JP2017105681A - SiC SINGLE CRYSTAL MANUFACTURING APPARATUS - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a SiC single crystal manufacturing apparatus capable of manufacturing inexpensively with excellent reproductivity, a highly-uniform and high-quality SiC single crystal.SOLUTION: There is provided a SiC single crystal manufacturing apparatus 100 for growing a SiC single crystal by a solution method. The SiC single crystal manufacturing apparatus 100 has an induction heating coil 22, and in the SiC single crystal manufacturing apparatus, a tilt angle of an alternate magnetic flux penetrating the inside of the induction heating coil 22 is within ±0.9° to a vertical direction.SELECTED DRAWING: Figure 1

Description

  The present disclosure relates to a SiC single crystal manufacturing apparatus.

  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. Therefore, SiC single crystal is a next-generation semiconductor material in a wide range of power device materials that enable high power control and energy saving, device materials for high-speed and large-capacity information communication, high-temperature device materials for vehicles, radiation-resistant device materials, etc. As expectations are growing.

  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 heating is performed in an electric furnace using silica and coke as raw materials, it is impossible to obtain a single crystal with high crystallinity due to the influence of 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. This is a method in which a seed crystal substrate bonded and placed in a low temperature part is brought into contact with the solution to deposit and grow a SiC crystal layer on the substrate. 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.

  Several apparatuses for producing an SiC single crystal have been proposed. For example, a single crystal manufacturing apparatus including an induction heating coil as a heating means has been proposed (Patent Document 1).

JP2013-35705A

  Patent Document 1 describes a single crystal manufacturing apparatus including an induction heating coil for heating a raw material in a crucible, and a high-quality SiC single crystal with high uniformity can be manufactured with high reproducibility by the manufacturing apparatus. It is explained. However, according to the study of the present inventor, according to the heating technique using the induction heating coil described in Patent Document 1, a difference occurs in the crystal expansion angle during crystal growth, and the uniformity of the obtained SiC single crystal The results are not necessarily high enough.

  The present invention has been made to solve the above-described drawbacks of the prior art. Accordingly, an object of the present invention is to provide a SiC single crystal manufacturing apparatus capable of manufacturing a high-quality SiC single crystal with high uniformity and low cost with high reproducibility.

The present disclosure is a SiC single crystal manufacturing apparatus for crystal growth of a SiC single crystal by a solution method,
The SiC single crystal manufacturing apparatus includes an induction heating coil, and an inclination angle of an alternating magnetic flux passing through the induction heating coil is within ± 0.9 ° with respect to a vertical direction. Targeting single crystal manufacturing equipment.

  According to the apparatus of the present disclosure, a high-quality SiC single crystal with high uniformity can be manufactured at a low cost with good reproducibility.

FIG. 1 is a schematic cross-sectional view showing a basic configuration of a SiC single crystal manufacturing apparatus. FIG. 2 is a diagram schematically showing a wound state of the induction heating coil of the apparatus of FIG. FIG. 3 is a schematic cross-sectional view for explaining the definition of the gradient of the alternating magnetic field. FIG. 4 is a diagram schematically showing a wound state of the induction heating coil having a crank-shaped bent portion. FIG. 5 is a diagram schematically showing a wound state of the induction heating coil having ribs. FIG. 6 is an inclination angle measured on diameter surfaces in three directions with respect to an alternating magnetic field in the SiC single crystal manufacturing apparatus of Example 1 and Comparative Example 1. FIG. 7 is a photograph showing a state of liquid surface flow of the Si—C solution in Example 1 and Comparative Example 1, a value of flow deviation, a crystal expansion angle difference, and a photograph of a crystal growth surface. FIG. 8 is a schematic diagram for explaining the direction of the sensor of the magnetic field measuring apparatus used in the examples and comparative examples. FIG. 9 is a schematic diagram for explaining a method of measuring the inclination angle of the alternating magnetic field in the example and the comparative example.

  In the present specification, “−1” in the notation such as “(000-1) plane” is originally expressed as “−1” where a horizontal line is added on a number.

The SiC single crystal manufacturing apparatus of the present disclosure is
An SiC single crystal manufacturing apparatus for growing an SiC single crystal by a solution method,
The SiC single crystal manufacturing apparatus includes an induction heating coil, and an inclination angle of an alternating magnetic flux passing through the induction heating coil is within ± 0.9 ° with respect to a vertical direction.

  The inventor considered variously the reason why the SiC single crystal produced by the technique of Patent Document 1 lacks uniformity. As a result, the Si-C solution heated by the induction heating coil using the technique of Patent Document 1 has a large extent that the solution flow deviates from the in-plane symmetry, so that the crystal growth at the growth interface is not uniform. I found out. And it discovered that the in-plane asymmetry in the solution flow of this Si-C solution originates in the alternating magnetic field which generate | occur | produces in this coil by the induction heating coil inclining with respect to the perpendicular direction. In other words, when the alternating magnetic field is tilted, both the direction and strength of the Lorentz force on the concentric circles in the solution surface become asymmetric, and therefore, in-plane asymmetry occurs in the solution flow of the Si-C solution, which causes uniform crystal growth. It is a loss of sex.

In-plane asymmetry in solution flow can be expressed by the concept of “flow deviation”. this"
“Flow deviation” refers to a phenomenon in which the flow on the surface of the Si—C solution deviates from a concentric circle, and is evaluated by planarly quantifying the asymmetric shape from an image obtained by photographing the solution surface.

  In order to obtain a SiC single crystal suitable as a semiconductor material by a solution method, it has been found that it is effective to set the flow deviation in the Si—C solution to approximately 0.5 mm or less. And in order to implement | achieve such a flow gap, it discovered that it was effective to adjust the alternating magnetic flux which penetrates the inside of an induction heating coil as close to the perpendicular | vertical direction as possible. By making the direction of the alternating magnetic flux close to vertical, the symmetry of the Lorentz force in the solution is ensured. Then, since the in-plane symmetry in the solution flow of the Si—C solution increases, uniform crystal growth becomes possible.

  The present disclosure enables uniform crystal growth by adjusting the inclination angle of the alternating magnetic flux generated by the induction heating coil installed around the crucible within ± 0.9 ° with respect to the vertical direction. Is to clarify.

  In general, the induction heating coil in the prior art is spirally wound around a heat insulating material surrounding the crucible. Since the crucibles are arranged in the vertical direction, the spirally wound coils are gradually stacked while changing the height on the vertical line. Hereinafter, the gradient of the alternating magnetic flux will be described by taking as an example the case where the heat insulating material surrounding the crucible is cylindrical.

  FIG. 1 shows a basic configuration of an SiC single crystal manufacturing apparatus for manufacturing an SiC single crystal by a solution method.

  The SiC single crystal manufacturing apparatus 100 of FIG. 1 includes a crucible 10 containing an Si—C solution 24, and contacts a seed crystal substrate 14 held at the tip of a seed crystal holding shaft 12 that can be raised and lowered, with the Si—C solution 24. Thus, a SiC single crystal can be grown. The outer periphery of the crucible 10 is covered with a heat insulating material 18, and an induction heating coil 22 is wound around the outer periphery.

  The Si—C solution 24 is heated and stirred by applying a high frequency current to the induction heating coil 22. When a current is applied to the induction heating coil 22, an alternating magnetic flux (not shown) penetrating through the coil 22 is generated.

  The Si-C solution 24 is prepared by preferably dissolving C derived from a graphite crucible in a Si melt containing Si prepared by charging a raw material into the crucible 10 and heating and melting it. By making the crucible 10 a carbonaceous crucible such as a graphite crucible or an SiC crucible, C is dissolved in the melt from the crucible 10 to form an Si—C solution 24.

  The Si melt preferably contains Cr in addition to Si, and further contains at least one other metal selected from Ni, Al, Ti, Mn, Ce, Co, V, Fe, and the like. Also good.

  FIG. 2 schematically shows a wound state of the conventional induction heating coil 22 in the apparatus of FIG.

  FIG. 3A is a cross-sectional view when the wound coil shown in FIG. 2 is cut in the vertical direction at a diameter surface facing 180 °. When the coil is wound, for example, when the coil reaches the same position one round after an arbitrary point shown on the right side of FIG. 3A, a step having a distance corresponding to d is generated. When this step d is expressed by a gradient (coil gradient) θ with respect to the diameter R of the coil, θ = arctan (d / R) is calculated.

  The inclination angle of the alternating magnetic flux is the average value abs (θ1) between the polar angle of the magnetic field (θ1 in FIG. 3B) at an arbitrary point of the coil and the polar angle (θ2) of the magnetic field at a position 180 ° opposite thereto. Since it is equal to the total average of −θ2) / 2, it coincides with the coil gradient θ calculated from the step d of the coil and the diameter R of the coil (FIG. 3C). However, “abs (θ1−θ2)” indicates the absolute value of the difference between the polar angles θ1 and θ2.

  The polar angles θ1 and θ2 of the magnetic field in the coil can be measured using a commercially available magnetic field measuring device.

  By reducing the coil gradient θ, the inclination angle of the alternating magnetic field penetrating the inside of the coil can be made closer to the vertical direction. Alternatively, it is possible to adjust the gradient angle of the alternating magnetic field while maintaining the coil gradient θ at the same level as in the prior art, and bring it closer to the vertical direction. Hereinafter, these methods will be described.

  The first method is a method of adjusting the diameter R of the coil and the step d so that the coil gradient θ is within ± 0.9 °.

  The second method is to wind the coil so that the coil gradient θ is within ± 0.9 °, and when the coil reaches the coil of the previous cycle or just before that, the coil is bent into a crank shape. In this method, the coil winding is continued so that the coil gradient θ is within ± 0.9 ° again, avoiding duplication with the coil of the previous cycle. FIG. 4 shows the coil winding shape when the coil gradient is 0 ° by this method. According to this method, the coil gradient θ can be set to an arbitrary desired value regardless of the diameter R of the coil and the thickness of the single coil wire, and it is possible to set θ = 0 °. It is preferable in that the effect of can be maximized.

  The third method is a method of adjusting the inclination angle of the alternating magnetic field while maintaining the coil gradient θ at the same level as that of the prior art. For example, a method of providing ribs on or below the wound coil or both of them can be exemplified. The rib can be formed of a material having a property of attracting an alternating magnetic flux, and is preferably formed of a conductor such as iron or copper. The shape of the rib can be, for example, a wedge shape. FIG. 5 schematically shows an example of an induction heating coil having ribs 30 both above and below the wound coil.

  In the apparatus of the present disclosure, the inclination angle of the alternating magnetic flux passing through the inside of the induction heating coil is preferably adjusted to ± 0.9 ° or less by one or more of the first to third methods. As a result, it is possible to manufacture a high-quality SiC single crystal with high uniformity and low cost with good reproducibility.

  When the SiC single crystal is manufactured by applying the apparatus of the present disclosure, the crystal growth temperature is preferably 1,800 to 2,100 ° C.

  The crystal growth time can be appropriately set depending on the desired crystal growth amount. For example, it can be 10 hours or more or 15 hours or more. When the apparatus of the present disclosure is used, uniform crystals can be formed with high yield even when crystal growth is performed continuously for a long time.

  The SiC single crystal obtained by applying the apparatus of the present disclosure is excellent in uniformity. The uniformity of the SiC single crystal can be evaluated by, for example, a crystal expansion angle difference in crystal growth.

  When the SiC single crystal is grown by the solution method using the apparatus of the present disclosure, the position of the seed crystal substrate is determined so that only the lower surface of the seed crystal substrate is wetted by the Si-C solution to form a meniscus. It is preferable to grow crystals. At this time, as the crystal growth proceeds, the crystal growth surface gradually expands to generate a crystal expansion angle. In the prior art, the landing position of the seed crystal substrate fluctuates due to the asymmetry in the flow of the Si-C solution caused by high-frequency heating, so that an error occurs in the crystal expansion angle, and a uniform crystal is stably produced It was difficult.

  According to the apparatus of the present disclosure, since the in-plane symmetry of the Si—C solution is increased, the error of the crystal expansion angle can be reduced. When the SiC single crystal is grown by applying the apparatus of the present disclosure, the difference between the crystal expansion angles at two positions opposed to the crystal growth surface by 180 ° can be set to 10.3 ° or less, for example.

(Comparative Example 1)
A SiC single crystal having a diameter of 50.8 mm (2 inches) and a disc-shaped 4H—SiC single crystal having a thickness of 700 μm and having a (000-1) plane on the bottom is prepared. Used as a 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.

  As the single crystal manufacturing apparatus, the apparatus shown in FIG. 1 was used. As the crucible, a graphite crucible having an inner diameter of 120 mm and an outer diameter of 160 mm was used. The Si—C solution was prepared by dissolving a sufficient amount of C from a graphite crucible in the Si—Cr melt.

The induction heating coil specifications were as follows:
Size: Diameter 260mm, polyvalent 138mm
Coil wire diameter: 12mm
Number of windings: 8 turns Power frequency: 1.1 kHz
Coil winding state: spiral winding (Figure 2)

  The surface temperature of the Si—C solution was set at 2,000 ° C., and crystal growth was performed for 10 hours. At this time, regarding the alternating magnetic field generated in the induction heating coil, the inclination angles respectively measured on the diameter surfaces in the three directions by the method described later are shown in Table 1 and FIG. Moreover, the photograph which shows the mode of the liquid surface flow of a Si-C solution, the value of a fluid shift | offset | difference, the crystal expansion angle difference, and the photograph of the crystal growth surface were shown in FIG. In FIG. 7, “Re” means rear (rear) and “Fr” means front (front), which are relative positions with the front of the single crystal manufacturing apparatus as the front. In FIG. 9A, the 90 ° position corresponds to “Fr”, and the 270 ° position corresponds to “Re”.

  In this comparative example 1, the gradient angle of the alternating magnetic field reaches a maximum of 2.4 °, the flow deviation of the Si—C solution is 19 mm, the crystal expansion angle difference is 35 °, and the crystal growth surface is non-uniform. there were.

Example 1
Crystal growth was performed under the same conditions as in Comparative Example 1 except that the induction heating coil was wound in the form of FIG. 4 having a crank-shaped bent portion with a coil gradient of 0 °. In Example 1, the inclination angle of the alternating magnetic field is ± 0.9 ° or less, the flow deviation of the Si—C solution is 0.5 mm, the crystal expansion angle difference is 10.3 °, and the crystal growth surface is It was uniform (Table 1, FIG. 6, and FIG. 7).

  From the above results, it is possible to obtain high-quality SiC crystals with high uniformity by the solution method by adjusting the inclination angle of the alternating magnetic flux passing through the induction heating coil within ± 0.9 ° with respect to the vertical direction. Was verified.

(Measurement method of tilt angle of alternating magnetic field)
When the induction coil was viewed from above, the position of the measurement location azimuth 0 ° was arbitrarily determined, and 6 measurement points were set in increments of 0 ° to 45 ° (FIG. 9A). Of these 6 measurement points, the 0 ° measurement point and the 180 ° measurement point are a pair of measurement points that define a diameter surface opposite to each other by 180 °, and the 45 ° measurement point and the 225 ° measurement point are a pair. The measurement point becomes a measurement point, and the measurement point of 90 ° and the measurement point of 270 ° become a pair of measurement points (FIG. 9B).

  A sensor of a commercially available magnetic field measuring device was set so that the direction of the cone formed an angle of 35.3 ° with respect to the horizontal axis (see FIG. 8), and the sensor in this state was placed in an induction heating coil. Here, at each measurement point, the cone of the sensor is parallel to the straight line connecting the pair of measurement points, the straight line passing through the center of the cone takes an offset of 35 mm from the straight line connecting the pair of measurement points, and the spherical shape of the sensor The distance between the tip of the part and the nearest coil was set to 30 mm (see FIG. 9).

  Although FIG. 9 depicts that the magnetic field measuring device has six sensors, this is for convenience of explanation, and one sensor is rotated as shown in FIG. The polar angle of the magnetic field was measured. Table 1 shows the measurement results at each measurement point and the inclination angle of the alternating magnetic field calculated from the measurement results.

DESCRIPTION OF SYMBOLS 100 Single crystal manufacturing apparatus 10 Crucible 12 Seed crystal holding shaft 14 Seed crystal substrate 18 Heat insulating material 22 Induction heating coil 24 Si-C solution 30 Rib d Step R Induction heating coil diameter θ1 Polar angle of magnetic field at arbitrary measurement point θ2 θ1 The polar angle of the magnetic field at the measurement point that makes a pair θ Coil gradient = inclination angle of the alternating magnetic field

Claims (1)

An SiC single crystal manufacturing apparatus for growing an SiC single crystal by a solution method,
The SiC single crystal manufacturing apparatus includes an induction heating coil, and an inclination angle of an alternating magnetic flux passing through the induction heating coil is within ± 0.9 ° with respect to a vertical direction. Single crystal manufacturing equipment.