JP6839526B2 - SiC single crystal growth device, SiC single crystal growth method and SiC single crystal - Google Patents

Description

The present invention relates to a SiC single crystal growth apparatus, a SiC single crystal growth method, and a SiC single crystal.

Silicon carbide (SiC) has characteristic properties. For example, the dielectric breakdown electric field is an order of magnitude larger, the band gap is three times larger, and the thermal conductivity is about three times higher than that of silicon (Si). Therefore, silicon carbide (SiC) is expected to be applied to power devices, high frequency devices, high temperature operation devices and the like.
In particular, in recent years, in order to obtain many semiconductor devices from a single substrate, it has been required to increase the diameter of the SiC single crystal substrate. Therefore, there is an increasing demand for a larger diameter of the SiC single crystal itself.

The SiC single crystal substrate is produced by cutting out a SiC ingot. SiC ingots are generally obtained by the sublimation method. In the sublimation method, a seed crystal composed of a SiC single crystal is placed on a pedestal placed in a graphite crucible, and by heating the crucible, sublimation gas sublimated from the raw material powder in the crucible is supplied to the seed crystal. Is a method of growing a larger SiC ingot.

However, it is difficult to obtain a large SiC ingot directly from a small seed crystal. Therefore, it is common to first grow a seed crystal into a large SiC single crystal and then use the SiC single crystal to prepare a SiC ingot.

Various methods have been studied as means for obtaining a large SiC single crystal.
For example, Patent Document 1 describes a method using a taper guide. A SiC single crystal grows along the taper guide, and a large SiC single crystal is produced.

Further, Patent Document 2 describes a RAF (Repeated a-face) method as a means for obtaining a large SiC single crystal. The RAF method is a method in which c-plane growth is performed after a-plane growth is performed at least once.

Further, Patent Document 3 describes a method of arranging a raw material of a SiC single crystal on the outer peripheral side of the furnace and growing the SiC single crystal in the a-axis direction and the c-axis direction.

JP-A-2002-60297 Japanese Patent No. 37455668 Japanese Unexamined Patent Publication No. 11-268990

However, the above method has a problem that it is difficult to easily expand the diameter in the a-axis direction.

For example, the method using the taper guide described in Patent Document 1 is not efficient because crystals grow in the c-axis direction as well. Further, when the polycrystal attached to the taper guide comes into contact with the single crystal, it causes defects. Therefore, the quality of the obtained single crystal may deteriorate.

On the other hand, when the RAF method of Patent Document 2 is used, a very high-quality large-sized SiC single crystal having almost no spiral dislocations and stacking defects can be produced. However, since crystal growth in the a-axis direction and crystal growth in the c-axis direction are performed respectively, there are many steps for increasing the size. Further, since the production method utilizes the crystal orientation, there is also a problem that it is difficult to obtain a large and circular single crystal.

Further, in the method described in Patent Document 3, since crystal growth proceeds in each of the a-axis direction and the c-axis direction, it is necessary to control the temperature gradients in both the a-axis direction and the c-axis direction with respect to the crystal. Further, if crystals grow on the a-axis and the c-axis at the same time, the quality of the obtained single crystal may deteriorate. For example, since the portion growing in the a-axis direction does not have a helical dislocation, a heterogeneous polymorph may be produced when the crystal grows in the c-axis direction.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a single crystal growth apparatus and a single crystal growth method capable of easily expanding the diameter. Another object of the present invention is to provide a characteristic single crystal obtained by a single crystal growth apparatus and a single crystal growth method.

As a result of diligent studies, the present inventors have found that the diameter of a single crystal can be easily expanded by protecting the c-plane of the single crystal and suppressing crystal growth in the c-axis direction, and completed the present invention. It was.
That is, the present invention provides the following means for solving the above problems.

(1) The single crystal growth apparatus according to one embodiment has a protective surface capable of protecting the first surface of the single crystal and the second surface facing the first surface, and holds the single crystal sandwiched between the protective surfaces. A single crystal holding portion that can be formed, a furnace body that covers the outer periphery of the single crystal holding portion when viewed from the first direction in which the single crystal is sandwiched by the protective surface, and the first in the furnace body from the single crystal holding portion. A raw material installation portion provided on the outer side in the radial direction intersecting the direction 1 and a heating means for heating the outer side in the radial direction of the furnace body to a higher temperature than the central portion are provided, and the single crystal holding portion holds the single crystal. The single crystal to be grown can be grown outward in the radial direction.

(2) In the furnace body of the single crystal growth apparatus according to the above aspect, a guide ring extending in the radial direction from the single crystal holding portion may be further provided.

(3) The single crystal growth apparatus according to the above aspect further includes a guide ring extending in the radial direction from the single crystal holding portion in the furnace body, and a gap between the single crystal holding portion and the guide ring. There may be.

(4) In the furnace body of the single crystal growth apparatus according to the above aspect, a taper guide that expands the diameter from the single crystal holding portion toward the raw material installation portion may be further provided.

(5) In the single crystal growth apparatus according to the above aspect, the single crystal growing apparatus is provided between the single crystal holding portion and the raw material setting portion in the radial direction and surrounds the outer periphery of the single crystal held by the single crystal holding portion. An additional shielding ring may be provided.

(6) In the single crystal growth apparatus according to the above aspect, the single crystal holding portion may be centered and symmetrical in the first direction.

(7) The single crystal growth method according to one embodiment is a single crystal growth method using the single crystal growth apparatus according to the above embodiment, in which both sides of the single crystal in the c-axis direction are sandwiched between the protective surfaces. It includes a step of holding a crystal and a step of heating the raw material provided in the raw material setting portion by the heating means and growing the single crystal in the radial direction intersecting the c-axis of the single crystal.

(8) In the single crystal growth method according to the above aspect, the raw material may be placed symmetrically in the first direction with the single crystal holding portion as the center.

(9) In the single crystal growth method according to the above embodiment, when the single crystal is grown, the heat accumulated in the single crystal may be exhausted through the single crystal holding portion.

(10) The single crystal growth method according to one embodiment protects both sides of the single crystal in the c-axis direction, suppresses the growth in the c-axis direction, and suppresses the growth of the single crystal in the radial direction intersecting the c-axis direction. To grow.

(11) The single crystal according to one embodiment has faceted growth regions extending radially in six directions from the central portion when viewed from the c-axis direction of the crystal structure.

(12) The single crystal according to the above aspect is circular when viewed from the c-axis direction, and may have concentric discontinuous regions.

(13) The single crystal according to the above aspect may have an enlarged portion on the outer periphery of the discontinuous region, and the enlarged portion may have a stacking defect.

According to the single crystal growth apparatus and the single crystal growth method according to the present embodiment, a high quality single crystal having a large diameter can be easily obtained.

A schematic diagram for explaining the crystal orientation and the crystal plane is shown. It is sectional drawing of the single crystal growth apparatus which concerns on 1st Embodiment. It is a figure which showed typically the growth process of a single crystal in the case of expanding the diameter of a single crystal by dividing it into a plurality of times. It is a figure which showed another example of the growth process of a single crystal in the case of expanding the diameter of a single crystal in a plurality of times. It is a plane schematic diagram of the single crystal which concerns on this embodiment. It is a figure which shows the flow of the raw material gas and the isotherm surface at the time of performing a simulation. It is a figure which shows the cross section of the single crystal growth apparatus after crystal growth was performed by the simulation.

Hereinafter, the single crystal growth apparatus, the single crystal growth method, and the single crystal will be described in detail with reference to the drawings as appropriate. The drawings used in the following description may be enlarged for convenience in order to make the features of the present invention easy to understand, and the dimensional ratios of the respective components may differ from the actual ones. is there. The materials, dimensions, etc. exemplified in the following description are examples, and the present invention is not limited thereto, and the present invention can be appropriately modified without changing the gist thereof.

First, the orientation and direction of the crystal are defined. FIG. 1 is a schematic view for explaining a crystal orientation and a crystal plane. The {0001} plane (c plane), the {1-100} plane (m plane) and the {11-20} plane (a plane) perpendicular to the c plane are known as the main crystal planes of the single crystal. There is. Here, in the surface index, the symbol "-" is usually attached above the number, but in the present specification and drawings, it is attached to the left side of the number for convenience. Further, <0001>, <1-100> and <11-20> indicating the crystal orientation are treated in the same manner.

The parentheses {} indicating the exponent representing the surface and the parentheses <> indicating the exponent indicating the direction indicate the surface and the direction having equivalent symmetry, and therefore the directions are not distinguished. In the present application, when distinguishing faces and directions, they may be distinguished by "direction". For example, if one side of a crystal having {11-20} planes on the front and back surfaces is the front surface, the back surface may be the surface in the opposite direction.

(Single crystal growth device)
FIG. 2 is a schematic cross-sectional view of the single crystal growth apparatus according to the present embodiment. The single crystal growth apparatus 100 shown in FIG. 2 includes a single crystal holding portion 10, a furnace body 20, a raw material setting portion 30, a heating means 40, a guide ring 50, a taper guide 60, and a shielding ring 70. .. FIG. 2 illustrates a state in which the single crystal S is held in the single crystal holding unit 10 and the raw material G is installed in the raw material setting unit 30 for easy understanding.

In FIG. 2, the first direction sandwiching the single crystal S is the z direction, one direction perpendicular to the z direction is the x direction, and the z direction and the direction perpendicular to the x direction are the y direction. Further, a direction that intersects the first direction and in which the xy plane spreads around the single crystal holding portion 10 may be referred to as a "diameter direction". Further, the radial outer side of the single crystal growth apparatus 100 may be referred to as an "outer peripheral side", and the radial inner side may be referred to as a "central portion". Hereinafter, each configuration of the single crystal growth apparatus 100 will be specifically described.

The single crystal holding portion 10 has a protective surface 10a capable of protecting the first surface of the single crystal S and the second surface facing the first surface. The protective surface 10a presses the single crystal S from both sides, so that the single crystal holding portion 10 holds the single crystal S.

The single crystal holding portion 10 may have a configuration capable of rotating about the central axis of the single crystal holding portion 10 extending in the z direction. The raw material gas is supplied to the single crystal S held by the single crystal holding unit 10 from the outer peripheral side. By rotating the single crystal holding portion 10, the crystal growth rate in the radial direction is equalized.

The single crystal holding portion 10 may be provided with a heat exhaust mechanism. Since the single crystal S grows at a high temperature, the single crystal holding portion 10 in contact with the single crystal S also becomes high temperature. When the heat accumulated in the single crystal holding portion 10 is efficiently exhausted, the temperature gradient between the outer peripheral side and the central portion of the single crystal growth apparatus 100 can be further increased. As a result, the growth rate of the single crystal S in the radial direction increases.

A known heat exhaust mechanism can be used. For example, a mechanism for forcibly cooling from the outside may be provided, or a substance having high thermal conductivity may be brought into contact with the substance.

The furnace body 20 covers the outer periphery of the single crystal holding portion 10 when viewed from the z direction. That is, the furnace body 20 covers the portion where the single crystal S is exposed from the single crystal holding portion 10. The space in which the single crystal S grows becomes a closed space by the furnace body 20, and the utilization efficiency of the raw material G is enhanced.

The raw material setting portion 30 is provided on the outside of the furnace body 20 in the radial direction. The structure of the raw material setting unit 30 is not particularly limited as long as the raw material G can be installed on the outer side in the radial direction with respect to the single crystal holding unit 10. By installing the raw material G in the raw material setting unit 30 and heating it, the raw material gas is supplied to the single crystal holding unit 10 from the outer peripheral side. It is preferable that the raw material setting unit 30 can install the raw material G symmetrically in the z direction with the single crystal holding unit 10 as the center.

The heating means 40 controls the temperature inside the furnace body 20 so that the outer peripheral side in the circumferential direction is higher than the central portion. As the heating means 40, a known heater or the like can be used. The temperature of each part of the furnace body 20 heated by the heating means 40 can be measured with a radiation thermometer or the like. Although heaters are provided above and below the furnace body in FIG. 2, heaters may be arranged on the outer periphery.

The guide ring 50 is a ring-shaped member extending in the radial direction from the single crystal holding portion 10. When the guide ring 50 is provided, the flow of the raw material gas in the vicinity of the single crystal S is controlled.

The guide ring 50 controls the flow of the raw material gas so that the raw material gas is supplied from a direction substantially perpendicular to the outer peripheral surface of the single crystal S. Controlling the flow of the raw material gas increases the radial crystal growth rate of the single crystal S. Further, when the guide ring 50 is provided, even when the grown single crystal S protrudes from the single crystal holding portion 10, the crystal grows stably in the radial direction.

It is preferable to provide a gap between the guide ring 50 and the single crystal holding portion 10. By letting a part of the raw material gas escape to the space R through the gap, the retention of the raw material gas can be prevented.

When the raw material gas stays, crystals grow in places other than the desired portion. For example, if unnecessary crystals are generated in the middle of the flow path in which the raw material gas flows from the raw material setting unit 30 to the single crystal holding unit 10, the flow of the raw material gas is disturbed. Further, when this unnecessary crystal comes into contact with the growing single crystal S, it causes a crystal defect.

The taper guide 60 is a member that expands in diameter from the single crystal holding portion 10 toward the raw material setting portion 30 in the furnace body 20. The raw material gas generated by the raw material G installed in the raw material setting unit 30 is supplied to the single crystal holding unit 10 along the taper guide 60. Therefore, by arranging the taper guide 60 so that the raw material gas converges from the raw material setting unit 30 toward the single crystal holding unit 10, the efficiency of supplying the raw material gas to the single crystal S can be improved.

The shielding ring 70 is a member provided between the single crystal holding portion 10 and the raw material setting portion 30 in the radial direction and surrounding the outer circumference of the single crystal S held by the single crystal holding portion 10 in the radial direction. The shielding ring 70 shields heat radiation from surrounding members. By suppressing the temperature rise of the single crystal S due to thermal radiation, the temperature of the central portion of the furnace body 20 in which the single crystal S is installed can be lowered. As a result, the temperature gradient between the outer peripheral side and the central portion of the furnace body 20 can be increased, and the growth rate of the single crystal S in the radial direction can be increased.

Further, the shielding ring 70 shields heat radiation and makes the isothermal surface in the vicinity of the single crystal S substantially parallel to the z direction. The single crystal S grows perpendicular to the isothermal plane. Therefore, the isothermal plane becomes substantially parallel to the z direction, so that the crystal growth rate of the single crystal S in the radial direction becomes uniform in the z direction. Therefore, the crystal growth of the single crystal S in the radial direction is more stable.

The materials constituting the single crystal holding portion 10, the furnace body 20, the raw material setting portion 30, the heating means 40, the guide ring 50, the taper guide 60, and the shielding ring 70 are not particularly limited as long as they are heat resistant materials. For example, carbon, tantalum carbide (TaC) and the like can be used.

The guide ring 50, the taper guide 60, and the shielding ring 70 are not essential configurations, but by having them, the crystal growth of the single crystal S in the radial direction can be performed more efficiently. Further, the heat insulating material 80 may be provided in the furnace body 20 to increase the thermal efficiency.

The single crystal growth apparatus 100 is preferably symmetrical in the z direction with the single crystal holding portion 10 as the center. When the single crystal growth apparatus 100 is symmetrical in the z direction, the raw material gas can be uniformly supplied to the single crystal holding portion 10 in the z direction. As a result, the growth of the single crystal S held in the single crystal holding portion 10 in the z direction can be made uniform.

(Operation of single crystal growth device, single crystal growth method)
Next, the single crystal growth method will be specifically described together with the operation of the single crystal growth apparatus. The single crystal growth method according to the present embodiment is a method of growing a single crystal in the radial direction intersecting the c-axis direction while protecting both sides of the single crystal in the c-axis direction and suppressing growth in the c-axis direction. is there. Hereinafter, a case where a single crystal is crystal-grown using the single crystal growth apparatus 100 shown in FIG. 2 will be specifically described as an example.

First, a single crystal S as a base is prepared. Hereinafter, the single crystal that forms the basis of this may be referred to as a seed crystal. The seed crystal is obtained by cutting out a single crystal produced by a known method.
The type of the single crystal S is not particularly limited, and for example, silicon carbide (SiC), silicon, or the like can be used.

The shape of the seed crystal does not matter, but it is cut into a columnar shape by, for example, ultrasonic processing. The height direction of the cylinder is substantially the same as the c-axis direction of the crystal. By cutting out in this way, the bottom surface and the top surface of the columnar seed crystal become a c-plane or a c-plane having an offset angle.

The cut out columnar seed crystal is preferably subjected to polishing and etching treatment. For polishing, lap polishing, chemical mechanical polishing (CMP), or the like can be used.

The damaged layer of the seed crystal can be removed by polishing and etching. The damaged layer is a layer in which the crystal structure is disturbed by external forces such as cutting, grinding, and polishing, and internal stress is applied. Therefore, the damaged layer produces distortion during crystal growth, which causes dislocations, stacking defects, and the like.

The damage layer is the part where the original stable structure is deviated. Therefore, it is structurally slightly unstable than other parts and can be preferentially removed by chemical etching.

Whether or not the damaged layer has been removed can be confirmed by observing the disorder of the crystal structure by X-ray topography or X-ray locking curve. Since the disorder of the crystal structure includes a portion where the original structure is deviated, the diffraction angle changes. Therefore, it can be judged from the contrast in the X-ray topography and from the increase in the half width (FWHM) of the peak from the X-ray locking curve.

Next, the bottom surface and the top surface of the seed crystal processed into a columnar shape are sandwiched between the protective surfaces 10a to hold the seed crystal. As described above, since the height direction of the columnar seed crystal substantially coincides with the c-axis direction, the protective surface 10a protects both sides of the seed crystal in the c-axis direction.

It is preferable that the protective surface 10a does not project radially from the retained seed crystal. If the protective surface 10a protrudes in the radial direction from the seed crystal, polycrystals are precipitated from the protective surface 10a when the seed crystal grows, and the quality deteriorates. At this time, if the temperature and the arrangement of the members are appropriate, both sides in the c-axis direction are protected by the protective surface 10a, so that crystal growth can be realized only in the radial direction.

Further, the raw material G is installed in the raw material installation unit 30 of the single crystal growth apparatus 100. As the raw material G, a sintered SiC powder raw material can be used when the SiC single crystal is crystal-grown.

Examples of the procedure for installing the raw material G in the raw material installation unit 30 along the outer circumference of the furnace body 20 include the following procedure.

First, the upper surface of the furnace body 20 in the z direction is opened, and a cylinder having a diameter smaller than the diameter of the furnace body 20 is inserted into the furnace body 20. Then, the raw material G is filled between the inserted cylinder and the outer circumference of the furnace body 20. After filling, the inserted cylinder is gently removed to close the upper surface of the furnace body 20 in the z direction. The raw material G is solid and does not melt even when heated. Therefore, the raw material G can be installed in the raw material installation unit 30 by such a procedure.

If the raw material G to be filled is fine powder or the like and it is difficult to remove the inserted cylinder, a porous hole through which the raw material gas can pass is provided in the cylinder. Since the raw material gas can pass through the porous holes, it is not necessary to remove the inserted cylinder. In this case, the cylinder to be inserted needs to have heat resistance. Therefore, when growing a SiC single crystal, for example, a cylinder made of carbon or the like can be used.

The raw material G is preferably installed symmetrically in the z direction with the single crystal holding portion 10 as the center. By installing the raw material G symmetrically in the z direction, the raw material gas can be uniformly supplied to the single crystal holding portion 10 in the z direction. That is, the growth rate of the single crystal in the radial direction can be made uniform in the z direction.

As described above, after the seed crystal and the raw material G are installed in the single crystal growth apparatus 100, the furnace body 20 is heated from the outside by the heating means 40. At this time, the outer peripheral side of the furnace body 20 is heated so that the temperature is higher than that of the central portion. Then, a temperature gradient is formed between the outer peripheral side and the central portion of the furnace body 20 by heating.

At this time, it is preferable to install the shielding ring 70 between the single crystal holding portion 10 and the raw material setting portion 30. By providing the shielding ring 70 as described above, the position of the isothermal surface of the temperature gradient can be controlled. In addition, the influence of heat radiation can be blocked and the temperature gradient can be increased.

Further, it is preferable that the single crystal holding portion 10 is provided with heat exhausting means. That is, when growing a single crystal, it is preferable to exhaust the heat accumulated in the single crystal S via the single crystal holding portion 10. By exhausting the heat of the single crystal holding portion 10, the temperature gradient between the outer peripheral side and the central portion of the furnace body 20 becomes large.

The raw material G installed in the raw material installation unit 30 generates a raw material gas by heating. The generated raw material gas goes to the single crystal holding portion 10 according to the temperature gradients of the outer peripheral side and the central portion of the furnace body 20. When the taper guide 60 is provided, the raw material gas can be efficiently supplied to the single crystal holding portion 10.

Then, the raw material gas flowing along the guide ring 50 is cooled and recrystallized in the vicinity of the seed crystal held in the single crystal holding portion 10. As a result, the seed crystal expands in the radial direction, and a large single crystal is obtained.

When there is a gap between the guide ring 50 and the single crystal holding portion 10, a part of the excessively supplied raw material gas flows into the space R through the gap. The raw material gas flowing into the space R is recrystallized in the space R and accumulated in the space R. In FIG. 2, the space R exists at a position of the single crystal holding portion 10 in the vertical direction in the z direction. Therefore, the crystal recrystallized in the space R does not affect the crystal growth of the seed crystal.

The expansion of the single crystal in the radial direction may be performed at one time, but it is preferably performed in a plurality of times. Hereinafter, a case of enlarging in a plurality of times will be described with reference to FIG. FIG. 3 is a diagram schematically showing the growth process of a single crystal when the diameter of the single crystal is expanded in a plurality of times.

As shown in FIG. 3, since the single crystal S is protected on both sides in the z direction by the single crystal holding portion 10, the crystal grows in the radial direction. When the single crystal S continues to expand in the radial direction, the outer peripheral end of the single crystal S in the radial direction is located radially outside the single crystal holding portion 10. In this state, if the single crystal S is expanded in the radial direction, the first enlarged portion S1 is formed.

Since the first enlarged portion S1 grows in a state where both sides in the z direction are not protected, it grows a little in the z direction as well. The amount of growth in the z direction can be controlled to some extent by controlling the isothermal surface by, for example, arranging the shielding ring 70, or by controlling the flow of the raw material gas by the guide ring 50. However, if the crystal growth is continued, the amount of growth in the z direction cannot be ignored.

Therefore, once the first enlarged portion S1 grows to a certain size, the growth is stopped once. Then, the single crystal S is removed from the single crystal holding portion 10. The removed single crystal S has a different thickness in the z direction between the portion protected by the single crystal holding portion 10 and the first enlarged portion S1. Therefore, the protruding portion P of the first enlarged portion S1 is removed by grinding, CMP polishing, or the like to make the thickness in the z direction uniform. At this stage, the diameter is larger than that of the initial single crystal S.

Next, the single crystal S having an enlarged diameter is held again by the single crystal holding unit 10. At this time, the size of the single crystal holding portion 10 is set to be larger than that of the first single crystal holding portion 10. Further, the size of the single crystal holding portion 10 is made larger than that of the single crystal S after the diameter is expanded.

Then, when the single crystal S is crystal-grown in this state, the second enlarged portion S2 is formed. Then, when the second enlarged portion S2 grows to some extent, the single crystal holding portion 10 is removed again and the protruding portion P is polished.

By repeating such a process, the diameter can be gradually increased. If the diameter is gradually increased in a plurality of times, it becomes easy to keep the thickness in the z direction uniform. In addition, distortion is less likely to occur as compared with the case where the diameter is expanded at one time, and it is possible to prevent the single crystal S from cracking in the growth process.

Further, when the diameter is expanded in a plurality of times, the procedure as shown in FIG. 4 may be performed. FIG. 4 is a diagram schematically showing another example of the growth process of a single crystal when the diameter of the single crystal is expanded in a plurality of times.

FIG. 4 is the same as the procedure shown in FIG. 3 until the protruding portion P of the first enlarged portion S1 in which the single crystal S is enlarged in the radial direction is removed.

In the procedure shown in FIG. 4, after removing the protruding portion P, crystal growth is once performed in the c-axis direction. When a defect occurs in the first enlarged portion S1, the defect is inherited when the growth proceeds in the same crystal orientation. By changing the growth direction, the generated defects can be removed.

For example, when the single crystal S has an offset angle, the generated defect D propagates to the downstream side of the offset. Therefore, the defect D can be removed by advancing the crystal growth in the c-axis direction to some extent. Therefore, the region from which the defect D has been removed is cut out and used as the second single crystal S'.

By using the second single crystal S', it is possible to prevent defects from remaining in the crystal when the diameter is expanded again. That is, by repeating the above steps, a large single crystal with few defects can be obtained.

As described above, according to the single crystal growth method according to the present embodiment, it is possible to carry out crystal growth in the radial direction intersecting the c-axis while suppressing crystal growth in the c-axis direction. Therefore, a single crystal having a large diameter can be easily obtained. Further, since there is almost no growth in the c-axis direction, the temperature gradient can be limited only in the radial direction, and the occurrence of cracks due to the temperature difference during growth can be reduced. Further, regardless of the shape of the seed crystal and whether the growth surface has an offset angle, it is possible to expand the diameter of the single crystal.

Further, according to the single crystal growth apparatus according to the present embodiment, the above-mentioned single crystal growth method can be easily realized. Further, if the size of the furnace body 20 in the radial direction is increased, the amount of expansion of the single crystal can be increased.

(Single crystal)
FIG. 5 is a schematic plan view of a single crystal according to the present embodiment. As shown in FIG. 5, the single crystal S according to the present embodiment has a facet growth region F extending radially from the central portion in 6 directions when viewed from the c-axis direction of the crystal structure.

A "facet" is a crystal plane that is flat on an atomic scale along the geometrical regularity of a crystal, and is a plane that appears as a flat plane due to a difference in the growth mechanism during crystal growth. For example, {0001} plane facet parallel to {0001} plane (c plane facet), {11-20} plane facet parallel to {11-20} plane (a plane facet), parallel to {1-100} plane. There are {1-100} plane facets (m plane facets) and the like. These appear as planes during crystal growth.

Further, the "facet growth region F" refers to a region composed of an aggregate of portions in which facets are formed on the outermost surface of the SiC ingot during the growth process. The facet growth region F has a different impurity concentration due to the difference in its growth mechanism as compared with other regions in which step flow growth occurs. Therefore, the facet growth region F can be discriminated from the grown crystal.

As shown in FIG. 1, a single crystal has crystal planes (a-plane and m-plane) on each plane of a regular hexagon when viewed from the c-axis direction. Therefore, when the single crystal is expanded only in the radial direction, a facet growth region F is formed at the position of each crystal plane. That is, in the first expansion portion S1 and the second expansion portion S2 whose diameters are expanded in the radial direction from the central base single crystal S0, the facet growth region F extending radially in the six directions from the base single crystal S0 It is formed. Therefore, the single crystal obtained by the above-mentioned single crystal growth method has a faceted growth region F extending radially from the base single crystal S0 in six directions.

Further, when the base single crystal S0 is circular when viewed from the c-axis direction, the first expansion portion S1 and the second expansion portion S2 are formed concentrically when the diameter is uniformly expanded from the base single crystal S0. Since the interface where the crystal growth has been performed a plurality of times has stopped growing once, a discontinuous region dc is formed. Therefore, a discontinuous region dc exists at the interface between the underlying single crystal S0, the first enlarged portion S1 and the second enlarged portion S2. The discontinuous region dc is arranged concentrically in the same manner as the shapes of the first enlarged portion S1 and the second enlarged portion S2.

Here, the circle is not limited to a perfect circle. For example, it may be a substantially circular shape in which a locally generated facet portion has a straight portion. When a circular substrate is produced, the peripheral portion is usually ground, so that such a case can also be treated as a substantially circular shape.

When the single crystal growth apparatus according to the present embodiment is used, the single crystal grows in a diameter method that intersects the c-axis direction while protecting both sides of the single crystal in the c-axis direction and suppressing the growth in the c-axis direction. .. That is, the enlarged portion (first enlarged portion or second enlarged portion) that grows on the outer peripheral side via the discontinuous region dc with respect to the base single crystal S0 grows in the direction perpendicular to the c-plane. There is a stacking defect in the discontinuous region at the interface, and this stacking defect has the effect of relaxing stress.

A stacking defect parallel to the (0001) plane is generated in the discontinuous region, and the generated stacking defect is taken over by the enlarged portion. In Japanese Patent Application Laid-Open No. 2012-72034, there is a method of creating a "stacked defect generation region" having many stacking defects on the (0001) plane by growing into a plane having an angle of 30 ° to 150 ° with the (0001) plane. Have been described. Stacking defects on the (0001) plane are likely to be formed in the enlarged portion grown on this discontinuous region. That is, the single crystal according to the present embodiment has a stacking defect in the enlarged portion located on the outer periphery of the discontinuous region.

In Japanese Patent Application Laid-Open No. 2012-72034, a seed crystal having a stacking defect generation region which is inclined by a predetermined angle larger than 4 ° and smaller than 30 ° from the (0001) plane and has a stacking defect generation region parallel to the (0001) plane is partially formed. It is described that the penetration dislocation can be reduced by growing a SiC single crystal on the SiC single crystal and carrying out the growth in which the stacking defect is inherited from the stacking defect generation region.

In the growth on the inclined surface, it is estimated that the spiral dislocations cannot be taken over on the growth direction side due to the stacking defect, which has been experimentally confirmed. The single crystal of the present embodiment has a stacking defect in the enlarged portion outside the crystal. Therefore, when a seed crystal inclined at a predetermined angle from the (0001) plane is produced and a SiC single crystal is grown on the seed crystal, the effect of discharging through dislocations due to stacking defects can be obtained. That is, the seed crystal can be suitably used for producing a SiC single crystal such as a SiC ingot.

The single crystal according to this embodiment is obtained as a feature when crystal growth is carried out in the radial direction about the c-axis. Therefore, it is presumed that the single crystal having the above-mentioned characteristics was produced by the above-mentioned single crystal growth apparatus or single crystal growth method.

Although the preferred embodiments of the present invention have been described in detail above, the present invention is not limited to the specific embodiments, and varies within the scope of the gist of the present invention described in the claims. Can be transformed / changed.

(Example 1)
A single crystal growth apparatus was assumed based on the configuration shown in FIG. 2, and a simulation was conducted. The conditions of the simulation were as follows.

Single crystal: on-axis single crystal without effective offset angle Single crystal holding state: Holds both sides of c-plane Reactor size: Width in radial direction is 30 cm
Heating temperature: The temperature at the outer peripheral edge of the furnace body is 2350 ° C, and the temperature at the center of the single crystal holding portion is 2250 ° C.
Taper guide: Yes Shielding ring: Yes Crystal growth time: 30 hours

FIG. 6 is a diagram showing the flow of the raw material gas and the isothermal surface when the simulation is performed under the above conditions. Further, FIG. 7 is a diagram showing a cross section of the single crystal growth apparatus after crystal growth has been performed by simulation.

As shown in FIG. 6, the flow of the raw material gas was formed substantially perpendicular to the side surface of the single crystal. The isothermal surface was substantially parallel to the side surface of the single crystal. As a result, as shown in FIG. 7, the single crystal grew in the radial direction.

Further, a part of the excessively supplied raw material gas flows into the space R through the gap between the single crystal holding portion and the guide ring. Therefore, as shown in FIG. 7, crystals grow at the coldest corners in the space. By preventing the retention of the raw material gas in this way, the single crystal S did not stick to other members.

Then, a single crystal was actually grown by the apparatus under the same conditions.
First, an a-plane-grown on-axis SiC single crystal was prepared. Then, the SiC single crystal was processed into a columnar shape so that the bottom surface and the top surface were c-planes, and the outer peripheral surface was mirror-polished. Then, the c-plane of the cylindrical SiC single crystal was held by a protective surface and installed in the single crystal holding portion. Then, the furnace body was heated with a heater so that the temperature at the outer peripheral edge of the furnace body was 2350 ° C. and the temperature at the center of the single crystal holding portion was 2250 ° C., and the raw material gas was sublimated. As the raw material gas, sintered SiC powder prepared as a raw material was used. As a result, the SiC single crystal could be enlarged by 12 mm in the radial direction without causing cracks or the like. This result was in agreement with the simulation result.

(Example 2)
The second embodiment is different from the first embodiment in that the simulation is performed without the taper guide and the shielding ring. Other conditions were the same as in Example 1.

As a result of the simulation, the single crystal was enlarged by 6 mm in the radial direction. At this time, the single crystal expanding in the radial direction did not stick to the portion other than the single crystal holding portion. Therefore, it is considered that cracks and heterogeneous polymorphisms do not occur when actually produced.

It is considered that the reason why the diameter expansion amount of Example 1 is larger than that of Example 2 is that the raw material gas can be efficiently supplied to the single crystal by the taper guide and the shielding ring.

(Example 3)
Example 3 is different from Example 2 in that the simulation is performed using a single crystal having an offset angle (4 °) as the single crystal. Other conditions were the same as in Example 2.

As a result of the simulation, the single crystal was enlarged by 6 mm in the radial direction. At this time, the single crystal expanding in the radial direction did not stick to the portion other than the single crystal holding portion. Therefore, it is considered that cracks and heterogeneous polymorphisms do not occur when actually produced.

In Example 3, the same result as in Example 2 was obtained. That is, the single crystal growth apparatus can expand the diameter even of a single crystal having an offset angle.

(Comparative Example 1)
Comparative Example 1 is different from Example 1 in that the simulation was performed without protecting the c-plane of the single crystal with a protective surface. Other conditions were the same as in Example 1. As a result, the single crystal expanded in the radial direction, but at the same time, it expanded in the z-axis direction (c-axis direction). Since it is assumed that the portion expanded in the radial direction does not include spiral dislocations, the probability of occurrence of heterogeneous polymorphism increases in the portion growing in the c-axis direction.

10 ... Single crystal holding part, 10a ... Protective surface, 20 ... Furnace, 30 ... Raw material installation part, 40 ... Heating means, 50 ... Guide ring, 60 ... Tapered guide, 70 ... Shielding ring, 80 ... Insulation material, 100 ... Single crystal growth apparatus, S ... single crystal, G ... raw material, R ... space, S1 ... first expansion part, S2 ... second expansion part, P ... protrusion, D ... defect, S'... second single crystal, F ... faceted growth region, dc ... discontinuous region

Claims (13)

A single crystal holding portion having a protective surface capable of protecting the first surface of the single crystal and the second surface facing the first surface and capable of sandwiching and holding the single crystal between the protective surfaces.
A furnace body that covers the outer periphery of the single crystal holding portion when viewed from the first direction in which the single crystal is sandwiched by the protective surface.
In the furnace body, a raw material installation portion provided outside the single crystal holding portion in the radial direction intersecting the first direction, and
A heating means for heating the outer side of the furnace body in the radial direction to a higher temperature than the central portion is provided.
A SiC single crystal growth apparatus capable of growing a single crystal held by the single crystal holding portion toward the outside in the radial direction. The SiC single crystal growth apparatus according to claim 1, further comprising a guide ring extending in the radial direction from the single crystal holding portion in the furnace body. The SiC single crystal growth apparatus according to claim 2, wherein there is a gap between the single crystal holding portion and the guide ring. The SiC single crystal growth apparatus according to any one of claims 1 to 3 , further comprising a taper guide that expands the diameter from the single crystal holding portion toward the raw material installation portion in the furnace body. Any of claims 1 to 4 , further comprising a shielding ring provided between the single crystal holding portion and the raw material setting portion in the radial direction and surrounding the outer periphery of the single crystal held by the single crystal holding portion. The SiC single crystal growth apparatus according to item 1. The SiC single crystal growing apparatus according to any one of claims 1 to 5, which is symmetrical with respect to the single crystal holding portion in the first direction. A method for growing a SiC single crystal using the SiC single crystal growth apparatus according to any one of claims 1 to 6.
A step of sandwiching both sides of the single crystal in the c-axis direction with the protective surface to hold the single crystal, and
A SiC single crystal growth method comprising a step of heating a raw material provided in the raw material setting portion by the heating means and growing the single crystal in a radial direction intersecting the c-axis of the single crystal. The SiC single crystal growth method according to claim 7, wherein the raw material is placed symmetrically in the first direction with the single crystal holding portion as the center. The SiC single crystal growth method according to claim 7 or 8, wherein when the single crystal is grown, the heat accumulated in the single crystal is exhausted through the single crystal holding portion. The single crystal grows in the radial direction intersecting the c-axis direction while protecting both sides of the columnar single crystal having a height direction in the c-axis direction in the c-axis direction and suppressing the growth in the c-axis direction. A method for growing a SiC single crystal. A SiC single crystal having a faceted growth region extending radially from the central portion in six directions on the c-plane. The SiC single crystal according to claim 11, which is circular when viewed from the c-axis direction and has concentric discontinuous regions. The SiC single crystal according to claim 12, which has an enlarged portion on the outer periphery of the discontinuous region and the enlarged portion has a stacking defect.

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