JP5213096B2 - Single phase silicon carbide liquid phase epitaxial growth method, single crystal silicon carbide substrate manufacturing method, and single crystal silicon carbide substrate - Google Patents

Description

  The present invention mainly relates to a method for liquid phase epitaxial growth of silicon carbide (SiC).

  Silicon carbide (SiC) has excellent heat resistance and mechanical strength, is resistant to radiation, can easily control the valence electrons of electrons and holes by adding impurities, and has a wide band gap (6H-type single crystal SiC). About 3.0 eV, 4H type single crystal SiC having about 3.3 eV). Therefore, silicon carbide is said to be able to realize high temperature, high frequency, withstand voltage and environmental resistance that cannot be realized with existing semiconductor materials such as silicon (Si) and gallium arsenide (GaAs). Expectations are growing as a material for semiconductors for devices and high-frequency devices. Further, hexagonal SiC has a lattice constant close to that of gallium nitride (GaN), and is expected as a GaN substrate.

For example, Patent Document 1 discloses that a sublimation recrystallization method (modified Rayleigh method) can be used for the growth of a SiC single crystal. This method will be described. A single-crystal SiC substrate is fixedly arranged as a seed crystal on the low temperature side in the crucible, and a powder containing Si as a raw material is arranged on the high temperature side, and the crucible is placed in an inert atmosphere at 1450 ° C. or higher and 2400 ° C. Heat to a high temperature below ℃. Thereby, the powder containing Si is sublimated, and SiC is recrystallized on the surface of the seed crystal on the low temperature side. In this way, single crystal SiC is grown.
Japanese Patent Laid-Open No. 2005-97040

  However, as pointed out in Patent Document 1, the above-mentioned sublimation recrystallization method (improved Rayleigh method), that is, the physical vapor transport method (Physical Vapor Transport method) is a very high cost production method.

  Semiconductor material wafers other than SiC are manufactured at low cost by growth from a liquid phase, but have not yet been established for SiC. This is because SiC is a non-congruent reaction (the solid phase and the liquid phase do not react directly with the same composition), and the solubility of carbon is very low when Si or an alloy obtained by adding a metal to them is used as a solvent. It is.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a novel method for epitaxially growing SiC from a liquid phase.

Means and effects for solving the problems

  The problems to be solved by the present invention are as described above. Next, means for solving the problems and the effects thereof will be described.

According to a first aspect of the present invention, a carbon feed substrate having a higher free energy than the seed substrate is disposed opposite to a seed substrate made of single crystal silicon carbide, and between the seed substrate and the carbon feed substrate. The single crystal silicon carbide is formed by liquid phase epitaxial growth of single crystal silicon carbide on the surface of the seed substrate by a metastable solvent epitaxy (MSE) method in which an ultrathin molten layer of silicon is interposed as a solvent in a vacuum at a high temperature. A liquid phase epitaxial growth method is provided. The crystal polymorph of the seed substrate is 4H—SiC or 6H—SiC, and the carbon feed substrate is a single crystal silicon carbide substrate having the same crystal polymorph as the seed substrate. The crystal plane orientation of the surface on which the liquid phase epitaxial growth is performed is a (000-1) C plane, and the crystal plane orientation of the surface of the carbon feed substrate facing the seed substrate is a (0001) Si plane, (1-10 n ) Plane, (11-2n) plane, (1-100) plane, or (11-20) plane. The crystal plane orientation of the surface on which liquid phase epitaxial growth is performed is the (0001) Si plane, and the crystal plane orientation of the surface of the carbon feed substrate facing the seed substrate is the (1-10n) plane, (11-2n) plane , (1-100) plane, or (11-20) plane.

  In this MSE method, growth kinetics is controlled only by a concentration gradient without a temperature gradient, so that epitaxial growth can be automatically stabilized and a high-quality epitaxial growth layer can be obtained. In addition, since free energy based on the difference in various chemical potentials can be used as a driving force, it is easy to epitaxially grow silicon carbide on a large area. Furthermore, since it is not necessary to form a temperature gradient in the system, the apparatus configuration for performing the process can be simplified, and the process control is also simplified. In addition, since the solvent thickness is extremely small, carbon diffusion from the carbon feed substrate is good, and it is not necessary to increase the solubility of the carbon in the molten layer (solvent) of silicon by increasing the temperature. Is easy. As described above, the formation cost of the epitaxial growth layer can be reduced.

  In the liquid crystal epitaxial growth method of the single crystal silicon carbide, the seed substrate and the carbon feed substrate are made of a tantalum metal and are provided in a storage container in which the upper and lower sides are fitted so as to expose the tantalum carbide layer to the internal space. It is stored and heat-treated at a temperature of 1500 ° C. or higher and 2300 ° C. or lower in a state where the internal vacuum of the storage container is higher than the external pressure and the vacuum environment in the container is maintained at the saturated vapor pressure of silicon. preferable.

  Thereby, the process of MSE method can be performed favorably and efficiently. In addition, since other impurities can be prevented from entering during the process, a high quality epitaxial growth layer can be obtained.

In the liquid phase epitaxial growth method of the single crystal silicon carbide, the heat treatment is preferably performed under a reduced pressure of 10 ⁻⁴ Pa or less.

  As a result, it is possible to prevent other impurities from entering the storage container during the MSE process, and an epitaxial growth layer with good quality can be obtained.

  Hereinafter, the liquid phase epitaxial growth method of the present invention will be described in detail. The liquid phase epitaxial growth method of the present invention has a part in common with the known solvent transfer method, but the method of the present invention is different from the solvent transfer method in that a temperature gradient is not used. In the method of the present invention, the driving force for solvent movement is the difference in chemical potential between 3C—SiC (carbon feed side) and 4H—SiC (seed side). Hereinafter, this principle will be described using a stable-metastable balanced double phase diagram.

  First, a configuration example when performing the process of the present invention will be described with reference to the schematic diagram of FIG. As shown in FIG. 1, a sandwich structure of SiC and Si is held inside a container 16 which is a TaC crucible. Specifically, a single crystal 4H—SiC substrate 15 as a seed substrate is arranged at the center in the vertical direction, and polycrystalline 3C—SiC substrates 20 and 20 as carbon feed substrates are arranged on the upper and lower sides, respectively. Between the single crystal 4H-SiC substrate 15 and the polycrystalline 3C-SiC substrates 20 and 20, silicon plates 23 and 23 are interposed, respectively.

  In the stacked structure of FIG. 1, the polycrystalline 3C-SiC substrates 20 and 20 are used as raw materials for supplying carbon, that is, the feed side, and the single crystal 4H-SiC substrate 15 is used as a substrate for liquid phase epitaxial growth (seed side). The With this configuration, the container 16 is uniformly heated to 1800 ° C. by a tungsten heater in a high vacuum environment. Then, the silicon plate 23 interposed between the substrates 15 and 20 is melted, and the silicon melt serves as a solvent for moving carbon. The thickness of this solvent is extremely small and is several tens to several hundreds μm. The container 16 is heated for several minutes to a sufficient degree and then cooled.

  FIG. 2 shows a scanning electron microscope image of the cross section of the sample when cooled after the heat treatment for 10 minutes. From FIG. 2, the stacked structure of the polycrystalline 3C-SiC substrate 20, the solidified solvent silicon (silicon melt) 19, the single crystal 4H-SiC epitaxial growth layer 15e, and the single crystal 4H-SiC substrate 15 is shown in this order from the top. It turns out that it is. In particular, it can be observed that 4H—SiC is epitaxially grown on the 4H—SiC substrate 15 by about 25 μm. Since the sample 4H-SiC substrate 15 is doped with nitrogen in advance, the single crystal 4H-SiC substrate 15 and the epitaxial growth layer 15e can be clearly distinguished in the microscopic image of FIG.

  As shown in FIG. 2, the polycrystalline 3C-SiC substrate 20 was more dense before the epitaxial growth, but is preferentially dissolved from the interface and is observed to be sparse after the heat treatment. During epitaxial growth, a portion of the liquid silicon 19 serves as a solvent for supplying carbon from the polycrystalline 3C—SiC substrate 20 on the feed side to the single crystal 4H—SiC substrate 15 on the seed side.

  FIG. 2 also shows the concentration profile of the wavelength dispersion X-ray of carbon. As shown by this profile, the limit of the carbon concentration in the solvent silicon 19 is extremely low, but since the thickness of the solvent is extremely small, a sufficient amount of carbon can be diffused for crystal growth.

  In addition to the sample configuration shown in FIG. 1, the experiment was also performed in a sample configuration in which the positional relationship between the polycrystalline 3C-SiC substrate 20 and the single crystal 4H-SiC substrate 15 is upside down. Similarly, epitaxial growth of 4H—SiC occurred. Therefore, an unintended temperature gradient is generated in the system, which cannot be considered as a driving force in this experiment.

  The driving force of this liquid phase epitaxial growth process is a concentration gradient, as in the case of alum crystal growth experiments conducted in elementary school science classes. Before explaining the driving force of the process, first, a solvent moving method (Traveling Solvent method) having a similar apparatus configuration will be described with reference to FIG.

  In the solvent transfer method, as shown in FIG. 3A, a laminated structure in which a thin Si layer is sandwiched between the SiC feed side and the seed side is heated from above so as to have a temperature gradient perpendicular to the Si layer. Since the interface on the feed side has a temperature of T + ΔT, the solubility of SiC in Si is X + ΔX%, as can be seen from the Si—C system phase diagram of FIG. On the other hand, the solubility limit at the temperature T at the seed side interface is X%. In the drawing, the solubility is exaggerated to a higher concentration.

  Due to this concentration gradient, excess SiC is dissolved from the interface on the feed side, diffuses into the liquid Si solvent, and precipitates on the interface on the seed side. Therefore, the liquid Si layer moves from the bottom to the top on the feed side. Thus, the driving force for moving the solvent in the solvent transfer method is a concentration gradient obtained from the temperature gradient.

  On the other hand, in the process of the present invention, the temperature is kept constant both spatially and temporally during crystal growth. The driving force in this system is the metastability of 3C-SiC on the feed side. This is derived from the Si—C stable / metastable equilibrium double phase diagram schematically showing the carbon concentration and temperature range in which each phase exists, schematically shown in FIG. The double phase diagram is familiar in the metallurgy like the Fe-C system, and generally appears in a system including a metastable phase.

As shown in FIG. 4A, when the liquid of Si is Si _L and the solid of Si is Si _S , the metastable eutectic temperature of Si _L → Si _S + SiC _3C is stable from Si _L → Si _S + SiC _4H . The temperature is lower than the eutectic temperature. FIG. 4B schematically shows a corresponding free energy concentration diagram. The solubility limit of each phase is obtained by the common tangent of the free energy of the coexisting phase, as shown in FIG.

At temperature T, the solubility of metastable 3C—SiC, that is, the metastable solid solubility limit, is C ^3C , and the corresponding liquidus line is indicated by the broken line in FIG. The solubility of another stable 4H—SiC, that is, the stable solid solubility limit is C ^4H , which corresponds to the liquidus shown by the solid line in FIG. Therefore, a concentration gradient is obtained in the Si thin film sandwiched between 3C—SiC and 4H—SiC. A schematic profile of this concentration gradient is shown in FIG.

  FIG. 5A is a concept showing how carbon atoms C move from the surface of the feed-side 3C-SiC substrate to the seed-side 4H-SiC substrate by the free energy driving force due to the difference between the stable and metastable equilibrium chemical potentials. FIG. FIG. 5B is a Si—C double state diagram showing the carbon concentration and temperature range where each phase exists.

  When the concentration of the solvent Si in contact with 3C-SiC on the feed side is lower than the metastable liquidus line drawn with a broken line, that is, the metastable solid solubility limit, as indicated by an arrow in FIG. The 3C-SiC substrate is eluted and supplied with carbon. This carbon is diffused by the concentration gradient existing in the solvent, and is supplied onto the 4H—SiC substrate on the seed side. Precipitation occurs when the concentration of the solvent Si in contact with 4H—SiC on the seed side is higher than the stable liquidus line drawn with a solid line in FIG.

  FIG. 6A is a diagram schematically showing changes in the concentration profile during the process. FIG. 6B is a Si—C-based double phase diagram showing the carbon concentration and temperature range in which each phase exists.

  The concentration profile at the start of the process is shaped like a well, as shown by the solid line in FIG. In the initial stage immediately after the start of the process, elution occurs because the carbon solid solubility of the Si solvent in contact with the 3C-SiC substrate on the feed side is lower than the metastable solid solubility limit. This also applies to the seed-side 4H—SiC substrate. Since the carbon solid solubility of the Si solvent in contact therewith is lower than the stable solid solubility limit at the beginning of the process, elution occurs. The density profile at this time is drawn by a one-dot chain line in FIG. As a result, the surface of the seed side 4H—SiC substrate is washed, and the substrate is activated.

  As time elapses, elution proceeds and the carbon concentration in the solvent Si increases. The carbon concentration of the solvent Si in contact with the 3C-SiC substrate on the feed side is in the metastable solid solubility limit, and the carbon concentration of the solvent Si in contact with the 4H-SiC substrate on the seed side is in the stable solid solubility limit and is between them. The solvent Si has a concentration gradient indicated by a dotted line in FIG. This concentration gradient drives elution of the feed side 3C-SiC substrate, carbon diffusion in the solvent Si, and precipitation of the seed side 4H-SiC substrate, and crystal growth proceeds.

FIG. 7 is a diagram for explaining the principle of Ostwald growth in which unstable fine grains disappear and larger grains are known as a physical phenomenon based on a principle very similar to the principle of the present invention. FIG. 7A is a free energy concentration diagram, in which the free energy of the solvent (G ^α ), the free energy of the precipitated particles with a small particle size (G ^β (S)), and the free energy of the precipitated particles with a large particle size ( G ^β (L)).

The difference in free energy due to the difference in particle size is manifested by the Gibbs-Thomson effect due to the interfacial energy. The solute concentration of the solvent in equilibrium with the precipitated particles having a small particle size is x _α (S) from the common tangent, and the solute concentration of the solvent in equilibrium with the precipitated particles having a large particle size is x _α (L).

In such a system in which precipitated particles having different particle diameters and a solvent coexist, a concentration profile as shown in FIG. 7B is shown. The solute concentration of the solvent in contact with the precipitated particles having a small particle size is x _α (S), and the solute concentration of the solvent in contact with the precipitated particles having a large particle size is x _α (L). Due to this concentration gradient, the solute is eluted from the precipitated particles having a small particle diameter, and this solute diffuses in the solvent and is supplied to the precipitated particles having a large particle diameter. As a result, the precipitated grains having a small particle size disappear, and the precipitated grains having a large particle size grow.

  When the polycrystalline SiC substrate 20 is installed on the feed side as in the case of FIG. 1, the tips of the polycrystalline grains are bent, corresponding to the precipitated grains having a small grain size in the Ostwald growth. On the other hand, the single-crystal SiC substrate 15 on the seed side is flat and corresponds to large precipitated grains with infinite curvature. This difference in curvature induces a difference in free energy, drives diffusion of solute from the feed-side polycrystalline SiC substrate 20 to the seed-side single-crystal SiC substrate 15, and the seed-side single-crystal SiC is based on the same principle as the Ostwald growth. The substrate 15 grows.

  The present inventor has named the process of the present invention described above as a metastable solvent epitaxy method (Metastable Solvent Epitaxy Method). Therefore, the name of the metastable solvent epitaxy method (abbreviation MSE method) is used also in this specification. In this metastable solvent epitaxy method, a carbon feed substrate having a higher free energy than the seed side is arranged as a feed side facing a seed substrate of single crystal SiC on the seed side, and the thickness is extremely small between both substrates. By performing heat treatment in a vacuum high temperature environment with a Si melt layer as a solvent, a concentration gradient (concentration gradient not based on a temperature gradient) generated in the Si melt layer based on the difference in free energy is used as a driving force. In this method, single crystal SiC is grown on a substrate by liquid phase epitaxial growth.

  The factors that become the driving force of liquid phase epitaxial growth in this MSE method are summarized as follows.

  The first is the difference in chemical potential of the metastable phase. When a 6H-SiC substrate is used as the seed side, the substrates that can be the feed side are [1] graphite, [2] amorphous SiC, and [3] single crystal 3C-SiC, in order of increasing free energy. [4] Single crystal 4H—SiC. When a 4H-SiC substrate is used as the seed side, the substrates that can be the feed side are [1] graphite, [2] amorphous SiC, and [3] single crystal 3C-SiC, in order of increasing free energy. It is.

  The second is the difference in chemical potential of the interface curvature, which is the Ostwald growth that has been known for a long time. When the substrates are listed in order of increasing free energy, they are [1] polycrystalline 3C-SiC (small particle size), [2] polycrystalline 3C-SiC (large particle size), and [3] polycrystalline 4H-SiC. Further, as described above, the polycrystalline SiC substrate has a larger free energy than the single crystal SiC substrate.

  The third is the difference in chemical potential of the interface orientation. When representative plane orientations in single crystal 4H—SiC or single crystal 6H—SiC are listed in order of increasing free energy, [1] (11-20) plane, [2] (1-100) plane, [3] ( 11-2n) plane, [4] (1-10n) plane, and [5] (0001) plane. Further, there is a difference in chemical potential between the Si surface and the C surface existing on the front and back surfaces of the single-crystal SiC substrate surface. In order of increasing free energy, [1] (0001) Si surface, [2] (000-1) C plane. The (0001) Si face, (000-1) C face, (1-100) face, and (11-20) face of hexagonal SiC are shown in FIGS. 8A to 8C.

  As described above, the MSE process according to the present invention provides the free energy due to the difference in the chemical potential of the metastable phase, the chemical potential of the interface curvature, and the chemical potential of the interface orientation. Since it can be used, there is no difficulty in epitaxially growing SiC in a large area, and it is possible to manufacture a large-diameter wafer in combination with the simplicity of the apparatus.

  In addition, the MSE method of the present invention is characterized in that there is no temperature gradient both spatially and temporally during crystal growth as compared with the solvent transfer method described above. For example, one of the major causes of the appearance of interface instabilities and polycrystals in the solvent transfer method described above is so-called compositional supercooling, and this compositional supercooling is caused by a failure in controlling the temperature gradient and concentration gradient. In this respect, the MSE method has no temperature gradient and the growth kinetics is controlled only by the concentration gradient, so that the epitaxial growth can be automatically stabilized.

  The MSE method of the present invention is also characterized in that the liquid Si solvent is extremely thin. While carbon diffuses in the liquid Si solvent, for example, as can be seen from the stable state diagram of FIG. 5B, the solvent is unstable because carbon is supersaturated. Therefore, if the thickness of the solvent is large, an opportunity to nucleate other than the seed side substrate is likely to occur. Therefore, the liquid Si solvent must be thin to suppress nucleation.

  In the MSE method, since the thickness of the liquid Si solvent is extremely small, convection in the solvent hardly occurs during the process. Further, since the solvent is a thin film, a sufficient amount of carbon can be diffused satisfactorily from the carbon feed substrate side into the Si melt layer having a low carbon solubility limit, and SiC can be smoothly liquid phase epitaxially grown.

  Further, in the MSE method of the present invention, as described above, a sufficient amount of carbon can be diffused from the carbon feed substrate side into the Si molten layer, so that it is not necessary to raise the temperature and increase the solubility of carbon in the Si molten layer. Therefore, it is easy to lower the process temperature. In addition, since the thickness of the solvent is small, the area where the Si molten layer is exposed to vacuum can be reduced, and the volatilization amount of the Si molten layer can be favorably reduced, coupled with the fact that the process can be lowered in temperature.

  FIG. 9A shows a model diagram of the above-described solvent transfer method, and FIG. 9B shows a model diagram of the MSE method of the present invention. As shown in FIG. 9A, the solvent transfer method is a method in which epitaxial growth is performed by positively utilizing a temperature gradient (temperature field). On the other hand, the MSE method of the present invention is an isothermal process and uses a concentration gradient (concentration field) due to a difference in free energy.

  Next, the control of carbon diffusion in the MSE method will be described. That is, as schematically shown by an arrow in FIG. 9B, in the MSE method of the present invention, a portion where the feed side and the seed side are brought close to each other (a portion where the liquid Si solvent is thin) is separated ( Compared with the thick portion of the liquid Si solvent, carbon is diffused more from the feed side.

  In addition, in the MSE method, it is expected that liquid phase epitaxial growth can be controlled by controlling the diffusion of carbon by variously combining substrates or members having different free energies.

  For example, FIG. 9C shows a layout in which substrates having the same free energy face each other. In this case, no carbon diffusion occurs and liquid phase epitaxial growth is not performed. On the other hand, FIG. 9D shows a layout in which substrates having the same free energy are opposed to each other and a small member having a lower free energy than that of the substrate is installed on the surface of one substrate. In this case, as indicated by the arrows, carbon diffuses from both substrates facing each other and precipitates on the small member side.

  FIG. 9E shows a layout in which a small member having a higher free energy is placed on a substrate having a lower free energy, and a substrate having a free energy equal to the smaller member is opposed to the substrate. In this case, as indicated by the arrows, carbon diffuses from the substrate and the small member on the higher free energy side and is deposited on the substrate having the lower free energy.

  FIG. 10 is a schematic conceptual diagram showing state transition and free energy change in the MSE process. FIG. 10 shows a case where a polycrystalline 3C-SiC substrate 20 is used on the feed side and a single crystal 4H-SiC substrate 15 (or 6H-SiC substrate) is used on the seed side, and free energy in each step of the MSE process. The transition is shown.

  In the MSE process, the carbon state is roughly divided into a crystal state crystallized on the feed-side polycrystalline SiC substrate 20, a dissolved state dissolved in the Si melt 19, and the surface of the seed-side single-crystal SiC substrate 15. The surface adsorption state adsorbed on the seed and the crystal state of crystal growth on the single-crystal SiC substrate 15 on the seed side can be taken. The free energy decreases in the order of the feed-side crystal state, the dissolved state, the surface adsorption state, and the seed-side crystal state described above, and this is the driving force that causes the state transition in the MSE method.

  The carbon state transition in the MSE process will be described with reference to FIG. That is, carbon is first eluted from the crystalline state crystallized on the polycrystalline 3C-SiC substrate 20 on the feed side into the solvent silicon 19 and enters a dissolved state (supply process). The dissolved carbon diffuses due to the concentration gradient of the solvent silicon 19 and moves to the seed side (transport process). On the surface of the single-crystal SiC substrate 15 on the seed side, carbon dissolved in the solvent silicon 19 becomes a surface adsorption state by desolvation, and further shifts to a crystal state to become an epitaxial growth layer 15e (surface kinetic process). .

  Next, an example of a heating furnace as a heat treatment apparatus suitable for performing the MSE process of the present invention will be described with reference to the schematic cross-sectional view of FIG.

  As shown in FIG. 11, the heating furnace 1 includes a main heating chamber 2, a preheating chamber 3, and a front chamber 4 in a portion following the preheating chamber 3 to the main heating chamber 2 as main portions. With this configuration, the container (heat treatment container) 16 in which the single crystal SiC substrate 15 or the like is stored sequentially moves from the preheating chamber 3 to the front chamber 4 and the main heating chamber 2, so that the single crystal SiC substrate 15 can be moved in a short time. The heating can be performed at a predetermined temperature (1500 ° C. to 2300 ° C., preferably 1600 ° C. to 2100 ° C., more preferably 1700 ° C. to 1900 ° C., for example, 1800 ° C.).

  In this heating furnace 1, as shown in FIG. 11, the connecting portion between the main heating chamber 2 and the front chamber 4 and the connecting portion between the front chamber 4 and the preheating chamber 3 are each partitioned with a communication portion. ing. For this reason, each of the chambers 2, 3, and 4 can be controlled under a predetermined pressure in advance. Further, if necessary, by providing a gate valve 7 for each chamber, the inside of the furnace under a predetermined pressure can be appropriately adjusted without touching the outside air when the container 16 containing the single crystal SiC substrate 15 or the like is moved. The moving means (not shown) can be moved, and contamination of impurities can be suppressed.

The preheating chamber 3 is provided with a halogen lamp 6 as preheating means. With this configuration, it is possible to rapidly heat to a predetermined range of temperature (for example, within a range of about 800 ° C. to 1000 ° C.) under a reduced pressure of about 10 ⁻² Pa or less. As described above, the gate valve 7 is provided at the connecting 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 container 16 in which the single crystal SiC substrate 15 or the like is stored is preheated to about 800 ° C. (a temperature lower than the temperature at the time of main heating described later) while being placed on the table 8 in the preheating chamber 3. The After that, pressure adjustment is performed between the preheating chamber 3 and the front chamber 4, and when the adjustment is completed, the container 16 is transported by a transport device (not shown) and is a liftable type provided in the front chamber 4. Placed on the susceptor 9.

The container 16 that has moved to the front chamber 4 is moved from the front chamber 4 to the main heating chamber 2 together with the susceptor 9 by the elevating type moving device 10. The main heating chamber 2 is preliminarily adjusted under a reduced pressure of about 10 ⁻⁴ Pa by a vacuum pump, and the temperature is adjusted by the heater 11 so as to reach a desired temperature (for example, 1800 ° C.).

The pressure environment of the main heating chamber 2 is preferably a vacuum of about 10 ⁻⁴ Pa or less as described above, but may be a vacuum of about 10 ⁻² Pa or less, for example. Further, for example, after a vacuum of about 10 ⁻² Pa or less, preferably about 10 ⁻⁴ Pa or less, a rare gas atmosphere into which some inert gas is introduced may be used.

  The state of the main heating chamber 2 is set in this way, and the container 16 is moved to the desired temperature by moving the container 16 from the front chamber 4 into the main heating chamber 2 at a high speed. It can be heated rapidly in a short time.

  In the main heating chamber 2, a reflecting mirror 12 is installed around the heater 11. The reflecting mirror 12 reflects the heat from the heater 11 so that the heat is concentrated on the single crystal SiC substrate 15 side located in the heater 11. The reflecting mirror 12 is preferably formed of gold-plated refractory metal such as W, Ta or Mo, or high heat resistant carbide such as WC, TaC or MoC.

  Further, a window 17 is provided in the main heating chamber 2, and the internal temperature of the main heating chamber 2 can be measured by an infrared radiation thermometer 18 installed outside the main heating chamber 2.

  The moving device 10 includes a convex stepped portion 21, while the heating chamber 2 includes a concave stepped portion 22. When the moving device 10 is driven and the container 16 is moved from the front chamber 4 to the main heating chamber 2, the convex stepped portion 21 is fitted to the concave stepped portion 22, and the fitting portion 25 is formed. An unillustrated seal member (for example, an O-ring) is provided at each step portion of the convex stepped portion 21, and the fitting portion 25 is sealed when the container 16 is moved to the main heating chamber 2. And it is comprised so that this heating chamber 2 can be sealed.

  A contaminant removal mechanism 29 is provided inside the heater 11 of the main heating chamber 2. The contaminant removal mechanism 29 removes impurities discharged out of the container 16 from the single crystal SiC substrate 15 or the like during the heat treatment so as not to come into contact with the heater 11. Thereby, it is possible to prevent the heater 11 from being deteriorated by reacting with the impurities. The contaminant removal mechanism 29 is not particularly limited as long as it can adsorb impurities discharged from the single crystal SiC substrate 15 or the like.

  The heater 11 is a resistance heater made of metal such as W or Ta, and includes a base heater 11a installed on the susceptor 9 side and an upper heater 11b provided on the main heating chamber 2 side. . When the container 16 rises and moves to the main heating chamber 2 side together with the base heater 11a by the moving device 10, the container 16 is surrounded by the heater 11 as shown by a chain line. With such a layout of the heater 11, it is possible to control the temperature distribution in the heating region to be uniform with high accuracy in combination with the reflector 12 described above. As a result, the container 16 can be heated uniformly, and an unintended temperature gradient can be prevented from occurring inside the container 16. Note that the heating method of the main heating chamber 2 is not limited to the resistance heater, and for example, a high frequency induction heating type can be adopted.

  Next, the container 16 used when performing liquid phase epitaxial growth by the MSE method of this embodiment is demonstrated, referring FIG. FIG. 12 is a perspective view of the container with the upper and lower containers removed.

  The aforementioned container 16 includes an upper container 16a and a lower container 16b as shown in FIG. Although the shape of the container 16 is substantially hexahedral as shown in the figure, this is an example, and may be configured in a cylindrical shape, for example. The upper container 16a and the lower container 16b are made of tantalum metal, and the entire surface thereof is covered with a tantalum carbide layer.

  Then, as shown in FIG. 13, a sandwich structure including the single crystal SiC substrate 15 is disposed in the container 16. This sandwich structure is substantially the same as the structure shown in FIG. 1, and a polycrystalline SiC substrate 20 on the feed side is arranged above and below a single crystal SiC substrate 15 on the seed side. In the embodiment shown in FIG. 13, the crystal polymorph of the single crystal SiC substrate 15 is 4H—SiC, but is not limited thereto. A silicon plate 23 is interposed between the single crystal SiC substrate 15 and the polycrystalline SiC substrate 20. In addition, the code | symbol 31 of FIG. 13 is the said tantalum carbide layer which has covered the surface of the upper container 16a and the lower container 16b.

  As the single crystal SiC substrate 15 on the seed side, a single crystal 4H—SiC substrate is used in the present embodiment. However, for example, a 6H—SiC substrate may be used. Further, the polycrystalline SiC substrate 20 on the feed side uses a polycrystalline 3C-SiC substrate in this embodiment, but another substrate may be used. As long as the seed side substrate and the feed side substrate are selected so as to express the difference in height of the chemical potential as described above, any combination can be adopted.

  Silicon pellets 14 are arranged at appropriate positions in the container 16. With this configuration, the silicon pellets 14 are evaporated during the heat treatment, and a Si atmosphere can be formed inside the container 16. A spacer 13 is interposed between the sandwich structure described above and the inner bottom surface of the lower container 16b.

  In the above storage state, the container 16 is set in the heating furnace 1 and heated. In addition, when performing MSE method, it is not limited to the board | substrate arrangement | positioning example of FIG. 13, Other various board | substrate arrangement | positionings can be employ | adopted. Moreover, the silicon pellet 14 installed in FIG. 13 can be omitted.

An example of temperature control for heat treatment is shown in FIG. As shown in FIG. 14, in the process of the present embodiment, the temperature of the preheating chamber 3 of the heating furnace 1 is raised to about 800 ° C. in advance, and the temperature of the main heating chamber 2 is set to about 1800 in advance. Raise to ℃. Then, as shown in FIG. 13, the container 16 containing the single crystal SiC substrate 15 and the polycrystalline SiC substrate 20 is inserted into the preheating chamber 3 and heated for several minutes to several tens of minutes (preheating). Thereafter, as described above, the lower container 16b is moved to the main heating chamber 2 together with the single crystal SiC substrate 15, and heated at a temperature of about 1800 ° C. for several minutes to several tens of minutes (main heating). At this time, the main heating chamber 2 is maintained at a vacuum of about 10 ⁻² Pa or less, preferably about 10 ⁻⁴ Pa or less. Thereafter, the container 16 and the single crystal SiC substrate 15 are returned to the preheating chamber 3 where the heating has been stopped, and are naturally cooled and taken out.

  In addition, it is preferable that the play of a fitting part when the upper container 16a and the lower container 16b are fitted together as shown in FIG. 13 is about 2 mm or less. As a result, a substantially sealed state is realized, and in the heat treatment in the main heating chamber 2, the Si pressure in the container 16 is increased to a pressure higher than the external pressure (pressure in the main heating chamber 2). Intrusion into the container 16 through this fitting portion can be prevented.

  Further, as described above, the surface of the container 16 of the present embodiment is covered with the tantalum carbide layer 31, and the tantalum carbide layer 31 is exposed to the internal space of the container 16. Therefore, as long as the high-temperature treatment is continued under vacuum as described above, the container 16 has a function of continuously adsorbing and taking in carbon molecules from the surface of the tantalum carbide layer 31. In this sense, it can be said that the container 16 of the present embodiment has a carbon molecule adsorption ion pump function (ion getter function).

  By the above heat treatment, the silicon plate 23 is melted to form an extremely thin (for example, a thickness of 10 μm to 1000 μm) Si melt layer between the single crystal SiC substrate 15 and the polycrystalline SiC substrate 20. By this Si melt layer acting as a solvent, a liquid crystal epitaxial growth layer 15e of single crystal SiC by the MSE method can be formed on the surface of the single crystal SiC substrate 15 on the seed side. Thereby, it is possible to obtain a single crystal silicon carbide substrate which is flat at the atomic level and does not have micropipes or crystal defects.

  FIG. 15A to FIG. 15C show scanning electron microscope images of sample cross sections after performing the MSE process of the present invention. FIG. 15A shows a case where single crystal 4H—SiC is used as a seed substrate and polycrystalline 3C—SiC is used as a carbon feed substrate.

  FIG. 15B1 and FIG. 15B2 both show the case where single crystal 4H—SiC is used as the seed substrate and single crystal 3C—SiC is used as the carbon feed substrate. However, in FIG. 15 (b1), epitaxial growth is performed on the Si surface of single crystal 4H—SiC, and in FIG. 15 (b2), epitaxial growth is performed on the C surface.

  FIG. 15C shows the case where single crystal 6H—SiC is used as the seed substrate and single crystal 4H—SiC is used as the carbon feed substrate.

  15A to 15C, it can be observed that an epitaxial growth layer is formed on the surface of the seed substrate.

  FIG. 16 is an AFM micrograph (range 10 μm × 10 μm) of the surface of the epitaxial growth layer obtained by the MSE process of the present invention. As shown in FIG. 16, the surface of the epitaxial growth layer formed by the MSE method of the present invention can be extremely flattened. Specifically, the epitaxial growth layer has a surface flatness in the sub-nano order (less than 1 nm), that is, an atomic level, and can realize a surface average roughness of 1.0 nm or less. Further, the surface of the epitaxial growth layer can realize a surface shape having a step height of 0.5 nm or less (that is, the unit cell length with respect to the stacking order direction when the crystal polymorph is 4H—SiC) or less.

  As described above, the single crystal SiC substrate on which a high-quality epitaxial growth layer is formed by the MSE process of the present invention is suitable for use as, for example, a light-emitting diode, various diodes, or an electronic device.

  Although the preferred embodiment of the present invention has been described above, the above configuration can be modified as follows, for example.

  The temperature of the preheating chamber 3 can be changed to be preheated at a temperature higher or lower than that at 800 ° C.

  The heat treatment is not limited to the heating furnace 1 having the configuration shown in FIG. 1, and can be performed by a heat treatment apparatus having another configuration.

The schematic cross section which shows the structural example when performing the liquid phase epitaxial growth process of this invention. The figure which shows the scanning electron microscope image and carbon concentration profile of the sample cross section after liquid phase epitaxial growth. FIG. 3A is a model diagram illustrating the solvent transfer method. FIG. 3B is a schematic state diagram of the Si—C system showing the carbon concentration and temperature range where each phase exists. FIG. 4A is a stable and metastable equilibrium double phase diagram of the Si—C system. FIG. 4B is a free energy concentration diagram corresponding to the metastable equilibrium double phase diagram. FIG.4 (c) is a figure which shows the typical profile of the concentration gradient of Si solvent. FIG. 5A is a concept showing how carbon atoms C move from the surface of the feed-side 3C-SiC substrate to the seed-side 4H-SiC substrate by the free energy driving force due to the difference between the stable and metastable equilibrium chemical potentials. Figure. FIG.5 (b) is a Si-C type double state diagram showing the carbon concentration and temperature range where each phase exists. FIG. 6A is a diagram schematically showing changes in the concentration profile in the course of the process. FIG. 6B is a Si—C double state diagram showing the carbon concentration and temperature range in which each phase exists. FIG. 7A is a free energy-concentration diagram illustrating the principle of Ostwald growth. FIG. 7B is a diagram showing a concentration profile in a system in which precipitated particles having different particle diameters and a solvent coexist. FIG. 8A is a view showing a (0001) Si plane and a (000-1) C plane in single crystal SiC having a hexagonal crystal structure. FIG. 8B shows the (1-100) plane. FIG. 9C shows the (11-20) plane. FIG. 9A is a model diagram of the solvent transfer method. FIG. 9B is a model diagram of the metastable solvent epitaxy method. FIG. 9C to FIG. 9E are model diagrams for explaining the behavior of carbon diffusion when various free energy substrates and small members are combined on the feed side and the seed side. The typical conceptual diagram which shows the state transition and change of free energy in a MSE process. The schematic cross section which shows an example of the heating furnace which performs the surface planarization method which concerns on one Embodiment of this invention. The perspective view which shows the structure of the container set to a heating furnace. Sectional drawing which shows the example of board | substrate arrangement | positioning in a container in the case of performing an MSE process. The graph which shows the temperature control example of the heating furnace in the case of performing an MSE process. FIG. 15A shows a scanning electron microscope image of a sample cross section when single crystal 4H—SiC is used as a seed substrate and polycrystalline 3C—SiC is used as a carbon feed substrate. FIGS. 15B1 and 15B2 are diagrams showing scanning electron microscope images of a sample cross section when single crystal 4H—SiC is used as a seed substrate and single crystal 3C—SiC is used as a carbon feed substrate. FIG. 15C shows a scanning electron microscope image of a sample cross section when single crystal 6H—SiC is used as a seed substrate and single crystal 4H—SiC is used as a carbon feed substrate. The figure which shows the AFM microscope image of the liquid phase epitaxial growth film | membrane surface.

Explanation of symbols

1 Heating furnace (heat treatment equipment)
2 heating chamber 3 preheating chamber 4 front chamber 5 single crystal SiC substrate 6 halogen lamp 7 gate valve 8 table 9 susceptor 10 moving means 11 heating heater 12 reflector 13 spacer 14 silicon 15 single crystal SiC substrate (seed substrate)
15e Epitaxial growth layer 16 Container 19 Solvent silicon (Si molten layer)
20 Polycrystalline SiC substrate (carbon feed substrate)
23 Silicon plate 29 Pollutant removal mechanism 31 Tantalum carbide layer

Claims (4)

A carbon feed substrate having a higher free energy than the seed substrate is disposed opposite to the seed substrate made of single crystal silicon carbide, and an ultrathin silicon melt layer is interposed between the seed substrate and the carbon feed substrate as a solvent. A liquid crystal epitaxial growth method of single crystal silicon carbide, wherein liquid crystal epitaxial growth of single crystal silicon carbide on the surface of the seed substrate is performed by a metastable solvent epitaxy (MSE) method in which heat treatment is performed in a vacuum high temperature environment ,
The crystal polymorph of the seed substrate is 4H—SiC or 6H—SiC, and the crystal plane orientation of the surface on which liquid phase epitaxial growth is performed in this seed substrate is a (000-1) C plane,
The carbon feed substrate is a single crystal silicon carbide substrate having the same crystal polymorph as the seed substrate, and the crystal plane orientation of the surface of the carbon feed substrate facing the seed substrate is a (0001) Si plane, (1-10 n ) Plane, (11-2n) plane, (1-100) plane, or (11-20) plane, and a liquid phase epitaxial growth method of single crystal silicon carbide.   A carbon feed substrate having a higher free energy than the seed substrate is disposed opposite to the seed substrate made of single crystal silicon carbide, and an ultrathin silicon melt layer is interposed between the seed substrate and the carbon feed substrate as a solvent. A liquid crystal epitaxial growth method of single crystal silicon carbide, wherein liquid crystal epitaxial growth of single crystal silicon carbide on the surface of the seed substrate is performed by a metastable solvent epitaxy (MSE) method in which heat treatment is performed in a vacuum high temperature environment,
  The crystal polymorph of the seed substrate is 4H—SiC or 6H—SiC, and the crystal plane orientation of the surface on which liquid phase epitaxial growth is performed in this seed substrate is a (0001) Si plane,
  The carbon feed substrate is a single crystal silicon carbide substrate having the same crystal polymorph as the seed substrate, and the crystal plane orientation of the surface of the carbon feed substrate facing the seed substrate is a (1-10n) plane, (11− A method for liquid phase epitaxial growth of single crystal silicon carbide, characterized in that it is a 2n) plane, a (1-100) plane, or a (11-20) plane. Claim 1 or a liquid phase epitaxial growth method of a single crystal silicon carbide according to 2,
The seed substrate and the carbon feed substrate are made of tantalum metal and stored in a storage container fitted with upper and lower portions so that the tantalum carbide layer is exposed to the internal space, and the internal pressure of the storage container is higher than the external pressure. A liquid phase epitaxial growth method of single crystal silicon carbide, characterized in that heat treatment is performed at a temperature of 1500 ° C. or higher and 2300 ° C. or lower in a state where the vacuum environment in the container is maintained at a saturated vapor pressure of silicon so as to increase. 4. The liquid crystal epitaxial growth method for single crystal silicon carbide according to claim 3 , wherein the heat treatment is performed under a reduced pressure of 10 ⁻⁴ Pa or less. 5.