JP4830973B2 - Method for producing silicon carbide single crystal - Google Patents

Description

  The present invention relates to a method for producing a silicon carbide single crystal, and more particularly to a preferred shape of a seed crystal used for the growth of a silicon carbide single crystal, and a technique for producing a seed crystal having a suitable shape. It can be suitably used for reducing the crystal defect density.

  Since silicon carbide has a wide forbidden band and excellent physical and chemical properties, silicon carbide has been developed as a substrate material for semiconductor devices capable of high output and high temperature operation and high-frequency semiconductor devices. Although silicon carbide has various polytypes, it is a hexagonal silicon carbide single crystal, such as 4H or 6H, which has attracted particular attention. For its production, the raw material is heated and sublimated, and the silicon carbide single crystal is formed on the seed crystal. Sublimation recrystallization (modified Lely method: described in J. Cryst. Growth 43 (1978) 209) is generally used.

  Usually, in the modified Lely method, a Lely crystal or an Atchison crystal, or a silicon carbide single crystal ingot produced by using the modified Lely method, machined into a wafer state is used as a seed crystal. Is produced when being machined into a wafer, the seed crystal surface is subject to processing damage due to processing. In the silicon carbide crystal obtained by growing on the seed crystal having processing damage, processing damage propagates from the seed crystal to the grown crystal during the growth. Therefore, a large number of defects such as strains, dislocations, and hollow penetrating defects with a diameter of several to several tens of μm, which are called micropipes, are generated in the grown crystal, and a quality equivalent to or higher than that of the seed crystal can be obtained. I can't. In order to remove the processing damage, a pretreatment is performed to remove the damaged layer by machining the seed crystal surface by subjecting the seed crystal surface to CMP or sacrificial oxidation. Nevertheless, many dislocations and micropipes may be generated in the single crystal produced by the improved Lely method. However, these defects are often generated at an early stage of growth.

The conventional manufacture of silicon carbide single crystal is intended to suppress many defects that have occurred near the surface of the seed crystal. Subsequent etching of the seed crystal or processing by sacrificial oxidation after shaping by cutting and polishing. A seed crystal shaped so as to have the same shape as the growth surface of the silicon carbide single crystal is used by removing it. (For example, refer to Patent Document 1.) Furthermore, as shown in FIG. 4, the seed crystal support 1 to which the seed crystal 6 is attached is structured to be movable up and down, and the seed crystal surface is formed prior to the growth of the single crystal. The seed crystal surface is sublimated and etched to a position where sublimation etching can be performed, and then moved to a place where single crystal growth occurs, thereby continuously depositing a single crystal.
JP 2003-63890 A

  However, in the conventional configuration, in order to enable shaping into the same shape as the growth surface, a seed crystal that is thicker than a commonly used wafer-shaped seed crystal, for example, the number of normal wafers is several to several times. A seed crystal having a tenfold thickness is required. For this reason, after a portion to be used as a seed crystal is cut out from the ingot, there is a problem that the portion that can be used for manufacturing the wafer is remarkably reduced.

  The present invention solves the above-described conventional problems. Before cutting a wafer from an ingot, the portion that has been conventionally cut off as an unnecessary portion from the ingot is used as a seed crystal, thereby increasing the ingot utilization efficiency. Another object is to provide a method for producing a silicon carbide single crystal.

In order to solve the above-described conventional problems, a method for producing a silicon carbide single crystal according to the present invention includes arranging a silicon carbide raw material in a crucible and forming a silicon carbide single crystal on a seed crystal support portion provided at a position facing the raw material. In the method for producing a silicon carbide single crystal, in which the seed crystal is <0001>, wherein the crucible is heated to sublimate the raw material to grow a silicon carbide single crystal on the surface of the seed crystal. look including the {0001} plane facets generated when grown crystal in the direction, the {0001} plane seed crystal including a facet, the said material and the surface facing the surface on the side including the {0001} plane facet It is connected to the seed crystal support part, and the cross-sectional shape in the growth direction of the seed crystal is convex to the raw material .

  According to the method for manufacturing a silicon carbide single crystal of the present invention, in the manufacturing process of a silicon carbide single crystal wafer, a portion including a {0001} facet that has been conventionally cut off from an ingot as an unnecessary portion is used as a seed. Since it is effectively used as a crystal, it is effective as a production method capable of effectively utilizing the ingot to the maximum extent in the production of a silicon carbide single crystal in which it is difficult to lengthen the ingot.

  Moreover, according to the silicon carbide single crystal manufacturing method of the present invention, since the surface of the seed crystal on which the single crystal grows is not subjected to machining, it is possible to suppress the occurrence of defects due to machining. it can.

  Furthermore, according to the method for producing a silicon carbide single crystal of the present invention, it is possible to prevent the area of the {0001} plane facet that easily takes in impurities from being increased, and thus it is likely to occur on the {0001} plane facet and its peripheral region. Defects can be reduced, and a high-quality silicon carbide single crystal with low defects can be produced.

  Embodiments of a method for producing a silicon carbide single crystal of the present invention will be described below in detail with reference to the drawings.

(Embodiment 1)
FIG. 1 shows an apparatus for producing a silicon carbide single crystal of the present invention. The manufacturing apparatus shown in FIG. 1 includes a crucible 7, a crucible lid 4, and a cylindrical seed crystal support portion 1 projecting downward from the crucible lid 4. The seed crystal 6 is connected to the seed crystal support 1 using an adhesive or the like. This apparatus is heated to an inert gas atmosphere, an atmospheric pressure of 5 to 100 Torr, a crucible lower part temperature of about 2200 to 2400 ° C., and a crucible upper part temperature of about 2000 to 2300 ° C. to sublimate the silicon carbide raw material 8, and the seed crystal surface 5 By recrystallization above, an ingot of silicon carbide single crystal can be produced.

The seed crystal 6 of the present invention is a single crystal piece including a {0001} facet 2 generated when the crystal is grown in the <0001> direction. The ingot end portion where the {0001} facet used in the seed crystal is present is not used for manufacturing a wafer, and thus is a portion which has been unnecessary in the prior art and is unnecessary.
Further, the seed crystal connection surface 3 which is the surface to be attached to the seed crystal support portion 1 is subjected to machining such as cutting and polishing, but the seed crystal surface 5 on which the single crystal growth is started is applied. Since no machining is applied, defects due to processing distortion and damage cannot occur. The shape of the seed crystal surface 5 is already the same as that of the growth surface, that is, the shape that matches the isosupersaturation curve, so there is no portion where the sublimation etching predominates locally. Thus, single crystal growth is started uniformly within the plane of 5, and it is possible to suppress the occurrence of defects such as mixing of different polytypes, micropipes, and dislocations, which are likely to occur in the early stage of growth.

  In single crystal growth, it is known that the amount of all impurities including dopants is increased on the {0001} facet compared to other growth surfaces. Various defects are likely to occur on the {0001} plane facet and the {0001} plane facet boundary region where the amount of impurities incorporated is large. Therefore, when the diameter of the {0001} facet existing on the seed crystal surface is A and the diameter of the connecting face of the seed crystal is D, the {0001} facet diameter A is Smaller is preferable. When the {0001} plane facet diameter A is relatively large with respect to the diameter D of the connection surface 3 of the seed crystal, 0.45 ≦ A / D, the {0001} plane facet with a large amount of impurity incorporation occupies the whole. Since the ratio is large, the defect density increases, but in addition to this, different polytypes are likely to occur near the {0001} facet boundary region, making it difficult to obtain a polytype of uniform silicon carbide single crystal. Even if 0 ≦ A / D <0.45 is satisfied, 0 <d / D <0.25 (d indicates the distance between the {0001} facet and the seed crystal connection surface). If not, the angle between the {0001} facet and the crystal surface other than the {0001} facet is an acute angle, so that different orientation crystals with different crystal orientations from the {0001} facet boundary region It becomes easy to generate | occur | produce and it becomes difficult to obtain the silicon carbide single crystal in which orientation was arranged.

  Accordingly, in order to achieve both prevention of mixing of different polytypes and differently oriented crystals and reduction of defects, seeds satisfying 0 ≦ A / D <0.45 and satisfying 0 <d / D <0.25. Must be in crystalline form.

  FIG. 2 shows a method for producing a silicon carbide single crystal ingot from which the seed crystal described above can be taken out. When the distance between the silicon carbide raw material 8 and the seed crystal connection surface 3 is L, and the maximum distance between the seed crystal connection surface 3 and the growth surface of the silicon carbide single crystal ingot 9 to be manufactured is H, (L− H) The single crystal growth has been completed up to the point where> 10 mm is satisfied. In FIG. 2, the seed crystal of the present invention is used for the seed crystal used first, but a general wafer-shaped substrate can be used here.

  However, when using a wafer-shaped seed crystal, if the amount of growth is extremely reduced, the surface morphology of the resulting single crystal may be poor, and the crystal shape may not be convex in the growth direction. L−H)> 10 mm and H ≧ 5 mm are preferably satisfied at the same time. When using the seed crystal of the present invention, it is sufficient if H> d.

In addition, when a single crystal is grown to a range satisfying (LH)> 10 mm using the seed crystal of the present invention, and a series of manufacturing steps are repeated such that a new seed crystal is cut out from the end of the obtained ingot. The {0001} facet of the ingot to be manufactured tends to have a smaller diameter than the {0001} facet that originally existed in the seed crystal used. Therefore, the quality can be improved by reducing the {0001} facet and the {0001} facet boundary region having a high defect density by such repeated growth.
In the production of silicon carbide single crystal, the composition of the input silicon carbide raw material changes during the growth process, so the packing density decreases, but the volume of the consumed silicon carbide raw material occupying the space in the crucible is Not much different from silicon carbide raw material. Therefore, as the silicon carbide single crystal grows, the distance (LH) between the silicon carbide raw material and the {0001} facet is gradually reduced.

  FIG. 3 shows a cross section parallel to the growth direction of the silicon carbide single crystal ingot. 3A is a cross-sectional view of an ingot obtained by completing single crystal growth in the range of (LH)> 10 mm, and FIG. 3B is a single crystal growth completed when (LH) ≦ 10 mm. The cross section of the ingot obtained by doing is shown. If the width of the portion 10 forming the {0001} facet during the growth is (LH)> 10 mm, the width becomes smaller as the growth proceeds. Therefore, defects occur in the {0001} facet and its vicinity. Can be reduced. It is also possible to cut out a new seed crystal satisfying the relational expressions of 0 ≦ A / D <0.45 and 0 <d / D <0.25 of the present invention from the obtained ingot.

  On the other hand, when (L−H) ≦ 10 mm, the width of the portion 10 forming the {0001} facet in the middle of growth decreases from the initial growth to the middle, but increases rapidly in the second half of the growth. End up. In this case, not only is it impossible to cut out a desired seed crystal, but the silicon carbide single crystal ingot 9 includes not only the {0001} facet and its boundary region, but also the silicon carbide raw material 8 of the silicon carbide single crystal ingot 9. Many defects, particularly stacking faults, are generated on the entire surface facing the substrate, and the crystal quality is significantly lowered.

  Further, when a silicon carbide single crystal having a polytype of 4H is manufactured, the silicon carbide single crystal ingot 9 is too close to the silicon carbide raw material 8, so that the surface of the silicon carbide single crystal ingot 9 is changed from 4H. It is converted to a 6H polytype, and a uniform polytype silicon carbide single crystal ingot and seed crystal cannot be obtained.

  From the above, not only to obtain a seed crystal of a suitable shape, but also to prevent the crystal quality of the entire silicon carbide single crystal ingot from being impaired, the single crystal growth satisfies (LH)> 10 mm. In other words, the lengthening needs to be performed in a range satisfying (LH)> 10 mm.

  In this embodiment, the diameter of the seed crystal support portion 1 is substantially the same as the diameter D of the connection surface 3 of the seed crystal, but the diameter of the seed crystal support portion 1 is the connection surface of the seed crystal. The diameter D may be smaller than 3. In that case, the connection surface 3 of the seed crystal is made to protrude evenly with respect to the seed crystal support 1, and the center of the {0001} facet 2 existing on the seed crystal surface 5 is substantially coincident with the central axis of the crucible 6. If fixed in such a manner, the seed crystal is affixed in a shape that substantially matches the isosupersaturation curve, and single crystal growth can be started uniformly within the surface of the seed crystal surface 5.

  As described above, in the present embodiment, a silicon carbide single crystal ingot end portion having a {0001} facet that cannot be used for manufacturing a silicon carbide single crystal wafer is cut out and a new silicon carbide single crystal after the next time is cut. Since it is used for the production of crystals, a silicon carbide single crystal ingot can be effectively utilized to the maximum extent. In addition, since machining is not performed on the surface of the seed crystal on which the single crystal is grown, generation of defects derived from the processing can be suppressed. Furthermore, since the {0001} facet and the boundary region where impurities are easily taken in and defects are easily generated can be reduced, a high-quality silicon carbide single crystal with a low defect density can be obtained.

  The method for producing a silicon carbide single crystal according to the present invention is useful as a method for producing a high-quality silicon carbide single crystal because it can reduce the {0001} facet that easily takes in impurities and easily causes defects. In addition, the silicon carbide single crystal manufacturing method according to the present invention cuts off the end portion of a silicon carbide single crystal ingot having a {0001} facet, which cannot be used for wafer manufacturing in the prior art, and creates a new single crystal after the next time. Production of single crystals other than silicon carbide single crystals by the sublimation recrystallization method, which makes it possible to make maximum use of silicon carbide single crystal ingots and are generally difficult to lengthen, because they are used as seed crystals for crystal production Is also useful.

The figure which shows the manufacturing apparatus of the silicon carbide single crystal in the Example of this invention The figure which shows the silicon carbide single crystal manufactured using the apparatus which manufactures the seed crystal used for the Example of this invention, and the seed crystal of this invention The figure which shows the cross section of a silicon carbide single crystal ingot The figure which shows the manufacturing apparatus of the conventional silicon carbide single crystal

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Seed crystal support part 2 {0001} facet 3 Seed crystal connection face 4 Crucible lid 5 Seed crystal surface 6 Seed crystal 7 Crucible 8 Raw material powder 9 Silicon carbide single crystal ingot 10 Form {0001} facet during growth Parts 11 Heat insulation material 12 High frequency furnace

Claims (6)

A silicon carbide raw material is arranged in a crucible, and after connecting a seed crystal made of a silicon carbide single crystal to a seed crystal support provided at a position facing the raw material, the crucible is heated to sublimate the raw material and the seed In a method for producing a silicon carbide single crystal in which a silicon carbide single crystal is grown on a crystal surface,
The seed crystal is <0001> direction to look including the {0001} plane facets generated when grown crystal, the seed containing the {0001} plane faceted crystal, the raw material and the surface opposed to the {0001} plane A method for producing a silicon carbide single crystal, which is connected to the seed crystal support portion as a surface on the side including a facet, and a cross-sectional shape in the growth direction of the seed crystal is convex with respect to the raw material . Among the distances from the connection surface of the seed the seed crystal supporting portion of the crystal to a surface opposed to the raw material, according to claim 1 distance to the {0001} plane facet from the connecting surface of the seed crystal is a maximum A method for producing a silicon carbide single crystal. The method for producing a silicon carbide single crystal according to claim 1, wherein the center of the {0001} facet and the center axis of the crucible substantially coincide. The diameter of the {0001} plane facet is A, the diameter of the surface connected to the seed crystal support portion of the seed crystal is D, and the distance from the connection surface of the seed crystal to the {0001} plane facet is d. and when,
The manufacturing method of the silicon carbide single crystal of Claim 2 which satisfies the following formula | equation.
0 ≦ A / D <0.45 and 0 <d / D <0.25 When the silicon carbide single crystal is grown on the seed crystal in the crucible,
The distance between the raw material and the connection surface of the seed crystal is L,
When the distance between the connection surface of the seed crystal and the {0001} facet is H,
The manufacturing method of the silicon carbide single crystal of Claim 4 which satisfies the following formula | equation.
(LH)> 10mm From the silicon carbide single crystal manufactured by the method for manufacturing a silicon carbide single crystal according to claim 4 or 5 , a small piece obtained by cutting a portion including the {0001} facet is produced.
A method for producing a silicon carbide single crystal, wherein the small piece is used as a seed crystal in the production of a silicon carbide single crystal.

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