JP2011068515A - METHOD FOR MANUFACTURING SiC SINGLE CRYSTAL - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a SiC single crystal in which the mixing probability of a polycrystal in a single crystal and a void density can be reduced without the need for a special apparatus even when a crystal growth temperature is high. <P>SOLUTION: The method for manufacturing the SiC single crystal which is grown up on a SiC seed crystal from a material solution by the solution method, wherein the ratio (Sc/Ss) of the surface area (Sc) of the SiC seed crystal relative to a solution area (Ss) of a solution interface is 0.13 or less, and atmospheric pressure in a crucible before the starting of a crystal growth is assumed to be 55 kPa or more. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a method for producing a SiC single crystal, and more specifically, in the method for producing a SiC single crystal by a solution method, the ratio of the surface area of the SiC seed crystal to the area of the solution interface and the atmospheric pressure in the crucible before starting crystal growth are specified. It is related with the manufacturing method of the SiC single crystal which can reduce the mixing probability and the void density of the polycrystal in the grown SiC crystal by growing the SiC single crystal in the range described above.

  SiC single crystal is very stable thermally and chemically, excellent in mechanical strength, resistant to radiation, and excellent in breakdown voltage and high thermal conductivity compared to Si (silicon) single crystal. It has physical properties and can easily control p- and n-conduction type electrons by adding impurities, and has a wide forbidden band width (about 3.3 eV for 4H-type single crystal SiC and about 3.3 eV for 6H-type single crystal SiC. 0 eV). For this reason, it is possible to realize high temperature, high frequency, withstand voltage and environmental resistance that cannot be realized with existing semiconductor materials such as Si single crystal and GaAs (gallium arsenide) single crystal. It is growing.

Conventionally, a vapor phase method and a solution method are known as typical growth methods for SiC single crystals. As the gas phase method, a sublimation method is usually used. In the sublimation method, a SiC raw material powder and a seed crystal that is a SiC single crystal are arranged facing each other in a graphite crucible, and the crucible is heated in an inert gas atmosphere to grow the single crystal epitaxially. However, in this vapor phase method, it is known that polycrystals grown from the inner wall of the crucible adversely affect the quality of the SiC single crystal.
In the solution method, a crucible for containing a raw material solution, for example, a graphite crucible, a raw material solution, an external heating device such as a high-frequency coil, a heat insulating material, a liftable seed crystal support member (for example, a graphite shaft), and a tip of the seed crystal support member C (carbon) supply source to Si-containing melt such as Si melt or Si compound financial liquid in which metal is dissolved in crucible using SiC single crystal production apparatus having basic structure consisting of seed crystal attached to For example, C is dissolved from a graphite crucible to obtain a raw material solution, and a SiC single crystal layer is grown on the SiC seed crystal substrate by solution precipitation.

In the growth method of SiC single crystal by this solution method, the raw material solution is grown with a temperature gradient so that the solution temperature in the vicinity of the seed crystal substrate is lower than the solution temperature of other parts, or the entire raw material solution is gradually added. Any of the SiC single crystal growth methods used for cooling and growth are used, but in any case, it is inevitable that crystals other than the single crystal are generated due to temperature distribution and concentration distribution in the solution when the raw material solution is cooled. It has been known.
On the other hand, in a conventional growth method in which a single crystal is grown from a melt, it is known that voids are formed in the resulting crystal. For this reason, various studies for reducing the void density in the crystal have been made.

For example, in Patent Document 1, when pulling up a bismuth germanate single crystal from a melt of bismuth oxide and germanium dioxide, the rotational speed of the seed crystal is limited so that the natural convection of the melt in the crucible becomes more dominant than forced convection. A method for producing a bismuth germanate single crystal that suppresses the generation of voids in the crystal by pulling up is described.
Patent Document 2 describes a method for producing a lithium borate single crystal in which the water content in the growth atmosphere of the lithium borate single crystal is 1% or less in the method for growing a lithium borate single crystal from a lithium borate glass melt. ing. And it is described that according to the said method, a single crystal with few bubbles can be obtained.

Patent Document 3 discloses a quartz crucible containing a gas-containing gas bubble and an insoluble gas having a gas content of less than about 0.5% in order to produce a silicon single crystal substantially free of crystal voids. The crucible used is described. However, no specific example of obtaining a silicon single crystal without crystal voids is described.
In Patent Document 4, a silicon carbide seed crystal is immersed in a melt under the condition of a non-oxidizing atmosphere gas having a viscosity at a single crystal growth temperature of 750 μP (micropoise) or less during single crystal growth. A method for producing a silicon carbide single crystal for growing crystals is described. And it is described that the bubble generation taken into the crystal by the above method can be completely suppressed. As a specific example, an example in which a single crystal is obtained by crystal growth using He as an atmospheric gas is shown together with a comparative example in which a single crystal is obtained by crystal growth using Ar as an atmospheric gas.
In Patent Document 5, in a method of pulling and growing a silicon single crystal from a silicon melt, the height of a solid-liquid interface is set to obtain a crystal having a high percentage of defect-free regions that do not contain void defects and the like. Describes a method for producing a silicon single crystal in a specific range in relation to the radius of.

In Patent Document 6, when growing a crystal by bringing a seed crystal substrate into contact with a melt, the single crystal has mirror symmetry with respect to the growth surface in order to grow a bulk single crystal having a reduced defect density. A method of manufacturing a single crystal having a crystal structure that does not have, and growing a crystal in an inert atmosphere while applying a voltage between a growth surface of the single crystal and a surface opposite to the single crystal growth surface of the substrate. Are listed. As a specific example, the fact that a bulk single crystal with few defects is obtained qualitatively by applying a pulse voltage to the substrate is shown together with a comparative example in the case where no pulse voltage is applied. However, no example of quantitatively measuring defects in the obtained crystal is described.
Patent Document 7 describes an improvement in the morphology of the surface of a crystal growth layer in which a silicon carbide single crystal is precipitated and grown by a melt obtained by adding Cr and X (X is at least one of Ni and Co) to a Si melt at a specific ratio. A method of growing a silicon carbide single crystal that can realize the above is described.

JP-A-2-239183 JP 7-33580 A Special table 2001-519752 gazette JP 2006-69861 A JP 2007-290907 A JP 2008-280225 A JP 2009-126770 A

According to the single crystal manufacturing methods described in the above patent documents, single crystals with few defects can be obtained. However, all of them require special equipment or have a high crystal growth temperature of about 2000 ° C. However, it is unclear whether the effect of suppressing voids can be achieved by growing SiC single crystals, and voids are reduced along with a reduction in the probability of polycrystals in SiC single crystals grown without the need for special equipment at high crystal growth temperatures. There is a need for a method of producing a SiC single crystal that can reduce the density.
Accordingly, an object of the present invention is to provide a method for producing an SiC single crystal that can reduce the probability of mixing polycrystals in the grown crystal and reduce the void density without requiring a special apparatus even at a high crystal growth temperature. It is to be.

As a result of examining the manufacturing method of the SiC single crystal by the solution method, the present inventors have found that the generation of voids in the single crystal is one of the causes due to gas adhering to the seed crystal. As a result, the present invention was completed.
The present invention is a method for growing a SiC single crystal on a SiC seed crystal (SiC seed crystal substrate) from a raw material solution by a solution method, and the ratio of the surface area (Sc) of the SiC seed crystal to the area (Ss) of the solution interface The present invention relates to a method for producing an SiC single crystal, characterized in that (Sc / Ss) is 0.13 or less and the atmospheric pressure in the crucible before starting crystal growth is 55 kPa or more.
In the present invention, the area (Ss) of the solution interface and the surface area (Sc) of the SiC seed crystal are each area described in detail in the column of Examples described later.
In the present invention, the atmospheric pressure in the crucible before the start of crystal growth is the time before the raw material solution (also referred to as melt) is brought into contact with the SiC seed crystal, and is described in detail in the section of Examples below. Means the atmospheric pressure in the crucible.

  According to the present invention, a special apparatus is not required even at a high crystal growth temperature, and the probability of mixing polycrystals in the grown crystal can be reduced and the void density in the single crystal can be easily reduced.

FIG. 1 is a graph showing the relationship between the ratio (Sc / Ss) of the seed crystal area (Sc) to the area (Ss) of the solution interface in the example of the present invention and the void density in the obtained grown SiC crystal. . FIG. 2 is a copy of a photograph showing a crystal surface image of the grown SiC crystal obtained in the example. FIG. 3 is a graph showing the relationship between the atmospheric pressure in the crucible (before and after the start of crystal growth) and the void density in the obtained grown SiC crystal in the example of the present invention. FIG. 4 is a graph showing the atmospheric pressure in the crucible (before the start of crystal growth and after the start of growth) and the polycrystal mixing probability in the obtained grown SiC crystal in the example of the present invention. FIG. 5 is a copy of a photograph showing a crystal transmission image of the grown SiC crystal obtained in the comparative example. FIG. 6 is a schematic diagram of an experimental apparatus for growing a SiC single crystal by a solution method used in an example of the present invention.

In the present invention, when the SiC single crystal is grown by the solution method, the ratio (Sc / Ss) of the surface area (Sc) of the SiC seed crystal to the area (Ss) of the solution interface is 0.13 or less, for example, 0.01 A special apparatus is used even at a high crystal growth temperature of 1800 to 2100 ° C. by setting the atmospheric pressure in the crucible in the crucible before starting crystal growth to 55 kPa or more, for example, 55 to 200 kPa. Therefore, it is possible to reduce the probability of polycrystals in the grown crystal and to reduce the void density in the grown SiC single crystal. Furthermore, by setting the atmospheric pressure in the crucible after the start of crystal growth to 150 kPa or less, for example, in the range of 20 to 150 kPa, particularly in the range of 20 to 125 kPa, the void density in the grown SiC single crystal can be significantly reduced.
In the above description, “without using a special apparatus” means an apparatus whose control of each manufacturing condition other than the apparatus applied in the normal SiC crystal growth and reactor technology is not well known to those skilled in the art. .

Hereinafter, the present invention will be described with reference to FIGS.
In the present invention, a SiC single crystal is grown by a solution method at a Sc / Ss of 0.13 or less and the atmospheric pressure in the crucible before the start of crystal growth is 55 kPa or more as shown in FIG. As shown in FIGS. 1 and 2, the void density in the grown SiC single crystal can be reduced.
In particular, the conditions regarding the Sc / Ss and the atmospheric pressure in the crucible before the start of crystal growth are satisfied, and the atmospheric pressure in the crucible after the start of crystal growth is 150 kPa or less, for example, in the range of 20 to 150 kPa, particularly 20 to 125 kPa. As shown in FIG. 3, the void density in the grown SiC single crystal is further eliminated or reduced by growing the SiC single crystal as shown in FIG. 3, and the polycrystalline inclusion in the grown SiC single crystal as shown in FIG. Probability can be eliminated or reduced.

On the other hand, when the crystal growth is performed with the atmospheric pressure before the start of crystal growth in the crucible being outside the above range in the present invention, for example, 20 kPa, as shown in FIG. 5, the target seed crystal ( For example, in addition to 4H-SiC, which is the same as 4H-SiC in FIG. 5, polycrystals such as 3C-SiC, 4H-SiC, and 6H-SiC are confirmed.
Although the theoretical elucidation of how the atmospheric pressure before the start of crystal growth in the crucible has an effect on the incorporation of polycrystals has not yet been made, the crucible inside the crucible is exposed to excessively negative pressure or low pressure. In some cases, the vapor of the solution adheres to the seed crystal and a crystal polymorphism other than the target single crystal (for example, 4H-SiC in FIG. 5) (for example, when the seed crystal is 4H-SiC, 6H-SiC or 3C- It is thought that SiC and the like) promote nucleation and growth.

  In the present invention, the raw material solution for growing the SiC single crystal can include any solution containing Si and C as essential components. For example, from the viewpoint of the quality of the grown crystal, Furthermore, the thing containing Ti and / or Cr is mentioned.

The temperature of the raw material solution may be in the range of 1600 to 2100 ° C., for example, in the range of 1800 to 2100 ° C., among which 1800 to 2050 ° C., particularly about 1850 to 2050 ° C.
The temperature of the raw material solution is controlled by high-frequency induction heating, for example, observation of the temperature of the raw material solution surface by a radiation thermometer and / or a thermocouple installed inside the carbon rod, for example, W-Re (tungsten / renium) The temperature can be measured by a temperature controller based on the measured temperature obtained by measuring the temperature using a thermocouple.

In the present invention, since it is necessary to control the atmospheric pressure in the crucible before the start of crystal growth and preferably after the start of crystal growth, a closed reaction vessel is used as the reaction vessel as shown in FIG. Is appropriate.
As a method for controlling the atmospheric pressure in the crucible, a known control technique in the reaction apparatus can be used. For example, the atmosphere in the crucible is not limited. For example, when an inert gas atmosphere is used, an inert gas storage container, for example, an inert gas cylinder, a pipe for supplying an inert gas from the cylinder to the crucible, and the crucible A crucible is provided with an inlet for introducing an inert gas, a discharge port for discharging the inert gas from the crucible, a vacuum pump for discharging the gas from the crucible, a device for controlling the atmospheric pressure in the crucible, such as a pressure gauge. Can be appropriately performed.
In the present invention, it is necessary to control the atmospheric pressure in the crucible before starting crystal growth, but the atmospheric pressure before starting crystal growth and after starting crystal growth may be the same or different, and usually the same. In order to change these pressures, it can be appropriately performed by the above-mentioned control method of atmospheric pressure.

In the method for producing SiC by the solution method of the present invention, conditions other than the Sc / Ss, the atmospheric pressure in the crucible before the start of crystal growth, and the atmospheric pressure in the crucible after the start of crystal growth, such as the shape of the graphite crucible, heating The method, heating time, heating rate and cooling rate can be determined by appropriately selecting optimum conditions from conventionally known conditions in the solution method.
For example, the heating time by high-frequency induction heating (the approximate time from the preparation of raw materials until reaching the SiC saturation concentration) is about 20 minutes to 10 hours (for example, about 3 to 7 hours), depending on the size of the crucible, The atmosphere includes a rare gas, for example, an inert gas such as He, Ne, or Ar, or a mixed gas of the inert gas and N ₂ or methane gas.

  The SiC single crystal growth by the solution method in the present invention described above reduces the void density in the grown SiC single crystal at a high temperature for a long time, for example, 2 hours or more, thereby preventing or suppressing the growth of the polycrystalline SiC single crystal. Can grow.

Hereinafter, although an example and a comparative example are given and the present invention is explained more concretely, the present invention is not limited to the following examples.
In each of the following examples, the SiC single crystal is grown by using an experimental apparatus (cylinder, piping, gas outlet, gas inlet, pressure gauge, vacuum pump not shown) for producing the SiC single crystal by the solution method shown in FIG. I went. Moreover, the temperature confirmation in the high temperature of a raw material solution was performed by the aspect which measures surface temperature. The radiation thermometer was installed in the observation window above the solution where the solution surface can be directly observed, and the temperature before and after contacting the seed crystal with the solution was measured. In addition, a thermocouple was installed inside the seed crystal axis for single crystal growth (position 2 mm from the seed crystal), and the temperature immediately after contact with the raw material solution was measured.

In each of the following examples, the atmospheric pressure in the crucible before the start of crystal growth indicates a value obtained by confirming the atmospheric pressure in the crucible at one minute before contacting the solution with the seed crystal substrate using a pressure gauge in the apparatus. The atmospheric pressure in the crucible after crystal growth is a value obtained by confirming the atmospheric pressure in the crucible with a pressure gauge in the apparatus after 2 to 5 minutes (time required for gas introduction) after contacting the solution with the seed crystal substrate. Indicate
Moreover, in each following example, the area (Ss) of a solution interface and the surface area (Sc) of a SiC seed crystal are the surface areas computed based on the following description.
Ss: Area of the seed crystal plane (C plane) Sc: Area of the solution interface In each of the following examples, the inclusion of voids and polycrystals in the obtained grown SiC crystal was confirmed by the following method. Measured.
Void: Measure the surface image of the grown crystal with an optical microscope, and visually measure the entire transmission enlarged image (× 20) over the entire area. Measure the probability of polycrystal contamination: Measure the transmitted image of the grown crystal with an optical microscope and Raman spectroscopy.

Examples 1-4
Si and Cr and Ni are simultaneously added to the graphite crucible, and heating is continued for 2 to 3 hours in an inert gas (Ar) atmosphere to maintain the set temperature (1800 to 2100 ° C.), and then C dissolves from the graphite crucible. When the SiC saturation concentration was reached, 4H—SiC was used as a seed crystal and growth was performed at a growth temperature of 1800 to 2100 ° C. The atmospheric pressure before the start of crystal growth and after the start of crystal growth at the time of growing the SiC single crystal on the SiC seed crystal was 180 kPa. Experiments were performed by changing the ratio of the graphite crucible diameter and the seed crystal diameter to change Sc / Ss in the range of 0.03 to 0.13. The void density was determined.
FIG. 1 shows the relationship between Sc / Sr and the void density in the grown single crystal.
It was confirmed that there was no polycrystal contamination in the grown crystal.
Moreover, the crystal surface image of the crystal obtained in Example 3 (Sc / Ss = 0.1) is shown in FIG.

Comparative Example 1
The experiment was performed in the same manner as in Example 1 except that Sc / Ss was set to 0.15, and the void density in the obtained grown crystal was obtained.
The relationship between Sc / Ss and the void density in the grown single crystal is shown together with the results of Example 1 in FIG.

Example 5
In an inert gas (Ar) atmosphere, 4H—SiC is used as a seed crystal, the growth temperature is 1800 to 2100 ° C., and the ratio of the graphite crucible diameter to the seed crystal diameter is adjusted to be Sc / Ss = 0.1. The SiC single crystal was grown by setting the atmospheric pressure in the crucible (before and after starting crystal growth) to 80 kPa. The void density and polycrystal mixing probability in the obtained grown crystal were measured.
FIG. 3 shows the relationship between the atmospheric pressure in the crucible and the void density in the grown single crystal together with other results.
FIG. 4 shows the relationship between the atmospheric pressure in the crucible and the polycrystal mixing probability of the grown single crystal together with other results.

Example 6
A SiC single crystal was grown in the same manner as in Example 5 except that the atmospheric pressure in the crucible (both the atmospheric pressure before the start of crystal growth and the atmospheric pressure after the start of crystal growth) was 120 kPa. The void density and polycrystal mixing probability in the obtained grown crystal were measured.
FIG. 3 shows the relationship between the atmospheric pressure in the crucible and the void density in the grown single crystal together with other results.
FIG. 4 shows the relationship between the atmospheric pressure in the crucible and the polycrystal mixing probability of the grown single crystal together with other results.

Example 7
A SiC single crystal was grown in the same manner as in Example 5 except that the atmospheric pressure in the crucible was set to 180 kPa before starting crystal growth and 20 kPa after starting crystal growth. The void density and polycrystal mixing probability in the obtained grown crystal were measured.
The void density in the grown single crystal was 72 / cm ² , and the probability of polycrystal contamination in the grown single crystal was 0%.

Comparative Example 2
A SiC single crystal was grown in the same manner as in Example 5 except that the atmospheric pressure in the crucible (both the atmospheric pressure before the start of crystal growth and the atmospheric pressure after the start of crystal growth) was 20 kPa. The void density and polycrystal mixing probability in the obtained grown crystal were measured.
The void density in the grown crystal was 10 / cm ² . FIG. 4 shows the polycrystal mixing probability in the crystal together with other results, and FIG. 5 shows the crystal surface image.
FIG. 5 shows that polycrystals were mixed in the crystal when the atmospheric pressure before and after the start of crystal growth in the crucible was 20 kPa.

From FIG. 1, when Sc / Ss increases, the void density tends to increase. When Sc / Ss is 0.13 or less, the void density in the crystal is small, but Sc / Ss is larger than 0.13. It was confirmed that the void density in the crystal increased rapidly.
In addition, it is confirmed from FIG. 3 that the void density in the grown SiC single crystal has been greatly reduced by growing the SiC single crystal at an atmospheric pressure of 20 kPa, 80 kPa, and 120 kPa after starting the crystal growth. It was.
Also, from FIG. 4, when the atmospheric pressure in the crucible before the start of crystal growth is 20 kPa (Comparative Example 2), the probability of polycrystals mixing in the grown crystal is about 80%, but in the crucible before the start of crystal growth, When the atmospheric pressure was 80 kPa (Example 5), 120 kPa (Example 6), and 180 kPa (Example 7), it was confirmed that the probability of mixing polycrystals in the grown crystal was 0%.
Therefore, if the atmospheric pressure in the crucible before the start of crystal growth is 55 kPa or more, it is estimated that the probability of polycrystals mixing in the grown crystal is low.
Further, from Example 7, if the pressure before the start of crystal growth is a relatively high pressure, the probability of polycrystal mixing in the grown crystal is low even at a pressure of 20 kPa after the start of crystal growth.

  According to the method of the present invention, it is expected as a next-generation semiconductor material by easily reducing the probability of mixing polycrystals and void density in a single crystal without requiring a special apparatus even at a high crystal growth temperature. It becomes possible to produce a SiC single crystal.

Claims (6)

  A method of growing a SiC single crystal on a SiC seed crystal from a raw material solution by a solution method, wherein the ratio (Sc / Ss) of the surface area (Sc) of the SiC seed crystal to the area (Ss) of the solution interface is 0.13 or less A method for producing a SiC single crystal, wherein the atmospheric pressure in the crucible before the start of crystal growth is 55 kPa or more.   The manufacturing method according to claim 1, wherein the atmospheric pressure in the crucible after the start of crystal growth is 150 kPa or less.   The manufacturing method according to claim 1 or 2, wherein the atmospheric pressure in the crucible before the start of crystal growth is in a range of 55 to 200 kPa, and the atmospheric pressure in the crucible after the start of crystal growth is in a range of 20 to 150 kPa.   The manufacturing method according to any one of claims 1 to 3, wherein the crystal growth temperature is a temperature within a range of 1800 to 2100 ° C.   The manufacturing method according to claim 1, wherein the crucible is a graphite crucible.   The manufacturing method according to any one of claims 1 to 5, wherein the raw material solution is a Si-Cr-X-C system (X is Ni and / or Co).