JP2004292305A - Liquid phase epitaxial growth method of single crystal silicon carbide and heat treatment apparatus used for the method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a high quality and high performance single crystal silicon carbide which has a micropipe defect density in the surface of ≤1 piece/cm<SP>2</SP>, a broad terrace, and a surface with a high flatness. <P>SOLUTION: A single crystal silicon carbide substrate used as a seed crystal and a polycrystalline silicon carbide substrate are superposed and they are placed in a closed vessel 5. The single crystal silicon carbide is epitaxially grown in a liquid phase on the single crystal silicon carbide substrate by previously heating the closed vessel 5 to a temperature of ≥800°C in a preheating chamber 3 having pressure of ≤10<SP>-5</SP>Pa, then reducing the pressure in the closed vessel 5 to pressure of ≤10<SP>-5</SP>Pa, transporting the closed vessel 5 into a heating chamber previously heated to 1,400-2,300°C and in a reduced pressure of ≤10<SP>-2</SP>Pa or in an inert gas atmosphere having prescribed reduced pressure, placing the vessel 5 in the chamber, and interposing a quite thin metallic silicon melt between the single crystal silicon carbide substrate and the polycrystalline silicon carbide substrate by heating the substrates to 1,400-2,300°C in a short period of time. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a liquid phase epitaxial growth method of single crystal silicon carbide and a heat treatment apparatus used for the method.

  Silicon carbide (hereinafter, referred to as SiC) is not only excellent in heat resistance and mechanical strength, but also resistant to radiation, easy to control valence electrons and holes by adding impurities, and has a wide range. Since it has a forbidden band width (about 3.0 eV for 6H-type SiC single crystal and 3.3 eV for 4H-type SiC single crystal), silicon (hereinafter, referred to as Si) and gallium arsenide (hereinafter, referred to as GaAs). ), Which can achieve high temperature, high frequency, withstand voltage and environmental resistance that cannot be realized with existing semiconductor materials, and is attracting attention and expected as a semiconductor material for next-generation power devices and high-frequency devices. ing. Hexagonal SiC has a lattice constant close to that of gallium nitride (hereinafter, referred to as GaN), and is expected to serve as a GaN substrate.

  As described in Patent Document 1, for example, a single crystal SiC of this type is configured such that a seed crystal is fixedly arranged on a low temperature side in a crucible, and a powder containing Si as a raw material is arranged on a high temperature side. By heating to a high temperature of 1450 to 2400 ° C. in an inert atmosphere, the powder containing Si is sublimated and recrystallized on the surface of the seed crystal on the low temperature side to grow a single crystal, which is a sublimation recrystallization method (improved). Some are formed by the Rayleigh method.

  Further, for example, as described in Patent Document 2, when a SiC single crystal substrate and a plate material composed of Si atoms and C atoms face each other in parallel with a small gap therebetween, a failure at a pressure lower than atmospheric pressure is caused. In an active gas atmosphere and a SiC saturated vapor atmosphere, a heat treatment is performed with a temperature gradient so that the SiC single crystal substrate side is lower than the plate material, so that Si atoms and C atoms are sublimated and recrystallized in the minute gap. In some cases, a single crystal is deposited on a SiC single crystal substrate.

  Further, for example, as described in Patent Document 3, after forming a first epitaxial layer on a SiC single crystal by a liquid phase epitaxial growth method, a second epitaxial layer is formed on the surface by a CVD method, Some also remove micropipe defects.

JP 2001-15869 A JP-A-11-315000 Japanese Patent Publication No. Hei 10-509943

However, among these single crystal SiC formation methods, for example, in the case of the sublimation recrystallization method described in Patent Literature 1 or Patent Literature 2, the growth rate is very fast, several hundreds μm / hr, but the SiC is sublimated during sublimation. The powder is once decomposed into Si, SiC ₂ , and Si ₂ C and vaporized, and further reacts with a part of the crucible. For this reason, the kind of gas that reaches the surface of the seed crystal varies depending on the temperature change, and it is technically very difficult to precisely control the partial pressure stoichiometrically. In addition, impurities are easily mixed, and crystal defects and micropipe defects are easily generated by the influence of the mixed impurities and heat-induced strain. There is a problem that monocrystalline SiC stable in terms of quality and quality cannot be obtained.

  On the other hand, in the case of the LPE method described in Patent Document 3, the occurrence of micropipe defects and crystal defects as seen in the sublimation recrystallization method is small, and the quality is lower than that produced by the sublimation recrystallization method. Excellent single crystal SiC is obtained. On the other hand, since the growth process is controlled by the solubility of C in the Si melt, the growth rate is very slow at 10 μm / hr or less, and the productivity of single crystal SiC is low. Temperature must be precisely controlled. In addition, the process becomes complicated, and the manufacturing cost of single crystal SiC becomes very expensive.

  SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problem, and has a low occurrence of micropipe defects and interface defects, and has a wide terrace and a high surface flatness. It is an object of the present invention to provide a phase epitaxial growth method and a heat treatment apparatus used for the method.

The liquid crystal epitaxial growth method of single crystal SiC according to the present invention for solving the above-mentioned problem is characterized in that a single crystal silicon carbide substrate serving as a seed crystal and a polycrystalline silicon carbide substrate are stacked, placed in a closed container, and subjected to a high-temperature heat treatment. By interposing an ultra-thin metal silicon melt during the heat treatment between the single-crystal silicon carbide substrate and the polycrystalline silicon carbide substrate, the single-crystal silicon carbide is liquefied on the single-crystal silicon carbide substrate. A liquid-phase epitaxial growth method of single-crystal silicon carbide to be subjected to phase epitaxial growth, wherein the closed vessel is heated to 800 ° C. or more in a high-vacuum preheating chamber having a pressure of 10 ⁻⁵ Pa or less, and the inside of the closed vessel is pressurized. The pressure is reduced to 10 ⁻⁵ Pa or less, and the pressure preliminarily heated to 1400 ° C. to 2,300 ° C. is 10 ⁻² Pa or less, preferably 10 ⁻⁵ Pa or less. After reaching a high vacuum of 10 ^-5 Pa or less, the single-crystal silicon carbide substrate and the polycrystalline silicon carbide substrate are moved to and set in a heating chamber under a rare gas atmosphere in which some inert gas is introduced. It is intended to produce a single-crystal silicon carbide which is heated to 1400 ° C. to 2,300 ° C. for a short time and has no microcrystalline boundaries and has a micropipe defect density of 1 / cm ² or less on the surface.

Since it can be heated to 1400 ° C. to 2,300 ° C. in a short time, single crystal SiC can be formed efficiently. In addition, since there is no fine crystal grain boundary inside the grown crystal and the density of micropipe defects on the surface can be single crystal SiC of 1 / cm ² or less, application to various semiconductor devices is possible. Here, the micropipe defect is also called a pinhole, and is a tubular void having a diameter of several μm or less that exists along the crystal growth direction. The single crystal SiC substrate serving as a seed crystal to be used can be formed on all crystal planes of 4H-SiC and 6H-SiC, but it is preferable to use a (0001) Si plane. The polycrystalline SiC substrate preferably has an average particle diameter of 5 μm to 10 μm and a substantially uniform particle diameter. Therefore, the crystal structure of polycrystalline SiC is not particularly limited, and any of 3C-SiC, 4H-SiC, and 6H-SiC can be used, but 3C-SiC is preferable.

  Further, according to the present invention, at the time of heat treatment, Si penetrates into every corner of the interface between the single-crystal SiC substrate and the polycrystalline SiC substrate due to a capillary phenomenon to form an ultrathin metal Si melt layer. The C atoms flowing out of the polycrystalline SiC substrate are supplied to the single crystal SiC substrate through the Si melt layer, and liquid phase epitaxially grow as single crystal SiC on the single crystal SiC substrate. Therefore, induction of defects can be suppressed from the beginning to the end of growth. Further, since it is not necessary to perform the treatment by immersion in molten Si as in the related art, the amount of Si deposited on the single-crystal SiC substrate and the polycrystalline SiC substrate serving as seed crystals after the heat treatment is extremely reduced. In addition, since an ultrathin metal Si melt is interposed between the single crystal SiC substrate and the polycrystalline SiC substrate during the heat treatment, only the metal Si necessary for epitaxial growth of single crystal SiC is used for liquid phase epitaxial growth of single crystal SiC. Can be used. For this reason, the contact area with the outside is minimized in the thin Si layer during the heat treatment, so that the probability of entry of impurities is reduced, and high-purity single-crystal SiC can be formed.

  Further, in the liquid-phase epitaxial growth method of single-crystal silicon carbide according to the present invention, in the above-described invention, when the closed container is moved to the heating chamber, no temperature difference is provided in the axial direction of the closed container, A temperature gradient is provided in the in-plane direction of the closed container, and the generation of fine crystal grain boundaries is suppressed by arbitrarily controlling the temperature gradient.

Since no temperature difference is provided in the axial direction of the closed container, no temperature difference is formed between the single crystal SiC substrate and the polycrystalline SiC substrate, so that heat treatment can be performed in a thermal equilibrium state, and a metal Si melt can be obtained. Is thin, thermal convection is suppressed. Therefore, induction of defects can be suppressed from the beginning to the end of growth. Further, since nucleation is suppressed during the heat treatment, generation of fine crystal grain boundaries of the formed single crystal SiC can be suppressed. In addition, a simple heat treatment apparatus can be used, and strict temperature control during heating is not required, so that the manufacturing cost can be significantly reduced. In addition, by providing a temperature gradient in the in-plane direction of the closed vessel, by controlling this temperature gradient arbitrarily, during the growth of single crystal SiC, the fine crystal grain boundaries are moved from the high temperature side to the low temperature side of the temperature gradient. As a result, single crystal SiC having a micropipe defect density of 1 / cm ² or less can be formed.

  In the liquid phase epitaxial growth method of single-crystal SiC according to the present invention, in the above-mentioned invention, the closed container is formed of either tantalum or tantalum carbide.

Since the closed container is made of tantalum or tantalum carbide, it is possible to suppress the formation of SiC in the closed container and to reliably set the pressure in the heating chamber to 10 ⁻² Pa or less.

  Further, in the liquid-phase epitaxial growth method of single-crystal SiC according to the present invention, in the above-described invention, the closed container is formed of an upper container and a lower container, and silicon vapor leaks from a fitting portion between the upper container and the lower container. The pressure in the closed container is controlled to be higher than the pressure in the heating chamber to such an extent that the impurities are discharged, so that impurities are prevented from entering the closed container.

With such a structure of the closed container, contamination of the closed container with impurities can be suppressed. As a result, the purity can be reduced to 5 × 10 ¹⁵ / cm ³ or less.

  In the liquid-phase epitaxial growth method of single-crystal SiC according to the present invention, in the above-mentioned invention, a contaminant removing mechanism for removing silicon vapor leaking from the closed vessel is provided in the heating chamber.

  Since a contaminant removing mechanism for removing silicon vapor leaking from the closed vessel is provided in the heating chamber, deterioration of heating means such as a heater provided in the heating chamber due to the silicon vapor can be prevented. Here, as the contaminant removing mechanism, a vacuum pump and other general exhaust means can be used.

  In the liquid-phase epitaxial growth method of single-crystal SiC according to the present invention, in the above-mentioned invention, the surface of the single-crystal SiC has an atomic order step having a minimum unit of three molecular layers, and a wide terrace. The width of the terrace is 10 μm or more.

  Since the terrace width is 10 μm or more, the growth surface does not need to be subjected to surface treatment such as machining after the formation of single crystal SiC. For this reason, it is possible to produce a product without a processing step.

  In the liquid-phase epitaxial growth method of single-crystal SiC according to the present invention, in the above-mentioned invention, the surface is a (0001) Si plane.

  Since the plane orientation of the surface is the (0001) Si plane, the surface energy is lower than that of other crystal planes, and therefore the nucleation energy during growth is higher, and nucleation is less likely to occur. For the above reasons, single crystal SiC having a wide terrace width can be obtained after liquid phase growth. The plane orientation of the surface is not limited to the (0001) Si plane, and it is possible to use all crystal planes of 4H-SiC and 6H-SiC.

  In the liquid phase epitaxial growth method of single crystal SiC according to the present invention, in the above-mentioned invention, the ultrathin metal Si melt has a thickness of 50 μm or less.

  Since the ultrathin metal Si melt interposed between the single crystal SiC substrate and the polycrystalline SiC substrate during the heat treatment is 50 μm or less, preferably 30 μm or less, C dissolved from the polycrystalline SiC substrate becomes a single crystal SiC substrate. It is transported to the surface by diffusion, and the growth of single crystal SiC is promoted. If the ultra-thin metal silicon melt has a thickness of 50 μm or more, the metal silicon melt becomes unstable and the transport of C is hindered, which is not suitable for growing the single crystal SiC according to the present invention.

  According to the present invention, since local liquid phase epitaxial growth can be performed at a high temperature in the same environment as a conventional high-temperature heat treatment environment such as a sublimation method, micropipe defects included in a seed crystal are not inherited, and micropipe defects are not inherited. Occlusion can be performed. In addition, since the growth surface is always in contact with the Si melt, an excess Si state is formed, and the generation of defects due to the shortage of Si is suppressed, and the contact area of the used Si melt with the outside is reduced. Because of the small size, impurities can be prevented from being mixed into the growth surface, and high-quality and high-performance single-crystal SiC having high purity and excellent crystallinity can be grown. Moreover, as compared with the conventional LPE method, the present growth method can be grown at a very high temperature and in a short time, so that the growth rate can be remarkably increased as compared with the conventional LPE method, and a high quality single crystal can be obtained. The growth efficiency of crystalline SiC can be made very high. Furthermore, there is no need to perform strict temperature gradient control during single crystal growth, and a simple apparatus can be used. From these facts, the practical use of single crystal SiC, which is expected to be used as a power device and a semiconductor material for high frequency devices, is excellent in high temperature, high frequency, withstand voltage and environmental resistance compared to existing semiconductor materials such as Si and GaAs. Can be promoted.

  Hereinafter, an embodiment of a liquid crystal growth method for single crystal SiC according to the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic cross-sectional view showing an example of an embodiment of a heat treatment furnace used for a liquid crystal epitaxial growth method of single crystal SiC according to the present invention. In FIG. 1, a heat treatment furnace 1 includes a heating chamber 2, a preheating chamber 3, and a prechamber 4 continuing from the preheating chamber 3 to the heating chamber 2. The closed vessel 5 containing single crystal SiC, seed crystal SiC, and the like is configured to grow single crystal SiC by sequentially moving from the preheating chamber 3 to the front chamber 4 and the heating chamber 2. I have.

  As shown in FIG. 1, in the heat treatment furnace 1, a heating chamber 2, a preheating chamber 3, and a front chamber 4 communicate with each other. For this reason, each chamber can be controlled under a predetermined pressure in advance. Further, by providing a gate valve 7 and the like for each chamber, it is possible to adjust the pressure for each chamber. Thereby, even when the closed container 5 is moved, the inside of the furnace under a predetermined pressure can be moved by the moving means (not shown) without contacting the outside air, so that contamination of impurities can be suppressed.

  The preheating chamber 3 is provided with heating means 6 such as a lamp or a rod heater (in this embodiment, a mode using a lamp is shown) 6, and can be rapidly heated to about 800 to 1000 ° C. Heating furnace. Further, a gate valve 7 is provided at a connection portion between the preheating chamber 3 and the front chamber 4 to facilitate the pressure control of the preheating chamber 3 and the front chamber 4. The sealed container 5 is pre-heated to 800 ° C. or higher in a state where it is placed on the table 8 in the pre-heating chamber 3, and after the pressure adjustment between the pre-heating chamber 3 and the front chamber 4 is completed, Is moved so as to be installed on the elevating type susceptor 9 provided in the apparatus.

The closed container 5 moved to the front chamber 4 is moved from the front chamber 4 to the heating chamber 2 by the vertically moving means 10 shown in part. At this time, the inside of the heating chamber 2 is preliminarily reduced to a predetermined pressure of 10 ^-1 Pa or less, preferably 10 ^-2 Pa or less, more preferably 10 ^-5 Pa or less, by a vacuum pump (not shown), or After reaching a high vacuum at a pressure of 10 ⁻⁵ Pa or less in advance, a slight inert gas is introduced, the atmosphere is set to a rare gas atmosphere of 10 ⁻¹ Pa or less, preferably 10 ⁻² Pa or less. It is preferable that the temperature is set to 2,300 ° C. By setting the state in the heating chamber 2 in this manner, the closed vessel 5 is rapidly moved from 1400 ° C. to 2,300 ° C. by moving the closed vessel 5 from the front chamber 4 into the heating chamber 2. can do. In the heating chamber 2, a reflecting mirror 12 is arranged around the heater 11 so that the heat of the heater 11 is reflected to concentrate on the closed container 5 located inside the heater 11. I have.

  A contaminant removing mechanism 20 is provided inside the heater 11 in the heating chamber 2 for removing Si vapor leaking from the inside of the closed vessel 5 so as not to contact the heater 11. Thereby, it is possible to suppress the heater 11 from reacting with the Si vapor and deteriorating. The contaminant removing mechanism 20 is not particularly limited as long as it removes silicon vapor leaking from the inside of the closed container 5.

  The heating heater 11 is a resistance heating heater made of metal such as tantalum, and includes a base heater 11a provided on the susceptor 9 and an upper heater 11b whose side and upper parts are integrally formed in a cylindrical shape. I have. As described above, since the heater 11 is disposed so as to cover the closed container 5, the closed container 5 can be heated evenly. Note that the heating method of the heating chamber 2 is not limited to the resistance heater shown in the present embodiment, and may be, for example, a high-frequency induction heating method.

  As shown in FIG. 2, the closed container 5 includes an upper container 5a and a lower container 5b, and is formed of either tantalum or tantalum carbide. The play of the fitting portion when fitting the upper container 5a and the lower container 5b is preferably 2 mm or less. This can suppress the entry of impurities into the closed container 5. Further, by setting the play to 2 mm or less, it is possible to control so that the Si partial pressure in the sealed container 5 does not become 10 Pa or less. For this reason, the SiC partial pressure and the Si partial pressure in the closed vessel 5 are increased, thereby contributing to the prevention of sublimation of the single crystal SiC substrate 16, the polycrystalline SiC substrates 14 and 15, and the ultra-thin metal Si melt 17. When the play of the fitting portion at the time of fitting the upper container 5a and the lower container 5b is larger than 2 mm, it is only difficult to control the Si partial pressure in the closed container 5 to a predetermined pressure. However, it is not preferable because impurities may enter the closed container 5 through the fitting portion. As shown in FIG. 2, the closed container 5 is not limited to a square shape, but may be a circular shape.

  Further, the lower container 5b is provided with three support portions 13 as shown in FIGS. The support portion 13 supports a polycrystalline SiC substrate 14 serving as a seed crystal described later. Note that the support portion 13 does not need to be in the form of a pin as shown in this embodiment, but may be in the form of a ring made of, for example, SiC.

  FIG. 3 shows a 6H-type single-crystal SiC substrate 16 serving as a seed crystal installed in the closed container 5 in a state where the upper container 5a and the lower container 5b are fitted to each other, and a polycrystal sandwiching the single-crystal SiC substrate 16 The state of the SiC substrate 15 and the ultra-thin metal Si melt 17 formed therebetween are shown. The ultra-thin metal Si melt 17 is formed at the time of heat treatment, and the source of Si of the ultra-thin metal Si melt 17 is a metal Si on the surface of a single crystal SiC substrate 16 serving as a seed crystal. The method is not particularly limited, such as forming a film to have a thickness of 10 μm to 50 μm by CVD or placing Si powder.

  As shown in FIG. 3, the single-crystal SiC substrate 16, the polycrystalline SiC substrates 14 and 15, and the ultrathin metal Si melt 17 are mounted on a support 13 provided in a lower container 5b constituting the closed container 5. And housed in the closed container 5. Here, the single crystal SiC substrate 16 is cut into a desired size (10 × 10 to 20 × 20 mm) from a single crystal 6H—SiC wafer manufactured by a sublimation method. Further, as the polycrystalline SiC substrates 14 and 15, those cut out to a desired size from SiC used as a dummy wafer in a Si semiconductor manufacturing process manufactured by a CVD method can be used. The surfaces of these substrates 16, 14, and 15 are polished to mirror surfaces, and oils, oxide films, metals, and the like attached to the surfaces are removed by washing or the like. Here, the polycrystalline SiC substrate 14 located on the lower side is for preventing erosion of the single crystal SiC substrate 16 from the closed container 5, and is intended to improve the quality of single crystal SiC grown by liquid phase epitaxial on the single crystal SiC substrate 16. It will contribute.

  Further, in the closed container 5, it can be installed together with a Si piece for controlling sublimation of SiC and evaporation of Si during the heat treatment. By simultaneously installing the Si pieces, they are sublimated during the heat treatment to increase the SiC partial pressure and the Si partial pressure in the closed vessel 5, and the single crystal SiC substrate 16, the polycrystalline SiC substrates 14 and 15, and the ultrathin metal Si melt 17 Contributes to the prevention of sublimation. In addition, the pressure in the sealed container 5 can be adjusted to be higher than the pressure in the heating chamber 2, whereby the Si vapor can be constantly released from the fitting portion between the upper container 5 a and the lower container 5 b, and impurities are sealed. Intrusion into the container 5 can be prevented.

After being set in the preheating chamber 3, the closed container 5 configured as described above is set to 10 ⁻⁵ Pa or less, and a heating means such as a lamp and / or a rod heater provided in the preheating chamber 3. 6 to 800 ° C. or higher, preferably 1000 ° C. or higher. At this time, it is preferable that the inside of the heating chamber 2 is similarly set to 10 ⁻² Pa or less and then heated to 1400 ° C. to 2,300 ° C.

  The sealed container 5 preheated in the preheating chamber 3 opens the gate valve 7 and moves to the susceptor 9 of the front chamber 4, and is heated by the elevating means 10 to 1400 ° C. to 2,300 ° C. It is moved into the room 2. As a result, the closed container 5 is rapidly heated to 1400 ° C. to 2,300 ° C. in a short time within 30 minutes. The heat treatment temperature in the heating chamber 2 may be a temperature at which the metal Si pieces simultaneously placed in the closed vessel 5 can be melted, but it is set to 1400 ° C. to 2,300 ° C. The higher the processing temperature, the higher the wettability between the molten Si and SiC, and the more easily the molten Si penetrates between the single-crystal SiC substrate 16 and the polycrystalline SiC substrates 14 and 15 by the capillary phenomenon. Thereby, an ultrathin metal Si melt 17 having a thickness of 50 μm or less can be interposed between the single crystal SiC substrate 16 and the polycrystalline SiC substrates 14 and 15.

  At this time, by setting the temperature to 1400 ° C. to 2,300 ° C. in a short time as possible, the crystal growth can be completed in a short time, and the efficiency of the crystal growth can be improved.

  The heat treatment time can be appropriately selected so that the generated single crystal SiC has a desired thickness. Here, as the amount of the metal Si serving as the Si source increases, the amount of the metal Si melted during the heat treatment increases, and when the ultrathin metal Si melt has a thickness of 50 μm or more, the metal Si melt becomes unstable, and The transport of C was inhibited, and Si that was not suitable for growing the single crystal SiC according to the present invention and that was not necessary for the formation of the single crystal SiC was melted and accumulated at the bottom of the closed vessel 5 and solidified again after the formation of the single crystal SiC. It is necessary to remove metal Si. For this reason, the size and thickness of the metal Si are appropriately selected according to the size of the single crystal SiC to be formed.

By the way, the growth mechanism of the single crystal SiC will be briefly described. Melt Si penetrates between the single crystal SiC substrate 16 and the upper polycrystalline SiC substrate 15 due to the heat treatment and enters the interface between the two substrates 16 and 15. A metal Si melt layer 17 having a thickness of about 30 μm to 50 μm is formed. The metal Si melt layer 17 becomes thinner to about 30 μm as the heat treatment temperature becomes higher. Then, the C atoms flowing out of the polycrystalline SiC substrate 2 are supplied to the single crystal SiC substrate 16 through the Si melt layer, and liquid phase epitaxial growth (hereinafter referred to as LPE) on the single crystal SiC substrate 1 as a 6H-SiC single crystal. ). As described above, since the space between the single crystal SiC substrate 16 serving as a seed crystal and the polycrystalline SiC substrate 14 is small, no thermal convection is generated during the heat treatment. Therefore, the interface between the formed single crystal SiC and the single crystal SiC substrate 16 serving as a seed crystal becomes very smooth, and no distortion or the like is formed at this interface. Therefore, very smooth single crystal SiC is formed. Further, since nucleation of SiC is suppressed during the heat treatment, generation of fine crystal grain boundaries of the formed single crystal SiC can be suppressed. In the method for growing single-crystal SiC according to the present embodiment, since molten Si penetrates only between single-crystal SiC substrate 16 and polycrystalline SiC substrate 15, other impurities grow in single-crystal SiC. Since there is no intrusion, it is possible to generate single crystal SiC having a high purity of 5 × 10 ¹⁵ / cm ³ or less in the background.

  FIG. 5 is a photomicrograph showing the surface state of single-crystal SiC grown by the method described above. In FIG. 5, (a) shows the surface morphology, and (b) shows the cross section. As shown in FIG. 5, a very flat terrace and a step structure can be observed on the crystal growth surface by the LPE method.

  FIG. 6 is a diagram showing the result of observing this surface with an atomic force microscope (hereinafter, referred to as AFM). As can be seen from FIG. 6, the step heights are 4.0 nm and 8.4 nm, respectively. This is an integral multiple of the height based on three molecular layers of SiC molecules (the height of one SiC molecular layer is 0.25 nm). Thus, it can be seen that the surface is very flat.

Further, as can be seen from the micrograph of the surface morphology in FIG. 5, no micropipe defects are observed on the surface. From these facts, in the single crystal SiC according to the present invention, the density of the micropipe defects formed on the surface is extremely low as 1 / cm ² or less, the width of the terrace formed on the surface is as wide as 10 μm or more, and the single crystal SiC is flat. It can be seen that there are few defects.

Generally, epitaxial growth of a crystal is performed for each molecular layer. However, the single-crystal SiC according to the present embodiment has a surface with a wide terrace of 10 μm or more and a height step of a minimum of three molecular layers. From this, it is considered that step bunching occurred during the crystal growth process. This step bunching mechanism can be explained by the effect of surface free energy during crystal growth. In the single crystal 6H-SiC according to the present embodiment, there are two kinds of stacking cycle directions ABC and ACB in the unit stacking cycle. Therefore, three types of surfaces can be defined as shown in FIG. 7 by assigning numbers 1, 2, and 3 from the layer that is bent in the stacking direction. The energy of each surface is determined as follows (T. Kimoto, et al., J. Appl. Phys. 81 (1997) 3494-3500).
6H1 = 1.33 meV
6H2 = 6.56 meV
6H3 = 2.34 meV
Since the energy varies depending on the surface, the spread speed of the terrace varies. That is, as the terrace has a higher surface free energy on each surface, the growth rate is higher, and step hunting occurs every three periods as shown in FIGS. 7 (a), 7 (b) and 7 (c). Further, in the present embodiment, the number of unbonded hands coming out of the step surface differs every other stage due to the difference in the lamination period (ABC or ACB). Due to the difference, it is considered that further step bunching occurs in units of three molecules. It is considered that the forward speed of one step is slow at one unjoined hand exiting the step, and fast at two unjoined hands. In this way, in 6H-SiC, step bunching proceeds in a height unit of a half integer multiple of the lattice constant, and after growth, the surface of single crystal SiC has a flat step with a height of three molecular layers as a minimum unit and a flat surface. It is thought to be covered with a terrace.

  As described above, the terrace of the single crystal SiC according to the present invention is formed by step bunching. Therefore, the steps are formed intensively near the end of the single crystal SiC. FIGS. 5 and 6 show the end portions of the single-crystal SiC in order to observe the step portions.

  Further, the single crystal SiC in the present embodiment has a growth temperature of 1400 ° C. to 2,300 ° C., which is much higher than the liquid phase growth temperature of the conventional single crystal SiC, and also has a growth temperature of 1400 ° C. to 2300 ° C. in a short time. , 300 ° C. As the growth temperature increases, the concentration of dissolved C in the Si melt formed between the single crystal SiC serving as a seed crystal and the polycrystalline SiC increases. Further, it is considered that the diffusion of C in the Si melt increases as the temperature increases. As described above, since the C source and the seed crystal are very close to each other, a high growth rate of 500 μm / hr can be achieved depending on conditions.

As described above, in the single-crystal SiC according to the present embodiment, the density of micropipe defects on the surface is 1 / cm ² or less, and a wide terrace of 10 μm or more is formed. No surface treatment such as machining is required. Further, since there are few crystal defects and the like, it can be used as a light emitting diode or various semiconductor diodes. In addition, since the growth of the crystal does not depend on the temperature but on the surface energies of the seed crystal and the crystal of the C source, there is no need for strict temperature control in the processing furnace. Significant reduction is possible. Further, since the distance between the single crystal SiC serving as a seed crystal and the polycrystalline SiC serving as a supply source of C is extremely small, thermal convection during heat treatment can be suppressed. Further, since a temperature difference is hardly formed between single crystal SiC as a seed crystal and polycrystalline SiC as a supply source of C, heat treatment can be performed in a thermal equilibrium state.

  In addition, as described above, since the single crystal SiC grows in the plane direction of the crystal surface, the crystal growth direction of the single crystal SiC is controlled by providing a temperature gradient in the plane direction of the closed vessel. It becomes possible to give directionality from a higher side to a lower side. The temperature gradient can be exemplified by a method of providing a temperature difference between the side heaters 11b located on the side wall side of the closed vessel 5 of the heater 11 provided in the heating chamber 2. At this time, by controlling the magnitude of the temperature gradient, the crystal growth rate can be controlled, and the generation of fine crystal grain boundaries on the crystal surface can be suppressed.

  In the present embodiment, 6H-SiC is used as the seed crystal, but 4H-SiC can be used.

  In the present embodiment, (0001) Si is used as the seed crystal, but other seeds such as (11-20) may be used.

  In the single crystal SiC according to the present invention, the size of the single crystal SiC formed by appropriately selecting the size of the single crystal SiC serving as a seed crystal and the size of the polycrystalline SiC substrate serving as a supply source of C is controlled. be able to. Further, since no strain is formed between the formed single crystal SiC and the seed crystal, the single crystal SiC having a very smooth surface can be obtained, so that it can be applied as a surface modified film. is there.

  Furthermore, a large amount of single-crystal SiC can be produced simultaneously by alternately stacking or arranging side-by-side single-crystal SiC as a seed crystal and polycrystalline SiC, which is a supply source of C, by the above-described method. It is.

In the method for producing single-crystal SiC according to the present invention, impurities of a Group III metal such as Al or B are added to the polycrystalline SiC substrate and the metal Si in advance, or nitrogen, By feeding a gas containing an element that controls the conductivity type of SiC, such as Al or B, the p-type and n-type conductivity types of the grown crystal can be arbitrarily controlled.

1 is a schematic cross-sectional view of one embodiment of a heat treatment apparatus used for a liquid crystal epitaxial growth method of single crystal SiC according to the present invention. FIG. 2 is a schematic view of an example of an embodiment of a closed container 5. A 6H-type single-crystal SiC substrate serving as a seed crystal placed in a closed container in which the upper container and the lower container are fitted, a polycrystalline SiC substrate sandwiching the single-crystal SiC substrate, and It is a figure showing the state of the ultra-thin metal Si melt formed. It is a figure showing the state where the substrate was installed in the lower container. It is a figure showing a microscope picture of the surface of the growth layer of single crystal SiC concerning this embodiment. (A) is a figure which shows the surface morphology, (b) shows the micrograph which shows the cross section. FIG. 6 is a diagram showing an AFM image of the surface of the single crystal SiC shown in FIG. 5. (a) is a figure which shows a surface morphology, (b) shows the AFM image which shows the cross section. FIG. 4 is a diagram for explaining a step bunching mechanism in a growth process of single crystal SiC according to the embodiment.

Explanation of reference numerals

DESCRIPTION OF SYMBOLS 1 Heat treatment furnace 2 Heating chamber 3 Preheating chamber 4 Front chamber 5 Closed container 5a Upper container 5b Lower container 6 Heating means 7 Gate valve 8 Table 9 Susceptor 10 Moving means 11 Heater 12 Reflecting mirror

Claims (9)

A single-crystal silicon carbide substrate serving as a seed crystal and a polycrystalline silicon carbide substrate are stacked, placed in a closed container, and subjected to a high-temperature heat treatment, so that the single-crystal silicon carbide substrate and the polycrystalline silicon carbide substrate In the liquid phase epitaxial growth method of single crystal silicon carbide, intervening ultra-thin metal silicon melt during heat treatment, liquid crystal epitaxial growth of single crystal silicon carbide on the single crystal silicon carbide substrate,
Heating said sealed container, with heating to 800 ° C. or higher in advance pressure 10 ^-5 Pa or less preheating chamber, the closed vessel was reduced to below the pressure 10 ^-5 Pa, in advance 1400 ℃ ~2,300 ℃ After moving to a heating chamber under a reduced pressure of 10 ⁻² Pa or less, preferably 10 ⁻⁵ Pa or less, or a rare gas atmosphere into which an inert gas is introduced after reaching a pressure of 10 ⁻⁵ Pa or less in advance. By heating the single-crystal silicon carbide substrate and the polycrystalline silicon carbide substrate to 1400 ° C. to 2,300 ° C. in a short time, the micropipe defect density on the surface where there is no fine crystal grain boundary is 1 / cm ^2. A liquid phase epitaxial growth method of a single crystal silicon carbide for producing the following single crystal silicon carbide.   When the closed container is moved to the heating chamber, a temperature gradient is not provided in the axial direction of the closed container, a temperature gradient is provided in an in-plane direction of the closed container, and the temperature gradient is arbitrarily controlled. 2. The method of claim 1, wherein the formation of fine crystal grain boundaries is suppressed.   3. The liquid phase epitaxial growth method for single-crystal silicon carbide according to claim 1, wherein the closed container is formed of either tantalum or tantalum carbide.   The closed container is formed of an upper container and a lower container, and the pressure in the closed container is higher than the pressure in the heating chamber to the extent that silicon vapor leaks from a fitting portion of the upper container and the lower container. The liquid phase epitaxial growth method of single-crystal silicon carbide according to claim 1, wherein the method controls and prevents impurities from being mixed into the closed vessel.   3. The liquid phase epitaxial growth method of single-crystal silicon carbide according to claim 1, wherein a contaminant removal mechanism for physically adsorbing silicon vapor leaking from the closed vessel is provided in the heating chamber.   3. The single crystal according to claim 1, wherein the surface of the single crystal silicon carbide has an atomic order step using a trimolecular layer as a minimum unit and a wide terrace, and the width of the terrace is 10 μm or more. 4. Liquid phase epitaxial growth of silicon carbide.   9. The method of claim 8, wherein the surface is a (0001) Si plane.   The liquid-phase epitaxial growth method for single-crystal silicon carbide according to claim 1, wherein the ultra-thin metal silicon melt has a thickness of 50 μm or less. A heat treatment apparatus used for the liquid phase epitaxial growth method of the single crystal silicon carbide according to claim 1.