Silicon carbide epitaxial growth pretreatment method and application thereof

Abstract

The invention discloses a pretreatment method for epitaxial growth of silicon carbide and application thereof, and relates to the technical field of semiconductors. The pretreatment method comprises the following steps: S1, placing a silicon carbide substrate in a reaction chamber of a silicon carbide epitaxial system; s2, the reaction pressure and the hydrogen flow are adjusted in at least one of the following modes a)-c): a) the reaction temperature is kept unchanged, the hydrogen flow is adjusted, then the reaction temperature and the hydrogen flow are kept unchanged, and the reaction pressure is adjusted; b) keeping the reaction temperature and the hydrogen flow unchanged, adjusting the reaction pressure, then keeping the reaction temperature and the reaction pressure unchanged, and adjusting the hydrogen flow; c) keeping the reaction temperature unchanged, and adjusting the hydrogen flow and the reaction pressure at the same time; s3, purging the surface of the silicon carbide substrate by using hydrogen; s4, keeping the hydrogen flow and the reaction pressure adjusted in the step S2 unchanged, and adjusting the reaction temperature; and S5, purging the surface of the silicon carbide substrate by using hydrogen.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor technology, and in particular to a pretreatment method for silicon carbide epitaxial growth and application thereof. Background Art

[0002] During the transmission and growth of SiC epitaxy, particles may fall on the wafer. Such falling objects are likely to cause triangular defects, which will expand with the increase of growth thickness, so the impact is very large when growing thick epitaxy. However, the growth conditions of the commonly used process for SiC epitaxial growth change too drastically, causing chamber disturbances and leading to an increase in falling objects.

[0003] In addition, the epitaxial growth process of silicon carbide often requires the chamber to be dismantled and polished. This is because a large amount of by-products are produced during the epitaxial growth process. After accumulating to a certain thickness, a large amount of by-products will fall on the wafer surface and affect the yield. Summary of the invention

[0004] The present invention aims to solve at least one of the above-mentioned technical problems existing in the prior art. To this end, the purpose of the present invention is to provide a pretreatment method for silicon carbide epitaxial growth, which solves the effect of falling objects on the wafer during silicon carbide epitaxial growth, especially thick epitaxial growth, by changing the pressure, temperature and gas flow in steps.

[0005] A second aspect of the present invention is to provide a method for epitaxial growth of silicon carbide.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] A first aspect of the present invention provides a pretreatment method for silicon carbide epitaxial growth, comprising the following steps:

[0008] S1. Placing a silicon carbide substrate in a reaction chamber of a silicon carbide epitaxial system;

[0009] S2. Adjust the reaction pressure and hydrogen flow rate, wherein the adjustment method is at least one of the following a) to c):

[0010] a) maintaining the reaction temperature unchanged, adjusting the hydrogen flow rate, and then maintaining the reaction temperature and the hydrogen flow rate unchanged, adjusting the reaction pressure;

[0011] b) maintaining the reaction temperature and the hydrogen flow rate unchanged, adjusting the reaction pressure, and then maintaining the reaction temperature and the reaction pressure unchanged, and adjusting the hydrogen flow rate;

[0012] c) maintaining the reaction temperature constant while adjusting the hydrogen flow rate and reaction pressure;

[0013] S3. Purge the surface of the silicon carbide substrate using hydrogen;

[0014] S4. Keep the hydrogen flow rate and the reaction pressure adjusted in step S2 unchanged and adjust the reaction temperature;

[0015] S5. Purge the surface of the silicon carbide substrate with hydrogen.

[0016] There may be dropped objects during the transmission process and the initial growth of silicon carbide epitaxial wafers. When the growth conditions such as pressure, temperature, and gas flow rate change simultaneously, a stable stratosphere cannot be formed in the initial stage, resulting in particles falling on the wafer and adhering to the wafer surface as the temperature rises. The present invention changes the change process of growth conditions in steps, and changes the pressure, temperature, and airflow in steps during the growth condition preparation process (i.e., the pretreatment process), as well as the wafer surface purge performed before the temperature is changed, to blow off the dropped objects during the transmission process and the initial stage, and then heat up to reduce the possibility of subsequent particles falling on the wafer surface, and then use it for subsequent epitaxial growth. The pretreatment method of the present invention can reduce a large number of by-products generated during the epitaxial growth process, thereby reducing the dropped objects that fall on the wafer surface to form defects, solves the impact of the early dropped objects on the wafer, and improves the growth yield of silicon carbide epitaxial wafers.

[0017] It should be understood that in a), the reaction temperature is kept constant and the pressure is also kept constant when the hydrogen flow rate is adjusted.

[0018] In some embodiments of the present invention, the silicon carbide substrate is placed on a graphite tray containing a silicon carbide and / or tantalum carbide coating in a reaction chamber of a silicon carbide epitaxial system.

[0019] The silicon carbide epitaxial growth system refers to a system used for silicon carbide epitaxial growth, and can be purchased commercially.

[0020] In some embodiments of the present invention, in step S2, the hydrogen flow rate is adjusted to 70-150 slm.

[0021] In some embodiments of the present invention, in step S2, the hydrogen flow rate is adjusted to 80-120 slm.

[0022] In some specific embodiments of the present invention, in step S2, the hydrogen flow rate is adjusted to 90-110 slm.

[0023] In some embodiments of the present invention, the rate of change during the hydrogen flow rate adjustment process is 0.05-0.15 slm / s.

[0024] In some embodiments of the present invention, the rate of change during the hydrogen flow rate adjustment process is 0.1-0.15 slm / s.

[0025] In some embodiments of the present invention, in step S2, the reaction pressure is adjusted to 50-150 mbar.

[0026] In some embodiments of the present invention, in step S2, the reaction pressure is adjusted to 80-120 mbar.

[0027] In some specific embodiments shown above, in step S2, the reaction pressure is adjusted to 90-110 mbar.

[0028] In some embodiments of the present invention, the rate of change during the reaction pressure adjustment process is 2-3 mbar / s.

[0029] In some embodiments of the present invention, the rate of change during the reaction pressure adjustment process is 2.5-3 mbar / s.

[0030] In some embodiments of the present invention, in step S4, the reaction temperature is adjusted to 950-1100°C.

[0031] In some embodiments of the present invention, in step S4, the reaction temperature is adjusted to 950-1050°C.

[0032] In some embodiments of the present invention, the rate of change during the reaction temperature adjustment process is 65-95 degC / min.

[0033] In some embodiments of the present invention, the rate of change during the reaction temperature adjustment process is 70-90 degC / min.

[0034] In some specific embodiments of the present invention, the rate of change during the reaction temperature adjustment process is 75-85 degC / min.

[0035] In some embodiments of the present invention, in step S4, the temperature before the reaction temperature is adjusted is 800-900°C.

[0036] In some embodiments of the present invention, in step S4, the temperature before the reaction temperature is adjusted is 850-900°C.

[0037] In some embodiments of the present invention, the hydrogen purging time in step S3 is 4 to 6 minutes.

[0038] In some embodiments of the present invention, the hydrogen purging time in step S5 is 2 to 4 minutes.

[0039] A second aspect of the present invention provides a method for epitaxial growth of silicon carbide, the method comprising the pretreatment method described in the first aspect of the present invention.

[0040] In some embodiments of the present invention, the method for epitaxial growth of silicon carbide comprises the following steps:

[0041] Preprocessing the silicon carbide substrate, wherein the preprocessing method is the preprocessing method described in the first aspect of the present invention;

[0042] Keeping the reaction pressure and hydrogen flow rate unchanged, continuing to raise the temperature to the buffer layer growth temperature, and etching the silicon carbide substrate;

[0043] Passing trichlorosilane, ethylene and nitrogen to grow a buffer layer;

[0044] The growth temperature of the buffer layer is kept unchanged, and the flow rates of ethylene and trichlorosilane are increased to grow the epitaxial layer.

[0045] In some embodiments of the present invention, the buffer layer growth temperature is 1550-1700°C.

[0046] In some embodiments of the present invention, the buffer layer growth temperature is 1580-1680°C.

[0047] In some specific embodiments of the present invention, the buffer layer growth temperature is 1600-1650°C.

[0048] In some embodiments of the present invention, after the temperature is raised to the buffer layer growth temperature, the temperature is maintained for 3 to 5 minutes to etch the silicon carbide substrate.

[0049] In some embodiments of the present invention, the buffer layer is grown to a thickness of 1 to 3 μm.

[0050] In some embodiments of the present invention, the doping concentration of the buffer layer is (1-2)×10 18 cm -3 .

[0051] In some embodiments of the present invention, the nitrogen gas is used as a doping source.

[0052] Compared with the prior art, the present invention has the following beneficial effects:

[0053] The pretreatment method of the present invention changes the pressure, temperature, and airflow in steps during the growth condition preparation process, and at the same time, the wafer surface is purged before the temperature is changed to blow off the dropped objects during the transmission process and the initial stage, and then the temperature is increased, which can reduce the large amount of byproducts generated during the epitaxial growth process from falling on the wafer surface, reduce the number of defects, and thus improve the growth yield of the epitaxial wafer. At the same time, epitaxial growth of silicon carbide is performed using the steps including the pretreatment method of the present invention, which not only reduces the defects of the silicon carbide epitaxial wafer and improves the yield, but also does not need to remove the chamber for polishing during the epitaxial growth process of silicon carbide, so the life of the equipment is extended each time it is used, and the frequency of equipment maintenance is reduced, which improves production efficiency and saves costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 The number of triangular defects caused by dropped objects in the three silicon carbide epitaxial wafers obtained in Example 1 of the present invention.

[0055] Figure 2 The number of triangular defects caused by dropped objects in the three silicon carbide epitaxial wafers obtained in Example 2 of the present invention.

[0056] Figure 3 The number of triangular defects caused by dropped objects in the three silicon carbide epitaxial wafers obtained in Example 3 of the present invention.

[0057] Figure 4 The number of triangular defects caused by dropped objects in the three silicon carbide epitaxial wafers obtained in Comparative Example 1 of the present invention.

[0058] Figure 5 The number of triangular defects caused by dropped objects in the three silicon carbide epitaxial wafers obtained in Comparative Example 2 of the present invention. DETAILED DESCRIPTION

[0059] The present invention is further described in detail below by specific examples. Unless otherwise specified, the raw materials, reagents or devices used in the examples and comparative examples can be obtained from conventional commercial sources or can be obtained by prior art methods. Unless otherwise specified, the experimental or testing methods are conventional methods in the art.

[0060] The specific examples and comparative examples are provided below for detailed description.

[0061] Example 1

[0062] A method for epitaxial growth of silicon carbide comprises the following steps:

[0063] Preprocessing:

[0064] S1. Select a standard silicon carbide substrate (Tianyue's P-grade N-type doped substrate) and place the substrate on a graphite tray containing a silicon carbide coating in the reaction chamber of the silicon carbide epitaxial system;

[0065] S2. The initial temperature of the reaction chamber is set to 900°C, the temperature is kept constant, the hydrogen flow rate is kept constant, and the pressure of the reaction chamber is reduced from 1008mbar to 100mbar, and the change rate is set to 2.5mbar / s; the temperature and pressure are kept constant, and the hydrogen flow rate of the reaction chamber of the silicon carbide epitaxial system is controlled to increase from 30slm to 100slm under a hydrogen atmosphere, and the change rate is set to 0.1slm / s;

[0066] S3. After the hydrogen flow rate and pressure of step S2 are stabilized, the surface of the silicon carbide substrate is purged with pure hydrogen for 5 minutes;

[0067] S4. Keeping the hydrogen flow rate and pressure unchanged, the temperature of the reaction chamber is controlled to rise from 900°C to 1000°C, and the change rate is set to 80degC / min;

[0068] S5. After the temperature stabilizes, purge with pure hydrogen for 3 minutes;

[0069] Growth Etching:

[0070] S6. Keeping other conditions unchanged, continue to raise the temperature to reach the buffer layer growth temperature of 1630°C, maintain the growth temperature for 3 minutes, and keep etching the silicon carbide substrate in situ;

[0071] Buffer layer growth:

[0072] S7. A flow rate of 70 sccm of trichlorosilane (SiHCl3), a flow rate of 21 sccm of ethylene (C2H4), and a flow rate of 40 sccm of doping source nitrogen (N2) were introduced into the reaction chamber to grow a layer with a thickness of 1 μm (±10%) and a doping concentration of 1×10 18 cm -3 (±15%) buffer layer.

[0073] Epitaxial layer growth:

[0074] S8. Maintaining the growth temperature unchanged, gradually increase the flow rates of ethylene, trichlorosilane and nitrogen to the stable flow rates required for conventional growth conditions, i.e., trichlorosilane is increased to 268 sccm, ethylene is increased to 113.5 sccm, and nitrogen is increased to 60 sccm, and an epitaxial layer is prepared at a conventional growth rate of 50 μm / h;

[0075] Growth completed:

[0076] S9. After the epitaxial layer structure growth is completed, the growth source and the doping source are turned off, and the wafer is taken out after the temperature is lowered to room temperature, thereby obtaining a silicon carbide epitaxial wafer.

[0077] Example 2

[0078] A method for epitaxial growth of silicon carbide, which differs from Example 1 in that, during the pretreatment process, the temperature is kept unchanged in step S2, and the hydrogen flow rate and the pressure of the reaction chamber are adjusted simultaneously with the same parameters as in Example 1; the rest is the same as in Example 1.

[0079] Example 3

[0080] A method for epitaxial growth of silicon carbide, which differs from Example 1 in that, during the pretreatment process, in step S2, the temperature and pressure are first kept unchanged, and the hydrogen flow rate of the reaction chamber of the silicon carbide epitaxial system is controlled to increase from 30 slm to 100 slm under a hydrogen atmosphere, and the change rate is set to 0.1 slm / s; the temperature is continued to be kept unchanged, the hydrogen flow rate is kept unchanged, the pressure of the reaction chamber is reduced from 1008 mbar to 100 mbar, and the change rate is set to 2.5 mbar / s; the rest is the same as Example 1.

[0081] Comparative Example 1

[0082] A method for epitaxial growth of silicon carbide, which differs from Example 1 in that, during the pretreatment process, step S4 is first performed, the hydrogen gas flow rate and the reaction chamber pressure are kept unchanged, and the temperature is adjusted to 1000°C with the same parameters as in Example 1, and then step S2 is performed, and step S2 is modified to keep the temperature unchanged and adjust the hydrogen gas flow rate and the reaction chamber pressure at the same time with the same parameters as in Example 1; the rest is the same as in Example 1.

[0083] Comparative Example 2

[0084] A method for epitaxial growth of silicon carbide is different from that of Example 1 in that, during the pretreatment process, step S2 and step S4 are performed simultaneously, that is, the pressure, temperature and hydrogen flow rate are adjusted simultaneously, and no purging is performed.

[0085] Results

[0086] The surface defects of the epitaxially grown silicon carbide epitaxial wafers obtained in the above embodiments and comparative examples were tested. Three epitaxial wafers were grown continuously for each embodiment or comparative example for testing. The wafer surface defect detector was Lasertec Sica88. The number of triangular defects caused by dropped objects in three samples of the same embodiment or comparative example was tested. The results are shown in FIG. Figures 1 to 5 And as shown in Table 1.

[0087] Table 1 Defect numbers at different angles of silicon carbide wafers obtained in the examples and comparative examples

[0088]

[0089]

[0090] Combination Figures 1 to 5As can be seen from Table 1, the silicon carbide substrate is pretreated by the step-by-step growth method of the present invention, and the number of defects of the silicon carbide wafer caused by the dropped objects is less than that of Comparative Example 1 and Comparative Example 2, especially when the reaction pressure, hydrogen flow rate and reaction temperature are adjusted step by step in Examples 1 and 3, the number of defects of the silicon carbide wafer obtained is the least, and the minimum in Example 1 is 5, with an average of 9.3, and the minimum in Example 3 is 6, with an average of 11.3. In Comparative Example 1, the adjustment order of the reaction temperature, reaction pressure and hydrogen flow rate is changed, and the reaction temperature is adjusted first, and the number of dropped defects of the obtained silicon carbide wafer increases significantly, and the number of defects is at least 3.5 times that of Example 1, and even more than the silicon carbide wafer obtained by adjusting the reaction pressure, reaction temperature and hydrogen flow rate at the same time in Comparative Example 1. It can be seen that the pretreatment method of the present invention can effectively reduce the number of defects formed by the dropped objects in the early stage of silicon carbide epitaxial growth by adjusting the pressure, temperature and airflow in steps, improve the growth yield, and help reduce the frequency of equipment maintenance, improve production efficiency and reduce costs.

[0091] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A pretreatment method for epitaxial growth of silicon carbide, characterized in that: The steps include: S1. Placing a silicon carbide substrate in a reaction chamber of a silicon carbide epitaxial system; S2. Adjust the reaction pressure and hydrogen flow rate, wherein the adjustment method is at least one of the following a) to c): a) maintaining the reaction temperature unchanged, adjusting the hydrogen flow rate, and then maintaining the reaction temperature and the hydrogen flow rate unchanged, adjusting the reaction pressure; b) maintaining the reaction temperature and the hydrogen flow rate unchanged, adjusting the reaction pressure, and then maintaining the reaction temperature and the reaction pressure unchanged, and adjusting the hydrogen flow rate; c) maintaining the reaction temperature constant while adjusting the hydrogen flow rate and reaction pressure; S3. Purge the surface of the silicon carbide substrate using hydrogen; S4. Keep the hydrogen flow rate and the reaction pressure adjusted in step S2 unchanged and adjust the reaction temperature; S5. Purge the surface of the silicon carbide substrate with hydrogen.

2. The pretreatment method according to claim 1, characterized in that In step S2, the hydrogen flow rate is adjusted to 70-150 slm; And / or, the rate of change during the hydrogen flow adjustment process is 0.05-0.15 slm / s.

3. The pretreatment method according to claim 1, characterized in that: In step S2, the reaction pressure is adjusted to 50-150 mbar; And / or, the change rate of the reaction pressure during the adjustment process is 2-3 mbar / s.

4. The pretreatment method according to claim 1, characterized in that: In step S4, the reaction temperature is adjusted to 950-1100° C.; And / or, the rate of change during the reaction temperature adjustment process is 65-95 degC / min.

5. The pretreatment method according to claim 4, characterized in that: In the step S4, the temperature before the reaction temperature is adjusted is 800-900°C.

6. The pretreatment method according to claim 1, characterized in that: The hydrogen purging time in step S3 is 4 to 6 minutes.

7. The pretreatment method according to claim 1, characterized in that: The hydrogen purging time in step S5 is 2 to 4 minutes.

8. A method for epitaxial growth of silicon carbide, characterized in that: The steps of the method include the pretreatment method according to any one of claims 1 to 7.

9. The method according to claim 8, characterized in that The following steps are involved: Preprocessing the silicon carbide substrate, wherein the preprocessing method is the preprocessing method according to any one of claims 1 to 7; Keeping the reaction pressure and hydrogen flow rate unchanged, continuing to raise the temperature to the buffer layer growth temperature, and etching the silicon carbide substrate; Passing trichlorosilane, ethylene and nitrogen to grow a buffer layer; The growth temperature of the buffer layer is kept unchanged, and the flow rates of ethylene and trichlorosilane are increased to grow the epitaxial layer.

10. The method according to claim 9, characterized in that The buffer layer growth temperature is 1550-1700°C; and / or, after the temperature is raised to the buffer layer growth temperature, the temperature is maintained for 3 to 5 minutes to etch the silicon carbide substrate; And / or, the buffer layer has a growth thickness of 1 to 3 μm.

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