shown to adjust the air flow intensity at this position.

[0105] Specifically, control Figure 2 The matching state of the fifth needle valve 35 from outside to inside on the distribution pipes 33 on the left and right sides and its corresponding air inlet hole 33. That is, the fifth needle valve 35 is controlled to be inserted into the fifth air inlet hole 33, so that the fifth air inlet hole 33 is adjusted from an open state to a closed state. By adjusting the working state of the two air inlet holes 33 on both sides. Then adjust the control valve 36 in the air inlet pipe 2 32 on both sides, and synchronously control the flow rate of the air inlet airflow in the air inlet pipe 2 32 on both sides, and adjust them from 29.2SLM to 29.6SLM, so as to improve the film thickness size at the V-groove position.

[0106] Based on the adjusted process, the film thickness uniformity of the epitaxial wafer finally obtained is Tuni=1.7%, which is less than the standard value of 2%. The surface flatness test of the epitaxial wafer is performed and TIR=4.2 is obtained, which meets the card control standard.

[0107] From the above, it can be seen that a method for controlling the surface flatness of a large-size epitaxial wafer designed in this application can be used. Through different control methods, the positions of different film thicknesses can be adjusted in a targeted manner, which can effectively solve the problem of large or abnormal surface flatness differences, obtain accurate and qualified surface flatness, improve the surface quality of epitaxial wafers, reduce production costs, and the control method is effective, safe and reliable.

[0108] The above detailed description of the embodiments of the present application is only a preferred embodiment of the present application and cannot be considered to limit the scope of implementation of the present application. All equivalent changes and improvements made within the scope of the present application should still fall within the scope of the patent coverage of the present application.

Claims

1. A method for controlling the surface flatness of a large-size epitaxial wafer, characterized in that the steps include: Detect the film thickness of the grown sample and obtain its film thickness uniformity; If the film thickness uniformity is greater than or equal to the standard value, obtain the radial film thickness linear graph of the sample; Based on the radial film thickness linear diagram, the radial film thickness linear relationship is obtained; Based on the linear relationship of the radial film thickness of the sample, the area where the minimum or maximum film thickness of the sample is located is determined; based on the area where the minimum or maximum film thickness is located, the corresponding process during the sheet growth is adjusted to obtain a qualified sheet.

2. The method for controlling the surface flatness of a large-size epitaxial wafer according to claim 1, characterized in that: The film thickness of the sample after growth is detected by: The diameter of the V-groove in the selected sample is the film thickness measurement path; Taking the end of the measuring path away from the V-groove as the starting point, n test points are selected in a preset range on the measuring path, and all the test points are symmetrical with respect to the center of the sample, where n is an odd number; The outermost edge of the preset range is 3 mm from the edge of the sample.

3. The method for controlling the surface flatness of a large-size epitaxial wafer according to claim 2, characterized in that: The obtaining of the uniformity of the film thickness is specifically as follows: Based on the film thickness results of each test point, select the maximum film thickness value Tmax and the minimum film thickness value Tmin; Then, based on the formula, the film thickness uniformity Tuni of the sample is calculated; The formula is: Tuni=(Tmax-Tmin) / (Tmax+Tmin).

4. The method for controlling the surface flatness of a large-size epitaxial wafer according to claim 1, characterized in that: The standard value of the film thickness uniformity is 2%; If the film thickness uniformity of the sample is measured to be less than 2%, the surface flatness of the sample is qualified and the sample can be directly produced into a sheet.

5. A method for controlling the surface flatness of a large-size epitaxial wafer according to any one of claims 2 to 4, characterized in that: The radial film thickness linear graph of the sample is obtained by taking the position of each test point in the test path as the X-axis and the film thickness corresponding to each test point as the Y-axis to form a line graph, which is the radial film thickness linear graph; The radial film thickness linear diagram includes a linear relationship and a nonlinear relationship.

6. The method for controlling the surface flatness of a large-size epitaxial wafer according to claim 5, characterized in that: When the radial film thickness line graph is linear, it can be determined that the area where the minimum film thickness of the sample is located is located at the edge of the sample, and its film thickness changes gradually from high to low or from low to high along the measurement path; adjust the flow rate of the intake pipeline during growth.

7. The method for controlling the surface flatness of a large-size epitaxial wafer according to claim 5, characterized in that: When the radial film thickness line graph is nonlinear, it can be determined that the area where the minimum film thickness of the sample is located includes the non-V-groove position of the edge of the sample, the inside of the sample and the V-groove position.

8. The method for controlling the surface flatness of a large-size epitaxial wafer according to claim 7, characterized in that: When the area where the minimum film thickness of the sample is located is at the non-V-groove position at the edge of the sample, it indicates that the film thickness at the edge is low, and the process temperature during its growth is adjusted, that is, the original growth temperature is increased by 1-10°C.

9. The method for controlling the surface flatness of a large-size epitaxial wafer according to claim 7, characterized in that: When the area where the minimum film thickness of the sample is located is inside the sample, it indicates that the film thickness inside the sample is thicker. The position of the coil used to heat the temperature inside the sample is adjusted to shorten the vertical distance between the coil and the sample.

10. The method for controlling the surface flatness of a large-size epitaxial wafer according to claim 7, characterized in that: When the area where the maximum film thickness of the sample is located is in the V-groove, the matching relationship between the needle valve on the air intake pipe corresponding to the V-groove position and the corresponding air intake hole is changed.

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