JP2014040333A - Method for producing silicon carbide substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a silicon carbide substrate, which can suppress occurrence of a discharge during crystal growth and produce a silicon carbide crystal with little dislocation.SOLUTION: The method for producing a silicon carbide substrate comprises following steps. A growth vessel 10 in which a silicon carbide raw material 8 and a seed substrate 1 are disposed is provided. A temperature of the growth vessel 10 is raised to a temperature within a range of growth temperature of a silicon carbide crystal by means of a resistance heater 5. The temperature of the growth vessel 10 is kept within the range of the growth temperature of the silicon carbide crystal to grow the silicon carbide crystal on the seed substrate 1. A pressure in the step for raising the temperature of the growth vessel is higher than that in the step for growing the silicon carbide crystal. In the step for raising the temperature of the growth vessel, the growth vessel 10 contains a gas consisting of an element having the atomic number larger than that of helium. The concentration of helium in the step for raising the temperature of the growth vessel is lower than the concentration of helium in the step for growing the silicon carbide crystal.

Description

  The present invention relates to a method for manufacturing a silicon carbide substrate, and more particularly to a method for manufacturing a silicon carbide substrate capable of suppressing the occurrence of dislocations.

  In recent years, silicon carbide substrates have begun to be used for manufacturing semiconductor devices. Silicon carbide has a larger band gap than silicon. Therefore, a semiconductor device using a silicon carbide substrate has advantages such as high breakdown voltage, low on-resistance, and small deterioration in characteristics under a high temperature environment.

  A silicon carbide single crystal can be produced by, for example, a sublimation recrystallization method. For example, Japanese Unexamined Patent Application Publication No. 2011-162414 (Patent Document 1) describes a method of growing a silicon carbide single crystal in an atmospheric gas containing helium. Since helium has higher ionization energy than argon, it is harder to ionize than argon. Therefore, the occurrence of discharge can be effectively suppressed when a resistance heater is used.

JP 2011-162414 A

  However, when a silicon carbide crystal is grown using helium as an atmospheric gas, the occurrence of discharge is suppressed, but it is difficult to obtain a silicon carbide single crystal with few dislocations.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide silicon carbide capable of suppressing generation of discharge during crystal growth and obtaining a silicon carbide crystal with few dislocations. It is to provide a method for manufacturing a substrate.

  As a result of diligent research on the cause of dislocation when the silicon carbide single crystal is produced by the sublimation recrystallization method using helium as an atmospheric gas, the present inventors have obtained the following knowledge and arrived at the present invention. As described above, since helium is less ionized than argon, the occurrence of discharge can be effectively suppressed when a resistance heater is used. Since discharge is likely to occur when the temperature is high and the pressure is low, it is very effective to use helium as the atmospheric gas when growing the silicon carbide crystal by reducing the pressure.

  On the other hand, when helium is used as the atmospheric gas at the stage of raising the temperature of the silicon carbide raw material and the seed substrate, a small amount of silicon carbide raw material is sublimated even at the stage of raising temperature. This is because the atomic radius of the helium gas is small, so the probability that the helium gas collides with the sublimated silicon carbide source gas is lower than when other gases are used, and the diffusion length of the silicon carbide source gas is large. It is thought that it is to become. Moreover, since the atomic weight of helium gas is small, the sublimated silicon carbide source gas cannot be sufficiently pushed back to the silicon carbide source side. Therefore, when helium is used as the atmospheric gas, the silicon carbide raw material is easily diffused from the raw material side to the seed crystal side. Then, the silicon carbide source gas sublimated in the temperature raising stage adheres to the seed substrate, which causes dislocation in the initial stage of crystal growth.

  Therefore, the method for manufacturing a silicon carbide substrate according to the present invention includes the following steps. A growth vessel in which a silicon carbide raw material and a seed substrate are arranged is prepared. The temperature of the growth vessel is raised to a temperature in the growth temperature range of the silicon carbide crystal by a resistance heater. A silicon carbide crystal grows on the seed substrate while maintaining the temperature of the growth vessel within the growth temperature range. The pressure in the growth vessel in the step of raising the temperature of the growth vessel is higher than the pressure in the growth vessel in the step of growing the silicon carbide crystal. In the step of raising the temperature of the growth vessel, the growth vessel contains a gas composed of an element having an atomic number larger than that of helium. The concentration of helium in the growth vessel in the step of raising the temperature of the growth vessel is lower than the concentration of helium in the growth vessel in the step of growing the silicon carbide crystal.

  Note that the growth temperature of the silicon carbide crystal is a temperature at which the silicon carbide crystal grows on the seed substrate by the sublimation method, for example, a temperature of about 2000 ° C. or less and about 2400 ° C. or less. Further, in the step of raising the temperature of the growth vessel, helium may not be present in the growth vessel.

  According to the method for manufacturing a silicon carbide substrate according to the present invention, the concentration of helium in the growth vessel in the step of growing the silicon carbide crystal is higher than the concentration of helium in the growth vessel in the step of raising the temperature of the growth vessel. . Therefore, generation of discharge can be effectively suppressed in the process of growing the silicon carbide crystal.

  Further, according to the method for manufacturing a silicon carbide substrate according to the present invention, the growth vessel includes a gas composed of an element having an atomic number larger than that of helium in the step of raising the temperature of the growth vessel. Thereby, sublimation of the silicon carbide raw material can be suppressed in the step of raising the temperature of the growth vessel. As a result, a silicon carbide crystal with few dislocations can be obtained.

  Preferably, in the method for manufacturing a silicon carbide substrate according to the above, the element having an atomic number larger than that of helium is any one of neon, argon, krypton, xenon, and radon. Thereby, sublimation of the silicon carbide raw material can be effectively suppressed in the growth vessel.

  Preferably, the method for manufacturing a silicon carbide substrate according to the above has a step of introducing helium into the growth vessel after the step of raising the temperature of the growth vessel and before the step of growing the silicon carbide crystal. Thereby, since the helium concentration in the growth vessel is increased, the discharge can be effectively suppressed.

  Preferably, the method for manufacturing a silicon carbide substrate according to the above has a step of reducing the pressure in the growth vessel after the step of raising the temperature of the growth vessel and before the step of growing the silicon carbide crystal. Thereby, the silicon carbide raw material is sublimated, and the growth of the silicon carbide crystal is substantially started.

  Preferably, in the method for manufacturing a silicon carbide substrate according to the above, the growth vessel contains nitrogen gas in the step of growing the silicon carbide crystal. Thereby, nitrogen is introduced as a dopant into the silicon carbide substrate.

  ADVANTAGE OF THE INVENTION According to this invention, generation | occurrence | production of the discharge during crystal growth can be suppressed and a silicon carbide crystal with few dislocations can be obtained.

It is a cross-sectional schematic diagram which shows schematically the manufacturing apparatus of the silicon carbide substrate which concerns on one embodiment of this invention. It is a flowchart of the manufacturing method of the silicon carbide substrate which concerns on one embodiment of this invention. It is a flowchart in the growth container temperature maintenance process of the manufacturing method of the silicon carbide substrate which concerns on one embodiment of this invention. It is a figure which shows the relationship between temperature and time in the manufacturing method of the silicon carbide substrate which concerns on one embodiment of this invention. It is a figure which shows the relationship between the pressure and time in the manufacturing method of the silicon carbide substrate which concerns on one embodiment of this invention. It is a figure which shows the relationship between the gas concentration and time in the manufacturing method of the silicon carbide substrate which concerns on one embodiment of this invention. It is a cross-sectional schematic diagram which shows schematically the structure of the growth container of the manufacturing apparatus of the silicon carbide substrate which concerns on one embodiment of this invention. FIG. 2 is a schematic end view taken along a line segment IIX-IIX in FIG. 1.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following drawings, the same or corresponding parts are denoted by the same reference numerals, and description thereof will not be repeated. In the crystallographic description in this specification, the individual orientation is indicated by [], the collective orientation is indicated by <>, the individual plane is indicated by (), and the collective plane is indicated by {}. As for the negative index, “−” (bar) is attached on the number in crystallography, but in this specification, a negative sign is attached before the number. The angle is described using a system in which the omnidirectional angle is 360 degrees.

  With reference to FIG. 1, the structure of the apparatus for manufacturing the silicon carbide substrate which concerns on this Embodiment is demonstrated.

  Referring to FIG. 1, silicon carbide substrate manufacturing apparatus 100 according to the present embodiment mainly includes growth vessel 10, heat insulating material 4, heating unit 5, and reaction vessel 123. The growth vessel 10 is a crucible made of, for example, purified graphite, and has a seed substrate holding unit 3 and a raw material storage unit 7 as shown in FIG. The seed substrate holding part 3 is for holding the seed substrate 1 made of single crystal silicon carbide. Raw material container 7 is for placing silicon carbide raw material 8 made of polycrystalline silicon carbide. The tip of the seed substrate holding part 3 is bent so that it can be fitted into the raw material storage part 7. The seed substrate holding unit 3 and the raw material container 7 are connected by a connection unit 10c.

  The heat insulating material 4 is made of, for example, carbon felt, and is for insulating the growth vessel 10 from the outside. The heat insulating material 4 is formed so as to surround the growth vessel 10 and the heating unit 5, for example. A reaction vessel 123 is provided around the heat insulating material 4. At both ends of the reaction vessel 123, a gas introduction port 123a for flowing atmospheric gas into the reaction vessel 123 and a gas discharge port 123b for discharging atmospheric gas to the outside of the reaction vessel 123 are formed. A radiation thermometer 127b for measuring the temperature of the seed substrate holding part 3 of the growth container 10 and a radiation thermometer 127a for measuring the temperature of the raw material container 7 are provided at the upper and lower parts of the reaction vessel 123. It has been.

  The heating unit 5 includes a resistance heater 125 and an electrode 126. The resistance heater 125 is made of, for example, graphite. As shown in FIGS. 1 and 8, the resistance heater 125 is disposed so as to surround the outer periphery of the growth vessel 10. The resistance heater 125 is configured to increase the temperature of the growth vessel 10 to the sublimation temperature of silicon carbide. The electrode 126 is configured to be able to supply current to the resistance heater 125. The electrode 126 is made of, for example, copper.

  A method for manufacturing a silicon carbide substrate according to the present embodiment will be described with reference to FIGS.

First, a growth vessel preparation step (S10: FIG. 2) is performed. Specifically, referring to FIG. 1, growth vessel 10 in which seed substrate 1 and silicon carbide raw material 8 are arranged is prepared. Seed substrate 1 is held by seed substrate holding unit 3, and is arranged such that main surface 1 </ b> A of seed substrate 1 faces silicon carbide raw material 8. Seed substrate 1 is made of single crystal silicon carbide. The polytype of the seed substrate 1 is 4H, for example. The diameter of the seed substrate 1 is preferably 4 inches (100 mm) or more, for example, 6 inches. The main surface 1A of the seed substrate 1 is, for example, a (0001) surface that is turned off by about 4 °. The dislocation density in the main surface 1A of the seed substrate 1 is, for example, about 10,000 cm ⁻² . Preferably, the main surface 1A of the seed substrate 1 is subjected to CMP (Chemical Mechanical Polishing) polishing. Silicon carbide raw material 8 is housed in raw material housing portion 7 and is, for example, polycrystalline silicon carbide powder.

  Next, the growth vessel temperature raising step (S20: FIG. 2) is performed. Specifically, referring to FIG. 4, growth vessel 10 in which seed substrate 1 and silicon carbide raw material 8 are arranged is heated to a temperature within a growth temperature range of silicon carbide crystals (for example, 2200) by resistance heater 125 made of graphite, for example. C.). The growth temperature of the silicon carbide crystal is, for example, 2000 ° C. or more and 2400 ° C. or less. Referring to FIG. 5, the pressure of the atmospheric gas in growth vessel 10 is, for example, about 80 kPa while growth vessel 10 is heated from room temperature to the growth temperature of the silicon carbide crystal (time T0 to time T1). Maintained.

  In the growth vessel heating step (S20: FIG. 2), the growth vessel 10 contains argon gas and nitrogen gas made of an element having an atomic number larger than that of helium. Preferably, the element having an atomic number larger than that of helium is a rare gas, specifically, neon, argon, krypton, xenon, radon, or the like. In this step (S20), argon gas is flowed into the growth vessel 10 at a flow rate of, for example, 0.3 slm. For example, nitrogen gas is flowed at a flow rate of 0.1 slm.

  Next, the growth container temperature maintaining step (S30: FIG. 2) is performed. Specifically, the temperature of the growth vessel 10 is maintained within the growth temperature range of the silicon carbide crystal. Here, the growth vessel temperature maintaining step (S30: FIG. 2) includes a helium gas introduction step (S31: FIG. 3), a growth vessel decompression step (S32: FIG. 3), and a silicon carbide crystal growth step (S33: FIG. 3). )including.

  First, a helium gas introduction step (S31: FIG. 3) is performed. In this step (S31), helium gas is introduced into the growth vessel 10 at time T1 while the temperature of the growth vessel 10 is maintained at a temperature of about 2200 ° C., for example. For example, helium gas is allowed to flow into the growth vessel 10 at a flow rate of 0.3 slm at time T1. At the same time, the supply of argon is stopped. Note that the flow rate of the nitrogen gas is maintained at 0.1 slm.

  With reference to FIG. 6, the kind and density | concentration of atmospheric gas in the growth container 10 are demonstrated. In FIG. 6, the solid line indicates the concentration of helium gas 21, the broken line indicates the concentration of nitrogen gas 23, and the alternate long and short dash line indicates the concentration of argon gas 22. For example, the concentration of the argon gas 22 at time T1 is 75%, but the concentration of the argon gas 22 at time T2 is almost 0%. The concentration of helium gas 21 at time T1 is 0%, but the concentration of helium gas 21 at time T2 is 75%. Note that the pressure of the entire atmospheric gas in the growth vessel 10 from time T1 to time T2 is maintained at about 80 kPa.

  Next, the growth vessel pressure reducing step (S32: FIG. 3) is performed. In this step (S32), referring to FIG. 5, the pressure in growth vessel 10 is reduced from about 80 kPa to a growth pressure (eg, 1.7 kPa) from time T2 to time T3. Thereby, silicon carbide raw material 8 in growth vessel 10 is sublimated and recrystallized on main surface 1A of seed substrate 1, whereby a silicon carbide single crystal is substantially grown on main surface 1 A of seed substrate 1. start. The growth pressure is a pressure at which the silicon carbide single crystal starts to grow substantially.

  The growth pressure is preferably from 0.5 kPa to 5 kPa. In the growth container decompression step, the temperature of the growth container 10 is maintained at about 2200 ° C. Further, the time for depressurizing the growth vessel (from time T2 to time T3) is preferably not less than 1 hour and not more than 24 hours.

  Next, a silicon carbide crystal growth step (S33: FIG. 3) is performed. Specifically, after the concentration of the atmospheric gas in the growth vessel 10 is reduced and the growth of the silicon carbide single crystal is substantially started, the temperature of the growth vessel 10 is maintained within the range of the growth temperature of silicon carbide. The Further, the pressure in the growth vessel 10 is also maintained at the growth pressure. Thereby, a silicon carbide single crystal grows along the normal direction on main surface 1A of seed substrate 1. As shown in FIG. 5, the pressure of the atmospheric gas in the growth vessel heating step (S20: FIG. 2) is higher than the pressure of the atmospheric gas in the silicon carbide crystal growth step (S33: FIG. 3).

  As shown in FIG. 6, the atmospheric gas in the growth vessel 10 in the growth vessel heating step (time T0 to time T1) is, for example, about 75% argon gas and about 25% nitrogen gas. On the other hand, the atmospheric gas in the growth vessel 10 in the silicon carbide crystal growth step (from time T3 to time T4) is, for example, about 75% helium gas and about 25% nitrogen gas. That is, the concentration of helium in the growth vessel 10 in the growth vessel heating step (S20: FIG. 2) is lower than the concentration of helium in the growth vessel 10 in the silicon carbide crystal growth step (S33: FIG. 3). Preferably, the growth vessel 10 does not contain helium gas in the growth vessel temperature raising step (S20), and the silicon carbide crystal growth step (S33) does not contain argon gas.

  Next, the silicon carbide single crystal grown on main surface 1 </ b> A of seed substrate 1 is taken out from growth vessel 10. Thereafter, the silicon carbide substrate is obtained by slicing the silicon carbide single crystal with, for example, a wire saw.

Next, the effect of the method for manufacturing the silicon carbide substrate according to the present embodiment will be described.
According to the method for manufacturing a silicon carbide substrate according to the present embodiment, the concentration of helium in growth vessel 10 in the step of growing silicon carbide crystals (S33) is the same as the growth in step (S20) of raising the temperature of the growth vessel. It is higher than the concentration of helium in the container 10. Therefore, the generation of discharge can be effectively suppressed in the step (S33) of growing the silicon carbide crystal.

  Further, according to the method for manufacturing the silicon carbide substrate according to the present embodiment, the growth vessel 10 contains a gas composed of an element having an atomic number larger than that of helium in the step of raising the temperature of the growth vessel (S20). Thereby, sublimation of silicon carbide raw material 8 can be suppressed in the step (S20) of raising the temperature of the growth vessel. As a result, a silicon carbide single crystal with few dislocations can be obtained.

  Furthermore, according to the method for manufacturing a silicon carbide substrate according to the present embodiment, the element having an atomic number larger than that of helium is any one of neon, argon, krypton, xenon, and radon. Thereby, sublimation of silicon carbide raw material 8 can be effectively suppressed in growth vessel 10.

  Furthermore, according to the method for manufacturing a silicon carbide substrate according to the present embodiment, after the step of raising the temperature of growth vessel 10 (S20) and before the step of growing silicon carbide crystals (S33), the inside of growth vessel 10 A step (S31) of introducing helium into the substrate. Thereby, since the helium density | concentration in the growth container 10 becomes high, discharge can be suppressed effectively.

  Furthermore, according to the method for manufacturing a silicon carbide substrate according to the present embodiment, after the step of raising the temperature of growth vessel 10 (S20) and before the step of growing silicon carbide crystals (S33), the inside of growth vessel 10 A step of reducing the pressure (S32). Thereby, silicon carbide raw material 8 is sublimated, and the growth of the silicon carbide single crystal is substantially started.

  Furthermore, according to the method for manufacturing a silicon carbide substrate according to the present embodiment, nitrogen gas is contained in growth vessel 10 in the step of growing a silicon carbide crystal (S33). Thereby, nitrogen is introduced as a dopant into the silicon carbide substrate.

In the present example, the temperature of the growth vessel was increased in the three types of atmospheric gases described below, and the dislocation density of the silicon carbide single crystal grown on the seed substrate 1 was investigated. First, the growth vessel 10 in which the silicon carbide raw material 8 and the seed substrate 1 were arranged was prepared. The dislocation density of the main surface 1A of the seed substrate 1 was 1 × 10 ⁴ cm ⁻² . The atmosphere gas in the growth vessel 10 at the time of raising the temperature was as follows. The atmospheric gas of Comparative Example 1 was nitrogen 25% helium 75%. The atmosphere gas of Invention Example 1 was set to 100% nitrogen. The atmosphere gas of Invention Example 2 was nitrogen 25% argon 75%. The growth vessel 10 was heated to two kinds of growth temperatures (2000 ° C. and 2200 ° C.) in the atmospheric gas in Comparative Example 1, Invention Example 1 and Invention Example 2. Thereafter, the seed substrate 1 was taken out from the growth vessel 10, and the dislocation density of the 4H silicon carbide single crystal grown on the main surface 1A of the seed substrate 1 was evaluated using KOH (potassium hydroxide) etching.

The result of the dislocation density of the 4H silicon carbide single crystal will be described with reference to Table 1. First, when the growth temperature was 2000 ° C., the silicon carbide single crystal did not grow on the main surface 1A of the seed substrate 1 in Invention Example 1 and Invention Example 2. Under the conditions of Comparative Example 1, a silicon carbide single crystal grew, and the dislocation density of the silicon carbide single crystal was about 5 × 10 ⁴ cm ⁻² to 1 × 10 ⁵ cm ⁻² . When the growth temperature was 2200 ° C., the dislocation density of the silicon carbide single crystal under the conditions of Invention Example 1 and Invention Example 2 was both about 2 × 10 ³ cm ^{−2 to} 6 × 10 ³ cm ⁻² . The dislocation density of the silicon carbide single crystal under the conditions of Comparative Example 1 was more than 1 × 10 ⁵ cm ⁻² .

  From the above results, when heating the growth vessel 10 in which the silicon carbide raw material 8 is arranged, silicon carbide is used when a gas composed of an element having a larger atomic number than helium such as nitrogen or argon is used as the atmosphere gas of the growth vessel 10. It was confirmed that sublimation of the raw material 8 can be suppressed. Further, when a gas composed of an element having an atomic number higher than that of helium such as nitrogen or argon is used as the atmosphere gas of the growth vessel 10, the growth is performed on the main surface 1A of the seed substrate 1 than when helium is used as the atmosphere gas. It was confirmed that the dislocation density of the silicon carbide single crystal to be reduced can be reduced.

  The embodiments and examples disclosed herein are illustrative in all respects and should not be construed as being restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  1 type substrate, 1A main surface, 3 type substrate holding part, 4 heat insulating material, 5 heating part, 7 raw material storage part, 8 silicon carbide raw material, 10 growth vessel, 21 helium gas, 22 argon gas, 23 nitrogen gas, 123 reaction Container, 123a gas inlet, 123b gas outlet, 125 resistance heater, 126 electrodes, 127a, 127b radiation thermometer.

Claims (5)

Preparing a growth vessel in which a silicon carbide raw material and a seed substrate are arranged;
Increasing the temperature of the growth vessel to a temperature within the growth temperature range of the silicon carbide crystal with a resistance heater;
Maintaining the temperature of the growth vessel within the growth temperature range, and growing the silicon carbide crystal on the seed substrate,
The pressure in the growth vessel in the step of raising the temperature of the growth vessel is higher than the pressure in the growth vessel in the step of growing the silicon carbide crystal,
In the step of raising the temperature of the growth vessel, the growth vessel contains a gas composed of an element having an atomic number larger than that of helium,
The method for manufacturing a silicon carbide substrate, wherein the concentration of helium in the growth vessel in the step of raising the temperature of the growth vessel is lower than the concentration of helium in the growth vessel in the step of growing the silicon carbide crystal.   2. The method for manufacturing a silicon carbide substrate according to claim 1, wherein the element having an atomic number larger than that of helium is any one of neon, argon, krypton, xenon, and radon.   The manufacturing of the silicon carbide substrate according to claim 1, further comprising a step of introducing helium into the growth vessel after the step of raising the temperature of the growth vessel and before the step of growing the silicon carbide crystal. Method.   4. The method according to claim 1, further comprising a step of reducing the pressure in the growth vessel after the step of raising the temperature of the growth vessel and before the step of growing the silicon carbide crystal. A method for manufacturing a silicon carbide substrate.   The method for manufacturing a silicon carbide substrate according to claim 1, wherein the growth vessel contains nitrogen gas in the step of growing the silicon carbide crystal.

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