JP2009051700A - Method for producing silicon carbide single crystal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method in which the incorporation of metallic impurities into a growing SiC single crystal can be minimized to prevent the SiC single crystal from taking different polymorphic crystal forms other than a desired crystal form. <P>SOLUTION: In this method, a super-high purity raw material 2a and a high purity raw material 2b are used together such that crystal growth is performed by a sublimation gas of the super-high purity raw material 2a in the stage of the initial period of growth of the SiC single crystal 4, and crystal growth is performed by a sublimation gas of the high purity raw material 2b after the initial period of growth. This can minimize the incorporation of metallic impurities into the growing SiC single crystal 4 even when the super-high purity raw material 2a and the high purity raw material 2b are used together, thereby capable of preventing the single crystal from taking different polymorphic crystal forms other than a desired crystal form in the initial period of growth of the SiC single crystal 4. This allows the reduction in material cost compared with the case where the SiC single crystal 4 is grown only by the super-high purity raw material 2a. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for producing a silicon carbide (hereinafter referred to as SiC) single crystal that can be used for a material such as a semiconductor or a light emitting diode.

  Conventionally, a sublimation recrystallization method has been widely used as a method for growing a SiC single crystal (for example, see Patent Document 1). This sublimation recrystallization method involves joining a seed crystal to a graphite pedestal placed in a graphite crucible, heating and sublimating the SiC raw material powder arranged at the bottom of the crucible, and supplying the sublimation gas to the seed crystal. A SiC single crystal is grown on top.

As SiC raw material powder used for the production of SiC single crystal using such a sublimation recrystallization method, a metal impurity called ultra-high purity raw material containing 10 ppm or less and a metal impurity called high purity raw material containing about 100 ppm to 4000 ppm There is something that has been. The ultra-high purity raw material has an advantage that metal impurities are very low at 10 ppm or less, so that it is possible to suppress the mixing of metal impurities into the growing SiC single crystal. However, the content of metal impurities should be reduced. Raw material cost is high due to difficulty. On the other hand, the high-purity raw material has an advantage that the raw material cost is low because there are many metal impurities compared to the ultra-high-purity raw material, but conversely, the contamination of the metal impurity into the growing SiC single crystal increases, and the SiC There is a possibility that the single crystal may have a different polymorphism other than the desired crystal form in the early stage of growth. In particular, in the temperature rising process leading to growth, the metal impurities remaining in the growth apparatus are melted, evaporated, and sublimated and fly around, and there is a possibility that metal impurities may be mixed in the initial growth. high. In addition, since the growth temperature and pressure are still unstable during the initial growth and the silicon / carbon ratio is also unstable, the influence of metal impurities contained in the SiC raw material on the crystal is extremely high. The SiC single crystal is manufactured using an ultra-high purity raw material even if the raw material cost is high, with an emphasis on obtaining a high-quality and long SiC single crystal by minimizing the influence of the metal impurities.
Japanese Patent Laid-Open No. 6-21989

  However, in the production of SiC single crystals, using only ultra-high-purity raw materials is costly for raw materials and is not suitable for mass production. Therefore, it is desirable to use high-purity raw materials. There is a problem that metal impurities are mixed into the crystal, and the SiC single crystal becomes a different polymorph other than the desired crystal form at the initial stage of growth.

  In view of the above points, the present invention can reduce the mixing of metal impurities into a growing SiC single crystal even when two raw materials having different metal impurity contents are used in combination, and the SiC single crystal is not in a desired crystal form. It aims at providing the manufacturing method of the SiC single crystal which can prevent becoming a heteropolymorph.

  In order to achieve the above object, in the present invention, the SiC raw material (2) and the SiC single crystal substrate (3) serving as a seed crystal are disposed in the container (1), and the SiC raw material (2) is heated and sublimated to produce SiC. In the SiC single crystal manufacturing method for growing the SiC single crystal (4) on the single crystal substrate (3), two raw materials (2a, 2b) having different metal impurity contents are prepared as the SiC raw material (2). The SiC raw material (2) is placed in the container (1) so that the surface of the raw material (2a, 2b) having a high metal impurity content (2b) is covered with the low metal impurity content (2a). Sublimation of the raw material (2a, 2b) having a low content of metal impurities (2a) at the initial growth stage when the SiC single crystal (4) is grown on the surface of the SiC single crystal substrate (3) Growing with gas, SiC single crystal (4) begins to grow Is characterized in that also continue to grow in sublimation gas of the raw material (2a, 2b) having a high content of the metal impurities of (2b) from.

  In this way, two raw materials (2a, 2b) having different metal impurity contents are used in combination, and at the initial growth stage of the SiC single crystal (4), the metal impurities of the raw materials (2a, 2b) By growing with a sublimation gas having a low content (2a), metal impurities can be reduced in the growing SiC single crystal (4), and the desired crystal form can be obtained at the initial stage of the growth of the SiC single crystal (4). It is possible to prevent heterogeneous polymorphism other than. Then, since it can be difficult to form a different polymorph other than the desired crystal form, the growth can be continued even in the sublimation gas of the raw material (2a, 2b) having a high metal impurity content (2b). it can. As a result, it is possible to reduce the mixing of metal impurities into the growing SiC single crystal (4) and to prevent the SiC single crystal from becoming a different polymorph other than the desired crystal form.

  Specifically, a crucible (1b) having a bottomed cylindrical crucible body (1a) whose one side is open as a container (1) and a lid member (1b) for closing the lid of the crucible body (1a). ), The SiC single crystal substrate (3) is attached to the lid (1b) of the crucible (1), and the content of metal impurities in the raw materials (2a, 2b) on the bottom of the crucible body (1a) Higher ones (2b) are arranged, and the metal impurities of the raw materials (2a, 2b) are closer to the SiC single crystal substrate (3) side than those of the raw materials (2a, 2b) having a higher metal impurity content (2b). (2a) with a low content of can be arranged.

  For example, a raw material (2a, 2b) having a low metal impurity content (2a) having a metal impurity content of 10 ppm or less can be used. If the metal impurity content is more than 10 ppm as the metal impurity content is low (2a), the contamination of the SiC single crystal grows so that the SiC single crystal has a desired crystal at the initial stage of growth. There is a risk of heterogeneous polymorphism other than shape. On the other hand, a raw material (2a, 2b) having a high metal impurity content (2b) having a metal impurity content of 100 ppm to 4000 ppm can be used. If the metal impurity content of the metal impurity content (2b) is less than 100 ppm, it is difficult to reduce the metal impurity content, resulting in an increase in raw material cost. If it exceeds 4000 ppm, even if a different polymorphism other than the desired crystal form is not obtained at the initial stage of growth, a large amount of sublimation gas having a high metal impurity content (2b) is generated and SiC grows. There is a risk that the metal impurity is mixed into the single crystal, and the SiC single crystal becomes a different polymorph other than the desired crystal form during the growth. For these reasons, the metal impurities having a high content (2b) are preferably those having a metal impurity content of 100 ppm to 4000 ppm.

  In this case, the mass of the raw material (2a, 2b) having a low content of metal impurities (2a) is 5 to 50% of the total mass of the raw material, and the content of the metal impurities (2b) is high. It can be the rest. If the mass of the metal impurities low content (2a) is less than 5% of the total mass of the raw material, sublimation of the metal impurities high content (2b) occurs from the initial growth, and the growing SiC There is a possibility that the metal impurities are mixed into the crystal and the SiC single crystal becomes a different polymorph other than the desired crystal form at the initial stage of growth. When the content of metal impurities (2a) exceeds 50%, the production cost of the SiC single crystal becomes expensive, which is not preferable. In particular, the mass of the raw material (2a, 2b) having a low metal impurity content (2a) is 30% of the total mass of the raw material, and the high metal impurity content (2b) is 70%. It is preferable.

  In addition, the code | symbol in the bracket | parenthesis of each said means shows the correspondence with the specific means as described in embodiment mentioned later.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(First embodiment)
A first embodiment of the present invention will be described. FIG. 1 is a cross-sectional view showing a state in which a SiC single crystal is grown using the SiC single crystal manufacturing apparatus according to the present embodiment.

  As shown in FIG. 1, a cylindrical graphite crucible 1 is used as a container of a SiC single crystal production apparatus. The graphite crucible 1 sublimates the SiC raw material powder (SiC raw material) 2 provided at the bottom of the graphite crucible 1 by heat treatment, and causes the SiC single crystal 4 to grow on the SiC single crystal substrate 3 as a seed crystal. Is.

  The graphite crucible 1 includes a bottomed cylindrical crucible body 1a having an open top surface and a lid 1b that closes the opening of the crucible body 1a. A portion protruding from the center of the lid 1b constituting the graphite crucible 1 is a pedestal 1c, and the SiC single crystal substrate 3 is bonded to the pedestal 1c via an adhesive (not shown).

  On the other hand, a heating device (not shown) such as an induction coil is provided outside the graphite crucible 1 so as to surround the outer periphery of the graphite crucible 1, and the graphite crucible 1 is controlled by controlling the power of the heating device. It is configured to control the temperature inside. For example, when the SiC single crystal 4 is grown, the temperature of the SiC single crystal substrate 3 as a seed crystal is kept at a temperature about 100 ° C. lower than the temperature of the SiC raw material powder 2 by adjusting the power of the heating device. Can be drunk. Although not shown, the graphite crucible 1 is housed in a vacuum vessel into which argon gas can be introduced, and can be heated in this vacuum vessel.

  An SiC single crystal manufacturing process using the SiC single crystal manufacturing apparatus configured as described above will be described.

  First, as SiC raw material powder 2, an ultra-high-purity raw material 2 a containing 10 ppm or less of metal impurities and a high-purity raw material 2 b containing 100 to 4000 ppm of metal impurities are prepared, and the high-purity raw material 2 b is used as the main body 1 a of the graphite crucible 1. The ultra-high purity raw material 2a is disposed on the high-purity raw material 2b, that is, closer to the lid 1b side of the graphite crucible 1 than the high-purity raw material 2b. At this time, the high-purity raw material 2b is completely covered with the ultra-high-purity raw material 2a. In this case, the mass relationship between the ultra-high purity raw material 2a and the high-purity raw material 2b is such that the mass of the ultra-high purity raw material 2a is 5 to 50%, preferably 30% with respect to the mass of the entire SiC raw material powder 2. The mass of the mass ratio of the purity raw material 2b may be the remainder (95 to 50%, preferably 70%).

  Then, after attaching SiC single crystal substrate 3 as a seed crystal to pedestal 1c, lid 1b is attached to main body 1a, graphite crucible 1 is housed in a vacuum container (not shown), and the inside of the vacuum container is filled with an argon gas atmosphere To. Then, the temperature of SiC raw material powder 2 is heated to 2000-2500 degreeC with the heating apparatus which is not illustrated, and the temperature of SiC single crystal substrate 3 becomes lower than the temperature of SiC raw material powder 2 by adjustment of a heating apparatus, etc. In addition, a temperature gradient is provided in the graphite crucible 1.

  Next, the pressure in the graphite crucible 1 is adjusted to 13.3 Pa to 26.7 kPa by adjusting the degree of vacuum of the vacuum vessel, and when the sublimation growth starts, the SiC raw material powder 2 sublimates to become a sublimation gas, and SiC The SiC single crystal 4 grows on the surface of the SiC single crystal substrate 3 that reaches the single crystal 4 and is at a relatively lower temperature than the SiC raw material powder 2 side.

  At this time, first, the sublimation gas of the ultra-high purity raw material 2a is supplied to the surface of the SiC single crystal substrate 3, and the SiC single crystal 4 begins to grow. It becomes possible to prevent mixing into the single crystal 4. Then, after the crystal growth of the SiC single crystal 4 proceeds, when the ultra-high purity raw material 2a is completely sublimated, or the SiC single crystal in which the sublimation gas of the high-purity raw material 2b is growing through the gap between the ultra-high purity raw material 2a. 4 is supplied to the surface.

  As described above, by supplying the sublimation gas of the ultra-high purity raw material 2a to the initial stage of the growth of the SiC single crystal 4, it is possible to generate different polymorphs other than the desired crystal form in the initial stage of growth. Can be prevented. If different polymorphs can be prevented from occurring in the early stage of growth, the underlying crystal form is easily inherited in subsequent growth. Therefore, after the initial stage of growth, the SiC single crystal 4 is grown by the sublimation gas of the high-purity raw material 2b. However, it becomes possible to grow long with high quality.

  Thereafter, the SiC single crystal 4 is grown while making the amount of reduction of the SiC raw material powder 2 substantially constant. For example, the temperature distribution in the graphite crucible 1 can be adjusted by adjusting the power of the heating device. By doing in this way, the silicon / carbon ratio in the crucible 1 can be stabilized, and the SiC single crystal 4 can be reliably formed in high quality and long.

  As described above, in this embodiment, while using the ultra-high purity raw material 2a and the high-purity raw material 2b in combination, crystal growth is caused by the sublimation gas of the ultra-high purity raw material 2a at the initial stage of the growth of the SiC single crystal 4. The crystal growth is performed using the sublimation gas of the high-purity raw material 2b after the initial stage of growth. By doing so, it is possible to reduce the mixing of metal impurities into the SiC single crystal 4 that grows even when the ultra-high purity raw material 2a and the high purity raw material 2b are used in combination, and a desired crystal at the initial growth stage of the SiC single crystal 4 It is possible to prevent different polymorphs other than shapes. According to the manufacturing method of the present embodiment, the raw material cost can be reduced as compared with the case where the SiC single crystal 4 is grown only by the ultra-high purity raw material 2a. It can be set as the manufacturing method of the crystal 4.

  When the SiC single crystal 4 is grown, the sublimation gas of the ultra high purity raw material 2a is first used for crystal growth, and then the sublimation gas of the high purity raw material 2b is used for crystal growth. The ultra-high purity raw material 2a needs to be disposed so as to cover at least the high-purity raw material 2b. The mass ratio between the ultra-high purity raw material 2a and the high-purity raw material 2b at this time is determined by the dimensions of the graphite crucible 1 and the like. The mass of the purity raw material 2a may be 5 to 50%, and the mass of the mass ratio of the high purity raw material 2b may be the rest (95 to 50%).

  The mass relationship between the ultra-high purity raw material 2a and the high-purity raw material 2b is determined based on experimental results. FIG. 2 is a chart showing an example of the result of examining the relationship between the masses of the ultra-high purity raw material 2a and the high-purity raw material 2b and the occurrence of different types of polymorphs. As shown in this figure, when the ratio of the mass of the ultra-high purity raw material 2a having a metal impurity content of 10 ppm and the mass of the high-purity raw material 2b having a metal impurity content of 100 ppm to 4000 ppm is 30:70 No heterogeneous polymorphism has occurred. On the other hand, when the metal impurity content of the ultra-high purity raw material 2a exceeds 10 ppm, a heterogeneous polymorph occurs, and when the metal impurity content of the high-purity raw material 2b reaches 5000 ppm, a heterogeneous polymorph occurs from the middle. Yes. And even if the metal impurity content of the ultra-high purity raw material 2a is 10 ppm, when the mass of the ultra-high purity raw material 2a is less than 5%, different polymorphs have occurred. From this, the mass relationship between the ultra-high purity raw material 2a and the high-purity raw material 2b is as described above.

(Other embodiments)
In the first and second embodiments, the cylindrical graphite crucible 1 is taken as an example of the container of the SiC single crystal manufacturing apparatus. However, this is merely an example, and the shape of the graphite crucible 1 is not necessarily limited. It does not have to be cylindrical, and not all may be made of graphite. For example, the outer shape of the container may be a regular polygonal column shape. Further, the metal impurity content of the container is also preferably 10 ppm or less.

  Moreover, although the case where the SiC raw materials having different metal impurity contents such as the ultra-high purity raw material 2a and the high-purity raw material 2b are used has been described here, the contents of these metal impurities are also an example. The present invention can be applied to a case where two different types of SiC raw materials are used in combination. Moreover, if the ultra-high purity raw material 2a is arranged on the closest side of the SiC single crystal substrate 3, the types of the SiC raw materials 2 having different metal impurity contents are not limited to two kinds, but the contents of two or more kinds of metal impurities. Different raw materials may be used.

It is a figure which shows the cross-sectional structure of the graphite crucible with which the manufacturing apparatus of the SiC single crystal concerning 1st Embodiment of this invention is equipped. It is the graph which showed an example of the experimental result which investigated the relationship between metal impurity content and mass of a very high purity raw material and a high purity raw material, and heterogeneous polymorphism generation | occurrence | production.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Graphite crucible, 1a ... Main body, 1b ... Cover material, 1c ... Base, 2 ... SiC raw material powder,
2a ... Ultra high purity raw material, 2b ... High purity raw material, 3 ... Single crystal substrate, 4 ... SiC single crystal

Claims (5)

In a container (1), a silicon carbide raw material (2) and a silicon carbide single crystal substrate (3) to be a seed crystal are arranged, and the silicon carbide raw material (2) is heated and sublimated to form the silicon carbide single crystal substrate (3). In the method for producing a silicon carbide single crystal in which a silicon carbide single crystal (4) is grown on
As the silicon carbide raw material (2), two raw materials (2a, 2b) having different metal impurity contents are prepared. Of the raw materials (2a, 2b), the metal impurity content (2b) is high. The silicon carbide raw material (2) is disposed in the container (1) so that the surface is covered with the low content of metal impurities (2a), and the surface of the silicon carbide single crystal substrate (3) is At the initial stage of growth when growing the silicon carbide single crystal (4), the raw material (2a, 2b) is grown with a sublimation gas having a low metal impurity content (2a), and the silicon carbide single crystal is grown. A method for producing a silicon carbide single crystal, characterized in that the growth continues even in the sublimation gas of the raw material (2a, 2b) having a high metal impurity content (2b) after the growth of (4) begins . A crucible (1) having a bottomed cylindrical crucible body (1a) having one open surface and a lid member (1b) for closing the open surface of the crucible body (1a) is used as the container. The silicon carbide single crystal substrate (3) is attached to the lid member (1b) in 1), and the content of the metal impurities in the raw materials (2a, 2b) is high on the bottom surface of the crucible body (1a). The material (2b) is placed on the silicon carbide single crystal substrate (3) side of the raw material (2a, 2b) having a higher metal impurity content (2b) than the material (2b). 2. The method for producing a silicon carbide single crystal according to claim 1, wherein one having a low metal impurity content (2a) is disposed. Among the raw materials (2a, 2b), those having a low metal impurity content (2a) having a metal impurity content of 10 ppm or less, and the raw metal (2a, 2b) content of the metal impurities. 3. The method for producing a silicon carbide single crystal according to claim 1, wherein the metal impurity content is 100 ppm to 4000 ppm. Among the raw materials (2a, 2b), the mass (2a) having a low content of the metal impurity is 5 to 50% of the total mass of the raw material, and the content (2b) having a high content of the metal impurity. The method for producing a silicon carbide single crystal according to claim 3, wherein the balance is the balance. Of the raw materials (2a, 2b), the mass of the low content of metal impurities (2a) is 30% of the total mass of the raw materials, and the high content of metal impurities (2b) is 70%. The method for producing a silicon carbide single crystal according to claim 4, wherein:

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