JP5273131B2 - Method for producing SiC single crystal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing an SiC single crystal increasing C solubility in a solution to improve a growth rate of the SiC single crystal, suppressing fluctuation in a solution composition due to consumption of an SiC component associated with the growth of the single crystal, and stabilizing conditions for single crystal growth. <P>SOLUTION: The method of producing an SiC single crystal includes: disposing an SiC seed crystal 20 at a bottom part inside a graphite crucible 10; causing a solution 30 containing Si, C and R (R is at least one selected from the rare earth elements inclusive of Sc and Y) to be present in the crucible 10; supercooling the solution 30 so as to cause the SiC single crystal to grow on the seed crystal 20; and adding powdery or granular Si and/or SiC raw material 41 to the solution 30 from above the graphite crucible 10 while keeping the growth of the SiC single crystal. <P>COPYRIGHT: (C)2012,JPO&amp;INPIT

Description

  The present invention relates to a method for producing a SiC (silicon carbide) single crystal using a solution method.

  SiC has excellent characteristics in terms of band gap, dielectric breakdown voltage, electron saturation speed, thermal conductivity, etc., so it is expected as a next-generation power device and high-temperature device that exceeds the limits of Si. Material development is also active.

  Conventionally, as a method for growing a SiC single crystal, a sublimation method, a CVD method, an Atchison method, a solution method, and the like are known.

The Atchison method has been practiced industrially for a long time, and SiC crystals are precipitated by heating silicic acid and carbon at a high temperature, but it is difficult to produce high-purity single crystals. In the sublimation method, the temperature of the SiC raw material powder is raised to 2,200 to 2,400 ° C., and once again deposited as SiC on a low-temperature seed crystal as a gas such as Si, Si ₂ C, or SiC ₂ under reduced pressure. At present, this is the mainstream method for producing SiC bulk single crystals, but since it is a vapor phase growth method, there is a problem that various defects are likely to occur in the crystal. In addition, it is difficult to produce a bulk single crystal in the CVD method because the raw material is a gas component.

  In the solution method, SiC and Si-containing alloys are dissolved in a graphite crucible, and carbon is also eluted from the graphite crucible, thereby precipitating a SiC single crystal on a seed crystal placed in a low temperature part from a solution containing Si and C. It is a way to grow. In general, since C is not sufficiently solid-solved with the Si melt alone, a method of increasing the C solubility by using a solution containing the third element is employed. In the solution method, it is possible to obtain a high-quality single crystal with fewer defects than in the sublimation method, but there is also a problem that a growth rate as high as the sublimation method cannot be obtained. For this reason, various investigations have been conducted so far on a method for producing an SiC single crystal using a solution method.

  Patent Document 1 (Japanese Patent Laid-Open No. 2000-264790) discloses a method of depositing and growing a SiC single crystal using a melt containing Si, C and a transition metal. In Patent Document 2 (Japanese Patent Laid-Open No. 2004-002173), Si-C-M (M: Mn or Ti) is used. In Patent Document 3 (Japanese Patent Laid-Open No. 2006-143555), Si-C-M (M: Fe and / or Co) and Patent Document 4 (Japanese Patent Laid-Open No. 2007-076986), an SiC single crystal is grown using a melt of Si—C—Ti—M (M: Co and / or Mn). Yes.

  Patent Document 5 (Japanese Patent Application Laid-Open No. 2006-321681) discloses a SiC single crystal having a desired crystal structure among 15R, 3C, and 6H using a melt obtained by melting a raw material containing Si, C and a third element or a compound thereof. This is a method for growing a crystal. Examples of the third element include borides, Sn (15R), Gd (3C), Al, Dy, La (6H), and the like. In Patent Document 6 (Japanese Patent Laid-Open No. 2007-277049), a melt obtained by adding a rare earth element and any of Sn, Al, and Ge to Si is used. Here, although the addition of rare earth elements has the effect of increasing the C solubility in the Si melt and improving the growth rate of the SiC single crystal, polynucleation or polycrystallization on the growth surface is not possible under conditions where the growth rate is high. Since it is likely to occur, a technique for stably ensuring flat growth by adding Sn, Al, and Ge as elements that uniformly activate the growth surface is shown. In Patent Document 7 (Japanese Patent Application Laid-Open No. 2009-167045), a melt of Si—Cr—X (X: Ce and / or Nd) is used. It has been shown that macroscopic defects in crystals can be reduced. Patent Documents 8 and 9 (Japanese Patent Laid-Open Nos. 2005-154190 and 2005-350324) sequentially stack a SiC raw material rod, a solvent, and a seed crystal from the bottom, and form a temperature gradient on the upper and lower end surfaces of the solvent. In this method, a SiC single crystal is grown, and a solvent comprising Si and an element selected from Y, lanthanoids, Group I elements, Group II elements, Group IIIB elements and the like is used.

  When a solution containing a rare earth element is used, the solubility of C can be increased, and the growth rate which is one of the problems in the solution method is improved. However, when the C solubility is increased, there is a problem that the growth surface is roughened or polycrystallized easily, and the quality of the SiC single crystal is lowered. In contrast, attempts have been made to add an element that suppresses C solubility at the same time as the rare earth element. However, since the solution becomes more multi-component, it is difficult to control the composition and the crystal growth method is sensitive to the growth conditions. Susceptible to changes. Further, as the SiC single crystal grows from the solution, Si and C are consumed from the solution components and the composition varies, so that the optimum conditions for growth greatly change with time. For this reason, it is difficult to produce a long and large-diameter SiC single crystal by a solution method. Patent Documents 8 and 9 (Japanese Patent Laid-Open Nos. 2005-154190 and 2005-350324) disclose a method of supplying a raw material from a SiC raw material rod, and in this case, the composition of the solvent does not vary greatly. It is necessary to prepare a SiC raw material rod in advance, which increases the manufacturing cost.

JP 2000-264790 A JP 2004-002173 A JP 2006-143555 A JP 2007-076986 A JP 2006-321681 A JP 2007-277049 A JP 2009-167045 A JP 2005-154190 A JP 2005-350324 A

  The present invention has been made in view of the above circumstances, and provides a method for producing a SiC single crystal capable of obtaining a long and large-diameter SiC single crystal in which defects such as polycrystallization are suppressed at a high growth rate. For the purpose.

  As a result of examining the means for solving such a problem, the present inventors have used a solution containing a rare earth element having an effect of increasing the solubility of C, and are liable to cause evaporation of solution components, and local condition fluctuation is severe. The SiC single crystal is grown from the bottom of the solution where the conditions are stable and surrounded by a graphite crucible rather than the top surface of the solution, and a gentler temperature gradient can be set. A method for keeping the solution composition constant without depending on the passage of time by adding Si and / or SiC raw materials in a timely manner has been found, and the present invention has been made.

Accordingly, the present invention provides the following method for producing a SiC single crystal.
[1] A SiC seed crystal is placed at the bottom of the graphite crucible, and a solution containing Si, C, and R (R is one or more selected from rare earth elements including Sc and Y) is present in the crucible. The solution is supercooled to grow a SiC single crystal on the seed crystal, and powder or granular Si and / or SiC raw material is added to the solution from the top of the graphite crucible while growing the SiC single crystal. A method for producing a SiC single crystal, comprising:
[2] The mass ratio [W _R / (W _Si + W _R )] of _R to the total of the mass W _{Si of Si} and the mass W _{R of} R in the solution when the SiC single crystal is grown is 0. The method for producing a SiC single crystal according to [1], wherein the amount of the powdered or granular Si and / or SiC raw material added to the solution is adjusted to be 05 or more and 0.75 or less.
[3] The difference between the mass ratio of R in the solution when the SiC single crystal is grown and the mass ratio of R in the raw material composition of the solution charged in the graphite crucible does not exceed ± 0.1. The method for producing a SiC single crystal according to [1] or [2], wherein an addition amount of the powdery or granular Si and / or SiC raw material is adjusted.
[4] The method for producing a SiC single crystal according to any one of [1] to [3], wherein R is one or more selected from La, Ce, Pr, Nd, Gd, and Dy.
[5] The interior of the furnace in which the graphite crucible is disposed is in a vacuum or an inert atmosphere, and has a temperature gradient region that continuously decreases downward, and the graphite crucible is disposed in the temperature gradient region. The method for producing a SiC single crystal according to any one of [1] to [4], wherein the SiC single crystal is grown on the seed crystal by being pulled down.

  According to the method for producing a SiC single crystal of the present invention, the C solubility in the solution is increased to improve the growth rate of the SiC single crystal, and the composition variation of the solution due to consumption of the SiC component accompanying the growth of the single crystal is suppressed. In addition, the conditions for single crystal growth can be stabilized.

It is the schematic which shows an example of the SiC single crystal manufacturing apparatus suitable for enforcing the method of this invention. It is the schematic which shows the other example of the SiC single crystal manufacturing apparatus suitable for implementing the method of this invention. The time change of the mass ratio of R is shown typically.

  1 and 2 show an example of an apparatus for carrying out the method of the present invention. In each figure, 1 indicates a furnace, and the inside of the furnace 1 is maintained in a vacuum or an inert gas atmosphere. A graphite crucible 10 is disposed in the furnace 1. The graphite crucible 10 is formed in a cylindrical shape having an upper end opened and a lower end closed, and is disposed on a support 2 disposed so as to be movable up and down. When the support 2 is lowered, the graphite crucible 10 is integrated with the graphite crucible 10. The graphite crucible 10 is lowered. Here, the graphite crucible 10 of FIG. 1 is formed in a funnel shape in which the inner wall gradually slopes downward as the inner wall moves from the inner wall middle part to the lower part, and the SiC seed crystal 20 is disposed at the center of the bottom part. On the other hand, the graphite crucible 10 of FIG. 2 has a cylindrical inner wall, and the SiC seed crystal 20 is disposed at the bottom center. In this state, a solution 30 containing Si, C, and R is present in the graphite crucible 10. Further, a raw material charging container 40 is disposed above the graphite crucible 10, and an input 41 (Si and / or SiC raw material) is supplied from the raw material charging container 40 to the solution 30 through the upper end opening of the graphite crucible 10. Is done. In the figure, 50 is a susceptor, 51 is a heat insulating material, and 52 is an induction coil.

  In the present invention, a SiC seed crystal is placed at the bottom of the graphite crucible, and a raw material that becomes a solution is charged. Since the solution contains Si, C, and R (R is one or more selected from rare earth elements including Sc and Y), it is preferable to use Si and R metal, a compound thereof, an alloy, or the like as a raw material. C may use SiC, R carbide, or the like as a raw material, or may utilize the dissolution of C from a graphite crucible into a solution.

  In order to increase the solubility of C in the solution, R (R is one or more selected from rare earth elements including Sc and Y) is selected as the third element. If R is one or more selected from La, Ce, Pr, Nd, Gd, and Dy, it is more preferable from the viewpoint of raw material costs. R may be a single metal or a compound.

In this case, the use ratio of Si, C, and R is appropriately selected, but the mass ratio of R in the solution [W _R / (W _Si + W _R )] is always 0.05 during the growth of the SiC single crystal. It is preferable that it is more than 0.75. When the mass ratio is less than 0.05, the solubility of C in the solution is small, and a sufficient growth rate of the SiC single crystal cannot be obtained, and when the mass ratio exceeds 0.75, SiC is easily crystallized. Therefore, it may be difficult to grow a single crystal. The mass ratio of R is more preferably from 0.1 to 0.7, and even more preferably from 0.15 to 0.6.

  The C concentration of the solution is preferably as high as possible. However, when the C concentration is too high, undissolved SiC or C exists in the solution, which adversely affects the growth of the single crystal. It is preferable to set the concentration within a range that does not exist. The optimum amount of C greatly depends on the R / (Si + R) mass ratio and the solution temperature, but is preferably adjusted in the range of 0.1 to 15 mass%, particularly 1 to 10 mass% as the C mass ratio in the entire solution. . If necessary, in addition to R, a fourth selected from Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ge, Al, Zr, Nb, Mo, Hf, Ta, W, etc. Element X may be further added. At this time, the addition amount of X is preferably 0.5 times or less of R by mass ratio.

  After the graphite crucible charged with the seed crystal and the solution raw material is placed in the furnace, the inside of the crucible is melted by heating with a vacuum or an inert atmosphere such as Ar. The heater may be a combination of an induction coil and a susceptor, or a resistance heating method. Inside the apparatus, a temperature gradient region that continuously decreases downward is formed. After the inside of the crucible reaches a predetermined temperature, the crucible is pulled down so as to pass through the temperature gradient region. At this time, the temperature of the solution in the crucible gradually decreases from the bottom, and the C solubility in the solution becomes small. Therefore, when the supersaturated state is reached near the seed crystal installed at the bottom, this supersaturation is used as a driving force. A SiC single crystal grows on the crystal.

Here, the raw material temperature in the crucible is preferably 1,400 to 2,200 ° C., more preferably 1,600 to 2,100 ° C. Moreover, it is preferable to make it fall continuously downward so that the temperature gradient in a furnace may be 5-100 degreeC / cm, especially 10-50 degreeC / cm.
The crucible is preferably pulled down at a speed of 10 to 1,000 μm / hr, particularly 50 to 500 μm / hr.

  When R is used as the third element, the solubility of C in the solution can be increased, but generally, the SiC single crystal is likely to be multinucleated or polycrystallized. In order to suppress this phenomenon, local condition fluctuations such as component evaporation and vibration from the solution surface are less likely to occur by growing the SiC single crystal not at the upper part near the solution surface but at the lower part of the stable solution. Also, the temperature gradient can be made uniform with little variation over the entire growth surface, so that a gradual temperature gradient can be set, so that SiC precipitation is moderated and polycrystallization can be suppressed.

  As the crucible continues to be pulled down, the SiC single crystal takes in Si and C elements from the solution and further grows, but with this, the solution gradually decreases in Si from the starting composition, The composition changes to a composition having a relatively large R. In addition, evaporation of Si component from the solution surface also causes composition variation. As the composition shifts to R-rich, the conditions under which the SiC phase precipitates from the solution also change. Accordingly, the conditions suitable for the growth of the SiC single crystal gradually change with the elapse of the pull-down time, and the SiC single crystal that was growing smoothly at the beginning is polycrystallized from the middle or various defects are observed. It comes to occur.

  On the other hand, the solution can be kept at a composition within a certain range by adding the raw material corresponding to the variation of the solution composition while continuing the growth of the SiC single crystal. The raw material is introduced into the solution from the top of the graphite crucible. If the seed material is immersed in the upper part of the solution and then pulled upward, the same material is added from above the solution surface in the same way. Disturbances near the solution surface and local fluctuations in composition greatly affect SiC precipitation. In the present invention, the growth of the SiC single crystal is performed in the lower part of the solution, and the raw material is charged in the upper part of the solution away from the crystal growth part, so that the work of adding the raw material avoids adversely affecting the growth of the SiC single crystal. be able to.

  As the raw material, powdery or granular Si that is easy to charge is used. In the condition where the C concentration of the solution decreases with time, powdery or granular SiC is also added simultaneously. The amount of raw material added is calculated from the relationship between the operating time and the amount of change after analyzing the composition of the residue of the remaining solution that has been cooled and solidified by conducting an experiment in the absence of addition in advance and grasping the amount of change in the composition. That's fine.

The addition of the raw materials may be performed continuously, or a method in which a constant amount is intermittently added in a range where the composition of the solution does not deviate significantly from the initial composition may be used. FIG. 3 schematically shows changes in the solution composition when intermittently charged. Here, when the ratio of the mass _R R of the _R to the sum of the mass W _{Si of the Si} and the mass W _R of the _R is a mass ratio [W _R / (W _Si + W _R )], The difference between the mass ratio of R [W _R / (W _Si + W _R )] and the mass ratio of R in the whole solution raw material charged into the graphite crucible preferably does not exceed 0.1, and if 0.05 or less More preferably, 0.03 or less is more preferable.

  EXAMPLES Hereinafter, although an Example and a comparative example are shown and this invention is demonstrated concretely, this invention is not restrict | limited to the following Example.

[Examples 1 to 6, Comparative Examples 1 and 2]
Using the apparatus shown in FIG. 1, an SiC seed crystal was placed at the bottom of a graphite crucible, and Si and R raw materials were charged thereon to a predetermined composition. After making the inside of the furnace Ar atmosphere, the temperature was raised to a set temperature and maintained for 30 minutes to 3 hours, and then the crucible pulling was started.
The pulling-down was performed for 100 hours, and during that time, SiC powder and Si powder were introduced into the solution from the upper part of the crucible. The input amount was calculated based on the difference between the residue composition analysis result and the raw material composition when the input was not performed. In each of the examples, a good SiC single crystal was obtained. Table 1 shows the mass ratio of the raw material and R at the time of charging and the holding temperature, and Table 2 shows the mass ratio of R of the residue after pulling down and the growth rate of the SiC single crystal.

  In Comparative Example 1, SiC powder and Si powder were not charged during pulling down. The SiC crystal taken out after the completion of the pulling was polycrystallized during the growth. In Comparative Example 2, a solution containing no R element was used, but only a very low growth rate was obtained, and sufficient crystallinity was not obtained.

  According to the present invention, even during long-term crystal growth in the solution method, the composition fluctuation is small and the conditions are stable, so that a high-quality and long SiC single crystal can be produced.

1 furnace 2 support 10 graphite crucible 20 SiC seed crystal 30 solution 40 charging vessel 41 charging 50 susceptor 51 heat insulating material 52 induction coil

Claims (5)

  A SiC seed crystal is placed at the bottom of the graphite crucible, and a solution containing Si, C, and R (R is one or more selected from rare earth elements including Sc and Y) is present in the crucible. The SiC single crystal is grown on the seed crystal by supercooling, and the powdered or granular Si and / or SiC raw material is added to the solution from the top of the graphite crucible while growing the SiC single crystal. A method for producing a SiC single crystal characterized. When the SiC single crystal is grown, the mass ratio [W _R / (W _Si + W _R )] of _R to the sum of the Si mass W _Si and the R mass W _R in the solution is 0.05 or more and The manufacturing method of the SiC single crystal of Claim 1 which adjusts the addition amount to the said solution of the said powdery or granular Si and / or SiC raw material so that it may become 0.75 or less.   The powder so that the difference between the mass ratio of R in the solution when the SiC single crystal is grown and the mass ratio of R in the raw material composition of the solution charged in the graphite crucible does not exceed ± 0.1 The manufacturing method of the SiC single crystal of Claim 1 or 2 which adjusts the addition amount of the shape or granular Si and / or SiC raw material.   The method for producing an SiC single crystal according to any one of claims 1 to 3, wherein R is at least one selected from La, Ce, Pr, Nd, Gd, and Dy.   The inside of the furnace in which the graphite crucible is disposed is a vacuum or an inert atmosphere, and has a temperature gradient region that continuously decreases downward, and by pulling down the graphite crucible in the temperature gradient region The method for producing an SiC single crystal according to claim 1, wherein an SiC single crystal is grown on the seed crystal.

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