JP2008100854A - Apparatus and method of manufacturing sic single crystal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing an SiC single crystal stably obtaining an SiC single crystal having a flat growing surface without occurrence of polycrystallization. <P>SOLUTION: In an apparatus for growing the SiC single crystal from an undersurface B as a starting point by bringing the undersurface B of an SiC seed crystal 110 supported at the lower end of a pulling axis 108 into contact with a molten liquid L while maintaining a temperature gradient in the Si molten liquid L in a graphite crucible 102 so that a temperature lowers from the inner toward the surface of the molten liquid, the apparatus of manufacturing the SiC single crystal is characterized in that the pulling axis 108 is rotatable about the axis center X of itself, and has an upper half part P along the axis center X and a lower half part Q including a part deviated from the axis center X, an SiC seed crystal supporting part at the lower end of the lower half part Q of the pulling axis 108 is supporting the SiC seed crystal 110 at the eccentric position which does not intersect the axis center X, and of orbiting on a horizontal circle whose center is the axis center X by the rotation of the pulling axis 108 around the axis center X. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an apparatus and a method for producing an SiC single crystal by a solution method.

  Since SiC has a larger energy band gap than Si, various techniques for producing high-quality SiC single crystals suitable as semiconductor materials have been proposed. A wide variety of SiC single crystal production methods have been tried so far, but the sublimation method and the solution method are currently most common. Although the sublimation method has a high growth rate, it has a defect that defects such as micropipes and transformation of crystal polymorphism are likely to occur. On the other hand, a solution method without these defects is considered promising, although the growth rate is relatively slow. Yes.

  The manufacturing method of the SiC single crystal by the solution method maintains a temperature gradient in which the temperature decreases from the inside toward the melt surface in the Si melt in the graphite crucible. C dissolved in the Si melt from the graphite crucible in the lower high temperature part rises mainly by the convection of the melt, reaches the low temperature part near the melt surface, and becomes supersaturated. An SiC seed crystal is held at the tip of the graphite rod immediately below the melt surface, and supersaturated C is crystallized as an SiC single crystal by epitaxial growth on the SiC seed crystal.

  In the solution method, a large number of growth hills are formed on the surface of crystal growth, and single crystals grow from each growth hill to be easily polycrystallized. Special consideration is necessary to obtain a single crystal stably.

  One of the main causes of polycrystallization is an excessive degree of C supersaturation on the crystal growth surface. C supersaturation on the crystal growth surface is necessary as a driving force for generating SiC crystals. However, if the C supersaturation degree becomes too high, the nucleation of crystals becomes unstable and polycrystallization occurs.

  As a countermeasure, Patent Document 1 discloses that when a SiC single crystal is grown by a solution method, a convection in the melt is suppressed by applying a downward vertical magnetic field into the melt, and the convection moves to the vicinity of the seed crystal. It has been proposed to prevent excessive C from being supplied.

  However, the proposed method has a problem that not only the cost increases but also the repair of the equipment for improvement becomes difficult because a large-scale equipment modification such as the installation of the magnetic field coil is necessary.

JP 2004-323247 A

  An object of the present invention is to provide a SiC single crystal manufacturing apparatus and a manufacturing method capable of stably obtaining a SiC single crystal having a flat growth surface without causing polycrystallization.

In order to achieve the above-mentioned object, the SiC single crystal manufacturing apparatus of the present invention maintains a temperature gradient in the Si melt in the graphite crucible that decreases in temperature from the inside toward the melt surface. In an apparatus for bringing a lower surface of a SiC seed crystal held at the lower end into contact with the melt and growing a SiC single crystal starting from the lower surface,
The lifting shaft is rotatable around its own axis, and has an upper half along the axis and a lower half including a portion deflected from the axis,
The SiC seed crystal holding portion at the lower end of the lower half of the pulling shaft can hold the SiC seed crystal in an eccentric position that does not intersect the shaft center, and the shaft center is rotated by rotation around the shaft center of the pulling shaft. It is possible to circulate on a horizontal circumference centered on

  The method for producing an SiC single crystal of the present invention uses the apparatus of the present invention to rotate the pulling shaft so that the lower surface of the SiC seed crystal held by the holding part is in a horizontal state in contact with the melt. It is characterized in that the SiC single crystal is grown while circulating on a circular circumference.

  According to the method of the present invention, the lower surface (crystal growth surface) of the SiC seed crystal is circulated on a horizontal circumference in a state where the lower surface (crystal growth surface) is in contact with the Si melt (C Si solution). Since the crystal growth surface is always separated from the melt region of the excessive C supersaturation degree that is continuously generated from time to time adjacent to the surface of the crystal, the contact with the melt of the appropriate C supersaturation level is maintained. Thus, polycrystallization due to the frequent occurrence of crystal nuclei due to excessive C supersaturation is prevented, and a SiC single crystal having a growth surface with excellent flatness can be stably obtained.

  In this specification, the “crystal growth surface” is the lower surface of the seed crystal at the start of single crystal growth, and the lower surface (growth front surface) of the growing single crystal thereafter.

  As already described, the cause of polycrystallization that is likely to occur in the solution method is that a large number of growth hills are generated on the surface of the crystal growth, and single crystals grow from the growth hills in a discrete manner. The present inventor considered the following mechanism from the viewpoint of the degree of C supersaturation of the melt (C Si solution) near the crystal growth surface.

  As a driving force for the generation of the SiC crystal, the C supersaturation degree of the melt (C Si solution) needs to be sufficiently high in the vicinity of the crystal growth surface. The term “sufficient” herein refers to the amount of C which is excessive in comparison with the amount of C, which is not the stoichiometric composition incorporated in the newly formed SiC crystal in order to stably maintain the actual crystal growth. Means that it needs to be kept inside. If the degree of supersaturation is maintained within a sufficient and appropriate range, single crystal growth can be stably maintained without polycrystallization. However, when the degree of supersaturation is sufficient but excessive, so-called compositional supercooling increases, resulting in frequent crystal nuclei and polycrystallization.

  The present inventor has paid attention to the fact that the excessive amount of C supersaturation in the vicinity of the crystal growth surface is a very limited region.

  A feature of the present invention is that the SiC seed crystal is continuously continuous with the growth of the SiC crystal by rotating the lower surface of the SiC seed crystal (crystal growth surface) on a horizontal circumference in contact with the Si melt (C Si solution). The crystal growth surface is always pulled away from the excess C supersaturated melt region generated in this manner, and the contact with the melt having the proper C supersaturation level is maintained. As a result, the progress of compositional supercooling is prevented, so that polycrystallization due to the frequent occurrence of crystal nuclei due to excessive C supersaturation in the vicinity of the crystal growth surface is prevented, and SiC having a growth surface with excellent flatness. A single crystal can be obtained stably.

  An embodiment of the present invention will be described with reference to FIG.

  FIG. 1 (1) schematically shows a longitudinal section of a solution method single crystal growth apparatus for carrying out the method for producing a SiC single crystal of the present invention.

  The growth apparatus 100 forms and maintains the Si melt L in the crucible 102 by the heating means 104 surrounding the graphite crucible 102, and holds the SiC seed crystal 110 at the lower end of the pulling shaft 108. The heating means 104 can independently control the heating power of a plurality of parts in the vertical direction, and thereby, the temperature gradient in which the temperature decreases from the inside toward the melt surface S in the Si melt in the graphite crucible 102. To maintain. The heating means 104 may be an electric resistance heating method or a high frequency induction heating method. The raw material Si is charged into the graphite crucible 102 and heated to a predetermined temperature in the range of 1700 to 2000 ° C. by the heating means 104 to melt Si. The entire assembly composed of the above components is housed in a heat-insulating sealed container 112, and the space 114 in the container 112 is filled with an inert atmosphere such as Ar gas.

  The feature of the present invention lies in the structure and operation of the lifting shaft 108. As shown in FIGS. 1A and 1B, the pulling shaft 108 includes an upper half P along the axis X and a lower half Q deflected from the axis X. There is a SiC seed crystal holding portion (not shown) at the lower end of the lower half Q, and the SiC seed crystal 110 is held at an eccentric position Y (FIG. 1 (2)) that does not intersect the axis X.

  In order to start the growth of the SiC single crystal, the pulling shaft 108 is lowered as indicated by the arrow d shown in FIG. 1 (1), and the lower surface B of the seed crystal 110 is melted as shown in FIG. 1 (2). Contact surface S. Specifically, the lower surface B of the seed crystal 110 is slightly immersed in the melt L from the melt surface S to ensure stable contact.

  In this state, when the lifting shaft 108 rotates around the axis X, the lower half Q rotates while forming a conical surface with the axis X as the rotation center, and is held at the lower end of the lower half Q. The seed crystal 110 circulates on a horizontal circumference around the axis X while maintaining contact with the melt S.

  In the melt L in the immediate region of the crystal growth surface, excessive C with respect to the stoichiometric composition is left without being incorporated into the crystal as the SiC single crystal grows, so it is originally necessary as a driving force for crystal growth. In addition to the degree of C supersaturation, unintentional excess C is constantly added from time to time, so that the degree of C supersaturation tends to exceed the proper range and become excessive.

  In the conventional apparatus, the pulling shaft 108A has a simple linear shape as shown in FIG. 2 (1), and the lower surface B of the seed crystal 110 is lowered as it is as shown in FIG. The SiC single crystal was grown by leaving it in contact with the substrate. For this reason, when the above-mentioned immediate region of excessive C supersaturation (compositional supercooling) is formed, the crystal growth surface is immediately affected, and the occurrence of SiC crystal nuclei is induced, making polycrystallization easy. It had occurred.

  On the other hand, according to the apparatus of the present invention shown in FIG. 1, the crystal growth surface (the seed crystal lower surface B) is around the surface S of the melt L, so that the C supersaturation degree is excessive. Since the contact with the fresh melt L that is always separated from the region and the C supersaturation is within the proper range is maintained, the SiC crystal is not affected by the excessive C supersaturation (compositional supercooling). There is no occurrence of polycrystallization due to the frequent occurrence of nuclei.

  In addition, since the production | generation of the SiC crystal in a Si-C type | system | group is based on a peritectic reaction, in the melt L near the crystal growth surface, C deficiency may occur, and conversely, the C supersaturation degree may decrease. By rotating the seed crystal according to the present invention, the C concentration in the vicinity of the crystal growth surface can always be maintained at an appropriate degree of supersaturation, so that high-speed growth can be realized while maintaining flat growth.

  The growth principle itself of the SiC single crystal starting from the lower surface B of the SiC seed crystal 110 is the same between the conventional technique and the present invention. The graphite crucible 102 has a function as a supply source of C into the Si melt L in addition to the function as an original crucible. C that has melted from the crucible 102 at the high temperature portion (lower portion) of the melt L becomes supersaturated when it reaches the low temperature portion (the portion near the melt surface S) of the melt L by convection and diffusion within the crucible 102. When the pulling shaft 108 is lowered as indicated by an arrow d and the SiC seed crystal 110 is held in contact with the melt L, the SiC seed in contact with the melt surface S in which C is supersaturated. SiC crystallizes on the lower surface B of the crystal 110, and the SiC single crystal continues to crystallize on the lower surface of the crystallized SiC single crystal, so that the SiC single crystal grows downward from the lower surface B of the seed crystal 110. Actually, the pulling shaft 108 is raised as indicated by an arrow g at a speed synchronized with the downward growth, and the lower surface (crystal growth surface) of the SiC single crystal is always maintained at a fixed position in the vertical direction in the melt L. . A solution containing Si melt L as a solvent and C as a solute is formed in the crucible 102, but a small amount of elements other than C can be added to the solution for various purposes.

  Hereinafter, the present invention will be described more specifically with reference to examples.

[Example 1]
Using the growth apparatus 100 shown in FIG. 1 (1), the SiC single crystal was grown by rotating the seed crystal 110 as shown in FIG. 1 (2). The amount of eccentricity h from the axis X was 12.5 mm, and the circumferential speed was 0.78 m / min. The heating temperature was 1750 ° C. and the growth time was 5 hours. The heating temperature is a temperature measured at a position where the immersion depth is 0 mm.

  The obtained results are shown in FIG. By carrying out the growth while rotating according to the present invention, an SiC single crystal having a flat crystal growth surface was obtained.

  For comparison, the conventional apparatus shown in FIG. 2 was used for growth without allowing the seed crystal to circulate, but polycrystallization occurred. When growth was carried out at a low C supersaturation degree, polycrystallization could be prevented, but the growth rate was reduced by about 50% compared to the present invention.

  The form of the lifting shaft 108 used in the present embodiment is a linear upper half P along the axis X and a lower half Q deflected linearly from the axis X as shown in FIG. It was a form consisting of. However, the lower half Q does not need to be deflected from the axis X itself as long as it includes a portion deflected from the axis X.

  FIG. 4 shows variations in form of the lifting shaft 108.

  The form shown in FIG. 4 (2) is the form used in this example, and the lower half Q itself is a form deflected linearly from the axis X. The holding part H of the SiC seed crystal 110 is at an eccentric position Y with an eccentricity amount h from the axis X, and the held SiC seed crystal 110 does not intersect the axis X.

  In the form shown in FIG. 4A, the lower half Q is connected to the upper half P in a straight line and is not deflected from the axis X itself, but is located near the outer periphery of the lower end. Is held at a position deviated from the axis X by the amount of eccentricity z. In the case of this form, the lower half portion Q actually indicates only the holding portion H at the lower end. The holding part H of the SiC seed crystal 110 is at an eccentric position Y with an eccentricity amount h from the axis X, and the held SiC seed crystal 110 does not intersect the axis X.

  The form shown in FIG. 4 (3) is a form in which the lower half Q itself is bent from the axis X. The holding part H of the SiC seed crystal 110 is at an eccentric position Y with an eccentricity amount h from the axis X, and the held SiC seed crystal 110 does not intersect the axis X.

  4 (1), (2), and (3), the hole that passes through the pulling shaft 108 is for inserting a sensor such as a thermocouple.

As yet another form, as shown in FIG. 5, the lower half Q of the deflection shaft 108 may be conical for reasons of processing convenience. The holding part H of the SiC seed crystal 110 is at an eccentric position Y with an eccentricity amount h from the axis X, and the held SiC seed crystal 110 does not intersect the axis X.
[Example 2]
In the SiC single crystal manufacturing apparatus of the present invention, in order to keep the temperature in the graphite crucible 102 including the melt L and the space above it as intended, a heat insulating lid that covers the upper end of the graphite crucible 102 is used. It is common.

  In the present embodiment, a lid suitable for a case where the form of the pulling shaft 108 is such that the eccentric amount h from the axis X to the seed crystal holding part H is large as shown in FIGS. An embodiment combining the above will be described.

  FIG. 6 shows a state during operation of the SiC single crystal manufacturing apparatus 200 according to a preferred embodiment of the present invention. The apparatus has the same structure as that of the apparatus 100 of Example 1 shown in FIG. 1 except for the lifting shaft and the lid assembly. is there. In order to simplify the illustration, the heating means 104 and the sealed container 112 are omitted in FIG.

  In SiC single crystal manufacturing apparatus 200 in FIG. 6, pulling shaft 108 has a flange portion 118 projecting radially at the lower end of upper half portion P along axis X. The flange 118 has a stepped portion 119 at the outer edge.

  A stepped lid 120 covering the upper end of the graphite crucible 102 has a center hole 122 that penetrates the upper half P of the lifting shaft 108 and an outer peripheral engagement portion 124 that can be seated and engaged on the upper periphery of the graphite crucible 102. 7 and a central engaging portion 126 that can be engaged with the stepped portion 119 of the flange 118 as shown in FIG.

  The operation of the pulling shaft 108 and the lid 120 at the time of crystal growth is as follows.

  The SiC seed crystal 110 is held in the SiC seed crystal holding part H at the lower end of the lower half Q of the pulling shaft 108.

  The lid 120 is seated and engaged on the flange 118 of the lifting shaft 108 with the upper half P of the lifting shaft 108 passing through the center hole 122 of the lid 120. As shown in FIG. 7, the seating engagement is performed by fitting the center engagement portion 126 (FIG. 6) at the lower end of the through hole 122 of the lid 120 into the outer edge stepped portion 119 (FIG. 6) of the flange 118. .

  The lifting shaft 108 is lowered into the graphite crucible 102, and the outer peripheral engagement portion 124 of the lid 120 is seated and engaged on the upper peripheral edge of the graphite crucible 102.

  By further lowering the lifting shaft 108, the seating engagement between the lid 120 and the flange 118 of the lifting shaft 108 is released as shown in FIG. 6, and the lid 120 is seated and engaged on the upper edge of the graphite crucible 102. Leave in state.

  By further lowering the pulling shaft 108, the SiC seed crystal 110 held at the lower end of the lower half Q of the pulling shaft 108 is brought into contact with the melt L to stop the lowering of the pulling shaft 108.

  By rotating the pulling shaft 108, the SiC single crystal 110 is rotated from the lower surface B (FIG. 1) of the SiC seed crystal 110 with the SiC seed crystal 110 rotating around the horizontal circumference in contact with the melt L. Grow.

  By using the assembly of the lifting shaft and the lid of the present embodiment, the operation using the lifting shaft 108 bent in the middle in the longitudinal direction can be advanced extremely smoothly and efficiently.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing apparatus and manufacturing method of a SiC single crystal from which the SiC single crystal with a flat growth surface is obtained stably, without raise | generating polycrystallization are provided.

It is a longitudinal cross-sectional view of the SiC single crystal manufacturing apparatus by one Embodiment of this invention. It is a longitudinal cross-sectional view of the conventional SiC single crystal manufacturing apparatus. It is an external appearance photograph which shows the state of the seed crystal vicinity after performing crystal growth with the manufacturing apparatus of this invention. It is a longitudinal cross-sectional view which shows the various forms of the raising shaft of the manufacturing apparatus of this invention. It is a longitudinal cross-sectional view which shows the other form of the raising shaft of the manufacturing apparatus of this invention. It is a longitudinal cross-sectional view which shows the form provided with the assembly with the raising shaft and crucible lid of the manufacturing apparatus of this invention. It is a longitudinal cross-sectional view which shows the state which engaged the pulling-up shaft and the crucible lid of the manufacturing apparatus of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Growth apparatus 102 Graphite crucible 104 Heating means 108 Lifting shaft 110 SiC seed crystal 112 Heat-insulating sealed container 118 Lifting shaft flange 120 Graphite crucible heat insulation lid P Upper half of the lifting shaft Q Lower half of the lifting shaft L Melt S Melt surface B Bottom surface of seed crystal 110

Claims (4)

The lower surface of the SiC seed crystal held at the lower end of the pulling shaft is brought into contact with the melt while maintaining a temperature gradient in the Si melt in the graphite crucible that decreases in temperature from the inside toward the melt surface. In an apparatus for growing a SiC single crystal as a starting point,
The lifting shaft is rotatable around its own axis, and has an upper half along the axis and a lower half including a portion deflected from the axis,
The SiC seed crystal holding portion at the lower end of the lower half of the pulling shaft can hold the SiC seed crystal in an eccentric position that does not intersect the shaft center, and the shaft center is rotated by rotation around the shaft center of the pulling shaft. A SiC single crystal manufacturing apparatus characterized in that it can circulate on a horizontal circumference centering on the substrate. In claim 1,
The lifting shaft has a flange portion projecting radially from the upper half portion along the axis,
The lid that covers the upper end of the graphite crucible has a center hole that penetrates the upper half of the lifting shaft, an outer peripheral engaging portion that can be engaged with the upper end periphery of the graphite crucible, and the penetrating state. A SiC single crystal manufacturing apparatus, comprising: a central engaging portion that can be engaged by being seated on the flange. A method for producing a SiC single crystal using the apparatus according to claim 1,
By rotating the pulling shaft, the SiC single crystal is grown while the lower surface of the SiC seed crystal held in the holding part is circulated on a horizontal circumference in contact with the melt. A method for producing a SiC single crystal. In claim 3,
Holding the SiC seed crystal in the SiC seed crystal holding part at the lower end of the lower half of the pulling shaft;
The lid is seated and engaged on the flange of the lifting shaft with the upper half of the lifting shaft penetrating through the center hole of the lid,
The lifting shaft is lowered into the crucible, and the lid is seated and engaged on the upper peripheral edge of the crucible at the outer peripheral engagement portion,
By further lowering the lifting shaft, the seating engagement between the lid and the flange of the lifting shaft is released, and the lid is left in the seating engagement state on the upper edge of the crucible,
By further lowering the pulling shaft, the lower surface of the SiC seed crystal held at the lower end of the lower half of the pulling shaft is brought into contact with the melt to stop the lowering of the pulling shaft.
By rotating the pulling shaft, the SiC single crystal is grown from the lower surface of the SiC seed crystal as a starting point while rotating around the horizontal circumference in a state where the SiC seed crystal is in contact with the melt. A method for producing a SiC single crystal, which is characterized.