JP7761938B2 - Raw material container for sublimation growth equipment - Google Patents

Description

This disclosure relates to a source container used in a sublimation growth apparatus that sublimates a source material, such as silicon carbide, to grow a single crystal on a seed crystal.

Silicon carbide (SiC) has a wide range of applications, including semiconductor devices, due to its ability to efficiently control large amounts of power compared to silicon (Si). To ensure uniformity in the characteristics of various devices, it is preferable to grow silicon carbide as a single crystal. A method known as sublimation recrystallization is used to produce silicon carbide single crystals. This method involves heating raw silicon carbide powder contained in a source container to a high temperature of 2000°C or higher, causing it to sublimate, and then growing the powder on a seed crystal placed away from the source material, thereby producing silicon carbide single crystals (see, for example, Patent Documents 1 and 2).

The raw material container in Patent Document 1 is composed of a graphite crucible whose upper opening has an inner diameter smaller than that of the center, and whose bottom has an inner diameter smaller than that of the upper opening. The raw material container in Patent Document 2 is composed of an upper crucible outer cylinder, a crucible bottom, and multiple additional crucible outer cylinders detachably arranged between them, and the additional crucible outer cylinders allow the length to be adjusted vertically.

Japanese Patent Application Publication No. 5-330995 Japanese Patent Application Publication No. 3-295898

When forming semiconductor elements from silicon carbide, silicon carbide substrates are used, but there is a demand to increase the diameter of silicon carbide substrates in order to improve the productivity of semiconductor elements. To manufacture substrates with a larger diameter, it is necessary to increase the size of the container in which the raw material is stored, particularly the diameter of the container.

If the raw material container is constructed using a graphite crucible as in Patent Documents 1 and 2, it becomes possible to use an induction heating source that utilizes electromagnetic induction as the heating source. With an induction heating source, if there are variations in the eddy current density in the raw material container, the temperature distribution inside the container will become uneven. This problem becomes even more pronounced as the container becomes larger, as mentioned above.

In this regard, with a one-piece raw material container like the one in Patent Document 1, it is not possible to actively eliminate variations in eddy current density, making it difficult to achieve a uniform temperature distribution within a large container. Furthermore, in Patent Document 2, an additional crucible outer cylinder is disposed between the upper crucible outer cylinder and the crucible bottom, but this additional crucible outer cylinder is only used to adjust the length of the raw material container and does not eliminate variations in eddy current density.

The present disclosure has been made in light of these issues, and its purpose is to reduce variations in eddy current density during induction heating and achieve uniform temperature distribution within the container, even when the container in which the raw materials are stored is enlarged.

To achieve the above objective, one aspect of the present disclosure can be based on a source material container for a sublimation growth apparatus used in a sublimation growth apparatus that sublimates a source material to grow a single crystal on a seed crystal. The source material container for a sublimation growth apparatus includes a bottom wall portion made of a bottom plate material that is circular in plan view, and a peripheral wall portion disposed on top of the bottom plate portion and placed within a circular induction heating source. The peripheral wall portion is circular in plan view and is composed of multiple peripheral wall components made of a conductive material connected in the vertical direction.

With this configuration, the induction heating source is positioned to surround the outside of the peripheral wall of the raw material container. When current is applied to the induction heating source, eddy currents are generated in each of the peripheral wall components that make up the peripheral wall, causing each peripheral wall component to heat up and heat the raw material. Because both the peripheral wall components and the induction heating source are annular, the eddy currents generated in each peripheral wall component can be contained within the peripheral wall component, making the eddy currents uniform in the circumferential direction. This also uniforms the temperature distribution within the container.

In addition, because the raw material container is made up of a bottom plate material and multiple peripheral wall components, each part is smaller than if they were molded as a single unit, making manufacturing easier. Furthermore, if any of the bottom plate material or multiple peripheral wall components becomes damaged, only the damaged component needs to be replaced, reducing maintenance costs.

The plurality of peripheral wall constituent members may also include a first peripheral wall constituent member and a second peripheral wall constituent member connected to the top of the first peripheral wall constituent member. In this case, a protrusion that protrudes upward and extends circumferentially can be formed on the upper part of the first peripheral wall constituent member, and a recess that accommodates the protrusion can be formed on the lower part of the second peripheral wall constituent member. With this configuration, by accommodating the protrusion of the first peripheral wall constituent member in the recess of the second peripheral wall constituent member, the first peripheral wall constituent member and the second peripheral wall constituent member can be fitted together in a recess-projection manner, thereby preventing relative positional misalignment.

Furthermore, the specific resistance of the conductive material can be set in the range of 10 ⁻⁵ Ωcm to 10 ⁻² Ωcm, thereby enabling induction heating to be carried out efficiently.

The raw material contained in the raw material container may also be silicon carbide powder. The peripheral wall portion may also be formed by connecting multiple peripheral wall components having different thicknesses or vertical dimensions. In other words, if the thicknesses or vertical dimensions of the peripheral wall components differ, the eddy current density during induction heating will change, making it possible to control the heating temperature depending on the location of the raw material container.

Furthermore, the multiple peripheral wall components may be the same shape and size. This allows the peripheral wall components to be constructed using common materials, thereby reducing costs.

As explained above, the peripheral wall of the source container is constructed by connecting annular peripheral wall components made of conductive material in the vertical direction, which makes it possible to homogenize eddy currents that occur during induction heating. This makes it possible to homogenize the temperature distribution inside the source container, even if the source container is large.

1 is a block diagram showing the configuration of a sublimation growth apparatus according to an embodiment of the present invention. FIG. 2 is a perspective view of the container seen from above. FIG. 4 is a cross-sectional view taken along line IV-IV in FIG. 3. FIG. 2 is a perspective view showing a state in which a raw material pot is placed on the bottom wall portion. FIG. 2 is a perspective view of a raw material pot. 10 is a flowchart showing an example of a control procedure performed by the control device. FIG. 10 is a diagram schematically illustrating the flow of a thermal fluid near a seed crystal when there is no gas outlet. FIG. 10 is a diagram schematically illustrating the flow of a thermal fluid near a seed crystal when a gas outlet is provided. 9A and 9B show a container and a resistance heating source according to a first modified example of the embodiment, in which FIG. 9A is a plan view and FIG. 9B is a cross-sectional view taken along line IX-IX. 10A and 10B show a container and a resistance heating source according to a second modified example of the embodiment, in which FIG. 10A is a plan view and FIG. 10B is a cross-sectional view taken along line XX.

Embodiments of the present invention will now be described in detail with reference to the accompanying drawings. Note that the following description of the preferred embodiment is merely exemplary in nature and is not intended to limit the present invention, its applications, or its uses.

Figure 1 is a block diagram showing the configuration of a sublimation growth apparatus 1 according to an embodiment of the present invention. The sublimation growth apparatus 1 is an apparatus for heating powdered raw material B to its sublimation temperature to sublimate it, and then attaching the sublimated raw material to a seed crystal A to grow a single crystal. Raw material B is, for example, silicon carbide (SiC) powder. Silicon carbide powder can be made into powder having an average particle size within a predetermined range by, for example, disintegrating or classifying it. The sublimation temperature of silicon carbide is 2000°C or higher, for example, 2100°C to 2400°C. The single crystal silicon carbide obtained in the sublimation growth apparatus 1 is processed, for example, into wafers and used as a material for semiconductor devices.

Sublimation growth apparatus 1 comprises a single crystal generation unit 10 that grows silicon carbide single crystals to produce large-diameter single crystals, a control unit 50 that controls single crystal generation unit 10, an operation panel 60, and a memory unit 61. Single crystal generation unit 10 and control unit 50 are spaced apart so that control unit 50 is not affected by heat radiated from single crystal generation unit 10. "Large diameter" refers to a large diameter of the silicon carbide single crystal; for example, single crystals with diameters of 6 inches or more or 8 inches or more can be produced using sublimation growth apparatus 1. Therefore, sublimation growth apparatus 1 can also be called a manufacturing apparatus for producing silicon carbide single crystals, and this sublimation growth apparatus 1 can be used to carry out a method for manufacturing silicon carbide single crystals.

(Configuration of single crystal generating unit 10)
The single crystal growing unit 10 includes a chamber 11, a container 20 containing raw material B, a support member 30 supporting a seed crystal A, induction heating sources 41-43, and a resistance heating source 44. The induction heating sources 41-43 and the resistance heating source 44 heat the raw material B contained in the container 20 to its sublimation temperature. The resistance heating source 44 can be used as a first heating source, and the induction heating sources 41-43 can be used as second heating sources. The chamber 11 is a water-cooled chamber made of, for example, quartz, and is airtight enough to maintain a vacuum state inside. A vacuum device (high vacuum exhaust device) for vacuuming is connected to the chamber 11 (not shown). Before starting single crystal production, the chamber 11 is evacuated by the vacuum device. The chamber 11 also includes a water channel (not shown) through which cooling water flows.

Container 20 is a source container for the sublimation growth apparatus 1, and is housed entirely within chamber 11. As shown in Figures 2 to 4, container 20 has a bottom wall 21 and a peripheral wall 22. Bottom wall 21 is composed of a bottom plate 21A that is circular in plan view, and is installed within chamber 11 so that bottom plate 21A is horizontal. A vertical line passing through the radial center of bottom plate 21A is the axis 200 of container 20, and container 20 has a rotationally symmetrical shape with axis 200 as its axis of symmetry.

As shown in Figure 4, an annular portion 21a that protrudes upward and extends continuously in the circumferential direction is integrally formed on the peripheral edge of the bottom plate material 21A. The integral formation of the annular portion 31a improves the rigidity of the bottom plate material 21A. A lower protrusion 21b that protrudes upward and extends continuously in the circumferential direction is formed on the outer peripheral side of the upper part of the annular portion 21a.

A through-hole 21c is formed in the center of the bottom plate material 21A, penetrating in the vertical direction, which is the thickness direction of the bottom plate material 21A. The through-hole 21c is circular, and the radial center of the through-hole 21c coincides with the radial center of the bottom plate material 21A. A recess 21d is formed in the upper surface (inner surface of the container) of the bottom plate material 21A. This recess 21d extends in an annular shape to surround the through-hole 21c. In addition, a protrusion 21e that protrudes downward is formed on the lower surface (outer surface of the container) of the bottom plate material 21A. The protrusion 21e also extends in an annular shape to surround the through-hole 21c.

As shown in Figure 1, the peripheral wall portion 22 is disposed on the bottom plate material 21A and is located within the annular induction heating sources 41-43. As shown in Figures 2-4, the peripheral wall portion 22 is annular in plan view and is configured by connecting multiple peripheral wall components 22A-22G made of conductive material in the vertical direction. In this embodiment, the cylindrical peripheral wall portion 22 is configured by combining seven peripheral wall components 22A-22G, but the number of peripheral wall components is not limited to seven and may be any number of six or less, or any number of eight or more.

Of the peripheral wall constituent members 22A-22G, the lowest one is designated the first peripheral wall constituent member 22A, the member connected to the first peripheral wall constituent member 22A while overlapping it is designated the second peripheral wall constituent member 22B, the member connected to the second peripheral wall constituent member 22B while overlapping it is designated the third peripheral wall constituent member 22C, the member connected to the third peripheral wall constituent member 22C while overlapping it is designated the fourth peripheral wall constituent member 22D, the member connected to the fourth peripheral wall constituent member 22D while overlapping it is designated the fifth peripheral wall constituent member 22E, the member connected to the fifth peripheral wall constituent member 22E while overlapping it is designated the sixth peripheral wall constituent member 22F, and the member connected to the sixth peripheral wall constituent member 22F while overlapping it is designated the seventh peripheral wall constituent member 22G. The first to seventh peripheral wall constituent members 22A-22G are members of the same shape and size, i.e., the same members. This allows the peripheral wall components 22A-22G to be constructed using common materials, reducing costs.

As shown in Figure 4, a first recess 22a is formed on the outer circumferential side of the lower portion of the first peripheral wall component 22A, into which the lower protrusion 21b of the bottom plate material 21A is accommodated. The first recess 22a extends continuously in the circumferential direction of the first peripheral wall component 22A. When the lower protrusion 21b of the bottom plate material 21A is accommodated in the first recess 22a, the two are fitted together, preventing relative radial movement of the first peripheral wall component 22A with respect to the bottom plate material 21A. This concave-convex fit also improves the airtightness of the container 20. The same applies to the joining structure of the peripheral wall components 22A-22G.

A first protrusion 22b that protrudes upward and extends circumferentially is formed on the outer periphery of the upper portion of the first peripheral wall component 22A. The shape and size of this first protrusion 22b are the same as the shape and size of the lower protrusion 21b of the bottom plate material 21A.

A second recess 22c is formed on the outer peripheral side of the lower part of the second peripheral wall component 22B, into which the first protrusion 22b of the first peripheral wall component 22A is accommodated. The shape and size of the second recess 22c are the same as those of the first recess 22a. When the first protrusion 22b of the first peripheral wall component 22A is accommodated in the second recess 22c of the second peripheral wall component 22B, the two are fitted together, and radial movement of the second peripheral wall component 22B relative to the first peripheral wall component 22A is prevented.

Similarly, a second protrusion 22d that protrudes upward and extends circumferentially is formed on the outer peripheral side of the upper part of the second peripheral wall component 22B, and a third recess 22e that accommodates the second protrusion 22d of the second peripheral wall component 22B is formed on the outer peripheral side of the lower part of the third peripheral wall component 22C. The same is true for the third to seventh peripheral wall component members 22C to 22G. As a result, the first to seventh peripheral wall component members 22A to 22G do not move radially relative to each other, and a peripheral wall portion 22 with a predetermined shape is formed.

The bottom plate material 21A and the first to seventh peripheral wall components 22A to 22G are made of a conductive material. The conductive material is, for example, high-purity graphite with an extremely low impurity content, and the specific resistance of this conductive material is 10 ⁻⁵ Ωcm or more and 10 ⁻² Ωcm or less. By setting the specific resistance within this range, eddy currents can be efficiently generated during induction heating by the induction heating sources 41 to 43 described below, thereby improving the heating efficiency of the raw material B. The graphite may contain trace amounts of impurities, such as B, Na, K, Si, Mg, Al, Fe, and Ca. Even if trace amounts of these elements are present, the heating efficiency is not significantly affected.

In this embodiment, the first through seventh peripheral wall constituent members 22A-22G are made of the same material, but this is not limited to this. For example, the peripheral wall portion 22 may be formed by vertically connecting the first through seventh peripheral wall constituent members 22A-22G that have different thicknesses or vertical dimensions. In other words, if the first through seventh peripheral wall constituent members 22A-22G have different thicknesses or vertical dimensions, the eddy current density during induction heating by the induction heating sources 41-43 will change, and it will become possible to control the heating temperature depending on the location of the container 20.

Furthermore, because the container 20 is composed of a bottom plate material 21A and multiple peripheral wall components 22A-22G, each part is smaller than if they were molded as a single unit, making manufacturing easier. Furthermore, if any of the bottom plate material 21A or multiple peripheral wall components 22A-22G is damaged, only the damaged component needs to be replaced, reducing maintenance costs.

The interior of the container 20 is provided with a cover member 23 for covering the resistance heating source 44 and multiple raw material pods 24. The cover member 23 has a cylindrical portion 23a and an upper plate portion 23b, and is entirely made of the above-mentioned conductive material. A flange portion 23c is formed at the lower end of the cylindrical portion 23a, protruding radially outward and extending continuously in the circumferential direction. This flange portion 23c is designed to fit into a recess portion 21d in the bottom plate material 21A. With the flange portion 23c fitted into the recess portion 21d, the cover member 23 is prevented from moving radially relative to the bottom plate material 21A.

The inner diameter of the cylindrical portion 23a is set to be the same as the inner diameter of the through-hole 21c of the bottom plate material 21A. The axis of the cylindrical portion 23a coincides with the axis 200 of the container 20, and the cylindrical portion 23a is positioned in the center of the container 20 in a plan view. The height of the cylindrical portion 23a is set to be the same as or higher than the height of the raw material pod 24. The upper plate portion 23b is provided at the upper end of the cylindrical portion 23a, and the upper opening of the cylindrical portion 23a is closed by the upper plate portion 23b. Meanwhile, the lower end of the cylindrical portion 23a is open downward, meaning that the cover member 23 is only open downward.

The raw material pods 24 are components that contain raw material B, and are placed on the upper surface of the bottom plate material 21A as shown in Figure 5. In this embodiment, six raw material pods 24 are arranged at equal intervals around the through-hole 21c, i.e., surrounding the axis 200 of the container 20. The number of raw material pods 24 is not limited to six, and may be any number up to five, or any number of seven or more. Furthermore, the raw material pods 24 do not have to be arranged at equal intervals, and may also be arranged at uneven intervals.

All six raw material pods 24 are constructed from materials of the same shape and size. This allows the raw material pods 24 to be constructed from common materials, reducing costs and ensuring uniform heating temperatures for raw material B in each raw material pod 24.

As shown in FIG. 6, each raw material pod 24 comprises a pod body 24a and a lid member 24b. The pod body 24a and lid member 24b are entirely made of the above-mentioned conductive material. The pod body 24a has a cylindrical shape with a bottom, and its outer diameter is set to be smaller than the outer diameter of the cylindrical portion 23a of the cover member 23. The outer diameter of the pod body 24a may be the same as the outer diameter of the cylindrical portion 23a of the cover member 23, or may be larger than the outer diameter of the cylindrical portion 23a.

The height of the pod body 24a is set to be approximately the same as the height of the cylindrical portion 23a of the cover member 23. In other words, the height dimensions of the pod body 24a and the cylindrical portion 23a are set so that the height of the pod body 24a and the height of the cylindrical portion 23a are approximately the same. Note that the height of the pod body 24a may be higher or lower than the height of the cylindrical portion 23a of the cover member 23.

The lid member 24b is provided to cover the upper end of the pod body 24a and is composed of a circular plate-shaped member. The lid member 24b is provided with an exhaust port 24c that penetrates the lid member 24b in the vertical direction, for exhausting the sublimation gas generated by the sublimation of the raw material B in the pod body 24a. In other words, by providing the exhaust port 24c in the upper part of the raw material pod 24, the sublimation gas generated within the pod body 24a can be efficiently released to the outside of the raw material pod 24. The exhaust port 24c opens at the upper end of the raw material pod 24, and is therefore an upper-end opening. The lid member 24b may be provided as needed, and may be omitted.

The exhaust port 24c is located at a position radially eccentric from the center of the lid member 24b. In this embodiment, the exhaust port 24c is located on the side of the lid member 24b that is closer to the axis 200 of the container 20. The exhaust port 24c may be located at the center of the lid member 24b, or on the side that is farther from the axis 200 of the container 20. The lid member 24b may have only one exhaust port 24c, or two or more exhaust ports 24c.

The exhaust port 24c is circular in shape. The diameter of the exhaust port 24c is set in the range of 1 mm to 30 mm. In other words, if the diameter of the exhaust port 24c is smaller than 1 mm, the exhaust port 24c is more likely to become clogged, hindering the growth of the single crystal. On the other hand, if the diameter of the exhaust port 24c is larger than 30 mm, large vapors are more likely to be released from the raw material pod 24, which can lead to a deterioration in the quality of the single crystal. Therefore, by setting the diameter of the exhaust port 24c within the above range, stable growth and improved quality of the single crystal can be achieved.

In this embodiment, the heat source for heating raw material B includes multiple induction heating sources 41-43 arranged at intervals from one another, and at least one resistance heating source 44 arranged in a location separate from the induction heating sources 41-43. Details of the heat sources are described below.

The induction heating sources 41-43 include an upper induction heating source (first induction heating source) 41, an intermediate induction heating source (second induction heating source) 42, and a lower induction heating source 43. The upper induction heating source 41, intermediate induction heating source 42, and lower induction heating source 43 each have an induction heating coil made of a conductor formed in a circular ring shape with a diameter larger than the outer diameter of the chamber 11, and are configured so that induction heating can be applied to the inner components by passing a current through this induction heating coil. The upper induction heating source 41, intermediate induction heating source 42, and lower induction heating source 43 can be fixed to the chamber 11 by fixing members (not shown).

The upper induction heating source 41 is disposed outside the peripheral wall 22 of the container 20 near the upper end, surrounding the peripheral wall 22 from the outside (outside the chamber 11). The height (vertical position) of the upper induction heating source 41 is higher than the upper end of the ingredient pod 24 and the upper end of the cover member 23, and is approximately the same height as the seventh peripheral wall component 22G. The lower induction heating source 43 is disposed outside the peripheral wall 22 of the container 20 near the lower end, surrounding the peripheral wall 22 from the outside (outside the chamber 11). The height of the lower induction heating source 43 is approximately the same height as the lower end of the ingredient pod 24 and the lower end of the cover member 23, and is set to be approximately the same height as the first peripheral wall component 22A. The intermediate induction heating source 42 is disposed outside the peripheral wall 22 between the lower induction heating source 43 and the upper induction heating source 41. The height of the intermediate induction heating source 42 is set to approximately the same height as the upper end of the raw material pod 24 and the upper end of the cover member 23.

A gap is formed between the upper induction heating source 41 and the intermediate induction heating source 42, and the upper induction heating source 41 and the intermediate induction heating source 42 are arranged vertically apart by a first predetermined distance. A gap is also formed between the intermediate induction heating source 42 and the lower induction heating source 43, and the intermediate induction heating source 42 and the lower induction heating source 43 are arranged vertically apart by a second predetermined distance. The first predetermined distance and the second predetermined distance may be the same or different.

The heating capacity per unit time of the upper induction heating source 41, intermediate induction heating source 42, and lower induction heating source 43 can be set as desired depending on the diameter and number of turns of the conductor wire used, the current value passed through the conductor wire, etc. The heating capacity per unit time of the lower induction heating source 43 is set higher than that of the upper induction heating source 41, and the heating capacity per unit time of the lower induction heating source 43 is set higher than that of the intermediate induction heating source 42. In other words, of the upper induction heating source 41, intermediate induction heating source 42, and lower induction heating source 43, the lower induction heating source 43 has the highest heating capacity. The heating capacity of the upper induction heating source 41 and intermediate induction heating source 42 may be the same, or the upper induction heating source 41 or the intermediate induction heating source 42 may be higher.

The number of induction heating sources is not limited to three, but may be two or less, or four or more.

The resistance heating source 44 is positioned so that it protrudes from the bottom wall 21 of the vessel 20 into the space enclosed by the peripheral wall 22. Specifically, the resistance heating source 44 has a conductor that generates Joule heat, and this conductor is formed so that it extends vertically. The vertical dimension of the resistance heating source 44 is set to be longer than the combined vertical dimensions of the multiple peripheral wall components 22A-22G. The resistance heating source 44 is positioned so that its longitudinal direction faces the vertical direction, extending from within the through-hole 21c of the bottom plate 21A to the cylindrical portion 23a of the cover member 23. The resistance heating source 44 is fixed to the chamber 11 or the like by a fixing member (not shown) so that the resistance heating source 44 is located in the radial center of the cylindrical portion 23a. As a result, the resistance heating source 44 is positioned in the center of the vessel 20 in a plan view. Furthermore, the positional relationship between the multiple raw material pods 24 and the resistance heating source 44 is such that the multiple raw material pods 24 surround the resistance heating source 44.

The upper end of the resistance heating source 44 arranged as described above is positioned at the same height as the upper portion of the raw material pod 24, and the lower end of the resistance heating source 44 is positioned below the lower portion of the raw material pod 24. This allows heat radiated from the resistance heating source 44 to be transferred from the upper portion to the lower portion of the raw material pod 24 via the cover member 23. The resistance heating source 44 is also configured to radiate heat in any horizontal direction. This allows multiple raw material pods 24 to be heated in the same way.

As shown in FIG. 1, the support member 30 is a member that supports the seed crystal A facing downward at the top of the vessel 20 inside the vessel 20. Specifically, the support member 30 is housed in the upper part of the chamber 11 and is composed of a circular plate arranged to cover the top opening of the vessel 20, with the seed crystal A provided on the underside of the support member 30. Therefore, the exhaust port 24c of each raw material pod 24 is positioned below the seed crystal A, and the seed crystal A and each exhaust port 24c are positioned opposite each other in the vertical direction. The growth direction of the seed crystal A is downward.

The single crystal generating unit 10 is equipped with a rotation mechanism 45 that rotates the support member 30 around an axis extending in the vertical direction. The rotation mechanism 45 is equipped with an electric motor 45a and a rotation shaft 45b to which the output of the electric motor 45a is transmitted. The rotation shaft 45b extends vertically and is positioned so as to penetrate the upper wall of the chamber 11 in the vertical direction, with the lower portion of the rotation shaft 45b fixed to the radial center of the support member 30. A bearing member 11a that rotatably supports the rotation shaft 45b is provided on the upper wall of the chamber 11. This bearing member 11a has a sealing mechanism that can maintain the vacuum state within the chamber 11 and is configured to withstand heat radiated from the heating source.

The output of the electric motor 45a is transmitted to the rotating shaft 45b via a transmission gear 45c, a transmission chain (not shown), etc. This causes the support member 30 to rotate above the exhaust port 24c of each raw material pod 24. The rotation speed of the support member 30 can be changed by controlling the electric motor 45a with the control device 50, and the rotation direction of the support member 30 and the timing of starting and stopping rotation can also be changed by controlling the electric motor 45a with the control device 50. Note that the support member 30 may also be driven directly by the electric motor 45a without the use of a transmission gear 45c, a transmission chain, etc.

A gas outlet 25 for discharging sublimation gas from the raw material is provided in the container 20 above the seed crystal A. Positioning the gas outlet 25 above the seed crystal A allows sublimation gas generated below the seed crystal A to flow upward and be guided to the seed crystal A. The gas outlet 25 is formed between the periphery of the support member 30 and the peripheral edge of the upper opening of the container 20. Although not shown, the gas outlet 25 may be formed around the seed crystal A on the support member 30. Multiple gas outlets 25 may also be formed. In this case, it is preferable to arrange the multiple gas outlets 25 at intervals around the circumference of the container 20. The diameter of the gas outlet 25 can be set to the same diameter as the exhaust port 24c of the raw material pod 24. The gas outlet 25 may also be a slit-shaped outlet that is long in the circumferential direction of the container 20.

The single crystal growing unit 10 is equipped with an upper temperature sensor (first temperature sensor) 46 and a lower temperature sensor (second temperature sensor) 47, which acquire the temperature of the vessel 20 and output the acquired data to the control device 50. The upper temperature sensor 46 and the lower temperature sensor 47 are infrared thermometers that measure the temperature based on infrared radiation emitted from an object without contacting the object. The upper temperature sensor 46 is positioned opposite the upper wall of the chamber 11 and directly measures the temperature of the upper wall of the chamber 11. However, since the upper wall of the chamber 11 and the upper part of the vessel 20 are close to each other, the temperature of the upper part of the vessel 20 can be acquired by measuring the temperature of the upper wall of the chamber 11. For example, by determining the temperature relationship between the upper wall of the chamber 11 and the upper part of the vessel 20 through prior experimentation, the temperature of the upper part of the vessel 20 can be estimated simply by measuring the temperature of the upper wall of the chamber 11. The estimated temperature is used as the temperature of the upper part of the vessel 20 in the PID control described below.

The lower temperature sensor 47 is positioned opposite the lower wall of the chamber 11 and directly measures the temperature of the lower wall of the chamber 11. However, as with the upper temperature sensor 46, by determining the relationship between the lower wall of the chamber 11 and the lower part of the container 20 (bottom wall 21) in advance through experiments, etc., it becomes possible to estimate the temperature of the lower part of the container 20 simply by measuring the temperature of the lower wall of the chamber 11. The estimated temperature is used in the PID control described below as the temperature state of the lower part of the container 20.

If a temperature sensor capable of directly measuring the temperature of the container 20 is available, the temperature state of the container 20 can be accurately obtained by using that temperature sensor. Even when the temperature state is obtained based on estimates from the upper temperature sensor 46 and the lower temperature sensor 47 described above, it is possible to control each heat source so that raw material B can be sublimated as intended. The number of temperature sensors is not limited to two, and may be one, or three or more. The upper temperature sensor 46 and the lower temperature sensor 47 are positioned to measure temperatures at locations distant from the induction heating sources 41-43, ensuring accurate temperature estimation of the container 20. Heating control of the upper induction heating source 41 may be performed based on the output value of the upper temperature sensor 46, or heating control of the induction heating sources 41-43 and the resistance heating source 44 may be performed based on the output values of both the upper temperature sensor 46 and the lower temperature sensor 47. A temperature sensor may also be provided to obtain the temperature state of the side of the container 20.

(Configuration of the control device 50)
The control device 50 is a device for controlling the induction heating sources 41 to 43, the resistance heating source 44, and the rotation mechanism 45, and includes a vacuum pressure sensor 51, a gas flow sensor 52, a PID control unit 53, a phase control unit 54, a power control module 55, and power supply circuits 56 to 58. The PID control unit 53 and the phase control unit 54 are configured by a combination of hardware such as a microcomputer and software executable by the hardware. The phase control unit 54, the power control module 55, and the power supply circuits 56 to 58 are connected to the PID control unit 53.

The vacuum pressure sensor 51 is a sensor that detects the pressure inside the chamber 11, i.e., whether the pressure inside the chamber 11 is equal to or lower than a predetermined pressure (a pressure that creates a vacuum state). In this embodiment, the vacuum state does not have to be a complete vacuum, but rather a vacuum that allows high-quality single crystals to be obtained stably. In this example, a vacuum of less than 10 ⁻³ Pa can be maintained, for example.

The gas flow sensor 52 is a sensor that measures the flow rate of gas within the chamber 11. The vacuum pressure sensor 51 and the gas flow sensor 52 are connected to the PID control unit 53.

The power supply circuits 56-58 include an upper power supply circuit (first power supply circuit) 56 that supplies current to the upper induction heating source 41, an intermediate power supply circuit (second power supply circuit) 57 that supplies current to the intermediate induction heating source 42, and a lower power supply circuit 58 that supplies current to the lower induction heating source 43. The upper power supply circuit 56, intermediate power supply circuit 57, and lower power supply circuit 58 are each composed of independent inverter circuits, etc., and the lower power supply circuit 58 is configured to be able to supply greater power than the upper power supply circuit 56 and intermediate power supply circuit 57. For example, the lower power supply circuit 58 is configured to be able to supply approximately 40 kW to 60 kW of power to the lower induction heating source 43, and the upper power supply circuit 56 and intermediate power supply circuit 57 are configured to be able to supply approximately 20 kW to 35 kW of power to the upper induction heating source 41 and intermediate induction heating source 42. This enables the production of large-diameter single crystals.

Here, if the power supplied to the induction heating sources 41-43 is large as described above, the increased heat generation capacity will increase the electrical capacity of the power supply and matching box, placing a limit on the power supply's output frequency. As a result, the efficiency of energy transmission to the container 20 may deteriorate, resulting in reduced heating efficiency. In response to this, in this embodiment, the phase difference between the voltages of the power output from the multiple independent power supply circuits 56-58 is set to zero, suppressing magnetic field interference between the induction heating sources 41-43.

That is, the control device 50 is configured to zero the phase difference between the voltage applied to the upper induction heating source 41 by the upper power supply circuit 56, the voltage applied to the intermediate induction heating source 42 by the intermediate power supply circuit 57, and the voltage applied to the lower induction heating source 43 by the lower power supply circuit 58. To achieve this, the upper power supply circuit 56, the intermediate power supply circuit 57, and the lower power supply circuit 58 are connected to the phase control unit 54 of the control device 50 to enable signal transmission and reception. The phase control unit 54 has a phase-locked circuit. The phase-locked circuit is composed of a phase-locked loop (PLL) that matches the phase of the input signal with the phase of the output signal. Based on the signals input from the upper power supply circuit 56, the intermediate power supply circuit 57, and the lower power supply circuit 58, it performs control to zero the phase difference between the voltages in the power output from the upper power supply circuit 56, the intermediate power supply circuit 57, and the lower power supply circuit 58. The power control module 55 is also used to supply power to the resistance heating source 44.

The PID control unit 53 is connected to the upper temperature sensor 46, the lower temperature sensor 47, the vacuum pressure sensor 51, and the gas flow sensor 52. The PID control unit 53 can obtain the current temperature state of the container 20 based on the values output from the upper temperature sensor 46 and the lower temperature sensor 47. Because raw material B is contained inside the container 20 and the container 20 is made of a material with good thermal conductivity, the temperature state of the container 20 is approximately the same as the temperature state of raw material B. Therefore, the PID control unit 53 can also indirectly obtain the temperature state of raw material B.

The PID control unit 53 determines whether a vacuum state exists within the chamber 11 based on the value output from the vacuum pressure sensor 51. The PID control unit 53 also obtains the gas flow rate within the chamber 11 based on the value output from the gas flow sensor 52. The PID control unit 53 is also connected to a control panel 60. The control panel 60 is provided with operation switches 60a for various settings and operation start/stop switches 60a. By operating the operation switches 60a on the control panel 60, the user can set the target temperature (set temperature) of the container 20, the heating rate of the container 20, the heating time of the container 20, etc. The set target temperature, heating rate, heating time, etc. are stored in the control device 50, memory unit 61, etc. The target temperature is a temperature at which silicon carbide powder can be sublimated, and is set to, for example, 2000°C or higher.

The control device 50 is configured to simultaneously energize the induction heating sources 41-43 and the resistance heating source 44. When controlling the energization, the control device 50 controls the induction heating sources 41-43 and the resistance heating source 44 by executing PID control based on a preset set temperature and the temperature state of the container 20 output from the temperature sensors 46 and 47. In other words, the deviation between the set temperature and the temperature state of the container 20 is determined, and the control amount is calculated by combining proportional control, integral control, and differential control. The output values of the upper temperature sensor 46 and the lower temperature sensor 47, the power control value, etc. are stored and managed as time-series data in the memory unit 61.

The control procedure by the control device 50 will be explained below based on the flowchart shown in Figure 7. This flow starts when the user operates the operation switch 60a on the operation panel 60 to set the target temperature, heating rate, heating time, etc., and single crystal production begins. The elapsed time from the start is measured, and the above flow is interrupted or terminated when the heating time set by the user has elapsed. The above flow is also interrupted or terminated if the user performs an operation to stop heating (operation to stop production).

In step S1 after starting, a current temperature measurement process is performed. In the current temperature measurement process, the PID control unit 53 reads the current measurement values measured by the upper temperature sensor 46 and the lower temperature sensor 47. The current measurement value indicates the temperature of the container 20 (estimated container temperature), i.e., the temperature of raw material B (estimated raw material temperature). In step S2, settings such as the target temperature, heating rate, and heating time set by the user on the operation panel 60 are read. The order of steps S1 and S2 may be reversed, or steps S1 and S2 may be performed simultaneously.

In step S3, the PID control unit 53 reads the output setting values of the upper, middle, and lower power supply circuits 56-58. In step S4, the PID control unit 53 reads the output setting value of the power control module 55. Each output setting value is set to a larger value the higher the target temperature is relative to the current temperature obtained in step S1, for example, and the faster the temperature rise rate is, the larger the value is. Each output setting value can be stored in the memory unit 61, etc. The order of steps S3 and S4 may be reversed, or steps S3 and S4 may be performed simultaneously.

In step S5, the PID control unit 53 performs PID control. In step S6 of the initial flow after starting, the PID control unit 53 controls the upper, middle, and lower power supply circuits 56-58 to output the power of the output setting value read in step S3, and also controls the power control module 55 to output the power of the output setting value read in step S4.

As a result, current flows through the upper induction heating source 41, the intermediate induction heating source 42, and the lower induction heating source 43, generating eddy currents in the peripheral wall 22 of the container 20 and generating heat. At this time, the phase difference between the voltages in the power output from the power supply circuits 56-58 is zero, suppressing magnetic field interference between the induction heating sources 41-43 and improving heating efficiency. Furthermore, because the peripheral wall components 22A-22G and the induction heating sources 41-43 are all annular, the eddy currents generated in each peripheral wall component 22A-22G can be contained within that component, making the eddy currents uniform in the circumferential direction. This results in a uniform temperature distribution within the container 20.

The heat generated in the peripheral wall portion 22 is transferred to the raw material pod 24 contained therein, heating the raw material pod 24. As the raw material pod 24 is heated, raw material B inside the raw material pod 24 is heated.

In addition, simultaneously with the supply of power to the induction heating sources 41-43, power is also supplied from the power control module 55 to the resistance heating source 44. When the resistance heating source 44 generates heat, the heat radiated from the resistance heating source 44 is transferred to the multiple raw material pods 24 via the cover member 23, heating the raw material B inside the raw material pod 24.

In step S8, the current temperature is measured in the same manner as in step S1, and the PID control unit 53 acquires the measurement result. In step S9, the PID control unit 53 performs a comparison process to compare the target temperature read in step S2 with the measured temperature measured in step S8. If the comparison process in step S9 shows a deviation between the target temperature and the measured temperature, the process proceeds to step S6, where the PID control unit 53 controls the upper, middle, and lower power supply circuits 56-58 and the power control module 55 to continue outputting power at the current output command value.

On the other hand, if the comparison process in step S9 shows that there is no deviation between the target temperature and the measured temperature, the process proceeds to step S5, where the PID control unit 53 executes PID control to control the upper, middle, and lower power supply circuits 56-58 and the power control module 55.

Before the target temperature is reached, the control device 50 activates the electric motor 45a of the rotation mechanism 45. This allows the seed crystal A to rotate before the raw material B begins to sublimate. Because the resistance heating source 44 is located directly below the seed crystal A, the heat radiated from the resistance heating source 44 is also transmitted to the seed crystal A via the upper plate portion 23b of the cover member 23. This maintains the temperature of the seed crystal A in a temperature range that promotes single crystal growth.

Because raw material B is housed in multiple raw material pods 24, raw material B can be heated on the inner wall surface of each raw material pod 24. This increases the area over which raw material B is heated. When the temperature of raw material B in a raw material pod 24 reaches the sublimation temperature, raw material B sublimes, generating sublimation gas within the raw material pod 24. The sublimation gas generated within the raw material pod 24 is exhausted upward through exhaust ports 24c located in the upper portion of the raw material pod 24. The sublimation gas exhausted from the raw material pod 24 flows toward the seed crystal A located directly above. At this time, because gas exhaust ports 25 are located around the seed crystal A at the top of the container 20, the flow of sublimation gas is directed toward the gas exhaust port 25, making it more likely to hit the seed crystal A. This allows silicon carbide single crystals to grow. The silicon carbide single crystals may take on a columnar shape, for example.

This will be explained based on Figures 8A and 8B. Figure 8A is a diagram that shows the results of a simulation of the flow of thermal fluid near seed crystal A when there is no gas outlet. In this case, fluid compression occurs near seed crystal A due to a large temperature difference, generating turbulence. The generation of turbulence hinders the stable growth of a single crystal.

On the other hand, Figure 8B is a diagram showing the results of a simulation of the flow of thermal fluid near seed crystal A when a gas outlet 25 is present. In this case, since gas outlet 25 is located to the side of seed crystal A, the thermal fluid (sublimation gas) flowing from below to above seed crystal A flows along the surface of seed crystal A while maintaining a laminar flow state until it reaches gas outlet 25. This allows for stable growth of a single crystal. Furthermore, because seed crystal A is rotating at this time, the temperature difference near seed crystal A is reduced, which also makes it easier to maintain a laminar flow state.

(Modification)
The above-described embodiment is merely illustrative in all respects and should not be construed as limiting. Furthermore, various modifications and variations within the scope of equivalents of the claims are all within the scope of the present invention. The size and shape of the vessel 20 can be set as desired, and the present invention can also be applied to the production of small-diameter single crystals of less than 6 inches. The heating range of the induction heating source is not limited to the illustrated range; for example, the bottom wall 21 of the vessel 20 may be heated by the induction heating source. The heating range of the resistance heating source is not limited to the illustrated range; for example, the peripheral wall 22 of the vessel 20 may be heated by the resistance heating source.

For example, as in Variation 1 of the embodiment shown in Figure 9, multiple cover members 23 may be provided. The cover members 23 are provided at intervals in the circumferential direction so as to surround the axis 200 of the container 20. A resistance heating source 44 is housed inside each cover member 23. This makes the temperature distribution inside the container 20 even more uniform. In other words, the number of resistance heating sources 44 is not limited to one, and multiple resistance heating sources 44 can be provided for one container 20. When multiple resistance heating sources 44 are provided, they can be arranged in point symmetry with the axis 200 of the container 20 as the center of symmetry.

Also, as in the second variation of the embodiment shown in Figure 10, the cover member 23 may be radially offset from the axis 200 of the container 20. Since the resistance heating source 44 is housed inside the cover member 23, the resistance heating source 44 will also be radially offset from the axis 200 of the container 20.

The resistance heating source 44 may also be omitted. The seed crystal A may be placed in the middle of the container 20 in the vertical direction.

(Effects of the embodiment)
As described above, according to this embodiment, the provision of multiple induction heating sources 41-43 that are energized simultaneously increases the heat capacity, so that even in a large vessel 20 capable of growing a single crystal, such as one with a 6-inch or 8-inch diameter, the raw material B inside can be heated to 2000°C or higher and sublimated. In addition, since the multiple induction heating sources 41-43 are arranged at intervals from one another, multiple locations on the vessel 20 are heated simultaneously by the multiple induction heating sources 41-43, and the vessel 20 is also heated simultaneously from the inside by the resistance heating source 44 arranged corresponding to the interior of the vessel 20. This makes it possible to achieve a more uniform temperature distribution within the vessel 20.

Furthermore, induction heating sources 41-43 are arranged to surround the outside of the peripheral wall 22 of the container 20. When current is applied to the induction heating sources 41-43, eddy currents are generated in each of the peripheral wall components 22A-22G that make up the peripheral wall 22, causing each of the peripheral wall components 22A-22G to generate heat and heat the raw material B. Because the peripheral wall components 22A-22G and the induction heating sources 41-43 are both annular, the eddy currents generated in each of the peripheral wall components 22A-22G can be contained within the peripheral wall components 22A-22G, making the eddy currents uniform in the circumferential direction. This also uniforms the temperature distribution within the container 20.

In addition, because seed crystal A is supported facing downward by support member 30, the growth direction of the single crystal coincides with the direction of gravity, and gravity does not hinder the growth of the single crystal. Furthermore, seed crystal A can be rotated by rotating support member 30 using rotation mechanism 45. This suppresses turbulence in the thermal fluid near seed crystal A, resulting in laminar flow of the thermal fluid and making it less likely for defects to be present in the single crystal.

In addition, because raw material B is divided into multiple raw material pods 24 and stored and heated on the inner wall surface of each raw material pod 24, the area over which raw material B is heated is larger than when raw material B is stored directly in a large-diameter container 20. This allows raw material B to sublimate efficiently and the sublimation state to stabilize, allowing more raw material B to be heated to the sublimation temperature, thereby increasing the utilization rate of raw material B.

As explained above, the present disclosure can be used, for example, when sublimating a raw material such as silicon carbide to grow a single crystal on a seed crystal.

REFERENCE SIGNS LIST 1 sublimation growth apparatus 20 container 24 raw material pod 24c exhaust port 25 gas exhaust port 30 support member 41 upper induction heating source 42 middle induction heating source 43 lower induction heating source 44 resistance heating source 45 rotation mechanism 46, 47 temperature sensor 50 control device A seed crystal B raw material

Claims (4)

A source container for a sublimation growth apparatus used in a sublimation growth apparatus that sublimates a source material to grow a single crystal on a seed crystal,
a bottom wall portion on which a plurality of raw material pods containing the raw materials are placed at intervals from one another and which is made of a bottom plate material having a circular shape in a plan view;
a peripheral wall portion disposed on the bottom plate material and disposed within a circular induction heating source;
the peripheral wall portion is configured by a plurality of peripheral wall constituent members that are annular in plan view and made of a conductive material and are connected in the vertical direction,
A source container for a sublimation growth apparatus, characterized in that a plurality of peripheral wall constituent members having thicknesses or vertical dimensions different from one another are connected to one another. 2. The source container for a sublimation growth apparatus according to claim 1,
the plurality of peripheral wall constituent members include a first peripheral wall constituent member and a second peripheral wall constituent member connected to an upper portion of the first peripheral wall constituent member;
a protrusion that protrudes upward and extends in the circumferential direction is formed on an upper portion of the first peripheral wall component,
a recess formed in a lower portion of the second peripheral wall component for accommodating the protrusion; 2. The source container for a sublimation growth apparatus according to claim 1,
A source container for a sublimation growth apparatus, wherein the conductive material has a resistivity of 10 ⁻⁵ Ωcm or more and 10 ⁻² Ωcm or less. 2. The source container for a sublimation growth apparatus according to claim 1,
A source container for a sublimation growth apparatus, wherein silicon carbide powder is contained as the source material in the source pod.