JP2018165227A - Manufacturing method of ingot of silicon carbide single crystal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method capable of manufacturing a high-quality SiC single crystal ingot having less defect by suppressing a generation of a micro crack while preventing a large stress applied to a grown crystal even in a case where a large diameter SiC single crystal of a diameter of 100 mm or more is grown.SOLUTION: Provided is a manufacturing method of an ingot of a silicon carbide single crystal by a sublimation recrystallization method in which the silicon carbide single crystal is grown on a crystal growth surface of a seed crystal substrate 1. In a central region of an attachment boundary between a substrate placing part of a crucible lid 3 and the seed crystal substrate 1, an adhesive 15 is used to bond them each other such that a bonding area ratio to the seed crystal substrate is 0.1 - 5%, in an outer peripheral region other than the central region they contact each other in a smooth plane with a surface roughness (Ra) of 1 μm or less, and furthermore, and an outer peripheral part of the seed crystal substrate 1 is mechanically fixed with a holding member 16 to the crucible lid 3.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a method for manufacturing a silicon carbide single crystal ingot, and more specifically, when a silicon carbide single crystal ingot is manufactured by a so-called sublimation recrystallization method, a seed crystal substrate is attached to a crucible lid of a graphite crucible. It is about the method.

  Since silicon carbide (SiC) has excellent semiconductor characteristics, it has recently attracted much attention as a substrate material for manufacturing a power device for high power control. In particular, development of SiC power devices such as SiC Schottky barrier diodes and MOSFETs (Metal Oxide-Semiconductor Field Effect Transistors) fabricated from SiC single crystal substrates is underway, withstand voltage exceeding 1000V, and Various power control devices have been developed, including an inverter for large power control with low power loss at the time of conversion because it can exhibit the advantage of reducing the on-resistance during conduction.

  At present, SiC single crystals are generally produced by a sublimation recrystallization method called an improved Rayleigh method, or technically synonymous, but a manufacturing method called a sublimation method (non-patent literature). 1). That is, a SiC raw material is loaded on the crucible body side of a graphite crucible composed of a crucible body and a crucible lid body, a seed crystal substrate made of SiC single crystal is attached to the crucible lid body side, and the SiC raw material is heated and sublimated to seed. A SiC single crystal is grown on the crystal growth surface of the crystal substrate.

  In order to stably realize SiC power devices with excellent withstand voltage characteristics and long-term operation reliability, in parallel with the increase in the diameter of SiC single crystals, the crystal quality realized with small-diameter SiC single crystals can be achieved. It is necessary to maintain even large-diameter crystals, that is, to reduce the defect density sufficiently. For example, basal plane dislocations that are edge dislocations on the (0001) basal plane are examples of defects in the SiC single crystal substrate that affect power device characteristics. When a SiC epitaxial film is grown on a SiC single crystal substrate, if basal plane dislocations are present in this SiC epitaxial layer, they are expanded to partial dislocations during device forward operation and form stacking faults. It is known that device electrical resistance, that is, on-resistance value gradually increases with time, and conversion loss increases (see Non-Patent Document 2). As described above, in the SiC single crystal substrate, it is important to reduce the defect density as much as possible for application as a power device.

  One of the causes of the occurrence of such defects is that the internal stress of the SiC single crystal is greatly increased. When the stress inside the crystal increases at a high temperature, plastic deformation is induced in the crystal itself, and this acts as a driving force to generate a large number of dislocation defects. For example, when crystal growth is performed by the sublimation recrystallization method, when a seed crystal substrate is attached to a graphite base provided on the crucible lid side using a heat-resistant adhesive, from the back surface of the seed crystal substrate, that is, the adhesive surface In order to suppress the occurrence of unnecessary macro defects such as voids due to thermal decomposition of the seed, it is considered necessary to make the seed crystal substrate as close as possible to the surface of the pedestal and eliminate the gap between the seed crystal substrate and the pedestal. (For example, see Patent Document 1). However, as a result, the seed crystal substrate and the pedestal are firmly fixed. In such a situation, the SiC single crystal constituting the seed crystal substrate and the graphite constituting the pedestal generally have a thermal expansion coefficient. Therefore, a large difference in thermal expansion occurs at the growth temperature, which causes a large stress on the grown crystal (see Non-Patent Document 3).

  From such a viewpoint, in order to suppress the occurrence of defects due to an increase in stress caused by the difference in thermal expansion coefficient between the pedestal serving as the substrate mounting portion of the crucible lid and the seed crystal substrate, the thermal expansion coefficient is almost the same as that of SiC. A method of reducing the difference in thermal expansion coefficient by using a pedestal (see Patent Document 2) or by devising an adhesive layer made of an adhesive to have a multilayer structure is performed (see Patent Document 3). It has been broken.

  Aside from the above-described method, there has been proposed a method of mechanically fixing the seed crystal substrate and the crucible lid body flattened with each other using a holding member such as a graphite screw without using any adhesive. (See Patent Document 4). According to such a method, unnecessary macro defects such as voids can be suppressed by bringing the back surface of the seed crystal substrate and the surface roughness (Ra) of the crucible lid body into close contact with each other to 5 μm or less. . In other words, bonding with an adhesive can be avoided at the same time, and unnecessary stress caused by the difference in thermal expansion coefficient between the SiC single crystal constituting the seed crystal substrate and the graphite constituting the crucible lid or pedestal is avoided. it can. However, in the method of fixing the outer peripheral edge of the seed crystal substrate by screw fixing or the like, when the diameter of the seed crystal substrate is increased, a gap is formed at a high temperature due to its own weight or the like in the central portion, resulting in macro defects. The problem of occurrence will rekindle. In recent years, development of SiC single crystal growth technology by the sublimation recrystallization method has made great progress, and the mainstream of the current market is the substrate with a diameter of 100 mm. Crystal ingots are also being developed. In such a situation, the problem described above will become more apparent.

  Further, as a method other than these, a pedestal and a seed crystal substrate serving as a substrate mounting portion of the crucible lid are formed by forming a heat-resistant intervening layer around the large-diameter seed crystal substrate having a diameter of 150 mm by a sputtering method or the like. In this state, a method of fixing only the center portion of the seed crystal substrate with an adhesive has been proposed (see Patent Document 5). However, in this method, it is necessary to strictly control the thickness of the interposed layer to about 10 μm or less in order to prevent the heat-resistant interposed layer from being peeled off. New manufacturing problems such as cost increase caused by the formation of the intervening layer made of metal are newly generated. In addition, when only the central portion is bonded and fixed, a gap is formed between the seed crystal substrate and the pedestal in the outer peripheral region due to the thickness of the adhesive, which causes macro defects.

Japanese Patent Laid-Open No. 2001-139394 JP 2012-46425 A JP 2009-120419 JP Special table 2002-308697 gazette Special table 2010-280547

Yu. M. Tairov and V. F. Tsvetkov, Journal of Crystal Growth, vol.52 (1981) p.146 M. Skowronski and S. Ha, Journal of Applied Physics, vol.99 (2006) p.011101. R. Ma, H. Zhang, V. Prasad, M. Dudley, Crystal Growth & Design vol.2 (2002) p.213.

  The present invention solves the above-mentioned problems and suppresses the occurrence of macro defects while preventing large stress from being applied to the grown crystal even when growing a large-diameter SiC single crystal having a diameter of 100 mm or more. An object of the present invention is to provide a method capable of producing a high-quality SiC single crystal ingot with few defects.

As a result of diligent studies to solve the above-described problems of the prior art, the inventors joined the central portion of the seed crystal substrate with an adhesive at the attachment interface between the seed crystal substrate and the substrate attachment portion of the crucible lid. In the other outer peripheral regions, the outer diameters of the seed crystal substrates are mechanically fixed by the holding member so as to be in contact with each other with smooth surfaces having a predetermined surface roughness. Even when growing a large-diameter SiC single crystal of 100 mm or more, it is possible to prevent a large stress from being generated in the grown crystal, and to suppress the generation of macro defects and to produce a high-quality SiC single crystal ingot with a low defect density. And the present invention was completed.
That is, the gist of the present invention is as follows.

(1) A silicon carbide raw material is loaded on the crucible body side of a graphite crucible composed of a crucible body and a crucible lid, a seed crystal substrate made of a silicon carbide single crystal is attached to the crucible lid, and the silicon carbide raw material is heated and sublimated. A silicon carbide single crystal ingot for growing a silicon carbide single crystal on a crystal growth surface of a seed crystal substrate,
In the central region corresponding to the central portion of the seed crystal substrate at the interface between the substrate mounting portion of the crucible lid and the seed crystal substrate, the bonding area is 0.1% or more and 5% or less in terms of the area ratio to the seed crystal substrate. The outer peripheral regions other than the central region are in contact with each other with smooth surfaces having a surface roughness (Ra) of 1 μm or less, and the outer peripheral edge of the seed crystal substrate is A method for manufacturing a silicon carbide single crystal ingot, wherein the silicon carbide single crystal is grown on a crystal growth surface of a seed crystal substrate by mechanically fixing the crucible lid with a holding member.
(2) A substrate mounting portion of the crucible lid is formed from a disk-shaped graphite pedestal, and the graphite pedestal includes a through hole at a position corresponding to a central portion of the seed crystal substrate and has a surface roughness ( Ra) has a smooth surface of 1 μm or less, and the seed crystal substrate has a smooth surface with a surface roughness (Ra) of 1 μm or less on the side opposite to the crystal growth surface, and fills the through hole of the graphite base. By means of the adhesive, the seed crystal substrate and the crucible lid are joined via the graphite pedestal, and the holding member attached to the outer peripheral edge of the seed crystal substrate, the graphite pedestal and the seed crystal substrate (1) The manufacturing method of the silicon carbide single crystal ingot as described in (1).
(3) The method for producing a silicon carbide single crystal ingot according to (1) or (2), wherein a silicon carbide single crystal ingot having a diameter of 100 mm or more is produced.

  According to the present invention, even when a large-diameter SiC single crystal having a diameter of 100 mm or more is grown, the generation of macro defects is suppressed while preventing large stress from being applied to the grown crystal, and high quality with few defects. It becomes possible to manufacture a simple SiC single crystal ingot more easily. Therefore, if a large-diameter SiC single crystal substrate cut out from the SiC single crystal ingot obtained by such a method is used, a power device for power control with extremely high performance and excellent reliability can be produced with high efficiency. it can.

FIG. 1 is a diagram illustrating an example of a procedure of a method for attaching a seed crystal substrate to the crucible lid body according to the present invention. FIG. 2 is a diagram illustrating an example of a state in which the seed crystal substrate is attached to the crucible lid body side in the present invention. FIG. 3 is a diagram for explaining another example of a state in which the seed crystal substrate is attached to the crucible lid body side in the present invention. FIG. 4 is a diagram for explaining the configuration of a sublimation recrystallization method (improved Rayleigh method) growth apparatus.

The present invention will be described in detail below.
In the present invention, a silicon carbide raw material is loaded on the crucible body side of a graphite crucible composed of a crucible body and a crucible lid, a seed crystal substrate made of a silicon carbide single crystal is attached to the crucible lid side, and the silicon carbide raw material is By sublimation recrystallization using a seed crystal substrate that is heated and sublimated to grow a silicon carbide single crystal on the crystal growth surface of the seed crystal substrate, for example, an SiC single crystal ingot from which an SiC single crystal wafer having a diameter of 100 mm or more can be taken out In manufacturing, in the central region corresponding to the central portion of the seed crystal substrate at the mounting interface between the seed crystal substrate and the substrate mounting portion of the crucible lid, the area ratio with respect to the seed crystal substrate is 0.1% or more and 5% or less. Bonded to each other with an adhesive so as to have a bonding area, and in the outer peripheral area other than the central area, the surface roughness (Ra) should be in contact with each other on a smooth surface of 1 μm or less. And the outer periphery of the seed crystal substrate is mechanically fixed to the crucible lid by holding member, so as to grow a silicon carbide single crystal on the crystal growth surface of the seed crystal substrate. Here, besides the adhesive in the central region, there is no intervening layer made of a heat-resistant special material such as a refractory metal or its carbide at the attachment interface between the seed crystal substrate and the substrate attachment part of the crucible lid, It is important that both are in contact with each other on a smooth surface having a surface roughness (Ra) of 1 μm or less.

  That is, the present inventors set the surface roughness (Ra) of both the substrate mounting portion of the crucible lid body to which the seed crystal substrate is attached and the back surface (opposite side of the crystal growth surface) of the seed crystal substrate to 1 μm or less. When they are brought into contact with each other, the back surface of the seed crystal substrate is uniformly thermally decomposed over the entire surface, and a very thin carbonized layer (estimated about several tens of μm or less) is formed, thereby suppressing adhesion of the crucible lid to the substrate mounting portion I found. Therefore, by bringing them into close contact with each other in a state where Ra is 1 μm or less, the occurrence of macro defects can be avoided, and at the same time, the mutual adhesion in the outer peripheral region can be avoided through the thin carbonized layer, Generation of unnecessary stress due to a slight difference in thermal expansion coefficient can be significantly reduced. Here, when at least one of the surface roughness (Ra) of both exceeds 1 μm, the formation of the carbonized layer becomes non-uniform, and separation between the seed crystal substrate and the substrate mounting portion of the crucible lid becomes insufficient, The basal plane dislocation density is greatly increased. The surface roughness Ra represents the arithmetic average roughness defined in JIS B0601: 2013.

  In this way, at the attachment interface between the seed crystal substrate and the crucible lid side, the outer peripheral regions other than the central region are in contact with each other with smooth surfaces having a surface roughness (Ra) of 1 μm or less. The bonding state by the adhesive is also important. In other words, if an adhesive layer made of an adhesive that joins the two is present at a predetermined thickness at these attachment interfaces, for example, there is a gap between the substrate attachment portion of the crucible lid such as a graphite pedestal and the seed crystal substrate. As a result, the contact with the smooth surface in the outer peripheral area becomes impossible. Therefore, in the present invention, for example, the seed crystal substrate is preferably bonded to the crucible lid side with an adhesive as follows.

  First, as shown in FIG. 1, a seed crystal substrate 1 used for growing a SiC single crystal ingot, and a graphite pedestal 13 serving as a substrate attaching portion when the seed crystal substrate 1 is attached to the crucible lid 3 side. Prepare. At that time, the surface on the side where both are in contact with each other needs to be finished to a surface roughness Ra of 1 μm or less in advance by machining using a surface grinding machine or a double-side polishing apparatus. The pedestal 13 is provided with a through hole 14 penetrating in the vertical direction at a position corresponding to the central portion of the seed crystal substrate 1. Therefore, the two are brought into close contact (FIG. 1A), and in this state, an adhesive 14 in which a phenol resin or the like is dissolved is poured into the organic solvent, and the through hole 14 is filled with the adhesive 15 (FIG. 1B). The crucible lid 3 is disposed on the upper surface of the pedestal 13 opposite to the surface to which the seed crystal substrate 1 is in close contact, taking care not to create a gap in the contact surface between the seed crystal substrate 1 and the pedestal 13. Then, by solidifying (curing) the adhesive 14 in this state, the seed crystal substrate 1 is joined to the crucible lid 3 via the pedestal 13 (through the through hole 14 of the pedestal 13) (FIG. 1 (c) )). At this time, heating may be appropriately performed in order to efficiently solidify the adhesive.

  By attaching the seed crystal substrate 1 to the crucible lid 3 in this manner, only the central region corresponding to the through hole 14 of the pedestal 13 is made of an adhesive at the attachment interface between the seed crystal substrate 1 and the graphite pedestal 13. In the other outer peripheral region, the seed crystal substrate 1 and the graphite pedestal 13 are physically in close contact with each other on the smooth surface, and the seed crystal substrate 1 is attached to the crucible lid 3 side. It is done. Without using such a graphite pedestal 13, for example, the crucible lid 3 is provided with the same through-hole as in the case of the graphite pedestal 13, and the seed crystal substrate 1 is adhered to the crucible lid 3. By filling the adhesive, or by providing a recess for filling the adhesive instead of the through-hole, the seed crystal substrate 1 is brought into close contact and the adhesive is solidified (cured), so that the substrate mounting portion of the crucible lid 3 is fixed. Thus, the attachment interface defined by the present invention can be realized by directly attaching the seed crystal substrate. However, when a through-hole is directly provided in the crucible lid 3 and the seed crystal substrate 1 is attached, depending on the material characteristics at the growth temperature of the adhesive, heat is generated from the through-hole during crystal growth, and the grown crystal It can also affect the quality. Further, since the graphite pedestal 13 is interposed, it is possible to avoid non-uniform heat flow on the back surface side of the seed crystal substrate 1. Therefore, preferably, as shown in FIG. The seed crystal substrate 1 is preferably attached to the crucible lid 3 side via 13.

  The shape of the graphite pedestal 13 is not particularly limited. However, when the graphite crucible is heated by high frequency induction, the sum of the thickness and the thickness of the crucible lid 3 is generally the high frequency induction electromagnetic wave. It is preferable that the depth is not less than the penetration depth. For example, when induction heating is performed at a frequency of 10 kHz, it is sufficient that the sum of the thicknesses is at least 15 mm. When the thickness is much less than 15 mm and becomes thin, high-frequency induction heating does not work effectively, and it becomes difficult to heat to a temperature necessary for the growth temperature. In addition, the shape is preferably a disk shape for the purpose of avoiding uneven temperature distribution in the circumferential direction.

  On the other hand, at the attachment region between the seed crystal substrate and the crucible lid body, with respect to the central region bonded with the adhesive, the bonding area by the adhesive is 0.1% or more and 5% or less in terms of the area ratio of the seed crystal substrate. Preferably, they are 0.1% or more and 2% or less, More preferably, they are 0.1% or more and 1% or less. If the area ratio with respect to the seed crystal substrate is less than 0.1%, the adhesive force is insufficient, and the adhesion may be peeled off during crystal growth. In this case, although the outer peripheral edge portion of the seed crystal substrate 1 is held by the holding member, a gap is generated at the attachment interface between the seed crystal substrate 1 and the substrate attachment portion of the crucible lid, so that the seed crystal substrate 1 is excessively decomposed and macro defects are generated. On the other hand, if it exceeds 5%, the influence of a slight difference in thermal expansion coefficient from the substrate mounting part on the crucible lid side such as a graphite pedestal becomes apparent, stress increases, and the basal plane dislocation density increases. The lower limit of the area ratio to be joined with the adhesive is preferably as small as possible if it is limited to the viewpoint of avoiding the generation of stress, but 0.1% in order to maintain the adhesive strength. % Or more is necessary. Also, this central region should be a circular region concentric with the seed crystal substrate, and the joint location is divided into a plurality of locations in an arbitrary shape within this circular region and partially joined by an adhesive. May be performed. However, it is necessary that the total area of the bonded portions actually bonded be 0.1% or more and 5% or less in the area ratio with the area of the seed crystal substrate as described above.

  For the adhesive used for bonding between the seed crystal substrate and the substrate mounting part of the crucible lid, the adhesive force can be maintained at high temperatures such as crystal growth by sublimation recrystallization, and macro defects such as voids can be maintained. There is no particular limitation as long as it does not form an occurrence factor. For example, a commercially available carbon adhesive can be used, an adhesive in which a polymer material such as a phenol resin is dissolved in an organic solvent such as ethyl alcohol, and an adhesive in which carbon powder is further mixed with the adhesive. Can be used. Further, in order to increase the adhesive force, a heat treatment at about 200 ° C. or higher may be performed in a state where the through hole of the base is filled.

  In the present invention, the outer peripheral edge of the seed crystal substrate is mechanically fixed to the crucible lid by the holding member. As a method of mechanically pressing (fixing) the outer peripheral edge of the seed crystal substrate, any method may be used as long as care is taken so that unnecessary stress is not applied to the seed crystal substrate. For example, as shown in FIG. 2, the seed crystal substrate is fixed to the crucible lid by pressing a plurality of outer peripheral edges of the seed crystal substrate with holding members made of graphite screws 16. Also, as shown in FIG. 3, a holding member such as a graphite support rod 17 having a groove formed on the outer peripheral side surface of the seed crystal substrate and having a claw-like protrusion at the tip. Is inserted into the front end projection to lock the seed crystal substrate 1, and a male screw portion (not shown) is formed on the other end of the support rod 17, and a female screw portion (not shown) provided on the crucible lid 3 is shown. It may be screwed to the outside. At this time, when the seed crystal substrate is attached to the crucible lid through a graphite pedestal or the like, as shown in FIGS. 2 and 3, the holding member (16 17), the graphite pedestal 13 and the seed crystal substrate 1 may be fixed to the crucible lid 3 integrally.

  In the method for producing a silicon carbide single crystal ingot according to the present invention, a known method is provided except that a seed crystal substrate is attached to a crucible lid of a graphite crucible comprising a crucible body and a crucible lid. A silicon carbide single crystal ingot can be produced in the same manner as in this method. In particular, the present invention is effective when a SiC single crystal ingot having a diameter of 100 mm (4 inches) or more is grown by a sublimation recrystallization method. Further, an SiC single crystal ingot having a diameter of 150 mm (6 inches) or more is used. Produces significant effects when manufactured.

  When manufacturing such a large-diameter SiC single crystal ingot, the diameter of the seed crystal substrate is increased, which increases the probability of occurrence of macro defects on the back surface of the seed crystal substrate. However, the grown crystal itself becomes larger (heavy). Therefore, the method of attaching the seed crystal substrate to the crucible lid of the graphite crucible as in the present invention is extremely important in producing a large-diameter SiC single crystal ingot, and when growing a large-diameter SiC single crystal However, it is possible to more easily manufacture a high-quality SiC single crystal ingot with few defects by suppressing the occurrence of macro defects while preventing a large stress from being applied to the grown crystal. An SiC single crystal thin film is epitaxially grown by, for example, chemical vapor deposition (CVD) on the large-diameter SiC single crystal substrate having a diameter of 100 mm or more cut out from the SiC single crystal ingot thus obtained. By doing so, it becomes possible to produce an epitaxial wafer with very few defects such as basal plane dislocations over substantially the entire region of the substrate. By using such an epitaxial wafer, the power conversion characteristics are improved. Various excellent power devices can be obtained efficiently.

  Hereinafter, the present invention will be specifically described with reference to examples. The present invention is not limited to these contents.

Example 1
The following SiC single crystal was grown using the sublimation recrystallization single crystal growth apparatus shown in FIG. FIG. 4 is an example of an apparatus for growing a SiC single crystal by a sublimation recrystallization method using the seed crystal substrate 1, and does not limit the constituent requirements of the present invention.

First, this single crystal growth apparatus will be briefly described. Crystal growth is performed by sublimating and recrystallizing SiC powder (SiC raw material) 2 as a raw material on the SiC single crystal 1 used as the seed crystal substrate 1 and further recrystallizing it onto the seed crystal. The SiC single crystal 1 that is the seed crystal substrate 1 is attached to the inner wall surface of a graphite crucible lid 3 that forms the crucible 5. The raw material SiC powder 2 is filled in a graphite crucible body 4 that also forms the crucible 5. Such a graphite crucible 5 is installed inside the double quartz tube 6 and has a mechanism capable of rotating the graphite crucible 5 at a rotational speed of less than 1 rpm in order to eliminate circumferential temperature non-uniformity. Thus, it can always rotate at a substantially constant speed during crystal growth. Around the graphite crucible 5, a heat insulating heat insulating material 7 for heat shielding is installed. The double quartz tube 6 can be highly evacuated (10 ⁻³ Pa or less) by the evacuation device 8, and the internal atmosphere can be pressure controlled by argon gas. In addition, a work coil 9 is installed on the outer periphery of the double quartz tube 6, and the graphite crucible 5 is heated by flowing a high-frequency current to heat the SiC raw material 2 and the seed crystal substrate 1 to a desired temperature. be able to. The temperature of the crucible is measured by providing an optical path 10 having a diameter of 2 to 4 mm at the center of the growth apparatus in the upper direction, taking out the radiant light from the heat insulating material heat removal hole 12 provided on the outer surface of the crucible lid 3, and This is done using the thermometer 11.

  As described later, the heat insulating material 7 and the like were placed in the graphite crucible 5 on which the seed crystal substrate 1 was fixed, and then placed in the double quartz tube 6. After the inside of the double quartz tube 6 was evacuated, a current was passed through the work coil 9 to raise the surface temperature of the crucible lid 3 to 1700 ° C. Then, a mixed gas of high-purity argon gas (purity 99.9995%) and high-purity nitrogen gas (purity 99.9995%) is introduced as the atmospheric gas, and the pressure in the double quartz tube 6 is maintained at about 80 kPa, while the crucible lid surface The temperature was raised to the target temperature of 2250 ° C. The nitrogen concentration in the atmospheric gas was 7%. Thereafter, the pressure was reduced to 1.3 kPa as a growth pressure over about 30 minutes. At this time, the temperature gradient between the SiC powder 2 in the graphite crucible 5 and the seed crystal substrate 1 is about 20 ° C./cm.

  In Example 1, a 4H—SiC single crystal composed of a {0001} substrate having a diameter of 152 mm and a thickness of 2 mm was prepared as the seed crystal substrate 1. It was attached to the crucible lid 3 so that the (000-1) plane (C plane) was the crystal growth plane. At that time, according to the procedure shown in FIGS. 1A to 1C, first, a disk-shaped graphite base 13 having a diameter of 160 mm and a thickness of 20 mm is prepared, and the base is formed so as to penetrate the upper and lower surfaces. A through hole 14 having a diameter of 5 mm was formed at the center of 13. Then, the substrate mounting surface of the pedestal 13 to which the seed crystal substrate 1 is fixed (attached) and the back surface of the seed crystal substrate 1 (the (0001) Si surface opposite to the crystal growth surface) are respectively surface grinders. Was mirror-finished. When the surface roughness Ra of the back surface of the seed crystal substrate 1 after processing and the substrate mounting surface of the pedestal 13 was measured with a contact-type surface roughness meter, the surface roughness Ra of the back surface of the seed crystal substrate 1 was 0. The surface roughness Ra of the substrate mounting surface of the pedestal 13 was 0.9 μm.

  Then, with the back surface of the seed crystal substrate 1 and the substrate mounting surface of the pedestal 13 being in close contact with each other, an adhesive 15 in which a phenol resin and carbon powder are mixed in an ethyl alcohol solvent is poured from the upper surface side of the pedestal 13, The through hole 14 was filled with the adhesive 15 so as to reach the upper surface side. Next, the graphite crucible lid 3 is allowed to stand on the upper surface side of the pedestal 13 (the side opposite to the seed crystal substrate 1) and heated to about 250 ° C. to solidify the adhesive 15 filled in the through holes 14. (Cured). After the adhesive 15 is solidified, as shown in FIG. 2, graphite screws 16 are used as holding members, and the outer peripheral edge of the seed crystal substrate 1 is pressed at four locations with the heads of the screws 16. Then, the screw 16 is inserted into the screw hole of the graphite pedestal 13 and the tip thereof is screwed into a female screw portion (not shown) provided in the crucible lid 3 so that the graphite pedestal 13 and the seed crystal substrate 1 are inserted. Were fixed integrally to the crucible lid 3. At this time, the bonding area with the seed crystal substrate 1 by the adhesive 15 filled in the through holes 14 of the graphite pedestal 13 is 0.11% in terms of the area ratio with respect to the seed crystal substrate 1.

  Crystal growth was performed using the single crystal growth apparatus prepared as described above, with a growth time of about 100 hours. After completion of the growth, the SiC single crystal ingot was recovered by cooling to room temperature. The diameter of the obtained test SiC single crystal ingot was about 150.2 mm, the shape of the growth surface at the tip of the ingot was a gentle convex shape, and the height near the crystal center was about 30 mm. Moreover, when the outer peripheral side surface of the obtained ingot, the crystal growth end face, and the back surface of the seed crystal substrate 1 (on the opposite side of the crystal growth end face) were observed visually and with a stereomicroscope, the thermal decomposition disappearance and subgrains of the seed crystal substrate 1 were observed. It was confirmed that there was no occurrence of macro defects such as boundaries, and that the grown crystal had a good crystal quality equivalent to that of the seed crystal substrate.

Further, the obtained SiC single crystal ingot is ground, cut, and polished, has a shape with a diameter of 150 mm, a thickness of 350 μm, and the crystal c axis (<0001> axis) is in the <11-20> direction. A 4-degree off-SiC single crystal wafer tilted 4 degrees was fabricated. The wafer was taken out from the top of the ingot, that is, from the growth end. The produced wafer was etched by being immersed in KOH (potassium hydroxide) melted at 500 ° C. for about 3 minutes to form dislocation pits. Of the pits that appear, measure the total number of shell-shaped etch pits corresponding to basal plane dislocations (see, for example, P. Wu, Journal of Crystal Growth 312 (2010) p. 1193) and divide by the area of the wafer. Thus, the basal plane dislocation density per unit area was obtained. As a result, it was found that an extremely small density value of 98 / cm ² was realized on the entire surface of the 150 mm wafer.

(Comparative Example 1)
After the back surface of the seed crystal substrate 1 and the substrate mounting surface of the graphite pedestal 13 are mirror-finished in the same manner as in Example 1, the through hole is not formed in the graphite pedestal 13 and the entire substrate mounting surface is used in Example 1. The same phenol-based adhesive is applied, and the seed crystal substrate 1 and the graphite pedestal 13 are joined so that the thickness of the adhesive layer after solidification is approximately 200 μm. Similarly, fixation of the seed crystal substrate 1 to the crucible lid 3 was completed by fixing the outer peripheral edge portion of the seed crystal substrate 1 at four locations using graphite screws 16. Using the single crystal growth apparatus thus prepared, crystal growth was performed in the same manner as in Example 1.

The SiC single crystal ingot taken out after the growth had a diameter of about 150.1 mm, the growth surface at the tip of the ingot had a gently convex shape, and the height near the center of the crystal was about 31 mm. However, unlike Example 1, the obtained SiC single crystal ingot was strongly adhered to the pedestal 13 even after being taken out from the graphite crucible 5, and therefore the entire pedestal 13 was processed into a wafer in the same manner as in Example 1. Then, a 4-degree off SiC single crystal wafer having a diameter of 150 mm and a thickness of 350 μm was produced from the top of the ingot and taken out. Then, when the basal plane dislocation density was evaluated by the molten KOH etching method in the same manner as in Example 1, a value of 32680 / cm ² was obtained over the entire wafer surface.

(Examples 2-4, Comparative Examples 2-4)
A single crystal growth apparatus is prepared by attaching the seed crystal substrate 1 to the crucible lid 3 side in the same manner as in Example 1 except that the diameter of the through hole 14 provided in the graphite crucible 5 is changed as shown in Table 1. did. Then, the crystal growth was performed in the same manner as in Example 1, and the obtained SiC single crystal ingot was observed with a visual microscope and a stereomicroscope in the same manner as in Example 1, and the wafer was processed to turn off four times. A SiC single crystal wafer was produced, and the basal plane dislocation density was evaluated by a molten KOH etching method. The results are summarized in Table 1. Table 1 also shows the results of Example 1.

  As can be seen from Table 1, when the diameter of the through hole 14 of the graphite pedestal 13 is 6 mm, 10 mm, and 30 mm (Examples 2 to 4), the SiC single crystal ingot having a small basal plane dislocation density is used. This shows that the present invention is effective. On the other hand, in the case where the diameter of the through hole is 3 mm (Comparative Example 2), it is considered that the bonded portion due to the adhesive is peeled off due to the weight of the growing ingot. 1 and the graphite base 13 were not in close contact with each other, and a gap was formed. For this reason, thermal decomposition of the seed crystal substrate 1 occurred, a large amount of macro defects were generated, and the basal plane dislocation density could not be evaluated. When the diameter of the through hole is 50 mm or more (Comparative Examples 3 and 4), the bonding area by the adhesive between the seed crystal substrate 1 and the graphite pedestal 13 becomes excessive, so that the stress in the growth ingot is increased. The basal plane dislocation density was very large.

(Example 5)
A commercially available carbon adhesive (ST-201 manufactured by Nisshinbo Co., Ltd.) is used as the adhesive 15 filling the through hole 14 of the graphite pedestal 13, and the temperature is increased to 200 ° C. in 20 hours in order to improve the adhesion when solidified. The seed crystal substrate 1 was joined to the crucible lid 3 in the same manner as in Example 1 except that the curing treatment was performed by heating and holding at that temperature for 1 hour. In addition, as shown in FIG. 3, the outer peripheral edge of the seed crystal substrate 1 is first fixed on the outer peripheral side surface of the seed crystal substrate 1 having a thickness of 2 mm along the circumferential direction at the center in the thickness direction. A concave groove having a height of about 0.5 mm in the substrate thickness direction and a depth of about 1 mm toward the center of the substrate is formed. On the other hand, a nail having a thickness of about 0.4 mm and a length of about 5 mm is formed at the tip. A support rod 17 made of graphite having a protruding portion was inserted. On the other hand, a male screw portion (not shown) is formed at the other end of the support rod 17, and is screwed into a female screw portion (not shown) provided in the crucible lid body 3, The seed crystal substrate 1 was fixed integrally to the crucible lid 3. A single crystal growth apparatus was prepared in the same manner as in Example 1 except for this, and crystal growth was performed in the same manner as in Example 1.

About the obtained SiC single crystal ingot, it was observed by visual observation and a stereoscopic microscope in the same manner as in Example 1, and there was no occurrence of macro defects such as disappearance of thermal decomposition of the seed crystal substrate 1 or subgrain boundaries, It was confirmed that the grown crystal had a good crystal quality equivalent to that of the seed crystal substrate. Further, wafer processing was performed in the same manner as in Example 1 to produce a 4-degree off-SiC single crystal wafer having a diameter of 150 mm and a thickness of 350 μm from the top of the ingot. When the basal plane dislocation density was evaluated by the melt KOH etching method in the same manner as in Example 1, a value of 56 / cm ² was obtained over the entire wafer surface.

(Comparative Example 5)
A single crystal growth apparatus was prepared and crystal growth was performed in the same manner as in Example 4 except that the fixation with the support rod 17 made of graphite was not performed. When the SiC single crystal ingot taken out after cooling (cooling) after growth was observed with a visual microscope and a stereomicroscope, almost the entire outer peripheral side surface of the seed crystal substrate 1 was thermally decomposed. It was observed that a large amount of macro defects occurred. In addition, wafer processing was performed in the same manner as in Example 1 to produce a 4-degree off-SiC single crystal wafer having a diameter of 150 mm and a thickness of 350 μm from the top of the ingot. When the surface dislocation density was evaluated, the basal plane dislocation density in the vicinity of the wafer center was about 340 / cm ^2, which was a relatively good value. However, the vicinity of the outer periphery was about 29300 / cm 2 due to the influence of macro defects. ^No good wafer having a low dislocation density over the entire surface was obtained.

  As can be seen from the above results, at the attachment interface between the seed crystal substrate and the substrate attachment portion of the crucible lid, i) bonding the central portion of the seed crystal substrate with an adhesive so as to have a predetermined bonding area, ii ) In other outer peripheral regions, they are brought into contact with each other with smooth surfaces having a predetermined surface roughness, and iii) by mechanically fixing the outer peripheral edge of the seed crystal substrate with a holding member, a large diameter of 150 mm Even when growing a SiC single crystal having a large diameter, it is possible to prevent the generation of a large stress in the grown crystal and to suppress the generation of macro defects and to produce a high-quality SiC single crystal ingot with a low defect density. Will be able to.

1 Seed crystal substrate 2 SiC powder (SiC raw material)
3 crucible lid 4 crucible body 4
5 Graphite crucible 6 Double quartz tube 7 Insulation heat insulation material 8 Vacuum exhaust device 9 Work coil 10 Optical path (temperature measuring window)
11 Two-color thermometer (radiation thermometer)
12 Insulation material heat removal hole (insulation material hole for temperature measurement)
13 Graphite base 14 Through hole 15 Adhesive 16 Graphite screw (holding member)
17 Graphite support rod (holding member)

Claims (3)

A silicon carbide raw material is loaded on the crucible body side of a graphite crucible composed of a crucible body and a crucible lid body, a seed crystal substrate made of a silicon carbide single crystal is attached on the crucible lid body side, and the silicon carbide raw material is heated and sublimated to seed. A method for producing a silicon carbide single crystal ingot for growing a silicon carbide single crystal on a crystal growth surface of a crystal substrate,
In the central region corresponding to the central portion of the seed crystal substrate at the interface between the substrate mounting portion of the crucible lid and the seed crystal substrate, the bonding area is 0.1% or more and 5% or less in terms of the area ratio to the seed crystal substrate. The outer peripheral regions other than the central region are in contact with each other with smooth surfaces having a surface roughness (Ra) of 1 μm or less, and the outer peripheral edge of the seed crystal substrate is A method for manufacturing a silicon carbide single crystal ingot, wherein the silicon carbide single crystal is grown on a crystal growth surface of a seed crystal substrate by mechanically fixing the crucible lid with a holding member.   A substrate mounting portion of the crucible lid is formed from a disk-shaped graphite pedestal, and the graphite pedestal has a through hole at a position corresponding to the central portion of the seed crystal substrate and has a surface roughness (Ra) of 1 μm. The seed crystal substrate has a smooth surface with a surface roughness (Ra) of 1 μm or less on the opposite side to the crystal growth surface, and the seed crystal substrate is filled in the through hole of the graphite base. The seed crystal substrate and the crucible lid are joined by the agent via the graphite pedestal, and the graphite pedestal and the seed crystal substrate are connected to the crucible lid by the holding member attached to the outer peripheral edge of the seed crystal substrate. The manufacturing method of the silicon carbide single crystal ingot of Claim 1 fixed integrally with a body. The manufacturing method of the silicon carbide single crystal ingot of Claim 1 or 2 which manufactures the silicon carbide single crystal ingot which has a diameter of 100 mm or more.

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