1. Field of the Invention
The present disclosure relates to a method for manufacturing a silicon carbide single crystal.
2. Description of the Background Art
In recent years, in order to achieve high breakdown voltage, low loss, and the like in a semiconductor device, silicon carbide has begun to be adopted as a material for the semiconductor device.
A sublimation method is exemplified as one of methods for manufacturing silicon carbide single crystals. For example, Japanese Patent Laying-Open No. 2009-120419 describes a method for manufacturing a silicon carbide single crystal by means of the sublimation method using a crucible made of graphite.
A method for manufacturing a silicon carbide single crystal according to the present disclosure includes the following steps. A silicon carbide source material and a seed crystal are prepared, the silicon carbide source material being provided in an accommodation unit, the seed crystal being provided to face the silicon carbide source material, the seed crystal being fixed to a first main surface of a base. A silicon carbide single crystal is grown on the seed crystal by sublimating the silicon carbide source material. The silicon carbide single crystal is cooled after growing the silicon carbide single crystal. The step of growing the silicon carbide single crystal includes a step of growing the silicon carbide single crystal while maintaining a temperature of a second main surface of the base opposite to the first main surface to be lower than a temperature of a surface of the silicon carbide single crystal facing the silicon carbide source material. In the step of cooling the silicon carbide single crystal, the silicon carbide single crystal is cooled while maintaining the temperature of the second main surface of the base to be not less than the temperature of the surface of the silicon carbide single crystal.
The following describes embodiments with reference to figures. It should be noted that in the below-mentioned figures, the same or corresponding portions are given the same reference characters and are not described repeatedly. Regarding crystallographic indications in the present specification, an individual orientation is represented by [ ], a group orientation is represented by < >, and an individual plane is represented by ( ) and a group plane is represented by { }. In addition, a negative index is supposed to be crystallographically indicated by putting “-” (bar) above a numeral, but is indicated by putting the negative sign before the numeral in the present specification.
It is an object of the present disclosure to provide a method for manufacturing a silicon carbide single crystal so as to achieve suppression of introduction or propagation of crystal defects.
As a result of diligent study on a cause of introduction or propagation of crystal defects in a silicon carbide single crystal, the inventors have obtained the following knowledge.
Crystal growth of a silicon carbide single crystal is performed in accordance with the sublimation method in the following manner. As shown in
After completion of the step of growing silicon carbide single crystal 5, the heat source is powered off to cool silicon carbide single crystal 5 thus grown. Just before powering off the heat source, the temperature of backside surface 2b of base 2 is lower than the temperature of surface 5a of silicon carbide single crystal 5 (see
When the heating is stopped in this state to start cooling of silicon carbide single crystal 5, the temperature of backside surface 2b of base 2 is decreased while being maintained to be lower than the temperature of silicon carbide single crystal 5. Base 2 is composed of carbon, for example. Carbon has a thermal expansion coefficient larger than the thermal expansion coefficient of silicon carbide. Hence, when the thermal shrinkage amount of base 2 becomes larger than the thermal shrinkage amount of silicon carbide single crystal 5 during the cooling of silicon carbide single crystal 5, thermal stress is caused in silicon carbide single crystal 5.
If the thermal stress is caused in silicon carbide single crystal 5 at a relatively high temperature (for example, not less than 1000° C.), crystal defects, such as dislocations, may be introduced into silicon carbide single crystal 5 or crystal defects existing in silicon carbide single crystal 5 may be propagated in silicon carbide single crystal 5. Meanwhile, if the thermal stress is caused in silicon carbide single crystal 5 at a relatively low temperature (for example, not less than 500° C. and less than 1000° C.), a crack may be generated in silicon carbide single crystal 5 or silicon carbide single crystal 5 may be fractured. These phenomena take place more significantly in the outer circumference portion of silicon carbide single crystal 5 and take place more significantly when silicon carbide single crystal 5 has a large diameter. Particularly, when a difference in thermal expansion coefficient is large between the material of base 2 and the silicon carbide single crystal, a difference in thermal shrinkage amount between base 2 and the silicon carbide single crystal becomes more significant.
As a result of diligent study, the inventors arrived at cooling silicon carbide single crystal 5 while maintaining the temperature of backside surface 2b of base 2 to be not less than the temperature of surface 5a of silicon carbide single crystal 5 in the step of cooling silicon carbide single crystal 5 after completion of the growth of silicon carbide single crystal 5. Accordingly, silicon carbide single crystal 5 can be cooled while maintaining the thermal shrinkage amount of base 2 as large as the thermal shrinkage amount of silicon carbide single crystal 5. As a result, thermal stress in silicon carbide single crystal 5 during the cooling of silicon carbide single crystal 5 can be reduced, thereby suppressing introduction or propagation of crystal defects. Particularly, when the difference in thermal expansion coefficient between the material of base 2 and silicon carbide single crystal 5 is large, the thermal stress in silicon carbide single crystal 5 can be reduced further.
(1) A method for manufacturing a silicon carbide single crystal in the present disclosure includes the following steps. A silicon carbide source material 3 and a seed crystal 4 are prepared, silicon carbide source material 3 being provided in an accommodation unit 1, seed crystal 4 being provided to face silicon carbide source material 3, seed crystal 4 being fixed to a first main surface 2a of a base 2. A silicon carbide single crystal 5 is grown on seed crystal 4 by sublimating silicon carbide source material 3. Silicon carbide single crystal 5 is cooled after growing silicon carbide single crystal 5. The step of growing silicon carbide single crystal 5 includes a step of growing silicon carbide single crystal 5 while maintaining a temperature of a second main surface 2b of base 2 opposite to first main surface 2a to be lower than a temperature of a surface 5a of silicon carbide single crystal 5 facing silicon carbide source material 3. In the step of cooling silicon carbide single crystal 5, silicon carbide single crystal 5 is cooled while maintaining the temperature of second main surface 2b of base 2 to be not less than the temperature of surface 5a of silicon carbide single crystal 5. Accordingly, during the cooling of silicon carbide single crystal 5, it is possible to suppress introduction or propagation of crystal defects to the silicon carbide single crystal.
(2) Preferably in the method for manufacturing the silicon carbide single crystal according to (1), in the step of cooling silicon carbide single crystal 5, in a temperature range in which the temperature of surface 5a of silicon carbide single crystal 5 is not less than 1800° C. and not more than 2000° C., silicon carbide single crystal 5 is cooled while maintaining the temperature of second main surface 2b of base 2 to be not less than the temperature of surface 5a of silicon carbide single crystal 5. In the step of cooling silicon carbide single crystal 5 in the temperature range in which the temperature of surface 5a of silicon carbide single crystal 5 is not less than 1800° C. and not more than 2000° C., atoms of silicon carbide single crystal 5 are facilitated to be moved. Hence, by cooling silicon carbide single crystal 5 in the temperature range while maintaining the temperature of second main surface 2b of base 2 to be not less than the temperature of surface 5a of silicon carbide single crystal 5, it is possible to further suppress introduction or propagation of crystal defects during the cooling.
(3) Preferably in the method for manufacturing the silicon carbide single crystal according to (2), in the step of cooling silicon carbide single crystal 5, in a temperature range in which the temperature of surface 5a of silicon carbide single crystal 5 is not less than 1000° C. and not more than 2000° C., silicon carbide single crystal 5 is cooled while maintaining the temperature of second main surface 2b of base 2 to be not less than the temperature of surface 5a of silicon carbide single crystal 5. Accordingly, also in a temperature range in which the temperature of surface 5a of silicon carbide single crystal 5 is not less than 1000° C. and less than 1800° C., thermal stress in silicon carbide single crystal 5 can be made small. This provides suppression of basal plane dislocation, which is considered to be introduced into silicon carbide single crystal 5 at not less than 1000° C. particularly due to the thermal stress.
(4) Preferably in the method for manufacturing the silicon carbide single crystal according to (3), in the step of cooling silicon carbide single crystal 5, in a temperature range in which the temperature of surface 5a of silicon carbide single crystal 5 is not less than 500° C. and not more than 2000° C., silicon carbide single crystal 5 is cooled while maintaining the temperature of second main surface 2b of base 2 to be not less than the temperature of surface 5a of silicon carbide single crystal 5. Accordingly, also in a temperature range in which the temperature of surface 5a of silicon carbide single crystal 5 is not less than 500° C. and less than 1000° C., thermal stress in silicon carbide single crystal 5 can be made small. This provides suppression of not only crystal defects but also crack or fracture otherwise caused in silicon carbide single crystal 5 due to the thermal stress.
(5) Preferably in the method for manufacturing the silicon carbide single crystal according to any one of (1) to (4), the step of cooling silicon carbide single crystal 5 includes a step of increasing a pressure in accommodation unit 1 before the temperature of second main surface 2b of base 2 becomes not less than the temperature of surface 5a of silicon carbide single crystal 5. This provides suppression of sublimation of grown silicon carbide single crystal 5 when the temperature of surface 5a of silicon carbide single crystal 5 becomes higher than the temperature of surface 3a of silicon carbide source material 3.
(6) Preferably in the method for manufacturing the silicon carbide single crystal according to any one of (1) to (5), in the step of cooling silicon carbide single crystal 5, silicon carbide single crystal 5 is cooled while heating base 2. Accordingly, the temperature of second main surface 2b of base 2 can be maintained to be not less than the temperature of surface 5a of silicon carbide single crystal 5.
(7) Preferably in the method for manufacturing the silicon carbide single crystal according to any one of (1) to (6), in the step of cooling silicon carbide single crystal 5, silicon carbide single crystal 5 is cooled while maintaining a temperature of a bottom portion 1b of accommodation unit 1 to be lower than the temperature of second main surface 2b of base 2. Accordingly, the temperature of second main surface 2b of base 2 can be more securely maintained to be not less than the temperature of surface 5a of silicon carbide single crystal 5, thereby achieving further suppression of introduction or propagation of crystal defects during the cooling.
(8) Preferably in the method for manufacturing the silicon carbide single crystal according to any one of (1) to (7), the step of cooling silicon carbide single crystal 5 includes a step of cooling silicon carbide single crystal 5 while maintaining the temperature of second main surface 2b of base 2 to be not less than the temperature of second main surface 2b of base 2 in the step of growing silicon carbide single crystal 5. Accordingly, the temperature of second main surface 2b of base 2 can be more securely maintained to be not less than the temperature of surface 5a of silicon carbide single crystal 5, thereby achieving further suppression of introduction or propagation of crystal defects during the cooling.
(9) Preferably, the method for manufacturing the silicon carbide single crystal according to any one of (1) to (8) further includes a step of annealing, after the step of growing silicon carbide single crystal 5 and before the step of cooling silicon carbide single crystal 5, silicon carbide single crystal 5 while maintaining a pressure in accommodation unit 1 to be higher than a pressure in the step of growing silicon carbide single crystal 5. This provides further suppression of introduction or propagation of crystal defects into silicon carbide single crystal 5.
The following describes a configuration of a manufacturing apparatus for a silicon carbide single crystal according to the present disclosure.
As shown in
The heat source is disposed outside accommodation unit 1 to surround accommodation unit 1, for example. The heat source may be a high-frequency induction-heating type coil or a resistive heating type heater. The heat source may be disposed at a location facing second main surface 2b of base 2. The heat source may be disposed at a location facing bottom portion 1b of accommodation unit 1. The thermometer is a radiation thermometer, for example. The thermometer may be configured to be capable of measuring each of temperatures of second main surface 2b of base 2 and side surface 1a and bottom portion 1b of accommodation unit 1, for example. The thermometer may be configured to be capable of measuring a temperature within accommodation unit 1.
The following describes a method for manufacturing the silicon carbide single crystal according to the present disclosure.
As shown in
Next, silicon carbide source material 3 provided in accommodation unit 1 is heated to a temperature of about not less than 2000° C. and not more than 2400° C., for example. While the temperature of silicon carbide source material 3 is being increased, the pressure of atmospheric gas in accommodation unit 1 is maintained at about 80 kPa, for example. The atmospheric gas includes an inert gas, such as argon gas, helium gas, or nitrogen gas, for example. Next, the pressure of the atmospheric gas in accommodation unit 1 is decreased to 1.7 kPa, for example. Accordingly, silicon carbide source material 3 in accommodation unit 1 starts to sublime and is recrystallized on the surface of seed crystal 4 disposed at the location facing the surface of silicon carbide source material 3, thereby starting to grow silicon carbide single crystal 5 on the surface of seed crystal 4. During the growth of the silicon carbide single crystal, the pressure in accommodation unit 1 is maintained at about not less than 0.5 kPa and not more than 5 kPa for about 10 hours, for example. By sublimating silicon carbide source material 3 as described above, silicon carbide single crystal 5 is grown on seed crystal 4.
As shown in
As shown in
Next, after completion of the crystal growth of silicon carbide single crystal 5, silicon carbide single crystal 5 is cooled. The step of cooling silicon carbide single crystal 5 includes a step of cooling silicon carbide single crystal 5 while maintaining the temperature of second main surface 2b of base 2 to be not less than the temperature of surface 5a of silicon carbide single crystal 5. Preferably, silicon carbide single crystal 5 is cooled while heating base 2. For example, silicon carbide single crystal 5 is cooled while heating base 2, by turning off the heat source facing side surface 1a of accommodation unit 1 while maintaining, at the on state, the heat source facing second main surface 2b of base 2. Alternatively, by cooling silicon carbide single crystal 5 actively without heating second main surface 2b of base 2, silicon carbide single crystal 5 may be cooled while maintaining the temperature of second main surface 2b of base 2 to be not less than the temperature of surface 5a of silicon carbide single crystal 5.
As shown in
As shown in
It should be noted that the temperature in each of the surfaces refers to the temperature of the center of the surface. For example, the temperature of second main surface 2b of base 2 refers to the temperature of the center of second main surface 2b of base 2. Preferably, in the step of cooling silicon carbide single crystal 5, silicon carbide single crystal 5 is cooled while maintaining the average value of the temperature of second main surface 2b of base 2 to be not less than the average value of the temperature of surface 5a of silicon carbide single crystal 5. More preferably, in the step of cooling silicon carbide single crystal 5, silicon carbide single crystal 5 is cooled while maintaining the average value of the temperature of bottom portion 1b of accommodation unit 1 to be lower than the average value of the temperature of second main surface 2b of base 2. It should be noted that the average value of the temperature in each of the surfaces refers to an average value of all the temperatures at a plurality of different locations of measurements in each of the surfaces (for example, five locations including the center). More preferably, in the step of cooling silicon carbide single crystal 5, silicon carbide single crystal 5 is cooled while maintaining the maximum value of the temperatures of the plurality of measurement locations in second main surface 2b of base 2 to be not less than the minimum value of the temperatures of the plurality of measurement locations in surface 5a of silicon carbide single crystal 5. More preferably, in the step of cooling silicon carbide single crystal 5, silicon carbide single crystal 5 is cooled while maintaining the maximum value of the temperatures of the plurality of measurement locations of bottom portion 1b of accommodation unit 1 to be lower than the minimum value of the temperatures of the plurality of measurement locations of second main surface 2b of base 2.
It should be noted that the temperature in each of the surfaces can be measured using a radiation thermometer, for example. When it is difficult to directly measure the temperature of surface 5a of silicon carbide single crystal 5 growing in accommodation unit 1, the temperature of a location 1a1 of side surface 1a of accommodation unit 1 in a plane along the surface of seed crystal 4 that is in contact with silicon carbide single crystal 5 can be used as a reference (see
As shown in
As shown in
Preferably, in a temperature range in which the temperature of surface 5a of silicon carbide single crystal 5 is not less than 1800° C. and not more than 2000° C., silicon carbide single crystal 5 is cooled while maintaining the temperature of second main surface 2b of base 2 to be not less than the temperature of surface 5a of silicon carbide single crystal 5. For example, in
Preferably, in a temperature range in which the temperature of surface 5a of silicon carbide single crystal 5 is not less than 1000° C. and not more than 2000° C., silicon carbide single crystal 5 is cooled while maintaining the temperature of second main surface 2b of base 2 to be not less than the temperature of surface 5a of silicon carbide single crystal 5. More preferably, in a temperature range in which the temperature of surface 5a of silicon carbide single crystal 5 is not less than 500° C. and not more than 2000° C., silicon carbide single crystal 5 is cooled while maintaining the temperature of second main surface 2b of base 2 to be not less than the temperature of surface 5a of silicon carbide single crystal 5.
As shown in
As shown in
As shown in
As shown in
As shown in
Next, the following describes function and effect of the method for manufacturing the silicon carbide single crystal according to the present embodiment.
According to the method for manufacturing the silicon carbide single crystal according to the present embodiment, silicon carbide source material 3 and seed crystal 4 are prepared, silicon carbide source material 3 being provided in accommodation unit 1, seed crystal 4 being provided to face silicon carbide source material 3, seed crystal 4 being fixed to first main surface 2a of base 2. By sublimating silicon carbide source material 3, silicon carbide single crystal 5 is grown on seed crystal 4. After growing silicon carbide single crystal 5, silicon carbide single crystal 5 is cooled. The step of growing silicon carbide single crystal 5 includes the step of growing silicon carbide single crystal 5 while maintaining the temperature of second main surface 2b of base 2 opposite to first main surface 2a to be lower than the temperature of surface 5a of silicon carbide single crystal 5 facing silicon carbide source material 3. In the step of cooling silicon carbide single crystal 5, silicon carbide single crystal 5 is cooled while maintaining the temperature of second main surface 2b of base 2 to be not less than the temperature of surface 5a of silicon carbide single crystal 5. Accordingly, during the cooling of silicon carbide single crystal 5, it is possible to suppress introduction or propagation of crystal defects to silicon carbide single crystal 5.
Moreover, according to the method for manufacturing the silicon carbide single crystal according to the present embodiment, in the step of cooling silicon carbide single crystal 5, in the temperature range in which the temperature of surface 5a of silicon carbide single crystal 5 is not less than 1800° C. and not more than 2000° C., silicon carbide single crystal 5 is cooled while maintaining the temperature of second main surface 2b of base 2 to be not less than the temperature of surface 5a of silicon carbide single crystal 5. In the step of cooling silicon carbide single crystal 5 in the temperature range in which the temperature of surface 5a of silicon carbide single crystal 5 is not less than 1800° C. and not more than 2000° C., atoms of silicon carbide single crystal 5 are facilitated to be moved. Hence, by cooling silicon carbide single crystal 5 in the temperature range while maintaining the temperature of second main surface 2b of base 2 to be not less than the temperature of surface 5a of silicon carbide single crystal 5, it is possible to suppress introduction or propagation of crystal defects during the cooling.
Further, according to the method for manufacturing the silicon carbide single crystal in the present embodiment, in the step of cooling silicon carbide single crystal 5, in the temperature range in which the temperature of surface 5a of silicon carbide single crystal 5 is not less than 1000° C. and not more than 2000° C., silicon carbide single crystal 5 is cooled while maintaining the temperature of second main surface 2b of base 2 to be not less than the temperature of surface 5a of silicon carbide single crystal 5. Accordingly, also in the temperature range in which the temperature of surface 5a of silicon carbide single crystal 5 is not less than 1000° C. and less than 1800° C., thermal stress in silicon carbide single crystal 5 can be made small. This provides suppression of basal plane dislocation, which is considered to be introduced into silicon carbide single crystal 5 at not less than 1000° C. particularly due to the thermal stress. Furthermore, according to the method for manufacturing the silicon carbide single crystal in the present embodiment, in the step of cooling silicon carbide single crystal 5, in the temperature range in which the temperature of surface 5a of silicon carbide single crystal 5 is not less than 500° C. and not more than 2000° C., silicon carbide single crystal 5 is cooled while maintaining the temperature of second main surface 2b of base 2 to be not less than the temperature of surface 5a of silicon carbide single crystal 5. Accordingly, also in the temperature range in which the temperature of surface 5a of silicon carbide single crystal 5 is not less than 500° C. and less than 1000° C., the thermal stress in silicon carbide single crystal 5 can be made small. This provides suppression of not only crystal defects but also crack or fracture otherwise caused in silicon carbide single crystal 5 due to the thermal stress.
Furthermore, according to the method for manufacturing the silicon carbide single crystal in the present embodiment, the step of cooling silicon carbide single crystal 5 includes the step of increasing the pressure in accommodation unit 1 before the temperature of second main surface 2b of base 2 becomes not less than the temperature of surface 5a of silicon carbide single crystal 5. This provides suppression of sublimation of grown silicon carbide single crystal 5 when the temperature of surface 5a of silicon carbide single crystal 5 becomes higher than the temperature of surface 3a of silicon carbide source material 3.
Furthermore, according to the method for manufacturing the silicon carbide single crystal in the present embodiment, in the step of cooling silicon carbide single crystal 5, silicon carbide single crystal 5 is cooled while heating base 2. Accordingly, the temperature of second main surface 2b of base 2 can be maintained to be not less than the temperature of surface 5a of silicon carbide single crystal 5.
Furthermore, according to the method for manufacturing the silicon carbide single crystal in the present embodiment, in the step of cooling silicon carbide single crystal 5, silicon carbide single crystal 5 is cooled while maintaining the temperature of bottom portion 1b of accommodation unit 1 to be lower than the temperature of second main surface 2b of base 2. Accordingly, the temperature of second main surface 2b of base 2 can be more securely maintained to be not less than the temperature of surface 5a of silicon carbide single crystal 5, thereby achieving further suppression of introduction or propagation of crystal defects during the cooling.
Furthermore, according to the method for manufacturing the silicon carbide single crystal in the present embodiment, the step of cooling silicon carbide single crystal 5 includes the step of cooling silicon carbide single crystal 5 while maintaining the temperature of second main surface 2b of base 2 to be not less than the temperature of second main surface 2b of base 2 in the step of growing silicon carbide single crystal 5. Accordingly, the temperature of second main surface 2b of base 2 can be more securely maintained to be not less than the temperature of surface 5a of silicon carbide single crystal 5, thereby achieving further suppression of introduction or propagation of crystal defects during the cooling.
Furthermore, the method for manufacturing the silicon carbide single crystal in the present embodiment further includes the step of annealing, after the step of growing silicon carbide single crystal 5 and before the step of cooling silicon carbide single crystal 5, silicon carbide single crystal 5 while maintaining the pressure in accommodation unit 1 to be higher than the pressure in the step of growing silicon carbide single crystal 5. This provides further suppression of introduction or propagation of crystal defects into silicon carbide single crystal 5.
It should be understood that the embodiments disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.
Number | Date | Country | Kind |
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2014-194088 | Sep 2014 | JP | national |
2015-088543 | Apr 2015 | JP | national |