JP2017095311A - PRODUCTION METHOD OF SiC SINGLE CRYSTAL - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method capable of obtaining a grown crystal in which a generation rate of 4H-SiC is improved, in production of a SiC single crystal by a solution method.SOLUTION: In a production method of a 4H-SiC single crystal for growing a crystal of the 4H-SiC single crystal by bringing a seed crystal substrate 14 held by a seed crystal holding shaft 12 into contact with Si-C solution 24 arranged in a crucible 10, and having a temperature gradient lowering a temperature from an inner part toward a liquid surface, the ratio of a diameter of the seed crystal substrate 14 to a diameter of the crucible 10 is 0.51 or more, and shaft rotational speed of the seed crystal holding shaft 12 is 50 rpm or higher.SELECTED DRAWING: Figure 1

Description

  The present disclosure relates to a method for producing a SiC single crystal.

  SiC single crystals are very thermally and chemically stable, excellent in mechanical strength, resistant to radiation, and have excellent physical properties such as high breakdown voltage and high thermal conductivity compared to Si single crystals. . Therefore, it is possible to realize high output, high frequency, withstand voltage, environmental resistance, etc. that cannot be realized with existing semiconductor materials such as Si single crystal and GaAs single crystal, and power devices that enable high power control and energy saving. Expectations are growing as next-generation semiconductor materials in a wide range of materials, high-speed and large-capacity information communication device materials, in-vehicle high-temperature device materials, radiation-resistant device materials, and the like.

  Conventionally, as a method for growing a SiC single crystal, a gas phase method, an Acheson method, and a solution method are typically known. Among the vapor phase methods, for example, the sublimation method has drawbacks such as a hollow through defect called a micropipe defect, a lattice defect such as a stacking fault, and a crystal polymorphism easily occur in the grown single crystal. Conventionally, since many SiC bulk single crystals have been manufactured by a sublimation method, attempts have been made to reduce defects in grown crystals.

  In the Atchison method, since silica and coke are used as raw materials and heated in an electric furnace, it is impossible to obtain a single crystal with high crystallinity due to impurities in the raw materials.

  In the solution method, a Si melt, which is a melt containing Si and possibly other metals, is formed in a graphite crucible, and C is dissolved in the melt to obtain a Si-C solution, which is placed in a low temperature part. In this method, a seed crystal substrate is brought into contact with the solution, and a SiC crystal layer is deposited on the substrate to grow. In the solution method, since crystal growth is performed in a state close to thermal equilibrium as compared with the gas phase method, the reduction in defects can be most expected. For this reason, several methods for producing SiC single crystals by the solution method have recently been proposed (Patent Document 1).

JP 2009-249192 A

  It is known that there are 200 or more types of SiC crystals called crystal polymorphs having different laminated structures. When applying SiC crystal to a device, 4H crystal having the most excellent physical property value is preferably used. However, according to a conventional method such as Patent Document 1, it is difficult to stably obtain a desired 4H—SiC crystal.

  The present inventor has found that the crystal polymorph produced in the solution method is affected by the ratio between the size (diameter) of the seed crystal and the crucible inner diameter, and the relative velocity between the Si-C solution and the seed crystal during crystal growth. As a result, if these parameters are not sufficiently optimized, 6H, 15R and other variants grow so much that the incidence of 4H is not sufficiently high.

  In the present disclosure, a 4H—SiC single crystal is obtained by bringing a seed crystal substrate held on a seed crystal holding shaft into contact with a Si—C solution having a temperature gradient that decreases from the inside to the liquid surface arranged in a crucible. A method for producing a 4H-SiC single crystal for crystal growth,

  A method for producing a SiC single crystal, comprising a ratio of the diameter of the seed crystal substrate to the diameter (inner diameter) of the crucible of 0.51 or more and an axial rotation speed of the seed crystal holding shaft of 50 rpm or more. To do.

  According to the method of the present disclosure, the generation rate of 4H can be improved as compared with the conventional case in the production of an SiC single crystal by a solution method.

It is a cross-sectional schematic diagram for demonstrating the structure of the single-crystal manufacturing apparatus used in the Example. It is a schematic diagram of the crystal growth surface which shows the measurement point of the Raman spectroscopic analysis measured in the Example. It is the measurement example which showed the 4H-SiC pattern among the Raman charts measured in the Example. It is the measurement example which showed the 6H-SiC pattern among the Raman charts measured in the Example. It is the schematic for demonstrating the concept of the step flow growth in this indication.

  In the prior art, polymorphism is controlled by controlling the growth temperature and using 4H—SiC for the seed crystal substrate. In general, when the growth temperature is less than 1,700 ° C., 3C, when the growth temperature is 1,700 ° C. or more and 2,000 ° C. or less, 4H, and when 2,000 ° C. or more, 6H and 15R are stable phases.

  However, the solution growth method in the prior art can stably obtain a 4H-SiC single crystal even when crystal growth is performed in a growth temperature range where 4H-SiC should be obtained using a 4H-SiC seed crystal substrate. was difficult. For example, even when crystal growth was performed at a temperature of 1,700 ° C. or more and 2,000 ° C. or less using a 4H—SiC seed crystal substrate, the generation rate of 4H was about 10 to 20%.

  The present inventor found that the ratio of the size (diameter) of the seed crystal substrate to the inner diameter of the crucible, and the axial rotation speed of the seed crystal holding shaft during crystal growth (rotation speed of the seed crystal substrate) are 4H-SiC crystal growth. It was found that the stability was greatly affected.

  In the method of the present disclosure, the ratio of the diameter of the seed crystal substrate to the inner diameter of the crucible is set to 0.51 or more, and the axial rotation speed of the seed crystal holding shaft is set to 50 rpm or more, thereby yielding a desired 4H—SiC single crystal. Successfully gained well.

  That is, in the present disclosure, a 4H—SiC single crystal is obtained by bringing a seed crystal substrate held on a seed crystal holding shaft into contact with a Si—C solution having a temperature gradient that decreases in temperature from the inside to the liquid surface disposed in the crucible. 4H-SiC single crystal manufacturing method,

  The present invention is directed to a method for producing an SiC single crystal, wherein the ratio of the diameter of the seed crystal substrate to the inner diameter of the crucible is 0.51 or more, and the axial rotation speed of the seed crystal holding shaft is 50 rpm or more.

  According to the method of the present disclosure, the 4H generation rate can be improved as compared to the conventional case, and is preferably increased to 60%, more preferably 70% or more, still more preferably 80% or more, and particularly preferably 90% or more. be able to.

  Although not bound by theory, the mechanism of 4H generation rate improvement by the method of the present disclosure will be described below.

  Crystal growth proceeds by step flow growth. Step flow growth refers to an aspect in which crystals grow in such a manner that steps having the same direction and substantially equal intervals are sequentially formed on the crystal growth surface. Of the steps, the portion not covered by the next grown step is called a terrace, and the width of this terrace is called the step terrace width.

  As shown in FIG. 5A, when the step terrace width increases during crystal growth, nuclei other than 4H are generated on the terrace. Then, starting from the nucleus, variants such as 6H and 15R grow.

  Here, the smaller the inner diameter of the crucible or the larger the diameter of the seed crystal substrate, the smaller the area exposed to the surface of the Si—C solution. The heat radiation from the surface is suppressed, and the in-plane temperature distribution difference (horizontal temperature distribution difference = in-plane temperature gradient) is reduced.

  When the temperature gradient in the Si-C solution surface is small, the growth rate of step flow growth using the in-plane temperature gradient as a driving force is slow. When the step flow growth rate is slowed down, the step terrace width is reduced as shown in FIG. By reducing the step terrace width, it is considered that two-dimensional nuclei other than 4H are less likely to adhere, and 4H is easily generated stably.

  In addition, the boundary diffusion layer at the crystal growth interface becomes thinner as the axial rotation speed of the seed crystal holding shaft is higher. Usually, it is considered that the crystal growth rate is increased by thinning the boundary diffusion layer that controls the growth rate. Therefore, as the growth rate increases, the starting point of step flow growth is easily generated, and step flow occurs with a small step flow width from one to the next. For this reason, it is considered that two-dimensional nuclei other than 4H are less likely to adhere to the terrace as the shaft rotation speed increases.

  According to the method of the present disclosure, it is considered that the 4H generation rate can be improved by the above mechanism.

  As the crucible, a graphite crucible is preferable. The shape of the crucible is preferably a cylindrical shape from the viewpoint of minimizing the area where the Si—C solution is exposed on the surface.

  As the seed crystal substrate, a substrate made of 4H—SiC is preferably used. The shape of the growth surface of the seed crystal substrate is preferably a circle from the viewpoint of minimizing the area where the Si—C solution is exposed on the surface.

  When the crucible is cylindrical, the ratio of the diameter of the seed crystal substrate to the inner diameter of the crucible is 0.51 or more, preferably 0.60 or more, more preferably 0.70 or more, and still more preferably It is 0.80 or more, and particularly preferably 0.90 or more. The upper limit of the ratio of the diameter of the seed crystal substrate to the inner diameter of the crucible is less than 1.0.

  The inner diameter of the crucible can be appropriately set according to the scale of the single crystal manufacturing apparatus to be used, and can be set to, for example, 50 to 85 mm. The diameter of the seed crystal substrate is appropriately determined in accordance with the inner diameter of the crucible to be used within a range in which the predetermined ratio of the present invention can be realized.

  The shaft rotation speed of the seed crystal holding shaft is 50 rpm or more, preferably 100 rpm or more. The upper limit of the shaft rotation speed of the crystal holding shaft can be set to 150 rpm or less, for example.

  The surface temperature of the Si—C solution during crystal growth is preferably 1,800 to 2,100 ° C.

  The growth time can be appropriately set depending on the desired crystal growth amount. For example, a numerical value of 10 to 15 hours can be exemplified.

  The Si—C solution is preferably a Si—Cr system. The Si-Cr-based solution can be obtained by sufficiently dissolving C derived from the graphite crucible in a Si melt containing Si and Cr, and further containing other metals as necessary. .

  The Si concentration in the Si melt is preferably 30 at% or more based on the total amount of metal elements contained in the Si melt. The Cr concentration in the Si melt is preferably 20 to 60 at% based on the total amount of metal elements contained in the Si melt.

  The Si melt can contain other metals in addition to Si and Cr. The other metal is not particularly limited as long as it can form a liquid phase (solution) in thermodynamic equilibrium with SiC (solid phase). For example, Ti, Mn, Ni, Ce, Co, V, Fe, Al Etc.

  The incidence of 4H in the grown crystal can be quantified by performing Raman spectroscopic analysis on the growth surface of the grown crystal. Specific examples of preferred quantification procedures are as described in the examples below.

  Calculation of the 4H ratio in the following examples and comparative examples was performed by the following means.

  First, Raman spectroscopic analysis was performed on the growth surface using 13 points indicated by diamonds in FIG. 2 as measurement points. When the ratio of the measurement points which showed the Raman pattern applicable to 4H among these measurement points was 50% or more, it was determined that 4H-SiC grew at the measurement points. About the growth crystal | crystallization obtained by each Example and the comparative example, 5-15 samples were evaluated, respectively, and the ratio of the number of the crystals determined to be 4H was made into 4H ratio.

Example 1
A SiC single crystal having a diameter of 36 mm and a thickness of 700 μm, which is a disc-shaped 4H—SiC single crystal and having a (000-1) plane on the bottom surface, was prepared and used as a seed crystal substrate.

  The upper surface of the seed crystal substrate was bonded to the substantially central portion of the end surface of the columnar graphite shaft using a graphite adhesive. Using the single crystal manufacturing apparatus shown in FIG. 1, Si and Cr are charged into a graphite crucible with an inner diameter of 70 mm at an atomic composition ratio of Si: Cr = 60: 40 (at%) to form a Si—C solution. A liquid raw material was used. At this time, the ratio of the diameter of the seed crystal substrate to the diameter (inner diameter) of the crucible was 0.51.

After evacuating the inside of the single crystal manufacturing apparatus to 1 × 10 ⁻³ Pa, helium gas was introduced until the pressure became 1 atm, and the air inside the single crystal manufacturing apparatus was replaced with helium. Next, the high-frequency coil was energized and heated to melt the raw material in the graphite crucible, thereby forming a Si melt. Then, a sufficient amount of C was dissolved in the Si melt from the graphite crucible to form a Si—C solution.

  The graphite crucible is heated by adjusting the output of the upper coil and the lower coil, the temperature on the surface of the Si—C solution is raised to 1,950 ° C., and the solution is introduced from the inside of the solution within a range of 1 cm from the surface of the Si—C solution. The temperature gradient for decreasing the temperature toward the surface was controlled to be 30 ° C./cm. The surface temperature of the Si—C solution was measured with a radiation thermometer, and the temperature gradient of the Si—C solution was measured using a thermocouple movable in the vertical direction.

  The bottom surface of the seed crystal substrate bonded to the graphite shaft is parallel to the Si-C solution surface, and the position of the bottom surface of the seed crystal substrate is arranged at a position coinciding with the liquid surface of the Si-C solution. A seed touch was made to contact the lower surface of the seed crystal substrate. Next, crystal growth was performed by rotating the graphite shaft at a rotation speed of 50 rpm and maintaining the rotation state for 10 hours.

  After completion of crystal growth, the graphite shaft was raised and the shaft and the solution were cooled by natural cooling. Next, the seed crystal substrate and the SiC single crystal grown from the seed crystal substrate as a starting point were separated from the Si-C solution and the graphite shaft and collected. The thickness of the obtained growth crystal was 3 mm, and no roughness was observed on the growth surface.

  When the polymorph of the grown crystal was examined by Raman spectroscopic analysis (excitation at 532 nm, backscattering configuration), the ratio of 4H was 57%. The method of calculating the ratio of 4H was performed by the above-described means.

  In the Raman spectroscopic analysis measured above, a measurement example showing a 4H—SiC Raman pattern is shown in FIG. 3, and a measurement example showing a 6H—SiC Raman pattern is shown in FIG.

(Examples 2 to 4 and Comparative Examples 1 to 3)
Except that the inner diameter of the crucible used in Example 1 (crucible diameter), the diameter of the seed crystal substrate (seed diameter), and the rotation speed (shaft rotation speed) of the graphite shaft were as shown in Table 1, respectively. Crystal growth was carried out in the same manner as in Example 1, and Raman spectroscopic analysis of the grown crystal was performed.

  The results are shown in Table 1.

100 single crystal production apparatus 10 crucible 12 seed crystal holding shaft (graphite shaft)
14 seed crystal substrate 18 heat insulating material 22 high frequency coil 22A upper high frequency coil 22B lower high frequency coil 24 Si-C solution 26 quartz tube

Claims (1)

4H-SiC single crystal is grown by bringing the seed crystal substrate held on the seed crystal holding shaft into contact with the Si-C solution having a temperature gradient that decreases from the inside to the liquid surface arranged in the crucible. 4H-SiC single crystal manufacturing method,
A method for producing an SiC single crystal, comprising: setting a ratio of a diameter of the seed crystal substrate to a diameter of the crucible to be 0.51 or more and setting an axial rotation speed of the seed crystal holding shaft to be 50 rpm or more.

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