JP2008001569A - Single crystal SiC, method for manufacturing the same, and apparatus for manufacturing single crystal SiC - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high quality, long single crystal SiC having a large diameter in which the occurrence of defects such as micropipes is suppressed. <P>SOLUTION: A production method for the single crystal SiC includes the steps of: fixing a SiC seed single crystal wafer 4 to a susceptor; and growing the single crystal SiC by continuously supplying raw materials for producing the single crystal SiC onto the SiC seed single crystal wafer 4 from outside, wherein the average temperature gradient of the susceptor 5, the SiC seed single crystal wafer 4 and the single crystal SiC having an increased thickness with growth is set to be within the range of 0.5 to 9°C/mm, the average temperature gradient being in the vertical direction (longitudinal direction) of the susceptor 5. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to single crystal SiC used as a semiconductor device material or LED material.

  Single crystal SiC has a large crystal bond energy, a large dielectric breakdown electric field, and a high thermal conductivity, and thus is useful as a material for a device for harsh environments and power devices. Moreover, since the lattice constant is close to the lattice constant of GaN, it is also useful as a substrate material for GaN-LED.

  Conventionally, for the production of single crystal SiC, the Rayleigh method in which SiC powder is sublimated in a graphite crucible and the single crystal SiC is recrystallized on the inner wall of the graphite crucible, and the raw material arrangement and temperature distribution are optimized based on this Rayleigh method. An improved Rayleigh method in which an SiC seed single crystal is placed in the recrystallized portion and epitaxially recrystallized, while a gas source is transported onto the heated SiC seed single crystal by a carrier gas and chemically reacted on the crystal surface. There are a CVD method for epitaxial growth, a sublimation proximity method for epitaxially recrystallizing SiC powder on the SiC seed single crystal in a state where the SiC powder and the SiC seed single crystal are brought close to each other in a graphite crucible.

By the way, at present, each of these single crystal SiC synthesis methods is considered to have a problem. Although the Rayleigh method can synthesize single-crystal SiC with good crystallinity, crystal growth is based on spontaneous nucleation, so shape control and crystal surface control are difficult, and large-diameter wafers can be obtained. There is no problem.
In the improved Rayleigh method, a large-diameter single crystal SiC ingot can be obtained at a high speed of about several hundred μm / h. However, since it grows epitaxially in a spiral shape, minute holes penetrating crystals called many micropipes in the crystal. There is a problem that occurs. Although the CVD method can produce high-quality single crystal SiC with high purity and low defect density, because of epitaxial growth with a dilute gas source, the growth rate is as slow as several tens of μm / h, and a long single crystal SiC ingot is formed. There is a problem that it cannot be obtained.
In the sublimation proximity method, high-purity SiC epitaxial growth can be realized with a relatively simple structure, but there is a problem that it is impossible to obtain a long single-crystal SiC ingot due to structural restrictions.

  Recently, ultrafine particles of silicon dioxide and ultrafine particles of carbon are supplied by inert carrier gas onto a heated SiC seed single crystal, and the single crystal SiC is reduced by reducing silicon dioxide with carbon on the SiC seed single crystal. A method of epitaxially growing at a high speed on a SiC seed single crystal has been invented (see Patent Document 1). In this method, it is described that high-quality single crystal SiC in which defects such as micropipes are suppressed can be obtained at high speed.

  The manufacturing method disclosed in Patent Document 1 is similar to the Atchison method, which is well known as an SiC manufacturing method for abrasives, in that solid silicon dioxide ultrafine particles and solid carbon ultrafine particles are used as raw materials for single crystal SiC production. ing. The Atchison method is a method for producing single-crystal SiC with volume shrinkage by heating anhydrous silicic acid and a carbon source to 2,000 ° C. or higher and reducing the anhydrous silicic acid with carbon. Since the Atchison method has a complicated reaction, SiC polycrystals having various polymorphs, sizes and orientations are produced. On the other hand, the manufacturing method disclosed in Patent Document 1 supplies a single crystal SiC raw material composed of silicon dioxide ultrafine particles and carbon ultrafine particles onto a heated and maintained SiC seed single crystal. It is expected to control the orientation and polymorphism of single crystal SiC produced with shrinkage and to be epitaxially arranged on the SiC seed single crystal.

  However, in practice, in the manufacturing method disclosed in Patent Document 1, it is difficult to control the crystal growth of single-crystal SiC. When 1 mol of solid silicon dioxide ultrafine particles and 3 mol of solid carbon ultrafine particles are subjected to a solid phase reaction, 1 mol of SiC is produced and 2 mol of carbon monoxide gas is generated. This carbon monoxide gas is presumed to be generated on the SiC seed single crystal where the reaction proceeds. Therefore, unless the SiC seed single crystal is quickly removed from the SiC seed single crystal, the SiC seed single crystal and the reaction growth layer are separated by the carbon monoxide gas. As a result, it is considered that the cause is that the crystal arrangement information on the surface of the SiC seed single crystal is not transmitted to the reaction growth layer.

Japanese Patent No. 3505597

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a high-quality long, large-diameter single crystal SiC in which defects such as micropipes are suppressed.

The above problems have been solved by the means described in <1>, <4> and <5> below. It is described below together with <2> and <3> which are preferred embodiments.
<1> A method for manufacturing single crystal SiC, the step of fixing a SiC seed single crystal wafer to a susceptor, and a single crystal SiC raw material by continuously supplying a raw material for manufacturing single crystal SiC onto the SiC seed crystal wafer from the outside. The average temperature gradient in the vertical direction (longitudinal direction) of the susceptor is 0.5 ° C./mm to 9 ° C./mm. A method for producing single-crystal SiC, characterized by:
<2> The method for producing single crystal SiC according to <1>, wherein the raw material for producing single crystal SiC is silica and carbon.
<3> The method for producing single-crystal SiC according to claim 1, wherein the average temperature gradient is 0.5 ° C./mm or more and 3 ° C./mm or less.
<4> Single-crystal SiC manufactured by the method according to any one of <1> to <3>,
<5> a chamber provided with a crucible, a means for heating the crucible, a susceptor for fixing the SiC seed single crystal wafer in the crucible, and a means for supplying a raw material for producing single crystal SiC to the SiC seed single crystal, An apparatus for producing single crystal SiC, wherein the susceptor has a controllable heat exchange function.

According to the present invention, it is possible to provide a single crystal SiC having a high growth rate and low cost, a method for manufacturing the same, and a single crystal SiC manufacturing apparatus.
The single crystal SiC obtained by the present invention has a high quality with reduced generation of micropipes. Furthermore, it is possible to provide single crystal SiC having a large large diameter.

The method for producing a single crystal SiC of the present invention includes a step of fixing a SiC seed single crystal wafer to a susceptor, and a step of growing single crystal SiC by continuously supplying a raw material for single crystal SiC from the outside onto the SiC seed crystal wafer. Including the susceptor, the SiC seed single crystal, and the single crystal SiC whose thickness increases with growth, an average temperature gradient in the vertical direction (longitudinal direction) of the susceptor is 0.5 ° C./mm or more and 9 ° C./mm or less. Features.
The average temperature gradient is from 0.5 ° C./mm to 9 ° C./mm, preferably from 0.5 ° C./mm to 3 ° C./mm.
The average temperature gradient is set so that the SiC single crystal growth layer has a high temperature and the susceptor side has a low temperature.

When the average temperature gradient is 0.5 ° C./mm or more and 9 ° C./mm or less, the produced single crystal SiC can be grown epitaxially. This is presumably because the crystal arrangement information on the surface of the SiC seed single crystal is transmitted to the growth layer of the SiC single crystal.
More specifically, since the average temperature gradient is low on the susceptor side and high on the growth layer side, the temperature of the grown single crystal SiC surface is higher than that of the SiC seed single crystal surface. By setting the temperature gradient in this manner, the carbon monoxide gas that is a reaction product quickly moves to the surface of the grown single crystal SiC by thermal diffusion and is released into the crucible. That is, the generated carbon monoxide gas does not stay inside the grown single crystal SiC, and the SiC seed single crystal and the reaction growth layer are not separated by the carbon monoxide gas. As a result, it is considered that the crystal arrangement information on the surface of the SiC seed single crystal is well transmitted to the reaction growth layer.
However, when the temperature gradient is larger than 9 ° C./mm, the supersaturation degree on the surface of the SiC seed single crystal increases, polymorphic nuclei unrelated to the crystal arrangement information on the surface of the SiC seed single crystal are generated, and the single crystal cannot be obtained. . On the other hand, when the temperature gradient is smaller than 0.5 ° C./mm, the growth rate is lowered, and conversely, etching may occur.

In the present invention, the average temperature gradient can be measured as follows.
The temperature gradient is measured on the susceptor side (low temperature side) and the growth layer side (high temperature side), and this temperature difference is the value divided by the distance from the temperature sensor installed in the heat exchanger section of the susceptor to the growth layer surface. is there. Specifically, a temperature sensor is installed in the portion of the susceptor to which the heat exchanger is provided, and the temperature is measured to obtain the temperature on the low temperature side. In addition, the temperature correlation between the surface of the SiC seed single crystal and the outer surface of the sealed crucible is measured in advance, and the temperature of the outer surface of the sealed crucible is actually measured with a radiation thermometer, and the calculated temperature is measured on the surface of the growth layer. It is regarded as the temperature and the temperature is on the high temperature side. The average temperature gradient can be calculated from these temperatures, the distance from the temperature sensor to the susceptor surface, the thickness of the seed single crystal, and the growth rate of the SiC single crystal.

Any method can be used to make the average temperature gradient within the above range, but it is preferable to control the temperature gradient by having a heat exchange function that the susceptor can control.
Specifically, the temperature on the high temperature side is fixed to the production temperature of the single crystal SiC, and the temperature gradient adjustment can be performed by adjusting the temperature on the low temperature side (the side to which the susceptor heat exchanger is provided). . When providing a temperature gradient, it is possible to control the temperature on the low temperature side by adjusting the contact area between the susceptor and the heat exchanger and the heat exchange capacity.
When using the above manufacturing equipment without a temperature gradient, the heat exchanger is stopped and a heat insulating material is inserted between the susceptor and the heat exchanger to control the temperature gradient. It can also be used for other purposes.

The raw material for producing single crystal SiC is preferably made of silica and carbon.
The type, particle size, particle shape and the like of the silica particles used in the present invention are not particularly limited, and for example, high purity silica obtained by a flame hydrolysis method can be suitably used.
The kind, particle size, particle shape and the like of the carbon particles used in the present invention are not particularly limited, and for example, commercially available high purity carbon black can be suitably used.

  The ratio of the continuous supply amount of the silica particles and the carbon particles is not particularly limited, and a desired composition ratio can be appropriately selected. Two or more of the above silica particles and carbon particles may be mixed and used. In addition, the silica particles and carbon particles may be pretreated or a small amount of other components may be added as necessary.

The supply of the silica particles and the carbon particles onto the SiC seed single crystal wafer is not particularly limited as long as it is a continuous supply method without interruption, and any known method can be used. Specifically, the thing which can convey a powder continuously like a commercially available powder feeder can be illustrated.
In addition, when supplying the raw material for producing the single crystal SiC, it is preferable to have a hermetic structure substituted with argon or nitrogen in order to prevent oxygen contamination.

With respect to the supply conditions of the silica particles and the carbon particles onto the SiC seed single crystal wafer, it is sufficient that these raw materials for producing single crystal SiC are supplied in a mixed state on the SiC seed single crystal wafer. Even if the raw materials for producing SiC are mixed, they may be supplied separately and mixed on the SiC seed single crystal wafer.
When doping is performed in single crystal SiC, the raw material for manufacturing single crystal SiC may be mixed as a solid source, or the doping component may be mixed as a gas source in the atmosphere in the single crystal SiC manufacturing apparatus. May be.

  The type, size, and shape of the SiC seed single crystal wafer used in the present invention are not particularly limited, and can be appropriately selected depending on the type, size, and shape of the target single crystal SiC. For example, an SiC single crystal obtained by an improved Rayleigh method, or an SiC seed single crystal wafer that has been pretreated if necessary can be suitably used.

In the present invention, the configuration of the single crystal SiC manufacturing apparatus used for obtaining single crystal SiC is not particularly limited. That is, the size, heating method, material, raw material supply method, atmosphere adjustment method, temperature control method, etc. are appropriately determined according to the size, shape and type of the target single crystal SiC, the type and amount of the raw material for producing single crystal SiC, etc. You can choose.
The atmosphere of the apparatus is preferably substituted with argon or nitrogen in order to prevent oxygen contamination, and preferably has a sealed structure.
The single crystal SiC production temperature is not particularly limited, and can be appropriately set according to the size, shape, and type of the target single crystal SiC, the type and amount of the raw material for producing single crystal SiC, and the like. A preferable production temperature is in the range of 1,600 to 2,400 ° C., and refers to the temperature outside the closed crucible, for example. The manufacturing apparatus used in the present invention is preferably an apparatus capable of controlling the temperature in the temperature range.
In the present invention, the heating method is not particularly limited, and any heating method can be used, and high frequency induction heating and electric resistance heating can be exemplified.

  The material of the susceptor holding the SiC seed single crystal wafer is preferably made of graphite in consideration of the operating temperature range, and a cooling mechanism for generating a heat flow in the vertical direction (longitudinal direction) of the susceptor is provided. preferable. The cooling method is not particularly limited, but the cooling method is preferably designed so that a preferable temperature gradient can be selected in accordance with the size, shape, and type of the target single crystal SiC.

  In the present invention, the SiC single crystal manufacturing apparatus includes a chamber provided with a crucible, a means for heating the crucible, a susceptor for fixing a SiC seed single crystal wafer in the crucible, and a raw material for manufacturing single crystal SiC on the SiC seed single crystal. It is particularly preferable that the single-crystal SiC manufacturing apparatus is characterized in that the susceptor has a controllable heat exchange function.

FIG. 1 shows an example of an apparatus for producing single crystal SiC of the present invention, and here, a high frequency induction heating furnace is used.
A carbon-made sealed crucible 2 (diameter 100 mm, height 150 mm) is disposed in a water-cooled sealed chamber 1, and a high-frequency induction heating coil 3 is disposed outside the water-cooled sealed chamber 1.
A susceptor 5 for holding the SiC seed single crystal wafer 4 is inserted through the lower portion of the sealed crucible. The susceptor extends to the lower side of the hermetic crucible, and can be rotated about the central axis of the susceptor by a rotation mechanism (not shown).

Further, a controllable heat exchange function is provided at a lower end (not shown) of the susceptor, and a heat flow can be generated in the susceptor vertical direction (longitudinal direction) 10. The heat flow rate can be adjusted.
It should be noted that the normal direction of the surface holding the SiC seed single crystal wafer at the upper end of the susceptor can be freely set from approximately parallel to the vertical direction of the susceptor to a maximum inclination of 45 °.

A supply pipe 6 for supplying raw material particles for producing single crystal SiC is inserted through the upper portion of the sealed crucible. Further, the supply pipe is disposed outside the high-frequency induction heating furnace, and a plurality of raw material storage tanks 7 and 7 ′ whose supply amount can be adjusted independently, and an inert carrier gas supply source (see FIG. (Not shown).
When using a raw material for producing single crystal SiC mixed in advance, one raw material storage tank is used, and when mixing inside the supply pipe, silica and carbon powder are filled in the raw material storage tank independently. After adjusting the supply amount from each storage layer with the control valves 8 and 8 ′, the inert carrier gas A is allowed to flow while adjusting the flow rate, so that an appropriate amount of raw material for producing single crystal SiC is contained in the sealed crucible. Can be continuously supplied one by one.
In this manner, a single crystal SiC layer (growth layer) 9 having a thickness increased with growth is formed on the SiC seed single crystal wafer 4.

The high-frequency induction heating furnace can be controlled by a vacuum exhaust system and a pressure control system (not shown), and includes an inert gas replacement mechanism (not shown).
In the embodiment shown in FIG. 1, the supply pipe is arranged on the top and the susceptor is arranged on the bottom. However, it is possible to arrange the supply pipe upside down as long as the operation of the present invention does not change. On the other hand, it can be arranged obliquely or horizontally.

Examples of the present invention will be described below.
Using the high frequency induction heating furnace, single crystal SiC was manufactured under the following conditions.
A SiC seed single crystal wafer was fixed to the upper end of the susceptor. The SiC seed single crystal wafer used here is both an approximately 10 mm square amorphous single crystal SiC manufactured by the Rayleigh method and a single crystal SiC having a diameter of 2 centimeters manufactured by the improved Rayleigh method. Moreover, each of the just surface, the inclined surface, the C surface, and the Si surface was prepared and used as a seed single crystal.
Carbon (carbon black MA600 manufactured by Mitsubishi Chemical) and silica (Aerosil 380 manufactured by Nippon Aerosil Co., Ltd.), which are raw materials for producing single crystal SiC, were independently filled in the raw material storage tank. Each supply ratio was adjusted to silica / carbon = 1.5 to 5.0 (weight ratio). At this time, SiC powder can be separately supplied as necessary.

After evacuating the inside of the high frequency induction heating furnace, the inside of the high frequency induction heating furnace was replaced with an inert gas (high purity argon or high purity nitrogen). Next, the carbon-made sealed crucible was heated by the high-frequency induction heating coil, and the surface temperature of the SiC seed single crystal wafer was adjusted to be in the range of 1,600 to 2,390 ° C.
Next, the susceptor on which the SiC seed single crystal wafer was fixed was rotated at a rotation speed of 0 to 20 rpm. In this state, the inert carrier gas (high-purity argon or high-purity nitrogen) is flowed with a flow rate adjusted to a range of 0.5 to 10 l / min, and the raw material for producing single crystal SiC passes through the inside of the supply pipe. Then, it was continuously supplied onto the surface of the SiC seed single crystal wafer disposed in the lower part of the sealed crucible, and single crystal SiC was produced for about 2 hours. As a result, single crystal SiC having a thickness of about 1 mm was obtained.
At this time, the heat exchange mechanism at the lower end of the susceptor is adjusted so that the average temperature gradient in the susceptor vertical direction (longitudinal direction) is 0.2 ° C./mm, 0.5 ° C./mm, 3 ° C./mm, 9 ° C./mm, 10 Single-crystal SiC was manufactured under the conditions of ° C / mm.

  The production results will be described based on Table 1. When the average temperature gradient in the susceptor vertical direction (longitudinal direction) was 0.5 ° C. or more, the average growth rate was equivalent to 50 to 500 μm / h. However, under the condition where the average temperature gradient is 0.2 ° C./mm, the growth rate is lowered, and in the worst case, the etching is reversed. In addition, under the condition that the average temperature gradient is 10 ° C., the obtained SiC is polycrystalline grown in a columnar shape in a substantially normal direction of the SiC seed single crystal wafer, and is not epitaxially grown on the SiC seed single crystal wafer. It was. In addition, although epitaxial growth was performed under an average temperature gradient of 9 ° C., the amount of micropipes generated increased. On the other hand, when the average temperature gradient is 0.5 ° C. and 3 ° C., it is possible to produce a good single crystal SiC with few defects such as micropipes without polycrystals mixed in the produced single crystal SiC. It was.

It is an example of the apparatus for manufacturing the single crystal SiC of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Sealed chamber 2 Sealed crucible 3 High frequency induction heating coil 4 Type single crystal wafer 5 Susceptor 6 Supply pipe 7, 7 'Raw material storage tank 8, 8' Control valve 9 Growth layer 10 Susceptor vertical direction A Inactive carrier gas

Claims (5)

A method for producing single crystal SiC, comprising:
Fixing a SiC seed single crystal wafer to a susceptor; and
Including a step of continuously supplying a raw material for producing single crystal SiC from the outside onto a SiC seed crystal wafer to grow single crystal SiC,
The average temperature gradient in the vertical direction (longitudinal direction) of the susceptor, the SiC seed single crystal, and the single crystal SiC whose thickness increases with growth is 0.5 ° C./mm or more and 9 ° C./mm or less. A method for producing single crystal SiC.   The method for producing single crystal SiC according to claim 1, wherein the raw materials for producing single crystal SiC are silica and carbon.   The method for producing single crystal SiC according to claim 1, wherein the average temperature gradient is 0.5 ° C./mm or more and 3 ° C./mm or less.   Single-crystal SiC manufactured by the method according to any one of claims 1 to 3. A chamber provided with the crucible and means for heating the crucible;
A susceptor for fixing the SiC seed single crystal wafer in the crucible; and
Means for supplying a raw material for producing single crystal SiC to the SiC seed single crystal;
The single crystal SiC manufacturing apparatus, wherein the susceptor has a controllable heat exchange function.

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