Method for improving the uniformity of the doping concentration of silicon carbide epitaxial wafer by double doping

Abstract

The application discloses a method for improving the doping concentration uniformity of a silicon carbide epitaxial wafer by double doping, and belongs to the field of semiconductors. The method uses N2 and NH3 double doping for epitaxy, combines the U-shaped concentration distribution caused by single doping of N2 and the A-shaped concentration distribution caused by single doping of NH3, uses the N2+NH3 double doping scheme, can flatten the concentration distribution in the silicon carbide wafer, forms a linear distribution, and further completely improves the doping concentration uniformity, and the uniformity can be controlled to be less than 2%. In addition, the concentration drift between furnaces is very small, and it is not necessary to real-time regulate and control an epitaxial process formula to ensure that the concentration average value and the uniformity are in the required range. The application has the advantages of saving cost, improving production efficiency, ensuring high-quality epitaxial uniformity and being suitable for large-batch epitaxial production.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of semiconductors, and in particular to a method for improving the doping concentration uniformity of silicon carbide epitaxial wafers by double doping. BACKGROUND

[0002] Silicon carbide material has excellent electrical properties such as wide band gap, high breakdown electric field, high saturation drift velocity, high thermal conductivity, etc., and is particularly suitable for making high-power, high-frequency, high-temperature and radiation-resistant electronic devices, and has a wide range of applications in solar and wind power generation, rail transportation, smart grid, electric vehicles, etc. The thickness and doping concentration and uniformity of silicon carbide epitaxial wafers play an important role in the voltage and current specifications of silicon carbide devices. At present, the non-uniformity of the doping concentration of silicon carbide epitaxial wafers produced by various manufacturers can be controlled to <5%.

[0003] Single-wafer and multi-wafer silicon carbide epitaxial furnaces mainly control the doping concentration uniformity by changing the N2 flow rate and ratio, C / Si ratio, temperature, and main hydrogen flow rate. Although the doping concentration uniformity can be relatively well controlled, the uniformity can be controlled to <5%. However, due to the complex relationship between the gas floating structure and the temperature field of the epitaxial furnace, the N2 single-doping scheme results in in-doping non-uniformity of the wafer, and the doping concentration curve presents a U-shaped distribution, as shown in Figure 1 .

[0004] In addition to N2, NH3 can also be used as an N-type dopant for silicon carbide epitaxy. Due to the difference in dissociation energy (435 kJ / mol) between NH3 and N2 (945 kJ / mol). The thermal decomposition temperature of NH3 is 400-500℃, while the decomposition temperature of N2 is higher, at 2000-3000℃, so the doping efficiency of NH3 is much higher than that of N2. Although the doping efficiency of NH3 is high, when used as a single dopant, it is also limited by the complex relationship between the gas floating structure and the temperature field of the epitaxial furnace. The NH3 single-doping scheme results in in-doping non-uniformity of the wafer, and the doping concentration curve presents an A-shaped distribution, as shown in Figure 2 .

[0005] In addition, the average value of the doping concentration will drift significantly with the increase of the furnace number. Therefore, the epitaxial process engineer needs to adjust the process recipe in real time and verify the concentration of the epitaxial wafer to control the doping concentration and uniformity. This often requires several growths to obtain a process recipe that meets the requirements. Considering the cost and efficiency, the N2 or NH3 single-doping scheme is not conducive to mass production of silicon carbide epitaxial wafers. SUMMARY

[0006] The present application overcomes at least one of the above problems and provides a method for improving the doping concentration uniformity of silicon carbide epitaxial wafers by double doping.

[0007] The technical solutions adopted by the present application are as follows:

[0008] A method for improving the uniformity of the doping concentration of a silicon carbide epitaxial wafer by double doping, comprising the following steps:

[0009] Using single N2 doping epitaxy, with an N2 flow rate of A sccm, the N2 doping concentration Bi at selected x coordinate points on the silicon carbide wafer is measured, and the N2 doping efficiency Ci at each coordinate point is obtained, Ci = Bi / A.

[0010] Using single NH3 doping epitaxy, with an NH3 flow rate of D sccm, the NH3 doping concentration Ei at selected x coordinate points on the silicon carbide wafer is measured, and the NH3 doping efficiency Fi at each coordinate point is obtained, Fi = Ei / D.

[0011] The flow rates of N2 and NH3 during double doping are calculated: the target doping concentration value is set to G, the doping concentration tolerance is set to M, the N2 flow rate is set to I sccm, the NH3 flow rate is set to J sccm, and the double doping concentration of N2 and NH3 at the selected x coordinate points on the silicon carbide wafer is Ki, Ki = Ci*I + Fi*J. The average value L of the double doping concentration of N2 and NH3 is obtained from the double doping concentrations of N2 and NH3 at the x different coordinate points on the silicon carbide wafer. The doping concentration tolerance M is obtained from the maximum value Max(Ki) of the double doping concentration of N2 and NH3 at different coordinate points on the silicon carbide wafer, the minimum value Min(Ki) of the double doping concentration of N2 and NH3, and the average value L of the double doping concentration of N2 and NH3. By setting two constraint conditions, the specific values of the N2 flow rate I and the NH3 flow rate J are obtained by optimization, wherein one constraint condition is that L reaches the target doping concentration value G, and the other constraint condition is that the doping concentration tolerance M takes the minimum value.

[0012] Using N2 and NH3 double doping for epitaxy, with an N2 flow rate of I sccm and an NH3 flow rate of J sccm, the double doping concentrations of N2 and NH3 at x different coordinate points on the silicon carbide wafer are measured, and the actual average doping concentration L' and the actual doping concentration tolerance M' are obtained. It is determined whether the deviation rate of the actual average doping concentration L' from the target doping concentration value G is less than a first set value, and whether the actual doping concentration tolerance M' is less than a second set value. If the deviation rate of the actual average doping concentration L' from the target doping concentration value G is less than the first set value and the actual doping concentration tolerance M' is less than the second set value, then continuous production can be repeated. Otherwise, adjust the N2 flow rate and the NH3 flow rate by a concentration correction factor N, obtain the specific value of the concentration correction factor N from the formula G = N*L', adjust the N2 flow rate to N*I sccm, and adjust the NH3 flow rate to N*J sccm.

[0013] This application proposes a dual-doping scheme of N2+NH3, which combines the U-shaped concentration distribution caused by single-doping N2 and the A-type concentration distribution caused by single-doping NH3. The dual-doping scheme of N2+NH3 can flatten the concentration distribution within the silicon carbide wafer to form a linear distribution, thereby completely improving the uniformity of the doping concentration, and the uniformity can be controlled to <2%. In addition, the concentration drift between furnaces is very small, and there is no need to adjust the epitaxial process recipe in real time to ensure that the concentration average and uniformity are within the required range. This application has the advantages of saving costs, improving production efficiency, ensuring high-quality epitaxial uniformity, and being suitable for large-scale epitaxial production.

[0014] In one embodiment of the present invention, the first setting value is 2% to 3%.

[0015] In one embodiment of the present invention, the first setting value is 1% to 2%.

[0016] In one embodiment of the present invention, the doping concentration on the silicon carbide wafer is measured using a mercury probe CV device.

[0017] In one embodiment of the present invention, x is any value between 5 and 25.

[0018] In one embodiment of the present invention, doping and epitaxy are performed on silicon carbide wafers using epitaxial growth equipment, which is a horizontal single-wafer or multi-wafer epitaxial furnace, a vertical single-wafer or multi-wafer epitaxial furnace, a hot-wall horizontal CVD, a warm-wall planetary CVD, or a quasi-hot-wall vertical CVD.

[0019] In one embodiment of the present invention, the size of the silicon carbide wafer is 4 inches to 12 inches.

[0020] In one embodiment of the present invention, the size of the silicon carbide wafer is 4 inches, 6 inches, 8 inches, or 12 inches.

[0021] The beneficial effects of the present invention are as follows: This application proposes a dual-doping scheme of N2+NH3, which combines the U-shaped concentration distribution caused by single-doping N2 and the A-type concentration distribution caused by single-doping NH3. Using the dual-doping scheme of N2+NH3, the concentration distribution within the silicon carbide wafer can be flattened to form a linear distribution, thereby completely improving the uniformity of the doping concentration, and the uniformity can be controlled to <2%. In addition, the concentration drift between furnaces is very small, and there is no need to adjust the epitaxial process recipe in real time to ensure that the concentration average and uniformity are within the required range. The present application has the advantages of saving costs, improving production efficiency, ensuring high-quality epitaxial uniformity, and being suitable for large-scale epitaxial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a schematic diagram of the U-shaped curve of doping concentration of a single doped N2 epitaxial wafer;

[0023] Figure 2 is a single-doped NH3epilayer doping concentration A-type curve schematic diagram;

[0024] Figure 3 is a double-doped N2and NH3epilayer doping concentration linear curve schematic diagram;

[0025] Figure 4 is a wafer doping concentration distribution curve diagram of four runs of continuous production using N2and NH3double-doped SiC epitaxial doping process;

[0026] Figure 5 is a wafer doping concentration mean value and uniformity data summary diagram of four runs of continuous production using N2and NH3double-doped SiC epitaxial doping process;

[0027] Figure 6 is a flowchart schematic diagram of a method for improving the doping concentration uniformity of a silicon carbide epitaxial wafer. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical scheme and advantages of the embodiments of the present application clearer, the technical scheme in the embodiments of the present application will be described clearly and completely below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are some embodiments of the present application, not all embodiments of the present application. The components of the embodiments of the present application described and shown in the drawings herein can be arranged and designed in various different configurations.

[0029] In the description of the present application, it should be noted that the directions or position relationships indicated by the terms “in”, “out” and the like are based on the directions or position relationships shown in the drawings, or the directions or position relationships in which the products of the present application are usually placed, and are only for the convenience of describing the present application and simplifying the description, and therefore cannot be understood as indicating or implying that the devices or elements referred to must have a particular direction, be constructed and operated in a particular direction, and therefore cannot be understood as limiting the present application. In addition, the terms “first”, “second” and the like are only used for differentiation and description, and cannot be understood as indicating or implying relative importance.

[0030] In the description of the present application, it should be noted that, unless otherwise explicitly specified and limited, the terms “set”, “connected” should be understood broadly, for example, can be fixedly connected, can be detachably connected, or integrally connected; can be directly connected, or indirectly connected through an intermediate medium, or can be connected inside two elements. For those skilled in the art, the specific meanings of the above terms in the present application can be understood according to the specific circumstances.

[0031] The present application will be described in detail below in conjunction with the drawings.

[0032] As Figure 6As shown, a method for improving the doping concentration uniformity of a double-doped silicon carbide epitaxial wafer includes the following steps:

[0033] Using single N2 doping epitaxy, N2 flow is A sccm, and the N2 doping concentration Bi at selected x (x is preferably 5-25, and 5 in this embodiment) coordinate points on the silicon carbide wafer is measured to obtain the N2 doping efficiency Ci (i = 1, 2, 3, 4, 5) of each coordinate point, Ci = Bi / A, as shown in Table 1.

[0034] Table 1 (N2 doping concentration and doping efficiency at different coordinate points)

[0035]

[0036] Using single NH3 doping epitaxy, NH3 flow is D sccm, and the NH3 doping concentration Ei at selected x coordinate points on the silicon carbide wafer is measured to obtain the NH3 doping efficiency Fi (i = 1, 2, 3, 4, 5) of each coordinate point, Fi = Ei / D, as shown in Table 2.

[0037] Table 2 (NH3 doping concentration and doping efficiency at different coordinate points)

[0038]

[0039] The flow rates of N2 and NH3 during N2 and NH3 double doping are calculated:

[0040] The target doping concentration is set to G, the doping concentration tolerance is set to M, the N2 flow rate is set to I sccm, and the NH3 flow rate is set to J sccm. At this time, the N2 and NH3 double doping concentration at the selected x coordinate points on the silicon carbide wafer is Ki, Ki = Ci*I + Fi*J (i = 1, 2, 3, 4, 5), as shown in Table 3. The average value L of the N2 and NH3 double doping concentration is obtained from the N2 and NH3 double doping concentration at the x different coordinate points on the silicon carbide wafer, The doping concentration tolerance M is obtained from the maximum value Max(Ki) of the N2 and NH3 double doping concentration at different coordinate points on the silicon carbide wafer, the minimum value Min(Ki) of the N2 and NH3 double doping concentration, and the average value L of the N2 and NH3 double doping concentration, By setting two constraint conditions, the specific values of N2 flow rate I and NH3 flow rate J are obtained, one of which is that L reaches the target doping concentration G, and the other is that the doping concentration tolerance M takes the minimum value;

[0041] Table 3. Doping concentration at different coordinate points during N2 and NH3 double doping.

[0042]

[0043] The N2 and NH3 double-doping is performed by using N2 flow rate of I sccm and NH3 flow rate of J sccm, and the actual N2 and NH3 double-doping concentrations K' i of five different coordinate points on the silicon carbide wafer are measured by mercury probe CV and other devices, the specific coordinate points are the same as above, and the actual doping concentration average L' is obtained, and the actual doping concentration tolerance M', whether the deviation rate of the actual doping concentration average L' and the doping concentration target value G is less than the first set value, the deviation rate=(L'-G) / G*100%, whether the actual doping concentration tolerance M' is less than the second set value, if the deviation rate of the actual doping concentration average L' and the doping concentration target value G is less than the first set value and the actual doping concentration tolerance M' is less than the second set value, the continuous production can be repeated, otherwise the N2 flow rate and the NH3 flow rate are adjusted by the concentration correction factor N, the specific value of the concentration correction factor N is obtained from the formula G=N*L', the N2 flow rate is adjusted to N*I sccm, and the NH3 flow rate is adjusted to N*J sccm.

[0044] As Figure 3 , Figure 4 and Figure 5 indicated, the embodiment proposes a N2+NH3 double-doping scheme, which combines the U-shaped concentration distribution caused by single-doping N2 and the A-shaped concentration distribution caused by single-doping NH3, and the N2+NH3 double-doping scheme can flatten the concentration distribution in the silicon carbide wafer to form a straight line distribution (see Figure 3 ), and further completely improve the doping concentration uniformity, and the uniformity can be controlled to be less than 2%. In addition, the concentration drift between furnaces is very small, and there is no need to real-time adjust the epitaxial process formula to ensure that the concentration average and the uniformity are in the required range. The application has the advantages of saving cost, improving production efficiency, ensuring high-quality epitaxial uniformity and being suitable for large-batch epitaxial production.

[0045] It should be noted that the N2 flow rate of the embodiment is A sccm, which is not a normal production value, but a set value, so that the corresponding doping concentration range is 1E16-6E16 (high concentration is selected to reduce the mercury probe CV concentration test error), and mainly to calculate the N2 doping efficiency corresponding to different positions on the wafer. Similarly, the NH3 flow rate of the embodiment is D sccm, which is a set value.

[0046] It should be noted that, in the three doping process parameters of "single N2 doping epitaxy", "single NH3 doping epitaxy" and "N2 and NH3 double-doping epitaxy", only the N2 flow rate and the NH3 flow rate are different, and other parameters are the same (other parameters include C / Si ratio, cavity pressure, temperature, main hydrogen flow rate, etc.).

[0047] In practical application, the first set value is 1% to 3%, preferably 2%. The x is any value in the range of 5 to 25.

[0048] In practical application, the silicon carbide wafer is doped and epitaxied by an epitaxial device, which is a horizontal single or multiple wafer epitaxial furnace, a vertical single or multiple wafer epitaxial furnace, a hot wall horizontal CVD, a warm wall planetary CVD or a quasi-hot wall vertical CVD.

[0049] In practical application, the embodiment can be used in the manufacture of 4-inch, 6-inch, 8-inch or 12-inch silicon carbide wafers. When the embodiment is used for specific epitaxy, a buffer layer is first epitaxially grown on a silicon carbide substrate, the buffer layer is only doped with N2 (temperature 1550°C to 1670°C, cavity pressure 80mbar to 120mbar, carbon to silicon ratio 0.9 to 1.5, growth rate 2um / h to 15um / h, growth time 4min to 30min), and then a voltage-resistant layer is epitaxially grown, the voltage-resistant layer is doped with N2 and NH3 (temperature 1550°C to 1670°C, cavity pressure 80mbar to 120mbar, carbon to silicon ratio 0.3 to 1.3, growth rate 20um / h to 90um / h, growth time 8min to 36min).

[0050] The above description is only the preferred embodiment of the present application, and does not limit the patent protection scope of the present application. Any equivalent structural transformation, direct or indirect application in other related technical fields, and the like are all included in the protection scope of the present application.

Claims

1. A method for improving the uniformity of doping concentration of silicon carbide epitaxial wafers by dual doping, characterized in that: The method comprises the following steps: using single N2-doped epitaxy, measuring N2-doping concentrations Bi at selected x coordinate points on the silicon carbide wafer with an N2 flow of A sccm, obtaining N2-doping efficiencies Ci of the coordinate points, Ci = Bi / A; using single NH3-doped epitaxy, measuring NH3-doping concentrations Ei at selected x coordinate points on the silicon carbide wafer with an NH3 flow of D sccm, obtaining NH3-doping efficiencies Fi of the coordinate points, Fi = Ei / D; Flow of N2 and NH3 when N2 and NH3 are doped: the target value of the doping concentration is G, the tolerance of the doping concentration is M, the flow of N2 is I sccm, the flow of NH3 is J sccm, the N2 and NH3 double doping concentration at selected x coordinate points on the silicon carbide wafer is Ki, Ki=Ci*I+Fi*J, the average value L of the N2 and NH3 double doping concentration is obtained from the N2 and NH3 double doping concentration at x different coordinate points on the silicon carbide wafer, The tolerance M of the doping concentration is obtained from the maximum value Max(Ki) of the N2 and NH3 double doping concentration at different coordinate points on the silicon carbide wafer, the minimum value Min(Ki) of the N2 and NH3 double doping concentration, and the average value L of the N2 and NH3 double doping concentration, By setting two constraint conditions, the specific values of the flow of N2 I and the flow of NH3 J are obtained by optimization, wherein one constraint condition is that L reaches the target value G of the doping concentration, and the other constraint condition is that the tolerance M of the doping concentration takes the minimum value; using N2 and NH3 double-doped epitaxy, measuring N2 and NH3 double-doping concentrations at x different coordinate points on the silicon carbide wafer with an N2 flow of I sccm and an NH3 flow of J sccm, obtaining an actual doping concentration average value L' and an actual doping concentration tolerance M', judging whether a deviation rate of the actual doping concentration average value L' from a doping concentration target value G is less than a first set value and whether the actual doping concentration tolerance M' is less than a second set value, if the deviation rate of the actual doping concentration average value L' from the doping concentration target value G is less than the first set value and the actual doping concentration tolerance M' is less than the second set value, then the continuous production can be repeated, otherwise, adjusting the N2 flow and the NH3 flow by a concentration correction factor N, obtaining a specific value of the concentration correction factor N from the formula G = N*L', adjusting the N2 flow to N*I sccm and adjusting the NH3 flow to N*J sccm.

2. The method for improving the dopant concentration uniformity of a dual-doped silicon carbide epitaxial layer as recited in claim 1, wherein, The first set value is 2% to 3%.

3. The method for improving the dopant concentration uniformity of a dual-doped silicon carbide epitaxial layer as recited in claim 1, wherein, The first set value is 1% to 2%.

4. The method for improving the dopant concentration uniformity of a dual doped silicon carbide epitaxial layer as recited in claim 1, wherein, The doping concentration on the silicon carbide wafer is measured by a mercury probe CV device.

5. The method for improving the dopant concentration uniformity of a silicon carbide epitaxial layer of a dual doped silicon carbide epitaxial wafer of claim 1, wherein, The x is any value in the range of 5 to 25.

6. The method for improving the dopant concentration uniformity of a dual doped silicon carbide epitaxial layer as recited in claim 1, wherein, The silicon carbide wafer is doped by an epitaxy device, which is a horizontal single-wafer or multi-wafer epitaxy furnace, a vertical single-wafer or multi-wafer epitaxy furnace, a hot-wall horizontal CVD, a warm-wall planetary CVD or a quasi-hot-wall vertical CVD.

7. The method for improving the dopant concentration uniformity of a silicon carbide epitaxial layer of a dual doped silicon carbide epitaxial wafer of claim 1, wherein, The size of the silicon carbide wafer is 4 inches to 12 inches.

8. The method for improving the dopant concentration uniformity of a dual-doped silicon carbide epitaxial layer as recited in claim 7, wherein, The size of the silicon carbide wafer is 4 inches, 6 inches, 8 inches or 12 inches.

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