JP2007261844A - Manufacturing method of silicon carbide single crystal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of silicon carbide single crystal having high quality at a high growing speed and stably using a raw material that is comparatively easily available for realizing the mass production, in manufacturing of silicon carbide single crystal by a liquid phase growth method in which the SiC single crystal is grown on a seed crystal substrate from a solution that is obtained by dissolving SiC in a solvent of a molten Si alloy. <P>SOLUTION: The manufacturing method uses an Si-Cr alloy as a solvent and its composition has a value of [Cr]/([Cr]+[Si]) of not smaller than 0.2 and not larger than 0.6 wherein [Cr] is the molar concentration of Cr and [Si] is the molar concentration of Si. By the manufacturing method, bulk or thin film single crystal can be stably and uniformly grown even when continuously growing the SiC single crystal by a temperature gradient method. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for producing a high-quality single crystal of silicon carbide that is particularly suitable as a material for optical devices and electronic devices, and in particular, a silicon carbide single crystal capable of producing a silicon carbide single crystal at a high growth rate by a liquid phase growth method. The present invention relates to a method for producing a crystal.

  Silicon carbide (SiC) is one of the thermally and chemically stable compound semiconductors. Compared to silicon (Si), the band gap is about 3 times, the breakdown voltage is about 10 times, and the electron saturation rate. Is about twice as large and the thermal conductivity is about three times as large. Due to such excellent features, silicon carbide is expected to be applied as an electronic device material such as a power device that breaks the physical limitations of Si devices and an environment-resistant device that operates at high temperatures.

  On the other hand, for optical devices, development of nitride-based materials (GaN, AlN) aimed at shortening the wavelength has been carried out. SiC is attracting attention as a substrate material for epitaxial growth of nitride-based materials, since the lattice mismatch with respect to nitride-based materials is much smaller than other compound semiconductor materials.

  However, SiC is famous as a substance exhibiting a crystal polymorph (polytype). Crystal polymorphism is a phenomenon that can take many crystal structures in which the stacking mode of atoms differs only in the C-axis direction while having the same stoichiometric composition. Typical crystal polymorphs of SiC are 6H type (hexagonal system with 6 molecules as one period), 4H type (hexagonal system with 4 molecules as one period), and 3C type (cube with 3 molecules as one period). Crystal system) and 15R type (rhombohedral system with 15 molecules as one period). Even when an SiC single crystal is grown at a certain temperature, two or more types of crystal polymorphs may be generated. However, the mixture of crystal polymorphs is not preferable in terms of application to a device.

  Application of silicon carbide to electronic or optical devices requires high-quality SiC single crystals in the form of bulk (self-supporting) or thin film in the sense that they have a single crystal polymorphism and no or very few defects. . In the present invention, the bulk single crystal of silicon carbide means a single crystal having a thickness of 200 μm or more, and the thin film single crystal means one having a smaller thickness.

Conventionally known methods for producing silicon carbide include a sublimation recrystallization method and chemical vapor deposition (CVD method) belonging to a vapor phase growth method, and a liquid phase growth method.
The sublimation recrystallization method is a method in which a silicon carbide powder as a raw material is sublimated at a high temperature of 2200 to 2500 ° C., and a silicon carbide single crystal is recrystallized on a seed crystal substrate made of a silicon carbide single crystal disposed in a low temperature portion. is there. Since bulk crystals are easily obtained by the sublimation recrystallization method, industrial production of SiC single crystal wafers is currently performed by the sublimation recrystallization method. However, the SiC single crystal grown by the sublimation recrystallization method has crystal defects such as hollow penetrating defects called micropipe defects, screw dislocations, and stacking faults.

  The CVD method is a method in which a silane-based gas and a hydrocarbon-based gas are used as raw materials, and a silicon carbide single crystal is epitaxially grown on a substrate made of silicon or a silicon carbide single crystal. The CVD method is mainly used for the growth of a thin silicon carbide crystal because the growth rate is relatively slow. Although the thin film silicon carbide single crystal is affected by the substrate, there is a limitation in improving the quality of the thin film because the substrate produced mainly by the sublimation recrystallization method has a problem in quality as described above.

  In the liquid phase growth method, carbon is dissolved in silicon or a silicon-containing compound financial solution, the seed crystal substrate is immersed in the melt, and at least around the seed crystal substrate, a supersaturated state of SiC concentration is created by supercooling the melt. In this method, a silicon carbide single crystal is grown on a seed crystal substrate. The melt is a SiC solution using Si as a solvent.

  In the liquid phase growth method, a so-called temperature difference method (only a solution near the seed crystal substrate becomes supersaturated) is provided with a temperature gradient in the melt so that the melt temperature in the vicinity of the seed crystal substrate is lower than other portions. And a so-called cooling method in which the entire melt immersed in the seed crystal substrate is cooled to obtain a supersaturated solution of SiC. There is also an evaporation method in which the solvent is evaporated to supersaturate the solution. Since the cooling method and the evaporation method are batch methods, it is preferable as a method for obtaining a single crystal of a thin film, and a temperature difference method capable of continuous growth is preferable for obtaining a bulk single crystal.

  In the liquid phase growth method, since crystal growth occurs in a state close to thermal equilibrium, it is known that a single crystal with significantly better crystallinity (no mixing of different polytypes) can be obtained compared to vapor phase growth. It has been. Therefore, according to the liquid phase growth method, it is possible to produce a SiC single crystal of higher quality than the sublimation recrystallization method. However, since the solubility of carbon in the melt is low and the SiC concentration in the melt is low, the slow growth rate of crystals has been a problem that hinders the practical use of the liquid phase growth method.

  The following Patent Document 1 discloses that a raw material containing at least one transition metal element and Si and C is heated and melted to form a melt, and this melt is cooled to precipitate and grow a SiC single crystal. ing. In this case, an alloy of Si and a transition metal serves as a solvent for SiC. In this patent document, an optimum melt composition is estimated based on a ternary phase diagram. However, there is only one melt composition specifically disclosed for each case where the transition metal element is Mo, Cr or Co.

  The technical problem in liquid phase growth of today's SiC single crystal is that the most reliable ternary phase diagram of Si-C-M (M is an additive metal) is not known. You cannot even narrow down. In reality, theoretically and experimentally reliable equilibrium diagrams of multicomponent melts are not limited to Si—C—M systems, and are generally unknown. Therefore, in order to select the transition metal element to be added and its amount, it is necessary to first calculate a multi-component equilibrium state diagram that requires advanced knowledge.

  The equilibrium diagram only shows the appearance and disappearance behavior of various phases in the equilibrium state. In the liquid phase growth method, a deviation from an equilibrium state of crystal growth from a supersaturated solution is used. Therefore, even if the optimum melt composition can be estimated from the equilibrium diagram, various situations that cannot be predicted from the equilibrium diagram occur in the actual single crystal growth, and a SiC single crystal can be obtained stably. Not exclusively. For example, during cooling for growth or under a temperature gradient, various secondary products are generated, and a uniform single crystal cannot be obtained, a seed crystal substrate is dissolved, or a melt is melted with a crucible. It may react and damage the crucible. Therefore, in order to know the optimum single crystal growth conditions, it is necessary to examine in detail what kind of phenomenon occurs by conducting actual growth experiments with various changes in the melt composition and other crystal growth conditions.

  Among various solvent systems, the Si-Cr system is one of the solvents with the highest carbon solubility, and the carbon solubility increases with temperature, and it is known that Cr is difficult to be taken into the SiC crystal. It can be sufficiently expected that a SiC single crystal can be efficiently obtained by using a Cr alloy.

  The melt composition specifically disclosed in Patent Document 1 for the case where the transition metal is Cr has the molar concentrations of Cr, Si and C (same as atomic%) of [Cr], [Si] and [C], respectively. [Cr]: [Si]: [C] = 54: 23: 23, that is, only one example in which the value of [Cr] / ([Cr] + [Si]) is 0.70. As will be described later, when the present inventors conducted a SiC single crystal growth experiment with this composition, a uniform SiC single crystal could not be obtained. The growth behavior of SiC with other melt compositions and the optimum composition for giving the highest growth rate are not disclosed.

The liquid phase growth method using a Si—Cr alloy as a solvent is also reported in Non-Patent Documents 1 and 2 below.
In Non-Patent Document 1, from a Cr-12 wt% Si solution, that is, a solution having a [Cr] / ([Cr] + [Si]) value of 0.798, a Traveling Solvent method which is a kind of liquid phase growth method. The SiC single crystal has been grown in the process, and the SiC crystal has been successfully grown. However, the crystal size is less than 1 mm and is difficult to put into practical use. The growth method is a method in which a small amount of melt is sandwiched between two SiC single crystals and grown under a temperature gradient, and is not in the scope of basic examination.

  Non-Patent Document 2 states that a Cr solvent does not show a simple equilibrium state with SiC at any temperature, and it is difficult to grow only SiC because various carbides of Cr crystallize out. Further, it is stated that the Cr solvent has a high vapor pressure and the solution may evaporate during the growth.

As described above, the effect of the Cr solvent on the growth of the SiC single crystal has not been determined yet, although there are certain examination results.
On the other hand, the present inventors previously developed a method using an alloy of Si and Ti or Mn as a solvent, and succeeded in obtaining a 6H—SiC bulk single crystal (Patent Document 2 below). By selecting Ti or Mn as an alloying element with Si, a growth rate several times higher than when using only Si as a solvent could be realized. This is presumably because the carbon solubility of the Si alloy with Ti or Mn is much higher than that of Si alone.

However, since Ti is an expensive metal, there is an economic difficulty that the crystal growth cost increases. Further, Ti is an active metal, and in some cases, it may react with various gas components to contaminate the SiC crystal. Mn is an inexpensive metal, but its vapor pressure is high, and in some cases, it may evaporate during crystal growth and contaminate the crystal growth furnace, or the crystal growth itself may become unstable due to concentration fluctuations due to evaporation. Remains.
JP 2000-264790 A JP 2004-2173 A MA Wright, Journal of The Electrochemical Society, vol. 112, p. 1114-1116 (1965) PW Pellegrini, JM Feldman, Journal of Crystal Growth, vol. 27, p. 320-324 (1974)

  Therefore, in order to realize mass production of SiC single crystals, it is required to select a Si alloy having a high carbon solubility as a solvent and to determine the optimum alloy composition so as to enable high-speed growth. It is desirable that such an alloy is relatively easily available and can be used stably.

  According to the present invention, the above-mentioned problem is solved by using a melt containing Si, C and Cr (the solvent of SiC is a Si—Cr alloy) and setting the Cr content in the melt to a specific range. be able to.

  First, the inventors of the present invention used the latest calculation method to earnestly calculate the equilibrium state diagram of Si—Cr—C, and obtained a state diagram at 2000K as shown in FIG. That is, according to the calculation by the present inventors, a liquid phase is widely present on the high Cr side at 2000K, and it is sufficiently possible to obtain SiC as the primary crystal, and single crystal synthesis of SiC can be performed by the liquid phase growth method. I can expect. The composition in which C is dissolved in the largest amount at this temperature is mol%, Cr: 57.33-C: 28.5-Si: 14.1, and [Cr] / ([Cr] + [Si]) The value of is 0.802.

  An earnest crystal growth experiment was conducted based on this phase diagram calculation. As a result, when a growth experiment is performed in a composition range where C is most dissolved, that is, [Cr] / ([Cr] + [Si]) is about 0.8, graphite is likely to crystallize, and the stability of the SiC single crystal is often stable. It was found to inhibit growth.

Further, in the composition specifically disclosed in the above-mentioned Patent Document 1, the value of [Cr] / ([Cr] + [Si]) is about 0.70, Cr ₃ Si is contained in the crucible for crystal growth. It has been found that a parasitic reaction to crystallize occurs and the uniform growth of the SiC single crystal is inhibited. That is, with the melt specifically disclosed in Patent Document 1, a uniform SiC single crystal cannot be obtained.

As a result of continuing the growth experiment of SiC single crystal with various [Cr] and [Si] compositions, the present inventors have a value of [Cr] / ([Cr] + [Si]) not exceeding 0.60. It has been found that the SiC single crystal grows at a higher speed than the case of the Ti solvent stably and uniformly without the above-described graphite crystallization and Cr ₃ Si crystallization. It was also found that when the value of [Cr] / ([Cr] + [Si]) is less than 0.2, the C concentration is remarkably reduced, and the SiC growth rate is lower than in the case of the Si—Ti alloy solvent. did.

  Based on the above knowledge, the present invention includes Si, C, and Cr, wherein Cr is [Cr] and Si is [Si], and [Cr] / ([Cr] + [Si] ]) Is brought into contact with a seed crystal substrate for SiC growth to a combined financial solution having a value of 0.2 or more and 0.6 or less, and the combined financial solution is brought into a supersaturated state of SiC at least around the seed crystal substrate. By this, it is the manufacturing method of a SiC single crystal which grows a SiC single crystal on the seed crystal substrate.

  The present invention relates to a method for producing a SiC single crystal by a liquid phase growth method in which SiC is grown from a liquid phase. The melt containing Si, C, and Cr used in the present invention is a SiC solution in which SiC is dissolved in a solvent made of a Si—Cr alloy. It has been known from Non-Patent Documents 1 and 2 and Patent Document 1 that the melt of the Si—Cr alloy exhibits high carbon solubility and can be a solvent for SiC in the liquid phase growth method. However, as Non-Patent Document 2 points out, it has been difficult to grow a SiC single crystal uniformly from a solvent system of a Si—Cr alloy.

  This is because the highest carbon solubility is in a composition region having a high Cr concentration with a value of [Cr] / ([Cr] + [Si]) of about 0.8, and such a composition region having a high Cr concentration. This is because precipitation of other crystals such as graphite and Cr—Si intermetallic compounds is inevitable. In both Patent Document 1 and Non-Patent Document 1, growth experiments are conducted only in a composition region having a high Cr concentration in which the value of [Cr] / ([Cr] + [Si]) is 0.7 or more.

  In the present invention, when the alloy element M is Ti by using, as a solvent, a Si—Cr alloy having a Cr concentration lower than that of [Cr] / ([Cr] + [Si]) of 0.6 or less. It has succeeded in growing a uniform single crystal of SiC at a higher growth rate. This is because Non-Patent Document 2 that a uniform SiC single crystal cannot be grown from a Si—Cr alloy system, or an alloy having a value of [Cr] / ([Cr] + [Si]) of 0.7 or more. It cannot be easily derived from the prior art such as Patent Document 1 and Non-Patent Document 1 that only illustrate the system.

In the present invention, means for “saturating SiC dissolved in the melt by supercooling the melt at least around the seed crystal substrate” is not particularly limited, and can be generally used in the liquid phase growth method. Any means can be employed. As described above, examples of such means include the following.
(1) A cooling method (slow cooling method) in which the entire melt is gradually cooled substantially uniformly to form a supercooled state (ie, a supersaturated state),
(2) A temperature difference method (temperature gradient method) in which a temperature gradient is provided in the melt so that the periphery of the seed crystal substrate becomes a low temperature portion and only this portion is in a supercooled state of the solution.
(3) An evaporation method in which the solvent is evaporated and the whole is supersaturated.

  In the cooling method, cooling of the melt is finished at a temperature higher than the solidus temperature of the melt, and then supercooling is repeatedly performed by repeating heating and cooling of the melt, so that the SiC single crystal on the seed crystal substrate is obtained. A bulk single crystal can be obtained by continuing crystal growth. However, since repeated heating and cooling consumes a large amount of heat energy, it is advantageous to perform bulk single crystal growth by the temperature difference method. The cooling method is suitable for obtaining an epitaxially grown thin film by a batch method by finishing the cooling to a temperature higher than the solidus line only once. As with the cooling method, the evaporation method is suitable for thin film single crystal growth.

  The temperature difference method is a method suitable for obtaining a bulk single crystal because crystal growth is performed continuously, but it is possible to obtain an epitaxial thin film by shortening the growth time even with the temperature difference method. is there. The temperature gradient of the melt in the temperature difference method may be formed either in the vertical direction or in the horizontal direction of the melt, or a combination of both. The temperature gradient in the vertical direction is usually such that the upper part of the melt in which the seed crystal substrate is immersed is the low temperature part and the lower part is the high temperature part. As for the temperature gradient in the horizontal direction, in the vicinity of the liquid surface of the melt, the central portion where the seed crystal substrate is immersed is usually a low temperature portion, and the vicinity of the crucible wall surface is a high temperature portion.

  According to the present invention, by growing a SiC single crystal by a liquid phase growth method using a Si alloy with Cr, which has a high carbon solubility, a low vapor pressure, and is chemically more stable than Ti, as a solvent, high A SiC single crystal can be uniformly grown at a crystal growth rate, and a high-quality SiC single crystal can be produced efficiently. Therefore, the present invention provides a technique that enables mass production of high-quality bulk and thin-film SiC single crystals that can be used as electronic and optical devices.

  In order to produce a SiC single crystal according to the present invention, first, a melt containing Si, Cr and C is prepared. This melt is a SiC solution in which SiC is dissolved in an Si—Cr alloy system (Cr: 20 to 60 mol%) as a solvent. In order to grow a single crystal from the melt, the SiC concentration (dissolved C concentration) in the melt needs to be a saturation concentration or a concentration close thereto.

  This melt can be prepared, for example, by charging Si and Cr at a predetermined ratio into a graphite crucible, heating the crucible into a molten state, and further heating to dissolve C from the graphite crucible. it can. That is, it is a method of supplying C from a carbonaceous crucible such as a graphite crucible. This method is desirable in that undissolved carbon that can be a nucleus of SiC precipitation does not remain in the melt. However, since the crucible is consumed, the replacement frequency becomes high.

  As another method for supplying C, a method via a gas phase in which hydrocarbon gas is blown into a melt of Si—Cr alloy having a predetermined composition to dissolve C in the melt, and further, a solid carbon source is introduced into the melt. It is also possible to dissolve them. In this case, a non-consumable crucible can be used. As a solid carbon source, in addition to graphite blocks, rods, granules, and powders, amorphous carbon raw materials other than graphite, SiC and Cr carbides, and the like can be used.

Of course, it is also possible to supply C by combining these two or more methods.
The heating temperature should just be more than the liquidus temperature of the mixture of Si and Cr with which the crucible was charged. Heating is continued until C is dissolved in the melt from the graphite crucible or added carbon source until the SiC concentration in the melt is at or near the saturation concentration. When a solid carbon source, particularly a powder or granule carbon source, is added to the crucible, if they remain undissolved and remain in the melt, SiC crystals will precipitate there, increasing the growth rate of the SiC single crystal. Since it may lower the quality of the crystal or the quality of the crystal, the heating is preferably continued so that the added carbon source is completely dissolved. The heating time of the melt is generally in the range of about 1 hour to 10 hours.

  The composition of the Si—Cr alloy constituting the solvent system is such that the value of [Cr] / ([Cr] + [Si]) is 0.2 to 0.6, that is, Cr is 20 with respect to the total of Cr and Si. The ratio is ˜60 mol%. As described above, if the amount of Cr is larger than this, precipitation of crystals other than SiC occurs, and a uniform SiC single crystal cannot be obtained. On the other hand, when the proportion of Cr is less than 20 mol%, the growth rate of the SiC single crystal is remarkably lowered, and the growth rate is lower than that when the alloy element is Ti. The value of [Cr] / ([Cr] + [Si]) is preferably 0.3 or more and 0.5 or less.

  As the crucible, when supplying carbon by melting the crucible, a carbonaceous crucible represented by a graphite crucible is used. When supplying carbon from the added carbon source, a crucible material stable in the SiC growth temperature range, for example, a crucible made of a refractory metal such as Ta, W, Mo, or a graphite crucible is used as an appropriate refractory material (eg A crucible lined with the above-mentioned refractory metal or ceramic) can be used. If a desired melt composition is realized, a method that does not use a crucible, such as a cold crucible or a levitation method, is also applicable.

  When a melt (SiC solution) in which SiC is dissolved at or near the saturation concentration is obtained, a seed crystal substrate for SiC growth is brought into contact with the melt, and at least the melt near the seed crystal substrate is in a supersaturated state of SiC. By doing so, SiC is grown on the seed crystal substrate.

  The seed crystal substrate is preferably an SiC single crystal obtained by sublimation recrystallization, but may be an SiC single crystal obtained by vapor phase growth such as CVD. As the seed crystal substrate, a substrate having the same crystal structure as that of the SiC single crystal to be grown is generally used. The seed crystal substrate is not limited to a SiC single crystal. Further, a heterogeneous substrate having the same crystal structure, for example, a silicon substrate, which can be heteroepitaxially grown on SiC and can exist stably in the melt, can be used as a seed crystal substrate.

  The seed crystal substrate is usually attached to a seed crystal substrate support jig attached to the tip of a rotatable seed shaft that passes through the lid of the crucible, and is immersed in the melt. In order to make the crystal growth uniform, it is preferable to rotate the crucible in addition to the seed shaft. The rotation directions of the seed shaft and the crucible may be the same or opposite directions. In the case of the temperature difference method, the position of the seed crystal substrate in the melt is usually the grazing free interface (liquid surface), but in the cooling method or evaporation method in which the entire melt is supersaturated. Is optional.

  As described above, the method for obtaining the supersaturated state of SiC includes the evaporation method for evaporating the solution to make it supersaturated, the cooling method for making the supersaturated state by supercooling after immersing the seed crystal substrate in a SiC solution of saturated concentration, and the temperature. A temperature difference method or the like in which a seed crystal substrate is immersed in a gradient SiC solution and a SiC crystal is crystallized at a low temperature portion is possible.

  In the evaporation method, the heating temperature becomes high and the treatment of the generated steam becomes complicated, so the cooling method or the temperature difference method is suitable for mass production. The temperature at the time of crystal growth (temperature at the end of cooling in the cooling method, temperature in the vicinity of the seed crystal substrate in the low temperature portion where crystal growth occurs in the temperature difference method) is slightly lower than the solidus temperature of the melt composition. It is preferable.

  In the case of the temperature difference method, the temperature gradient in the vertical direction can be achieved by controlling the heating means arranged around the crucible, but in some cases, a cooling means is arranged around the part where the seed crystal substrate that becomes the low temperature part is immersed. May be. Regarding the temperature gradient in the horizontal direction, when the melt is heated by heat transfer from the heated crucible, heat is removed from the melt surface, so the periphery of the melt in contact with the crucible wall surface is melted. A temperature gradient that is higher than the temperature in the liquid center is naturally formed. Therefore, if it is immersed in the vicinity of the liquid surface of the melt central portion, the vicinity thereof becomes a low temperature portion. When the seed shaft on which the seed crystal substrate is attached is water-cooled, this horizontal temperature gradient is further increased, so that the crystal growth rate is increased.

  The temperature gradient in the temperature difference method is preferably in the range of 5 to 100 ° C./cm. If it is less than 5 ° C./cm, the driving force for transport of SiC, which is the solute in the melt, is small, and the growth rate of SiC is small. When the temperature gradient exceeds 100 ° C./cm, SiC crystals are generated near the seed crystal substrate due to the generation of natural nuclei, and the uniform solute supply onto the seed crystal substrate is hindered. As a result, crystals with uniform layer growth cannot be obtained. The cooling rate in the cooling method is preferably 5 ° C./min or less.

  As described above, the method of the present invention can produce both SiC thin film single crystals and bulk single crystals. In order to obtain a bulk single crystal by an evaporation method or a cooling method, crystal growth (dissolution and evaporation or cooling of C) may be repeated. In the temperature difference method, a thin film single crystal and a bulk single crystal can be formed separately depending on the growth time.

A growth test was conducted in which a SiC single crystal was grown by a cooling method using 6H—SiC as a seed crystal substrate. A soaking furnace using resistance heating was used as a heating furnace for crystal growth.
As alloy raw materials for the melt, Si and Cr were weighed so as to have various ratios shown in Table 1, and placed in a graphite crucible having a height of 120 mm × inner diameter of 40 mm (outer diameter of 50 mm), and then the crucible was closed with a graphite lid. It was. A 6H-SiC single crystal substrate having a thickness of 10 mm × 10 mm × 0.35 mm obtained by sublimation recrystallization was attached as a seed crystal substrate to a seed crystal support jig at the tip of a cylindrical graphite seed shaft. .

After setting a graphite crucible with a graphite lid and a seed shaft attached with a seed crystal substrate in a soaking furnace, the inside of the furnace was first evacuated to 5 × 10 ⁻² Torr or less. After evacuation, the atmosphere in the furnace was replaced with Ar by filling with argon (Ar). After Ar substitution, the furnace was heated at 10 ° C / min until the furnace temperature reached 1700 ° C. After maintaining the melting temperature for 2.5 hours to sufficiently dissolve the carbon from the crucible, the seed shaft is inserted from the seed shaft insertion port of the graphite lid, and the seed shaft is reached until the seed crystal substrate reaches near the bottom of the graphite crucible. The seed crystal substrate was immersed in the solution. After immersing the seed crystal substrate, the dissolution temperature was maintained for 7.5 hours. Thereafter, cooling (slow cooling) was started at 1 ° C./min. After reaching 1600 ° C., the seed shaft was pulled up on the melt, the heater was turned off, and further cooled to room temperature. The heat pattern of heating and cooling at this time is schematically shown in FIG.

  The cross-section of the seed crystal substrate collected after the growth experiment was cut in the vertical direction and observed with an optical microscope to measure the thickness of the epitaxial growth layer (SiC single crystal thin film grown on the substrate) and the uniformity of growth. Was also evaluated. For the uniformity of growth, the maximum value, the minimum value, and the average value of the thin film thickness are obtained. When the maximum value and the minimum value are within 20% of the average value, “◯” is indicated. “×”. The growth rate calculated from the thickness of the growth layer and the holding time after immersion is shown in Table 1 together with the presence or absence of uniform growth.

  In order to determine the effect of the present invention, from the ternary melt of Si—Ti—C (the solvent is a Si—Ti alloy) (disclosed in the above-mentioned Patent Document 2) that can perform the liquid phase growth method of SiC most stably at present. A method for growing a SiC single crystal was used as a comparison target. In this example, based on the growth rate obtained with the Si-Ti solution, the growth rate is more than twice as high as the growth from the Si-Ti solution, and the result of uniform growth is "◯" Was evaluated as having an effect on both the growth rate and the stability of the growth (shown as “Yes” in the effect column in the table).

  From Table 1, the condition for obtaining a growth rate equal to or more than twice the growth rate when the solvent is a Si—Ti alloy and a uniform film thickness is [Cr] / ([Cr] + [Si]). It can be seen that it is 0.2 or more and 0.6 or less. In this range, the SiC crystal grows uniformly, and it becomes possible to produce a SiC single crystal stably at a high growth rate.

  In this example, the SiC thin film single crystal was grown by the cooling method. However, as described below, the present invention can be applied to the temperature difference method in which it is allowed to stand under a temperature gradient to grow a bulk SiC single crystal. I have confirmed that I can do it.

That is, after putting the alloy raw material adjusted so that the value of [Cr] / ([Cr] + [Si]) is 0.5, into a graphite crucible having a height of 150 mm × inner diameter of 80 mm (outer diameter of 100 mm), The crucible was closed with a graphite lid. A seed crystal substrate support jig provided at the tip of a cylindrical graphite seed shaft is a 6-SiC single crystal substrate having a diameter of 1 inch × 0.35 mm obtained by sublimation recrystallization as a seed crystal substrate. Attached. After setting the graphite crucible with a graphite lid and the seed shaft to which the seed crystal substrate is attached to a high-frequency heating furnace (a heating furnace provided with a high-frequency coil for induction heating around a furnace made of heat insulating material) The air was exhausted to 5 × 10 ⁻² Torr or less.

  After evacuation, the atmosphere in the furnace was replaced with Ar by filling with argon (Ar). After Ar substitution, the melt was formed by heating at 10 ° C./min until the furnace temperature reached a predetermined melting temperature. At this time, by controlling the relative positional relationship between the graphite crucible and the high-frequency coil, a temperature gradient in the vertical direction of 20 ° C./cm was formed in the melt so that the vicinity of the liquid surface became a low temperature portion (1700 ° C.). After heating so that sufficient C is dissolved from the crucible, the seed shaft is inserted from the seed shaft insertion port of the graphite lid, and the melt temperature at the position of 5 mm immediately below the solution surface is set to 1700 ° C. Soaked in the area. After soaking the seed crystal substrate, the above heating was maintained for 50 hours. Thereafter, the seed shaft was pulled up on the melt, and then the heater was turned off and further cooled to room temperature.

  The obtained ingot was cut, ground, and polished to obtain a 1 inch bulk crystal having a thickness of 500 μm. The obtained SiC bulk single crystal was a high-quality crystal having no or few defects and containing no different polytypes.

  The seed crystal substrate obtained by the sublimation recrystallization method contained micropipes. However, in the initial stage of liquid phase growth, the micropipe in the seed crystal substrate was blocked by the penetration of the melt into the micropipe and the lateral growth of SiC. Therefore, this defect does not propagate in the growth layer, and the obtained crystal does not include a micropipe, and the quality is significantly improved as compared with the seed crystal substrate. Further, since Cr has a low vapor pressure and is not as active as Ti, the growth reaction system was stable even when crystal growth was continued for a long time by the temperature difference method.

It is the Si-Cr-C ternary system phase diagram in 2000K obtained by calculation. The heat pattern of the melt used for the growth of the SiC single crystal in the examples is shown.

Claims (1)

  Including Si, C and Cr, the molar concentration of Cr is [Cr], the molar concentration of Si is [Si], and the value of [Cr] / ([Cr] + [Si]) is 0.2 or more, 0 A seed crystal substrate for SiC growth is brought into contact with a compound financial solution that is less than or equal to .6, and at least the seed crystal substrate is brought into a supersaturated state of SiC at least in the vicinity of the seed crystal substrate. A method for producing a SiC single crystal, wherein crystals are grown.

Images