JP2008100890A - Method for producing SiC single crystal - Google Patents

Abstract

The present invention provides a method for producing a SiC single crystal capable of stably and stably growing a large-diameter, high-quality SiC single crystal at low cost.
In production of a SiC single crystal by a liquid phase growth method in which SiC is epitaxially grown on a substrate by bringing the seed crystal substrate into contact with a SiC solution using a Si alloy melt contained in a crucible as a solvent, the seed crystal substrate As a sapphire crystal substrate. The solvent is a Si-Al alloy or a Si-Al-M alloy (M is one or more additive elements selected from Ti, Mn, Fe, Co, Cr, Cu and V).
[Selection] Figure 4

Description

  The present invention can produce a high-quality, large-diameter silicon carbide (SiC) single crystal, which is particularly suitable as a substrate material for optical devices and electronic devices, at a low cost, and enables the industrial production thereof. About.

  SiC is one type of thermally and chemically stable compound semiconductor, and has a band gap of about 3 times, a breakdown voltage of about 10 times, an electron saturation speed of about 2 times, compared to silicon (Si), It has a physical property advantage over Si that its thermal conductivity is about three times larger. Due to such excellent characteristics, SiC is expected to be applied as an electronic device material such as a power device that overcomes the physical limitations of Si devices and an environmental device that operates at high temperatures.

  On the other hand, for optical devices, nitride-based materials (GaN, AlN) aiming at shorter wavelengths have been developed. SiC has attracted attention as a substrate material for epitaxial growth of nitride-based materials because it has a smaller lattice mismatch to nitride-based materials than other compound semiconductors.

  By the way, SiC is famous as a material exhibiting many crystal polymorphs (polytypes). Crystal polymorphism is a phenomenon in which the stacking mode of atoms takes a different crystal structure in the C-axis direction, while having the same stoichiometric composition. Typical crystal polymorphs of SiC include 6H (hexagonal crystal with one Si-C6 layer), 4H (hexagonal crystal with one Si-C4 layer), and 3C (one Si-C3 layer). And cubic crystal). Mixing two or more types of crystal polymorphs is not preferable for application as a device.

  Application of SiC to electronic devices and optical devices requires high-quality SiC bulk single crystals and thin films that have a single crystal form (no intermingling of crystal polymorphs) and have few or very few crystal defects. Become. Further, from the viewpoint of increasing the number of devices that can be collected from one obtained substrate and increasing industrial productivity, a large-diameter SiC single crystal substrate is required.

  Compared with existing semiconductor device substrate materials such as Si single crystal, SiC single crystal has many crystal defects at present and has a problem in quality. Moreover, although the price is high due to low productivity, and the SiC device is expected to have high performance, the applicable area is limited. Therefore, there is a strong demand for high-quality and inexpensive large-diameter SiC single crystals having a diameter of 4 inches or more.

Conventionally known SiC production methods include a sublimation recrystallization method and a chemical reaction deposition method (CVD method) belonging to a vapor phase growth method, and a liquid phase growth method (LPE method).
In the sublimation recrystallization method, raw SiC powder is sublimated at an ultrahigh temperature of 2200 ° C. to 2500 ° C., and the SiC single crystal is recrystallized on a seed crystal substrate made of an SiC single crystal arranged in a low temperature portion. In this method, 4H—SiC and 6H—SiC are mainly obtained.

  Since the sublimation recrystallization method has a relatively high growth rate and a bulk crystal can be easily obtained, this method is mainly used for industrial production of the present SiC single crystal wafer. However, because crystal growth proceeds under thermodynamic non-equilibrium conditions, SiC single crystals grown by sublimation recrystallization have crystal defects such as hollow through defects called micropipe defects, screw dislocations, and stacking faults. Is likely to occur and there is a problem with the quality of the crystals. As for the diameter of the wafer, what is currently mass-produced and marketed is limited to a diameter of 3 inches. Furthermore, it is a big problem that the price of the SiC single crystal used for the substrate is much higher than that of the existing semiconductor substrate material.

  In the CVD method, SiC is epitaxially grown on a substrate made of Si or SiC single crystal using silane-based gas and hydrocarbon-based gas as raw materials. Since the CVD method has a slower growth rate than the sublimation recrystallization method, it is mainly used for the growth of a thin film SiC single crystal. When Si is used for the seed crystal substrate, the growth is performed at a temperature not higher than the Si melting point, so that a 3C—SiC single crystal that is a low-temperature stable phase can be obtained.

  Since the thin film SiC single crystal is affected by the seed crystal substrate, it is possible to obtain a large area thin film single crystal having a diameter of about 6 inches by using the Si substrate, and also relative to the sublimation recrystallization method. There is an advantage that the manufacturing unit price can be suppressed. However, when SiC having a large lattice constant mismatch of about 20% is grown on a Si substrate, crystal defects such as stacking faults are likely to occur in the growth layer, resulting in a problem in crystal quality. On the other hand, when an SiC single crystal is used for the seed crystal substrate, it is possible to grow an SiC single crystal having the same crystal polymorphism (eg, 4H—SiC, 6H—SiC) as the seed crystal substrate. However, since this seed crystal substrate is currently produced by the sublimation recrystallization method and there is a problem with the quality as described above, there is a limitation in improving the quality of the SiC single crystal thin film.

  In the liquid phase growth method, carbon is dissolved in a melt of Si or Si alloy, and an SiC solution using the melt as a solvent is prepared. A seed crystal substrate is immersed in this SiC solution, and at least a solution in the vicinity of the substrate is brought into a supercooled state to create a SiC supersaturated state, and an SiC single crystal is epitaxially grown on the seed crystal substrate. In the liquid phase growth method, the change in energy associated with molecular rearrangement is small, so there is less possibility of causing crystal polymorphic transitions compared to single crystals obtained by vapor phase growth. A SiC single crystal can be grown.

  The present inventors have previously developed a method for producing a SiC single crystal by a liquid phase growth method using Si and Ti or an alloy of Si and Mn as a solvent, and succeeded in obtaining a high-quality SiC bulk single crystal. (Japanese Unexamined Patent Application Publication No. 2004-2173). In this method, the crystal growth rate showing productivity is several times higher than when only Si is used as a solvent. When a so-called crucible accelerated rotation technique (ACTR) is applied to this method, the stirring effect in the melt is improved and the growth rate of the SiC single crystal can be further increased (Japanese Patent Application Laid-Open (JP-A)). 2006-117441).

  As another method, a method of liquid-phase growth of a single crystal such as SiC using a cooling crucible was also proposed (Japanese Patent Laid-Open No. 2005-179080). In this method, electromagnetic stirring of the melt is promoted, so that the melt temperature becomes substantially uniform and the surface temperature of the crucible is low, so that crystal growth can be realized under a large temperature gradient condition. The crystal growth rate can be increased.

However, in any technique, a SiC single crystal is used for the seed crystal substrate, and as described above, the SiC bulk single crystal that can be used as the seed crystal substrate is expensive, so that the production unit cost becomes relatively large. Therefore, improvement in cost was desired.
JP 2004-2173 A JP 2006-117441 A JP 2005-179080 A

  An object of the present invention is to provide an inexpensive method for producing a SiC single crystal capable of growing a large-diameter, high-quality SiC single crystal. More specifically, this purpose is achieved by a liquid phase growth method.

  According to the present invention, by using a sapphire crystal as a seed crystal substrate and using a specific Si alloy as a solvent of an SiC solution, it is possible to inexpensively manufacture a high-quality SiC single crystal by a liquid phase growth method. Become.

Sapphire single crystal, a high-purity alumina (Al ₂ O ₃ ) single crystal, is a material that combines extremely excellent optical transparency, heat resistance, wear resistance, chemical resistance, thermal conductivity, and insulation. is there. Sapphire crystals are industrially manufactured by the CZ method, Bernoulli method, EFG (Edge-defined Film fed Growth) method, etc., and are high-quality crystals that are inexpensive and have very few defects due to their excellent mass productivity. . In addition, single crystal sapphire having a large diameter of 6 inches or more is already on the market.

  In order to obtain a high-quality SiC single crystal, it is necessary that the lattice mismatch between the seed crystal substrate and the SiC single crystal is small. The sapphire crystal has a lattice constant mismatch with SiC of 16%, which is small compared to the lattice constant mismatch between Si and SiC. Therefore, when crystal defects caused by the lattice mismatch are grown on the Si single crystal. Can be reduced compared to. Furthermore, by performing SiC crystal growth by the liquid phase growth method, it is possible to expect dramatic reduction of crystal defects generated at the SiC / sapphire interface as the growth progresses. Finally, it becomes possible to grow a high-quality SiC single crystal with few crystal defects. Moreover, since a large-diameter crystal is commercially available, a large-diameter SiC single crystal can be grown on the sapphire substrate.

  Up to now, the SiC single crystal heteroepitaxial technology on the sapphire crystal has been reported slightly by the CVD method, but all are basic studies and are not for obtaining the SiC single crystal. There has been no report on the liquid phase growth of SiC single crystal on sapphire crystal, and it is not known that this is possible.

  The present inventors have repeatedly studied the liquid phase growth of a SiC single crystal on a sapphire crystal in consideration of the reaction between sapphire and the melt that can occur when the sapphire crystal of the seed crystal substrate is brought into contact with the melt. The inventors have found that when a specific Si alloy is used, a high-quality SiC single crystal can be grown, and the present invention has been achieved.

The present invention relates to a method for producing a SiC single crystal by a liquid phase growth method in which a seed crystal substrate is brought into contact with a SiC solution containing a Si alloy melt contained in a crucible as a solvent and SiC is epitaxially grown on the substrate. ,
The seed crystal substrate is a sapphire crystal substrate;
The Si alloy is a Si—Al alloy (that is, an alloy of Si and Al) or a Si—Al—M alloy (that is, an alloy of Si, Al, and an additive element M, where M is Ti, Mn, Fe, One or more elements selected from Co, Cr, Cu and V).
It is the manufacturing method of the SiC single crystal characterized by the above-mentioned.

  Further, on the surface layer of the sapphire seed crystal substrate, a group III element nitride (AlN, GaN, InN, InGaN, InAlN, InGaAlN, etc.) having a smaller lattice matching with SiC, MOCVD (Metal Organic Chemical Vapor Deposition), etc. Thin film heteroepitaxial growth is possible by the vapor phase growth method. A group III element nitride / sapphire substrate obtained by heteroepitaxially growing such a group III element nitride thin film on a sapphire surface layer can also be used as a substrate for SiC crystal growth. In this way, it is possible to reduce crystal defects themselves that occur in the early stage of growth due to lattice mismatch with SiC.

  The epitaxial growth of SiC on the seed crystal substrate by the liquid phase growth method is performed by at least bringing the SiC solution around the seed crystal substrate into a supersaturated state. The means for creating this supersaturated state is not particularly limited, and any means generally available in the liquid phase growth method can be adopted. As such means, (1) so-called slow cooling method in which the whole solution is gradually cooled to be supersaturated substantially uniformly, (2) only the temperature of the solution in the part where the seed crystal substrate contacts is slightly lowered There are a temperature difference method and (3) an evaporation method in which the solvent is evaporated to bring the whole solution into a supersaturated state.

  The slow cooling method and evaporation method that supersaturate the entire solution are batch operations and are suitable for the production of thin film single crystals. On the other hand, the temperature difference method is suitable for obtaining a bulk single crystal because it allows continuous crystal growth. However, the temperature difference method can be applied to a thin film single crystal by shortening the growth time. It is also possible to manufacture by the method. The temperature difference is created by, for example, bringing the seed crystal substrate into contact with the center of the solution surface and cooling the holding jig for the seed crystal substrate to cool the solution around the substrate from the holder through the seed crystal substrate. This can be achieved. In this case, a temperature difference is created in the horizontal direction (the surface of the solution when the solution is raised). As another method, it is also possible to create a temperature difference in the vertical direction of the solution by controlling the heating means arranged around the crucible containing the solution, or simply by cooling from the atmospheric gas in contact with the solution.

The selection of the solvent for the SiC solution is determined in consideration of the reaction between sapphire and the melted solvent (melt) that may occur when the sapphire crystal of the seed crystal substrate is brought into contact with the SiC solution. That is, if the sapphire crystal reacts with the melt and the produced reaction product exhibits a liquid phase at the single crystal growth temperature, it means that the sapphire crystal of the substrate is dissolved in the melt. In this case, generation of SiC crystal nuclei on the surface of the sapphire substrate hardly occurs. On the other hand, it is most preferable that the reaction product produced by the reaction of the sapphire crystal with the melt exhibits a solid phase at the single crystal growth temperature, and the reaction product is Al ₂ O ₃ . At this time, dissolution of the seed crystal substrate is suppressed, and SiC crystal growth can proceed. Therefore, the solvent needs to contain at least Al in addition to Si. That is, the solvent is a Si alloy containing at least Si and Al, and the Si alloy can further contain the additional element M in some cases.

  Further, the SiC solution temperature (hereinafter referred to as melt temperature) when growing the SiC crystal is also an important process factor. The higher the melt temperature, the more the SiC concentration in the melt can be increased. However, if the melt temperature is too high, the reaction product of the melt and sapphire often becomes a liquid phase, and dissolution of the sapphire substrate becomes severe. For this reason, it is appropriate that the melt temperature is 1500 ° C. or lower. When the solvent Si alloy has a high melting point metal such as Cr or V as an alloy element, a low melting point metal such as Cu or Mn may be simultaneously added to the melt for the purpose of lowering the liquidus temperature.

  In this way, in order to know the optimum crystal growth conditions for growing a SiC single crystal on a sapphire crystal, what phenomenon will occur from growth experiments with various changes in the liquid phase composition and crystal growth conditions? It is necessary to consider carefully. In addition, the reaction between sapphire and the liquid phase must be considered, and the knowledge from the prior art is hardly helpful.

  Liquid phase growth using a Si alloy containing Al as a solvent makes it possible to stably heteroepitaxially grow a SiC single crystal on a sapphire crystal, which makes it possible to produce high-quality and large-diameter SiC single crystals by liquid phase growth. The fact that industrial production is feasible is completely impossible to predict from the prior art.

  A SiC solution is formed by dissolving C in a solvent (melt) which is a melted Si alloy. The carbon-containing material that is a supply source of C is not particularly limited as long as it can be dissolved in the melt, but in order to avoid introduction of impurities into the melt, a pure carbon material such as graphite or Si It is preferable to use SiC which is a compound of C and C. C is a material containing at least a part of the crucible containing the melt as a carbon-containing material, and may be supplied by dissolving the material, or supplied by dissolving the carbon-containing material charged into the melt. May be.

  As the crucible for storing the melt, a so-called cooling crucible (also called a cold crucible) in which water cooling means is incorporated at least in a part of the side wall of the crucible can be used. The side wall portion has a slit at least partially, and a normal coil (high frequency coil) is disposed around the crucible. When a high-frequency alternating current is applied to the induction coil using this crucible, the Lorentz force acts on the melt in the crucible and the melt rises like a dome, increasing the contact interface between the gas phase and the melt. At the same time, the melt does not make much contact with the side wall. In this case, C is dissolved in the melt by using a crucible material (eg, graphite) containing carbon in the melt holding part (bottom part and its peripheral part) of the crucible that supports the melt from below. It is good to let them.

  Although this melt holding part becomes a consumable item, the melt can proceed with crystal growth without contacting the substantial part of the side of the crucible, and the side wall part can be used as a non-consumable part for a long time. Compared to the case where the melt is stored in a crucible made of a carbon-containing material that becomes a consumable, it is possible to reduce the production unit cost of the SiC single crystal.

  Further, when the cooling crucible having the above structure is used, since the slit becomes an insulating portion, the melt can be effectively subjected to electromagnetic stirring generated by electromagnetic induction by energization of the coil. Compared with direct current application, the alternating current supply stabilizes the shape raised by the Lorentz force, and at the same time, the effect of heating the melt by Joule heat can be expected. By increasing the area of the interface and electromagnetic stirring, transport of SiC as a solute to the vicinity of the seed crystal substrate can be promoted, and SiC crystal growth on the sapphire crystal proceeds stably.

  Another form of the crucible that can be used in the present invention is a crucible in which the crucible containing the melt itself is made of a material containing carbon. When this type of crucible is used, C can be supplied to the melt by melting from the crucible. Examples of such a crucible include a graphite crucible, a SiC crucible, and a crucible whose inner wall is coated with SiC (the crucible body may be made of refractory metal or ceramic).

  When a graphite crucible is used, most of the induced current generated by high-frequency heating is consumed by the crucible, so that the effect of electromagnetic stirring on the melt itself is reduced. Therefore, when using a crucible containing carbon, stirring of the melt is strengthened by periodically changing the rotation speed or rotation speed and rotation direction of the crucible, and transporting SiC as a solute to the seed crystal substrate Can be promoted. It is also possible to install a stirring rod for stirring the melt at the bottom of the crucible.

  In this embodiment, a crucible made of a carbon-containing material that contains a high-temperature melt is melted and damaged little by little during use, so that the entire crucible becomes a consumable item. Therefore, the value of the SiC single crystal is slightly higher than when a cooling crucible is used. However, in the present invention, since the sapphire single crystal, which is less expensive than the conventional SiC single crystal, is used as the seed crystal substrate, the manufacturing unit cost can be reduced.

  According to the method of the present invention, since the sapphire crystal, which is cheaper and can easily obtain a good quality crystal than the conventional SiC single crystal substrate, is used for the seed crystal substrate, the production unit cost of the SiC single crystal to be grown is greatly reduced. It becomes possible. Further, since the sapphire crystal has a smaller lattice mismatch with SiC than the Si single crystal, the generation of crystal defects due to the lattice mismatch can be reduced. Further, by performing SiC crystal growth by liquid phase growth, crystal defects generated at the SiC / sapphire interface can be dramatically reduced as the crystal growth progresses. As a result, when the film is made thick (bulk) by continuous growth for a long time, it is possible to grow a high-quality SiC single crystal with few crystal defects.

  The crystal growth rate of SiC can be increased by selecting the composition of the melt used for crystal growth and enhancing the flow in the melt during crystal growth. Since a large-diameter crystal is commercially available, a large-diameter SiC single crystal can be grown on the sapphire substrate.

  Thus, the present invention is the first successful heteroepitaxial growth of a high quality, large diameter bulk or thin film SiC single crystal. It is expected that the field of application of SiC single crystals as new high-frequency device substrates will be expanded by making it possible to realize low-cost production of high-quality and large-diameter SiC single crystals. Therefore, the industrial contribution of the present invention is very significant.

Hereinafter, a preferred embodiment of a method for producing a SiC single crystal of the present invention will be described with reference to the drawings. In the following description, the SiC solution may be referred to as a melt.
In the first embodiment of the present invention, a SiC single crystal is grown using the single crystal manufacturing apparatus shown in FIGS. In the illustrated single crystal manufacturing apparatus, the side wall 1 of the crucible has a substantially cylindrical shape, an inner diameter of about 100 mm, a height of about 150 mm, and made of a copper material. As shown in FIG. 2, the side wall 1 is assembled from a plurality of segments 16 that are divided by slits 14 that are longer than the winding height of the normal coil 8 and extend in the vertical direction. Since the slit 14 exhibits an insulating function, the segment 16 of the side wall 1 is insulated in the circumferential direction through the slit. The winding height of the normal conductive coil is 100 mm, and the length of the slit 14 is about 200 mm.

  As shown in FIG. 2, double pipes are arranged inside the plurality of segments 16, and the side wall 1 can be cooled with water by flowing cooling water therethrough. An opening 12 having a circular cross section having an inner diameter of about 100 mm is provided on the side wall 1 so that the seed crystal substrate holding jig 5 can be inserted into the crucible.

  A crucible melt holding portion 3 is inserted inside the side wall portion 1 of the crucible in a state of partial contact with the inner wall. The distance between the side wall portion of the crucible and the melt holding portion is 1 mm in a wide area and 0 mm in a narrow area (both are in contact with each other). The melt holding part is graphite and the material thereof is carbon.

  On the outer periphery of the side wall of the crucible, a normal coil 8 made of copper and having a hollow circular cross section is arranged in a multiple spiral structure of about 4 to 5 turns so that one turn is included in a substantially horizontal plane. That is, the slit 14 and the normal conducting coil 8 are in a torsional positional relationship that is substantially orthogonal. There is no point where the normal conducting coil 8 and the crucible side wall 1 are brought into contact with each other and conduction is possible, and the distance between them is about 1 mm when they are close and about 10 mm when they are apart. The normal conducting coil 8 is connected to a high frequency power source (not shown) through a bus bar. The high-frequency power source has a maximum output of 300 kW and a frequency variable between 5 kHz and 30 kHz.

  The diameter of the crystal holding jig 5 inserted into the crucible from the opening 12 varies between 30 mm and 60 mm depending on the height, the length is about 500 mm, and a material mainly made of carbon (eg, graphite) )belongs to. A seed crystal substrate 6 made of sapphire crystal is held at the tip of the crystal holding jig 5.

  The side wall and melt holding part of the crucible, part of the seed crystal substrate holding jig, part of the normal conductive coil, etc. are accommodated in a partially water-cooled chamber 11 that can be pressurized and depressurized and gas can be supplied and discharged. The chamber 11 is coupled to a gas supply device (not shown), a vacuum pump, an exhaust gas treatment device (not shown), and the like. The chamber 11 has airtightness and pressure resistance, and the material is stainless steel. The chamber 11 is appropriately equipped with valves, pressure gauges, flow meters, thermocouple insertion ports, radiation thermometer windows, observation windows and the like necessary for operation.

  The melt 9 is a SiC solution in which a Si alloy composed of Si and Al and optionally one or more kinds of additive elements M is used as a solvent. This melt 9 is charged in a crucible produced by inserting the melt holding part 3 into the side wall part 1 with Si and Al and optionally an additive element M as raw materials, It is formed by melting and dissolving C from the melt holding part 3 in the resulting melt.

  In the present embodiment, the material in the crucible is heated by induction heating by passing a high-frequency alternating current through the normal coil 8. Due to the insulation provided by the slits provided in the side wall 1, the induction current is not consumed at the side wall and is efficiently used for induction heating of the material accommodated in the crucible. When the charging raw material (Si and Al and optionally one or more additive elements M) is melted by this heating, the resulting melt rises in a dome shape by the Lorentz force generated by energizing the coil. When heating is continued by adjusting the energization output and frequency to the coil so as to keep the melt at a predetermined temperature, C melts into the melt (melted solvent) due to dissolution of the melt holding part 3 during that time. The liquid becomes a SiC solution.

  When heating is continued and the SiC concentration in the melt reaches a substantially saturated concentration, a temperature necessary for crystal growth is created in the melt. The creation of this temperature difference can be achieved, for example, by forming a temperature difference in the melt in the vertical direction by adjusting the number of turns and the interval of the normal coil 8. Thereby, the vicinity of the liquid surface of the melt with which the substrate is brought into contact is in a supercooled state, and the SiC concentration in that portion becomes supersaturated. Thereafter, when the crystal holding jig 5 is lowered and the sapphire seed crystal substrate 6 attached to the tip of the crystal holding jig 5 is brought into contact with the top of the raised melt 9, epitaxial growth of the SiC single crystal on the substrate occurs.

  As another method of creating a temperature difference, when the entire melt is kept soaking, by incorporating a water-cooled structure into the crystal holding jig 5 to enhance heat removal from the jig, The temperature of the melt at the portion in contact with the sapphire crystal substrate 6 may be lowered. In this case, the crystal holding jig 5 is first lowered and brought into contact with the top of the melt 9 on which the sapphire seed crystal substrate 6 attached to the tip is raised. As a result, the melt 9 in the portion in contact with the substrate 6 is cooled by heat removal from the cooled crystal holding jig 5 to be in a supercooled state, and the SiC concentration becomes supersaturated. Begins.

  In any method, C is consumed during the growth of the SiC single crystal, but the consumed C is replenished by melting the melt holding unit 3. As the single crystal 7 grown on the substrate becomes thicker, continuous growth can be performed by pulling up the crystal holding jig 5 as necessary. Finally, the crystal holding jig 5 is pulled up so that the growth crystal 7 at the tip thereof is detached from the melt to complete the growth, and the SiC single crystal is cut and recovered from the seed crystal substrate 6.

  The addition of Al to the solvent is essential for stabilizing the surface state of the sapphire seed crystal substrate 6 and stably maintaining the growth of the SiC single crystal. Therefore, the solvent is a Si alloy containing at least Al, that is, a Si—Al alloy or a Si—Al—M alloy. The additive element M is optionally added in order to increase the amount of carbon dissolved in the melt, and is one or more elements selected from Ti, Mn, Fe, Co, Cr, Cu, and V.

When the solvent is a Si—Al alloy, it is preferable that the composition at the molar concentration has an Al content satisfying the following formula.
0.01 ≦ [Al] / ([Al] + [Si]) ≦ 0.7.

Even when the solvent is a Si-Al-M alloy, the composition in molar concentration is
As for the Al content, the value of [Al] / ([Al] + [Si]) is preferably 0.01 or more and 0.7 or less, as described above.
Regarding the content of the additive element M, it is preferable that the value of [M] / ([M] + [Si]) be within the following range for each M element:
When M is Ti, 0.1 or more and 0.25 or less;
When M is Mn, 0.1 or more and 0.7 or less;
When M is Fe, 0.2 or more and 0.7 or less;
When M is Co, 0.05 or more and 0.25 or less;
When M is Cr, 0.2 or more and 0.6 or less;
When M is Cu, it is 0.05 or more and 0.5 or less;
When M is V, it is 0.1 or more and 0.45 or less.

When M contains two or more elements, each element may be set within the above range.
If the amount of Al or M is less than the above range, the amount of carbon dissolved in the melt (and hence the solute SiC concentration) decreases, and the SiC crystal growth rate decreases. On the other hand, when the amount of Al or M is larger than the above range, a compound different from SiC, such as carbide and graphite, may crystallize from the melt, and SiC crystal growth may not proceed.

  In the second embodiment of the present invention, the single crystal manufacturing apparatus shown in FIG. 3 is used. This single crystal manufacturing apparatus includes a crucible 22 containing a melt 21, and a sapphire seed crystal substrate 24 held at the tip of a crystal holding jig 23 that can be raised and lowered is immersed in the melt 21. The crucible 22 has a diameter of about 200 mm, a height of about 200 mm, and is made of a material containing carbon. As a material for such a crucible, in addition to graphite, SiC or SiC coated on the inner wall of the crucible can be used.

  For example, when a graphite crucible is used for the crucible 22, this melt is charged with Si and Al or one or more additive elements M in Si and Al, and the crucible is heated to a molten state. It can be adjusted by further heating and dissolving carbon from the graphite crucible. This method of supplying carbon into the melt by melting from a graphite crucible is preferable in that unmelted carbon does not remain in the melt. In addition to melting from the graphite crucible, it is also possible to add graphite particles etc. to the melt, but in this case, it is necessary to adjust the addition amount strictly so that there are no unmelted graphite particles in the melt. is there. If unmelted graphite grains remain in the melt, natural nuclei of SiC crystals are generated, which may hinder single crystal growth. The types and amounts of Al and additive element M are the same as described above.

  The crucible 22 is disposed on a crucible base 26 attached to the tip of the crucible shaft 25. The crucible shaft 25 is rotatable. It is preferable to stir the melt 21 in the crucible by periodically changing the number of revolutions or the number of revolutions and the direction of rotation of the crucible shaft 25, because transport to the growth interface of solute SiC is promoted.

  The crucible 22 is substantially closed by a crucible lid 27 through which the crystal holding jig 23 passes, and the outer periphery of the crucible 22 is covered with a heat insulating material 28 for heat insulation. A normal coil 29 having a multi-helical structure for inductively heating the crucible 22 is disposed on the outer periphery of the heat insulating material 28. The normal conducting coil 29 is connected to a high frequency power source (not shown). The maximum output of the high frequency power supply is 60 kW, and the frequency is 6 kHz.

  The crystal holding jig 23 is made of a carbon material (for example, graphite). The diameter of the crystal holding jig varies between 50 mm and 150 mm depending on the size of the sapphire substrate held at the tip, and the length also varies between about 150 mm and 400 mm.

  When crystal growth is performed by the temperature difference method, a temperature difference (temperature gradient) is formed in the melt in the vertical direction by adjusting the number of turns and the interval of the normal coil 29, or the entire melt is In the case of a soaking melt, the temperature of the melt in the portion in contact with the sapphire seed crystal substrate 24 is lowered by incorporating a water cooling structure in the crystal holding jig 23 to enhance heat removal from the crystal holding jig. It is good to make it. Since these crucible 22, heat insulating material 28, and normal conductive coil 29 become high temperature, they are arranged inside the water-cooled chamber 30. The water cooling chamber 30 includes a gas inlet 31 and a gas outlet 32 so that the atmosphere in the apparatus can be adjusted. The water cooling chamber is coupled to an evacuation device (not shown). Valves, pressure gauge, flow meter, thermocouple inlet, radiation thermometer window, observation window, etc. necessary for operation are installed.

  In the SiC single crystal growth using this graphite crucible, when the normal coil 29 is energized for heating, the graphite crucible is induction-heated and generates heat, but the magnetic flux penetration is attenuated in the graphite crucible, so that the electromagnetic stirring effect Is smaller than the method in which the melt is raised using the Lorentz force shown in FIGS. 1 and 2, and as a result, the growth rate is relatively slow. However, in this case, as described above, the melt can be effectively stirred by rotating the crucible and periodically changing the number of rotations or the number of rotations and the direction of rotation. The growth rate of the single crystal can be increased. The charging raw material, the heating method, the method for creating the temperature difference, and the like may be the same as in the first embodiment.

(Example 1)
In this example, the production of an SiC single crystal on a sapphire seed crystal substrate using the single crystal production apparatus shown in FIGS. 1 and 2 by the liquid phase growth method is exemplified.

  As described above, a part of the height direction is divided into a plurality of segments by slits, and a water-cooled tube built-in copper side wall portion and a graphite melt holding portion are included in the crucible. In a free space, 1 kg of a solid material composed of Si, Ti, Cu, and Al was charged. The composition of the charged raw materials is [Ti] / ([Ti] + [Si]) where Ti molar concentration is [Ti], Cu molar concentration [Cu], Al molar concentration [Al], and Si molar concentration [Si]. , [Cu] / ([Cu] + [Si]), [Al] / ([Al] + [Si]) so that the values are 0.23, 0.14, and 0.05, respectively. did.

  After reducing the pressure in the chamber to about 0.13 Pa, a gas composed of Ar gas was supplied into the chamber and the supply was exhausted to maintain the pressure in the chamber at about 0.2 MPa. Subsequently, a high frequency alternating current having a frequency of 10 kHz and an output of 100 kW was supplied to the normal conducting coil using a high frequency power source. In a few minutes, the solid raw material was heated and melted and changed into a melt, and the melt was raised in a dome shape and held in such a manner that its periphery did not contact the cold wall. At the same time, the melt was stirred under the influence of electromagnetic stirring.

  Under this condition, after operating for about 5 hours to dissolve a sufficient amount of carbon in the melt, a 50 mm diameter sapphire seed crystal substrate is placed on the melt holding surface at the tip of the crystal holding jig. It was fixed so as to face. The descent of the crystal holding jig was started, and the descent of the crystal holding jig was stopped when the sapphire substrate came into contact with the apex of the melt that rose like a dome, and the operation was continued for 10 hours. The temperature difference, which is the driving force for crystal growth, was created in the melt in the vertical direction by adjusting the number of windings and intervals of the normal coil.

  Thereafter, the crystal holding jig was pulled upward to separate the melt and the grown crystal, and then the temperature was gradually lowered to take out the single crystal. During this time, the melt was always in contact with the melt holding portion of the crucible and the gas, but was not in contact with the side wall of the crucible. As a result, a new SiC single crystal was grown to a thickness of about 0.4 mm on the entire surface of the sapphire crystal having a diameter of 50 mm.

  As a result of TEM (transmission electron microscope) and Raman spectroscopic analysis, it was confirmed that the grown SiC crystal was a 3C-SiC single phase in which other crystal polymorphs were not mixed. FIG. 4 shows a cross-sectional TEM image of the interface between the SiC crystal obtained in Example 1 and the sapphire substrate. Due to the dissimilar materials, crystal defects are confirmed at the SiC / sapphire interface, but the crystal defects are reduced as the SiC crystal thickness is increased. It turns out that it is obtained. From the crystal orientation analysis, it was also found that the SiC crystal grown on the sapphire substrate was epitaxially grown on the sapphire substrate in the relationship of (111) 3C-SiC // (0001) sapphire.

(Example 2)
In this example, the production of an SiC single crystal on a sapphire seed crystal substrate using the single crystal production apparatus shown in FIG. 3 by the liquid phase growth method is exemplified.

  A graphite crucible was charged with 1 kg of a solid material composed of Si and Al. The charge material was such that the Al molar concentration was [Al] and the Si molar concentration was [Si], and the value of [Al] / ([Al] + [Si]) was 0.3.

After reducing the pressure in the chamber to 3 × 10 ⁻⁴ Pa, a gas consisting of He gas was supplied into the chamber and the supply was discharged out of the chamber to maintain the pressure in the chamber at about 0.11 MPa. Subsequently, a high frequency alternating current having a frequency of 6 kHz and an output of 30 kW was supplied to the normal conducting coil using a high frequency power source. After the graphite crucible was induction heated, the solid raw material in the crucible melted and changed to a melt. The melt did not cause any visible bumps.

  After operating for about 1 hour under these conditions to dissolve enough carbon in the melt, a 50 mm diameter sapphire substrate is placed at the tip of the crystal holding jig so that its (0001) surface faces the melt surface. Fixed. The descent of the crystal holding jig was started, and the sapphire substrate was deposited on the melt surface. The operation was continued for 10 hours in this state. The temperature difference, which is the driving force for crystal growth, was created in the vertical direction by adjusting the relative positional relationship between the normal coil and the graphite crucible.

  Thereafter, the crystal holding jig was pulled upward to separate the grown crystal from the melt, and then the temperature was gradually lowered to take out the single crystal. As a result, a new SiC single crystal was grown to a thickness of about 0.15 mm on the entire surface of the sapphire crystal having a diameter of 50 mm. As a result of TEM and Raman spectroscopic analysis, it was confirmed that the grown SiC crystal was a 3C—SiC single phase in which other crystal polymorphs were not mixed.

(Comparative example)
This comparative example shows an example in which a liquid crystal growth method of a SiC single crystal on a sapphire seed crystal substrate is attempted using a single crystal manufacturing apparatus shown in FIG. 3 using a Si alloy not containing Al as a solvent.

  A graphite crucible was charged with 1 kg of a solid material composed of Si and Mn. The charging raw material was an example except that the Mn molar concentration was [Mn], the Si molar concentration was [Si], and the value of [Mn] / ([Mn] + [Si]) was 0.3. In the same manner as in Example 2, SiC crystal growth was performed by a liquid phase growth method. As a result, a SiC single crystal grew on the entire surface of the sapphire crystal having a diameter of 50 mm.

  However, there is a complex oxide composed of Si-Mn-O at the sapphire / SiC interface, and the TEM observation does not show the matching of crystal orientation between the SiC crystal and sapphire. It was found that no epitaxial growth occurred.

(Example 3)
At the same time when the sapphire seed crystal substrate was in contact with the melt surface, the graphite crucible was rotated, and the rotational speed and direction of rotation were changed periodically. Crystal growth was performed.

  After lowering the crystal holding jig until the sapphire substrate contacts the melt surface, the graphite crucible was first rotated counterclockwise. The reached rotation speed was 20 rpm, and the time until reaching the set rotation speed was 5 seconds. After reaching the reached rotation speed, the rotation was performed at the rotation speed for 10 seconds, and then stopped at 5 seconds. Next, the crucible was rotated rightward, and reached 20 rpm in 5 seconds in the same manner as described above. After maintaining the rotation at 20 rpm for 10 seconds, the rotation was stopped in 5 seconds. The above was one cycle, and the operation was continued for 10 hours while repeating the cycle during crystal growth. The time for one cycle is 40 seconds. Thereafter, the crystal holding jig was pulled upward to separate the grown crystal from the melt. Thereafter, the temperature was gradually lowered to take out the single crystal.

  As a result, a new SiC single crystal was grown to a thickness of about 0.4 mm on the entire surface of the sapphire crystal having a diameter of 50 mm. As a result of TEM and Raman spectroscopic analysis, it was confirmed that the grown SiC crystal was a 3C—SiC single phase in which other crystal polymorphs were not mixed.

  In Example 3, compared with Example 2, the growth rate was increased. This is because if the graphite crucible is rotated to periodically change the rotation speed and the rotation direction, stirring of the melt can be promoted, and as a result, transport to the growth interface of the solute SiC can be promoted. it is conceivable that.

  It was found that the SiC single crystals grown in the above examples all have the same quality as shown in FIG. 1 and have good quality suitable for semiconductor materials. Since an inexpensive sapphire crystal is used for the seed crystal substrate, a high-quality SiC single crystal can be grown at a low cost. Moreover, the SiC single crystal on this sapphire substrate can be lengthened.

  In the embodiment, the diameter of the sapphire substrate is as small as 2 inches, but since a sapphire substrate having a diameter of about 6 inches is commercially available, it is easy to increase the diameter. A SiC bulk single crystal can also be produced by growing a large-diameter SiC single crystal and using this as a seed crystal substrate by a liquid phase growth method, a chemical reaction deposition method (CVD method), and a sublimation recrystallization method.

  As mentioned above, although this invention was demonstrated about the specific form, embodiment and the Example which were disclosed here are illustrations in all the points, Comprising: It is not restrictive. The scope of the present invention includes all modifications within the meaning and range equivalent to the scope of the claims.

1 is a schematic cross-sectional view showing a single crystal growth apparatus that can be used in a first embodiment of a method for producing an SiC single crystal of the present invention. FIG. 2 is a schematic perspective view partially showing the single crystal growth apparatus shown in FIG. 1 in a perspective manner. It is a schematic sectional drawing which shows the single crystal growth apparatus which can be used for 2nd Embodiment of the manufacturing method of the SiC single crystal of this invention. It is a cross-sectional TEM image of the SiC / sapphire substrate interface vicinity of the SiC single crystal grown on the sapphire substrate in the Example.

Explanation of symbols

  1: crucible side wall, 3: melt holding section, 5, 23: crystal holding jig, 6, 24: seed crystal substrate, 7: growth crystal, 8, 29: normal coil, 9, 21: melt ( SiC solution), 10: growth interface, 11, 30: chamber, 14: slit, 22: crucible, 25: crucible rotating shaft, 26: crucible base, 27: crucible lid, 28: heat insulating material

Claims (8)

A method for producing a SiC single crystal by a liquid phase growth method in which a seed crystal substrate is brought into contact with a SiC solution containing a Si alloy melt contained in a crucible as a solvent and SiC is epitaxially grown on the substrate,
The seed crystal substrate is a sapphire crystal substrate;
The Si alloy is a Si—Al alloy or a Si—Al—M alloy (M is one or more elements selected from Ti, Mn, Fe, Co, Cr, Cu and V).
A method for producing a SiC single crystal. The composition at a molar concentration of the Si-Al alloy has an Al content such that a value of [Al] / ([Al] + [Si]) is 0.01 or more and 0.7 or less, or the Si The composition of the Al-M alloy at the molar concentration is such that the Al content is such that the value of [Al] / ([Al] + [Si]) is 0.01 or more and 0.7 or less, and [M] / ( The method for producing a SiC single crystal according to claim 1, wherein the value of [M] + [Si]) has a content of M element that falls within the following range for each M element.
When M is Ti, 0.1 or more and 0.25 or less;
When M is Mn, 0.1 or more and 0.7 or less;
When M is Fe, 0.2 or more and 0.7 or less;
When M is Co, 0.05 or more and 0.25 or less;
When M is Cr, 0.2 or more and 0.6 or less;
When M is Cu, it is 0.05 or more and 0.5 or less;
When M is V, it is 0.1 or more and 0.45 or less.   The manufacturing method of the SiC single crystal of Claim 1 or 2 with which the material which comprises at least one part of the said crucible contains carbon (C), and C of a SiC solution is supplied from a crucible.   The method for producing a SiC single crystal according to claim 3, wherein the crucible is rotatable, and the melt is stirred by periodically changing the number of revolutions or the number of revolutions and the direction of rotation of the crucible.   The SiC single unit according to any one of claims 1 to 3, wherein the SiC solution is raised by a Lorentz force induced by passing an alternating current through a normal coil, and a seed crystal substrate is brought into contact with the vicinity of the raised vertex. Crystal production method.   The method for producing a SiC single crystal according to claim 5, wherein the melt is electromagnetically stirred by applying an alternating current to the normal conducting coil.   The crucible has a side wall portion made of a material not containing C and a melt holding portion made of a material containing C, and at least a part of the side wall portion has a structure of a water-cooled crucible having a slit, The manufacturing method of the SiC single crystal of Claim 5 or 6 with which the high frequency induction coil is arrange | positioned around.   The SiC single crystal grown on the seed crystal substrate is 3C-SiC, and the SiC single crystal grows on the {0001} plane of the sapphire crystal. Production method.

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