JP4888432B2 - Method for producing 4H-SiC single crystal - Google Patents

Description

  The present invention relates to a method for producing a 4H—SiC single crystal by a solution method.

  Up to now, various methods for growing SiC single crystals by a solution method have been proposed. Important points in the growth of the SiC single crystal are the growth rate and flat growth.

  Patent Document 1 proposes high-speed growth using a solvent obtained by adding Ti or Mn to a Si melt. However, according to the inventors' experiments, flat growth cannot be ensured. When Ti or Mn is added alone, the amount of C dissolved increases and the amount of precipitated SiC increases, but it is in a polycrystallized state, and flat growth, that is, single crystal growth cannot be obtained. Further, Patent Document 1 grows a 6H—SiC single crystal in Examples, and does not particularly take into consideration the growth of 4H—SiC single crystal.

  Similarly, Patent Document 2 proposes adding Fe and Co in place of Ti for the purpose of improving speed and reducing cost. Since flat growth cannot be maintained at high temperatures, only examples at low temperatures are shown. According to the experiment of the present inventor, the amount of dissolved C increases when Fe is added, but flat growth cannot be maintained as in the case of adding Ti. When Co was added, neither an increase in the amount of dissolved C nor flatness was obtained.

  There has also been proposed a method of adding two or more elements to the Si melt. Patent Document 3 adds V and Ti, Patent Document 4 adds Ti and any one of Co, Mn, and Al. Patent Document 5 describes any one of Ti, Fe, Mn, and Co. Each has been proposed to add more than seeds. All of these grow 6H—SiC single crystals in the examples, and no particular consideration is given to the growth of 4H—SiC single crystals.

  In addition, Patent Document 6 proposes adding a gas containing hydrocarbons, and Patent Document 7 proposes adding a transition metal. However, even if an improvement in the growth rate is obtained, both are flat. We cannot secure growth.

  Furthermore, Non-Patent Document 1 reports that the amount of C dissolved increases with the addition of rare earth elements. Certainly, if the amount of dissolved C is increased, growth is possible even with a small temperature gradient, but the C concentration becomes too high, and the three-dimensional growth is promoted to roughen the growth surface, so that flat growth cannot be obtained.

  Thus, conventionally, a 4H—SiC single crystal could not be stably grown on a flat surface. On the other hand, when applied to a power device or the like as a SiC semiconductor, device characteristics of the polymorph 4H SiC single crystal are the best. Therefore, a method for stably flatly growing 4H—SiC single crystals by a solution method has been demanded.

JP 2004-002173 A JP 2006-143555 A JP 2007-261843 A JP 2007-076986 A JP 2006-069861 A JP 2002356563 A JP 2000-264790 A Dieter H. Hofman, "Prospect of the use of liquid phase techniques for the growth of bulk silicon carbide crystals", Material Science and Engineering, B61-62 (1999) 29-39.

  An object of this invention is to provide the manufacturing method of 4H-SiC single crystal which can carry out the stable flat growth of 4H-SiC single crystal by a solution method.

In order to achieve the above object, according to the present invention, in a method of growing a 4H-SiC single crystal on a 4H-SiC seed crystal from a solution in which Si melt is used as a solvent and C is dissolved therein,
As the solvent, a Si—Ti—X ternary solvent in which Ti and an element X that is one of Al, Sn, and Ge are added to a Si melt, and 1780 is formed on the Si surface of the 4H—SiC seed crystal. A method for producing a 4H—SiC single crystal, characterized by growing a 4H—SiC single crystal at a growth temperature of at least ° C. is provided.

  According to the method of the present invention, as detailed below, (1) the solvent composition, (2) the growth surface polarity of the seed crystal, and (3) the three conditions of the growth temperature are simultaneously limited, so that 4H-SiC A single crystal can be stably grown on a flat surface.

(1) Solvent composition By using a ternary solvent of Si-Ti-X (X = any one of Al, Sn, and Ge), a practical growth rate is obtained by increasing the amount of C dissolved by adding Ti. At the same time, the surface activation action of Al, Sn, and Ge prevents polycrystallization and mixed crystal formation and promotes flat growth.

  That is, when Ti alone is added, the amount of crystal precipitation increases, but the flatness of the growth surface cannot be ensured. Even if the concentration of C in the solvent increases, an interface activation action is essential in order to incorporate the C and grow a uniform single crystal. Elements that can exhibit this interface activation action are Al, Sn, and Ge. The interfacial activation of these elements reduces the solid / liquid interface energy (or the solvent surface energy), and further activates atom migration on the terrace surface of the growing crystal while maintaining a high growth rate. Flat growth (two-dimensional growth) can be ensured.

(2) Seed crystal growth surface polarity However, as a result of various experiments, the present inventors have found that the growth surface polarity of the SiC seed crystal, which is the seed crystal, is also increased in the solvent composition in which Ti is added like the solvent of the present invention. It was newly found that it greatly affects the flat growth. It is well known that a SiC single crystal has a crystal structure in which Si and C planes are alternately and repeatedly stacked. As a phenomenon peculiar when 4H-SiC single crystal is grown using 4H-SiC single crystal as a seed crystal, flat growth cannot be secured unless the polarity of the growth surface is Si surface. This phenomenon is peculiar when 4H-SiC single crystal is used as a seed crystal, and when other crystal polymorphs, for example, 6H-SiC single crystal is used as a seed crystal, there is no influence of the polarity of the growth surface. Using the solvent composition of the present invention, it is possible to ensure flat growth on both the Si and C planes.

  Limiting the crystal growth surface of the 4H—SiC seed crystal as a seed crystal to the Si surface is essential to prevent polycrystallization and ensure flat growth of the 4H—SiC single crystal.

(3) Growth temperature The growth temperature is set to a high temperature of 1780 ° C. or higher, thereby preventing mixed crystal formation in which a plurality of crystal polymorphs are mixed. In order to grow the 4H—SiC single crystal by taking over the crystal polymorph 4H of the seed crystal, the growth temperature needs to be 1780 ° C. or higher. When grown at a temperature lower than 1780 ° C., the crystal polymorph 4H of the seed crystal is not inherited, and a mixed crystal with a crystal polymorph other than 4H—SiC (3C, 15R, etc.) is generated.

  As the solvent composition, three kinds of ternary compositions of Si-20 at% Ti-10 at% Al, Si-20 at% Ti-5 at% Sn, and Si-20 at% Ti-5 at% Ge were used. That is, each raw material of Si, Ti, and X (X = Al, Sn, or Ge) having a blending composition corresponding to these solvent compositions is inserted into a graphite crucible and heated and dissolved to generate a ternary solvent. C was dissolved from a graphite crucible in a solvent to form a quaternary solution of Si-C-Ti-X.

  According to the present invention, a 4H—SiC single crystal was used as a seed crystal, and its Si surface was brought into contact with the surface of the quaternary solution as a crystal growth surface.

  The temperature on the back side of the solution contact surface of the 4H—SiC seed crystal was controlled as the growth temperature, and controlled to 1780 ° C. or higher according to the present invention.

  For comparison, when the crystal growth surface of the 4H—SiC seed crystal is the C plane, when the crystal growth surface is the Si surface and the growth temperature is less than 1780 ° C., the 6H—SiC seed crystal is used as the seed crystal. Crystal growth was also performed when the C-plane and Si-plane were used as crystal growth planes.

  The results are summarized in Table 1.

  In the present invention, it is essential to satisfy the following conditions (1), (2), and (3) after using a 4H—SiC single crystal as a seed crystal.

(1) Solvent composition: Si—Ti—X (X = any one of Al, Sn, Ge)
(2) Polarity of crystal growth surface of seed crystal: Si surface (3) Growth temperature: 1780 ° C. or higher As shown in Table 1, Examples (sample Nos. 1 to 5) satisfying the above requirements of the present invention 4H-SiC single crystal was obtained by good flat growth.

  On the other hand, the comparative example (sample Nos. C1 to C7) that does not satisfy at least one of the above requirements could not flatly grow the 4H—SiC single crystal.

  In Comparative Example C1, the seed crystal, the solvent composition, and the growth temperature satisfy the requirements of the present invention, but the crystallinity occurred because the polarity of the growth surface was the C surface.

  In Comparative Example C2, the seed crystal, the solvent composition, and the polarity of the growth surface satisfy the requirements of the present invention, but the growth temperature was 1750 ° C., which was lower than the specified range of the present invention. A crystal polymorph other than the crystal polymorph 4H-SiC (3C-SiC, 15R-SiC, etc.) was formed as a mixed crystal.

  Comparative Examples C3 and C4 are cases where 6H-SiC single crystals outside the scope of the present invention were used as seed crystals, and by setting the solvent composition and the growth temperature within the scope of the present invention, the polarity of the growth surface was increased. A 6H—SiC single crystal was obtained by good flat growth regardless of whether it was a Si plane according to the present invention or a C plane outside the present invention. Thus, 6H—SiC can be satisfactorily grown flat regardless of the polarity of the crystal growth surface. It is a phenomenon peculiar to 4H-SiC that the crystal growth plane polarity needs to be limited to the Si plane.

  In Comparative Example C5, the seed crystal, the polarity of the growth surface, and the growth temperature were in accordance with the provisions of the present invention, but polycrystallization occurred because the Si—Ti binary composition outside the scope of the present invention was used as the solvent composition.

  In Comparative Examples C6 and C7, the seed crystal, the solvent composition, and the growth temperature were in accordance with the provisions of the present invention, but polycrystallization occurred because the polarity of the growth surface was a C-plane that was outside the provisions of the present invention.

  FIG. 1 (A) shows a micrograph of the growth surface of sample No. 1 of the example in which the polarity of the crystal growth surface of the seed crystal according to the present invention is Si surface, and FIG. 1 (B) shows the crystal of the seed crystal. The microscope picture of the growth surface of sample No. C1 of the comparative example which made the growth surface polarity the C surface outside the regulation of the present invention is shown. In both cases, (2) is a high-magnification photograph of the portion surrounded by the broken line in (1). When the Si surface according to the present invention shown in FIG. 1 (A) is used as a growth surface, high flatness is obtained, whereas C outside the specified range shown in FIG. 1 (B) is obtained. When the surface is used as a growth surface, it is polycrystallized.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of 4H-SiC single crystal which can carry out the flat growth of 4H-SiC single crystal stably by the solution method is provided.

FIG. 1A is a photomicrograph of the growth surface of sample No. 1 in the example in which the polarity of the crystal growth surface of the seed crystal according to the present invention is Si surface, and FIG. 1B is the crystal of the seed crystal. It is a microscope picture of the growth surface of sample No. C1 of the comparative example which made the growth surface polarity the C surface outside the specification of the present invention.

Claims (1)

In a method of growing a 4H—SiC single crystal on a 4H—SiC seed crystal from a solution in which Si melt is used as a solvent and C is dissolved therein,
As the solvent, a Si—Ti—X ternary solvent in which Ti and an element X that is one of Al, Sn, and Ge are added to a Si melt, and 1780 is formed on the Si surface of the 4H—SiC seed crystal. A method for producing a 4H-SiC single crystal, comprising growing a 4H-SiC single crystal at a growth temperature of at least ° C.