Gallium oxide crystal manufacturing equipment

Abstract

To provide a manufacturing apparatus of a gallium oxide crystal equipped with a low-cost resistive heating element capable of suppressing deformation and breakage due to heat.SOLUTION: A manufacturing apparatus 10 of a gallium oxide crystal relating to the invention includes a furnace body 14 made of heat resistant materials 14a, a crucible 22 installed in the furnace body 14, and heating elements 34 arranged around the crucible 22. The heating element 34 is a resistive heating element where a heat generation part 34a and a conductive part 34b having a larger diameter than the heat generation part 34a are connected. The heat generation part 34a is made of a material having heat resistance at 1,850°C and the conductive part 34b is made of a material having heat resistance at 1,800°C.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to an apparatus for producing gallium oxide crystals. [Background technology]

[0002] There are known devices that manufacture single crystals of gallium oxide (hereinafter, sometimes referred to as "gallium oxide crystals"), which is attracting attention as a wide-gap semiconductor for power devices, etc. In such devices, gallium oxide crystals are manufactured by methods such as the VB method (vertical Bridgman method), the VGF method (vertical thermal gradient freeze method), the HB method (horizontal Bridgman method), and the HGF method (horizontal thermal gradient freeze method).

[0003] As an example, the VB method and the VGF method utilize a vertical temperature gradient. Specifically, in the gallium oxide crystal manufacturing apparatus described in Patent Document 1 (JP Patent Publication No. 2017-193466), a crucible containing a gallium oxide raw material (crystal raw material) is placed in a furnace body provided as a VB furnace, and a plurality of heating elements extending in the vertical direction are arranged around the crucible. According to this, a vertical temperature gradient is formed around the crucible in the furnace body, with the temperature on the upper side being higher and the temperature on the lower side being lower. When the crucible is heated by the heating element, the crystal raw material melts. Next, the crucible is lowered to crystallize the raw material melt from the lower side, thereby obtaining gallium oxide crystals.

[0004] The heating element may be a high-frequency induction heating element or a resistance heating element. The resistance heating element has a heating part and a conductive part, and when the heating part is energized through the conductive part connected to an external power source, the heating part generates heat to heat the crucible. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2017-193466 A Summary of the Invention [Problem to be solved by the invention]

[0006] Here, the melting point of gallium oxide is very high at about 1795°C for β-Ga2O3, and when the crucible is heated by a resistance heating element until the crystal raw material melts, the temperature of the heating element reaches nearly 1850°C. Therefore, in the past, the entire heating element was made of materials that could withstand a heat of about 1850°C.

[0007] However, even with this configuration, repeated use of the device causes the heating element to deform and break due to deterioration over time caused by heating, necessitating replacement of the heating element. In contrast, the heating element is relatively expensive, and considering that in the future, when the crystals to be manufactured become larger, the overall configuration of the device including the heating element will also become larger, it is strongly desired to provide a heating element that is less likely to deform or break due to heat at a lower cost. [Means for solving the problem]

[0008] The present invention has been made in view of the above circumstances, and aims to provide a crystal manufacturing apparatus using a resistance heating element, which is low-cost and has a heating element that can suppress deformation and damage due to heat. An object of the present invention is to provide an apparatus for manufacturing gallium oxide crystals.

[0009] The present invention solves the above problems by the solution means described below as one embodiment.

[0010] The gallium oxide crystal manufacturing apparatus according to the present invention comprises a furnace body made of a heat-resistant material, a crucible disposed in the furnace body, and a heating element disposed around the crucible, the heating element being a resistance heating element having a heating portion, a connection portion, and a conductive portion, the heating portion, the connection portion, and the conductive portion each being a cylindrical portion having a constant diameter, The conductive part is inserted through the upper part of the furnace body and is provided in the vertical direction within the furnace body, the connection part is provided to extend vertically from the tip of the conductive part within the furnace body, and the heat generating part is provided to extend vertically from the tip of the connection part within the furnace body, and is formed in a straight line when viewed from the side;The heat generating part is connected to the conductive part via the connecting part which is formed to have a diameter larger than that of the heat generating part and smaller than that of the conductive part. The heat generating part is made of a material having a heat resistance of 1850 [°C], the connecting part is made of a material having a heat resistance of 1850 [°C], and the conductive part is made of a material having a heat resistance of 1800 [°C].

[0011] According to this, for the heat generating part that generates heat and reaches nearly 1850 [°C], it can be made of a material having a heat resistance of 1850 [°C] to suppress deformation and damage due to heat. On the other hand, for the conductive part that does not reach as high a temperature as the heat generating part, it can be made of a relatively inexpensive material having a heat resistance of 1800 [°C] to reduce the material cost of the entire heating element.

[0012] Also , Issue By connecting the heat generating part and the conductive part via a connecting part that is formed to have a larger diameter than the heat generating part while being made of the same material having a heat resistance of 1850 [°C] as the heat generating part, it is possible to protect from heat from the base end of the heat generating part, which is located in the highest temperature region in the furnace body and is most likely to reach the highest temperature, to the connecting part with the conductive part. As a result, deformation and damage of the heating element can be further suppressed.

[0013] Further, for the heating element, in the ratio (x:y:z) of the diameter (x) of the heat generating part, the diameter (y) of the connecting part, and the diameter (z) of the conductive part, it is preferably 3≤x≤9, 4≤y≤12, 6≤z≤18 (however, x < y < z), and more preferably y≤3x, and z≤2y, and z≤4x (however, x < y < z). Also, the heating element is preferably made of molybdenum disilicide (MoSi2).

[0015] And, for the heating element, with respect to the heat generating part whose tip is formed in a U shape, two The connection parts are connected, and each of the two connection parts isIt is preferable that the conductive part is connected, the diameter of the heat generating part is 3 mm to 9 mm, and the bending width of the heat generating part is less than 40 mm. By reducing the bending width of the heat generating part, interference between members involved in the installation of the heat generating element can be prevented. Also, it becomes possible to increase the number of heat generating elements without moving them farther from the crucible. Effect of the Invention

[0016] According to the present invention, it is possible to realize a gallium oxide crystal manufacturing apparatus that is low cost and includes a resistance heating element that is capable of suppressing deformation or damage due to heat. [Brief description of the drawings]

[0017] [Figure 1] FIG. 1 is a schematic diagram (vertical cross-sectional view) illustrating an example of a gallium oxide crystal manufacturing apparatus according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a schematic diagram (front view) showing an example of a heating element in the gallium oxide crystal manufacturing apparatus shown in FIG. [Diagram 3] FIG. 2 is an explanatory diagram illustrating the bending width of a heat generating portion of a heat generating element in the gallium oxide crystal manufacturing apparatus shown in FIG. 1 (a cross-sectional view taken along line III-III in FIG. 1(a)). [Figure 4] 1 is a photograph of the heating element according to Example 1 after the production of β-Ga2O3 crystals. [Diagram 5] 13 is a photograph of the heating element according to Example 2 after the production of β-Ga2O3 crystals. [Figure 6] 1 is a photograph of a heating element according to a reference example after β-Ga2O3 crystals were produced. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. Fig. 1 is a schematic diagram (vertical cross section) showing an example of a gallium oxide crystal manufacturing apparatus 10 according to this embodiment. Of these, Fig. 1(a) shows a gallium oxide crystal manufacturing apparatus 10 equipped with a heating element 34 that is linear in side view, and Fig. 1(b) shows a gallium oxide crystal manufacturing apparatus 10 equipped with a heating element 34 that is L-shaped in side view. For ease of viewing, two heating elements 34 are shown here, one on the left and one on the right, although more heating elements 34 are usually provided.

[0019] The gallium oxide crystal manufacturing apparatus 10 according to this embodiment is a gallium oxide crystal (single crystal) manufacturing apparatus that uses a heating element 34 to heat the crucible 22 (inside the furnace body 14) to melt the raw material for the gallium oxide crystal, and then cools it at a predetermined rate, using the supercooling as a driving force for crystal growth. Below, an example will be described in which the furnace body 14 of the gallium oxide crystal manufacturing apparatus 10 is a VB furnace in an air atmosphere, but the furnace body 14 may also be, for example, a VGF furnace, an HB furnace, or an HGF furnace.

[0020] The gallium oxide crystal manufacturing apparatus 10 shown in Fig. 1 comprises a furnace body 14 on a base 12. The furnace body 14 is formed into a cylindrical shape by stacking multiple ring members having a required height and made of heat-resistant material 14a in the vertical direction, forming a furnace space 15 therein (the stacked structure of the ring members is not shown). The bottom surface of the furnace space 15 is formed with a recess 15a recessed along the central axis of the furnace body 14.

[0021] Also provided is a crucible holder shaft 16 that passes through the base 12 and the bottom of the furnace body 14 along the central axis of the furnace body 14, passes through the recess 15a, and extends vertically to near the central height of the furnace space 15. The crucible holder shaft 16 is configured to be movable up and down and rotatable about its axis by a drive mechanism (not shown) (see the arrow in FIG. 1). A thermocouple 18 is disposed within the crucible holder shaft 16, making it possible to measure the temperature of the crucible 22. The crucible holder shaft 16 is also made of a heat-resistant material.

[0022] An adapter 20 for supporting a crucible 22 is provided on the crucible holder 16 (the upper end of the crucible holder 16), and the crucible 22 is placed on the adapter 20. For the crucible 22 for growing β-Ga2O3 crystals, a platinum-based alloy such as a platinum (Pt)-rhodium (Rh) alloy with a rhodium (Rh) content of 10 [wt%] to 30 [wt%] can be suitably used. The adapter 20 is also made of a heat-resistant material.

[0023] The periphery of the crucible support shaft 16 is surrounded by a ring member made of heat-resistant material 14a from the bottom surface of the recess 15a to near the central height, thereby insulating the lower part of the furnace body 14. To insert or remove the crucible 22 in the furnace body 14, this ring member is removed to open the bottom of the recess 15a, or a ring member relating to the layered structure of the furnace body 14 is removed at a required height position to open the furnace space 15 (not shown).

[0024] An intake pipe 24 is provided at the bottom of the furnace body 14 to communicate between the inside and outside of the furnace body 14. An exhaust pipe 26 is provided at the top of the furnace body 14 to communicate between the inside and outside of the furnace body 14. As a result, the inside of the furnace body 14 is configured as an air atmosphere, but a specified gas may be actively introduced through the intake pipe 24 to create an oxidizing atmosphere.

[0025] Further, a furnace core tube 28 is provided in the furnace body 14, surrounding the crucible 22 and the crucible support shaft 16. The furnace core tube 28 extends from the bottom surface of the recess 15a to the top surface of the furnace space 15, and a top plate 28a is provided on the upper part, covering the sides and the top of the crucible 22 and the crucible support shaft 16 (however, the above-mentioned exhaust pipe 26 penetrates the top plate 28a). The furnace core tube 28 can isolate the crucible 22 and the heating element 34. Therefore, even if a part of the heating element 34 melts due to high temperature, it is possible to prevent impurities from being mixed into the crucible 22 (i.e., the gallium oxide crystals to be generated).

[0026] In addition, a tubular inner furnace tube 30 is provided in the furnace body 14, surrounding the core tube 28. The inner furnace tube 30 extends from the bottom surface of the furnace space 15 to the top surface, covering the sides of the core tube 28 from the center height to the top. A ring-shaped support member 32 is provided on the bottom surface of the furnace space 15 to support the inner furnace tube 30. The inner furnace tube 30 can insulate the space between the heating element 34 (described later) and the heat-resistant material 14a constituting the outer wall of the furnace space 15, thereby preventing sintering, deformation, and cracking of the heat-resistant material 14a due to heat. In addition, the heat of the heating element 34 can be reflected to the core tube 28 side to heat the inside of the furnace space 15, and the heat can be used without waste. The core tube 28 and the inner furnace tube 30 are also made of heat-resistant materials.

[0027] A heating element 34 is provided between the furnace core tube 28 and the furnace inner tube 30 in the furnace body 14. The heating element 34 is a resistance heating element having a heating portion 34a and a conductive portion 34b, and is configured so that the heating portion 34a generates high-temperature heat when electricity is applied to the heating portion 34a via the conductive portion 34b. The heating element 34 (heat-generating portion 34a and conductive portion 34b) is provided in the furnace body 14, and a portion of the conductive portion 34b penetrates the furnace body 14 (heat-resistant material 14a) and is connected to an external power source outside the furnace body 14 (external power source not shown).

[0028] More specifically, the heating element 34 shown in FIG. 1(a) is formed in a straight line in a side view, with the conductive part 34b penetrating the upper part of the furnace body 14 and disposed in the vertical direction within the furnace body 14, and the heating part 34a extending vertically from the tip of the conductive part 34b within the furnace body 14. On the other hand, the heating element 34 shown in FIG. 1(b) is formed in an L-shape in a side view, with the conductive part 34b penetrating the side part of the furnace body 14 and disposed in a bent vertical direction within the furnace body 14, and the heating part 34a extending vertically from the tip of the conductive part 34b within the furnace body 14. Although two heating elements 34 are shown in FIG. 1, usually, as shown in FIG. 3, a plurality of heating elements 34 (here, ten heating elements 34 with U-shaped tips) are disposed in a circular shape around the crucible 22 located on the central axis within the furnace body 14 (however, the number of heating elements 34 is not particularly limited). By arranging the heating element 34 in this manner, the heating portion 34a can be extended vertically around the crucible 22, making it possible to form a vertical temperature gradient around the crucible in the furnace body 14, with the temperature higher at the top and lower at the bottom.

[0029] In addition, when applying the heating element 34 having an L-shape in side view in FIG. 1(b), as an example, in the stacked structure of ring members constituting the furnace body 14 described above, a semicircular groove is provided on the lower surface of the upper ring member and on the upper surface of the lower ring member, and the semicircular grooves are butted together to form the through hole 13 through which the conductive part 34b is inserted. Similarly, by forming the inner furnace tube 30 into a stacked structure of ring members, the through hole 31 can be formed in the inner furnace tube 30 as well. In this way, the conductive part 34b can be attached to the furnace body 14 and the inner furnace tube 30 so as to pass through the through hole 13 of the furnace body 14 and the through hole 31 of the inner furnace tube 30, that is, so as to be sandwiched between the upper and lower ring members of the furnace body 14 and the inner furnace tube 30.

[0030] Next, the heating element 34, which is a characteristic feature of this embodiment, will be described in more detail. The heating element 34 is configured by connecting a heating portion 34a and a conductive portion 34b having a larger diameter than the heating portion 34a. The heating portion 34a and the conductive portion 34b are made of the same or almost the same material, and due to the difference in electrical resistance caused by the difference in diameter, the heating portion 34a, which generates high-temperature heat when current is applied, and the conductive portion 34b, which supplies current to the heating portion 34a, act separately. Molybdenum disilicide (MoSi2) or the like can be suitably used as a material for the heating element 34 (heating portion 34a and conductive portion 34b).

[0031] Here, the heating element 34 according to this embodiment is characterized in that the heating part 34a is made of a material having a heat resistance of 1850 [°C], and the conductive part 34b is made of a material having a heat resistance of 1800 [°C]. When the heating part 34a is energized until a part of the raw material of the gallium oxide crystal, such as a sintered body of β-Ga2O3, or the seed crystal is melted in the furnace body 14, the heating part 34a itself reaches nearly 1850 [°C] (the melting point of β-Ga2O3 is about 1795 [°C]). Therefore, by making the heating part 34a of a material having a heat resistance of 1850 [°C], deformation and damage of the heating part 34a due to heat can be suppressed. On the other hand, the conductive part 34b, which does not reach a high temperature as high as the heating part 34a, can be made of a relatively inexpensive material having a heat resistance of 1800 [°C], thereby reducing the material cost of the entire heating element 34.

[0032] The heating element 34 according to this embodiment is characterized in that the heating part 34a is connected to the conductive part 34b via the connecting part 34c, which is formed to have a larger diameter than the heating part 34a and a smaller diameter than the conductive part 34b and is made of a material having a heat resistance of 1850°C. In the furnace body 14, which is a VB furnace, the heating part 34a is vertically extended around the crucible 22, forming a vertical temperature gradient around the crucible in the furnace body 14 such that the temperature is higher on the upper side and lower on the lower side. Therefore, in the heating element 34, the connecting part between the base end of the heating part 34a and the conductive part 34b is located in the highest temperature area in the furnace body 14 and is likely to become the hottest. Therefore, by connecting the heat generating portion 34a and the conductive portion 34b via the connecting portion 34c, which is made of the same material as the heat generating portion 34a and has a heat resistance of 1850°C, and has a larger diameter than the heat generating portion 34a, it is possible to protect the area from the base end of the heat generating portion 34a to the connecting portion with the conductive portion 34b from heat. As a result, deformation and damage of the heat generating element 34 can be further suppressed.

[0033] Further, since the diameters of the conductive portion 34b, the connecting portion 34c, and the heat generating portion 34a gradually decrease in this order, it is possible to energize the heat generating portion 34a from an external power source through the conductive portion 34b and further through the connecting portion 34c to cause the heat generating portion 34a to generate heat at a high temperature. Here, in the ratio (x:y:z) of the diameter (x) of the heat generating portion 34a, the diameter (y) of the connecting portion 34c, and the diameter (z) of the conductive portion 34b, it is preferable to form each diameter such that 3≦x≦9, 4≦y≦12, 6≦z≦18 (however, x<y<z). More preferably, in the above ratio (x:y:z), 3≦x≦9, 6≦y≦12, 9≦z≦18 (however, x<y<z), or y≦3x, and z≦2y, and z≦4x (however, x<y<z). Specifically, for example, it is good to set as "x = 3, y = 6, z = 9", "x = 3, y = 6, z = 12", "x = 3, y = 9, z = 12", "x = 4, y = 6, z = 9", "x = 4, y = 9, z = 12", "x = 6, y = 9, z = 12", "x = 6, y = 9, z = 18", "x = 6, y = 12, z = 18", "x = 9, y = 12, z = 18", etc. However, according to the present embodiment, although the heating element 34 can be manufactured at a lower cost than before, generally the heating element 34 is expensive, and it is not practical to manufacture heating elements 34 of all such combinations and test for suitability because it requires a significantly excessive economic expenditure. In the examples described later, in particular, the heating element 34 with x = 6, y = 9, z = 12 was used (Example 2).

[0034] The "diameter" referred to here means "the diameter φ (phi) of the cross section". Note that the conductive portion 34b, the connecting portion 34c, and the heat generating portion 34a made of different materials can be joined by welding or the like.

[0035] Also, as shown in FIG. 2, the heating element 34 is formed by connecting two conductive portions 34b to a heat generating portion 34a having a U-shaped tip, and the heat generating portion 34a has a predetermined bending width (the distance between the centers of each heat generating portion 34a, the length indicated by the symbol A). Here, the heating element 34 according to the present embodiment is characterized in that the bending width A of the heat generating portion 34a is formed to be small.

[0036] FIG. 3 shows a cross-sectional view of line III-III in FIG. 1(a) as an explanatory diagram for explaining the bending width A. However, FIG. 3 shows only the inner peripheral side of the furnace inner tube 30, which is necessary for the explanation. As described above, the crucible 22 (the crucible support shaft 16) is arranged on the central axis in the furnace body 14, and a plurality of heating elements 34 are arranged so as to surround the crucible 22 in a circular shape. Here, as shown in FIG. 3(a), if the bending width A of the heating part 34a is large, the members 36 (for example, the members fixing the heating element 34 to the furnace body 14 (heat-resistant material 14a)) related to the attachment of the heating element 34 interfere with each other. Therefore, in order to avoid the interference, it is necessary to shift the heating element 34 further outward from the central axis where the crucible 22 is located, or to reduce the number of heating elements 34, which is likely to cause problems such as an extension of the heating time and a deterioration in the quality of the crystals produced. In contrast, in this embodiment, as shown in Fig. 3(b), by reducing the bending width A of the heat generating portion 34a, it is possible to prevent interference between the members 36 involved in the attachment of the heat generating element 34. In addition, it becomes possible to increase the number of heat generating elements 34 without moving them farther away from the crucible 22.

[0037] Specifically, for example, when the diameter of the heat generating portion 34a is formed to be approximately 3 mm to 9 mm, it is preferable to form the bending width A of the heat generating portion 34a to be less than 40 mm, and more preferably to be approximately 30 mm. EXAMPLES

[0038] An attempt was made to grow β-Ga2O3 crystals using the gallium oxide crystal manufacturing apparatus 10 according to this embodiment, in which the furnace body 14 is provided as a VB furnace. The heating elements 34 were resistance heating elements that were U-shaped when viewed from the front, and formed linearly when viewed from the side as shown in FIG. 1(a), with eight of them being disposed at equal intervals within the furnace body 14 so as to surround the periphery of the crucible 22 in a circular shape. However, the heating elements 34 used in each example had the following configuration.

[0039] The heating element 34 in Example 1 was a resistance heating element (made by JX Metals) with a two-stage structure (heating portion 34a and conductive portion 34b) made of molybdenum disilicide (MoSi2), in which the heating portion 34a was made of 1900 grade material and had a diameter of 6 mm, and the conductive portion 34b was made of 1800 grade material and had a diameter of 12 mm. The heating element 34 in Example 2 was a resistance heating element (made by JX Metals) made of molybdenum disilicide (MoSi2) and having a three-stage structure (heating portion 34a, connecting portion 34c, and conductive portion 34b), in which heating portion 34a was made of 1900 grade material and had a diameter of 6 mm, connecting portion 34c was made of 1900 grade material and had a diameter of 9 mm, and conductive portion 34b was made of 1800 grade material and had a diameter of 12 mm. The "1900 grade" is a standard indicating a heat resistance of 1850°C, and the "1800 grade" is a standard indicating a heat resistance of 1800°C.

[0040] A seed crystal and a sintered body of β-Ga2O3 (crystal raw material) were filled in a crucible 22 (φ: 100 [mm]) made of a Pt-Rh alloy with a composition of Pt: 80 [wt%] and Rh: 20 [wt%], and melted in an air atmosphere of 1800 [℃] or more in a furnace body 14 where the temperature distribution was set so that the temperature gradient near the melting point of β-Ga2O3 (about 1795 [℃]) was 2 to 10 [℃ / cm]. Next, unidirectional solidification was performed by combining the downward movement of the crucible 22 and the temperature drop in the furnace body 14. After that, the cooled crucible 22 was peeled off to take out the grown crystal. In this way, a certain number of β-Ga2O3 crystals of 4 [in] size were produced, and the state of the cooled heating element 34 was confirmed.

[0041] FIG. 4 shows the heating element 34 after the growth of the β-Ga2O3 crystal according to Example 1, and FIG. 5 shows the heating element 34 after the growth of the β-Ga2O3 crystal according to Example 2. FIG. 4(a) and FIG. 5(a) show the heating element 34 installed in the furnace body 14, and FIG. 4(b) and FIG. 5(b) show the heating element 34 removed from the furnace body 14. The broken parts are indicated by solid arrows, and the deformed parts are indicated by dashed arrows. In the text, the frequency of breakage is expressed as "how many of the 16 heating parts 34a (here, one U-shaped heating part 34a is counted as two parts) that have broken" and the frequency of deformation is expressed as "how many of the 8 heating parts 34 that have deformed".

[0042] FIG. 6 shows a reference example of a heating element 34, which is a conventional resistance heating element (manufactured by Sandvik) made of molybdenum disilicide (MoSi2), with the entire heating element 34 (heating part 34a and conductive part 34b) being made of a material having a heat resistance of 1850°C (heating part 34a: φ4 mm, conductive part 34b: φ9 mm). Ten heating elements 34 (heating part 34a: φ4 mm, conductive part 34b: φ9 mm) are arranged in the furnace body 14 and used to produce β-Ga2O3 crystals.

[0043] When the heating element 34 according to Example 1 was used, after the crystal was grown, one heating element 34 was deformed (deformation frequency: 1 / 8) and three heating parts 34a were broken (breakage frequency: 3 / 16) as shown in FIG. 4(a). When this heating element 34 was removed from the furnace body 14, each heating element 34 (heating part 34a) was somewhat brittle, and as shown in FIG. 4(b), eight heating parts 34a were broken when removed from the furnace body 14 (breakage frequency: 8 / 16). However, it is also possible to produce further β-Ga2O3 crystals in the state shown in FIG. 4(a) without replacing (removing) the heating element 34. In addition, the adhesion of powder, which is thought to be a part of the surface layer melted, was confirmed in the conductive part 34b. Thus, the degree of deformation and damage of the heating element 34 according to Example 1 was comparable to that of the conventional heating element 34 (as shown by the solid arrows in FIG. 6, six locations of the heating element 34 were damaged while the heating element 34 was installed in the furnace body 14). Therefore, even when the heating element 34 according to Example 1 is used, although the conductive portion 34b deteriorates slightly, it was shown that the deformation and damage of the heating element 34 due to heat can be suppressed to the same extent as in the conventional case, and further the cost can be reduced.

[0044] The furnace body 14 according to the reference example was not provided with an inner furnace tube 30, and the heat-resistant material 14a constituting the outer wall of the furnace space 15 was easily deformed. Therefore, in the heating element 34 according to the reference example, the conductive part 34b was not sufficiently supported, and the heating part 34a was displaced, resulting in damage mainly occurring at the tip of the heating part 34a.

[0045] In addition, when the heating element 34 according to Example 2 was used, after the crystal was grown, one heating element 34 was deformed (deformation frequency: 1 / 8) and one heating part 34a was broken (breakage frequency: 1 / 16) as shown in FIG. 5(a). When this heating element 34 was removed from the furnace body 14, each heating element 34 maintained a firm strength, and as shown in FIG. 4(b), when it was removed from the furnace body 14, two heating parts 34a were finally broken (breakage frequency: 2 / 16). Thus, it was shown that the heating element 34 according to Example 2 can further suppress the deformation and breakage of the heating element 34 compared to the conventional heating element 34 according to the reference example and the heating element 34 according to Example 1. The heating element 34 shown in FIG. 5 is after β-Ga2O3 crystals were produced multiple times, but it is also possible to produce further β-Ga2O3 crystals in the state shown in FIG. 5(a) without replacing (removing) the heating element 34. Moreover, as shown in FIG. 5(b), in the heating element 34 of Example 2, there was almost no adhesion of powder to the conductive portion 34b, and the connection portion 34c protects the connection portion between the base end of the heating portion 34a and the conductive portion 34b, thereby preventing deterioration of the conductive portion 34b.

[0046] The present invention is not limited to the above-described embodiment, and various modifications are possible without departing from the scope of the present invention. In particular, the VB furnace has been described as an example here, but the present invention can also be applied to a VGF furnace that uses a vertical temperature gradient. In addition, the present invention can also be applied to an HB furnace and an HGF furnace that use a horizontal temperature gradient, since the locations where deformation or damage of the resistance heating element is likely to occur are common. [Explanation of symbols]

[0047] 10 manufacturing device, 12 base body, 14 furnace body, 16 crucible support shaft, 18 thermocouple, 20 adapter, 22 crucible, 24 intake pipe, 26 exhaust pipe, 28 furnace core tube, 30 furnace inner tube, 34 heating element, 34a heating part, 34b conductive part, 34c connection part

Claims

1. A furnace body made of a heat-resistant material; a crucible disposed within the furnace body; a heating element disposed around the crucible; The heating element is a resistance heating element having a heating portion, a connection portion, and a conductive portion, the heat generating portion, the connection portion, and the conductive portion are each a cylindrical portion having a constant diameter, The conductive part is inserted through the upper part of the furnace body and is provided in the vertical direction within the furnace body, the connection part is provided to extend vertically from the tip of the conductive part within the furnace body, and the heat generating part is provided to extend vertically from the tip of the connection part within the furnace body, and is formed in a straight line when viewed from the side; the heat generating portion is connected to the conductive portion via the connection portion that is formed to have a diameter larger than that of the heat generating portion and smaller than that of the conductive portion, The heat generating portion is made of a material having a heat resistance of 1850°C, the connection portion is made of a material having a heat resistance of 1850°C, and the conductive portion is made of a material having a heat resistance of 1800°C. A gallium oxide crystal manufacturing device characterized by:

2. The heating element has a ratio (x:y:z) of a diameter (x) of the heating portion, a diameter (y) of the connection portion, and a diameter (z) of the conductive portion, 3≦x≦9, 4≦y≦12, 6≦z≦18 (where x<y<z).

2. The apparatus for producing gallium oxide crystals according to claim 1 .

3. The heating element has a ratio (x:y:z) of a diameter (x) of the heating portion, a diameter (y) of the connection portion, and a diameter (z) of the conductive portion, y≦3x, z≦2y, and z≦4x (where x<y<z).

3. The apparatus for producing gallium oxide crystals according to claim 2 .

4. The heating element is made of MoSi ２ Consists of The apparatus for producing gallium oxide crystals according to any one of claims 1 to 3.

5. The heating element has a heating portion having a U-shaped tip, and two of the connection portions are connected to the heating portion, and the conductive portion is further connected to each of the two connection portions, The diameter of the heat generating part is 3 mm to 9 mm, The bending width of the heat generating portion is less than 40 mm. The gallium oxide crystal manufacturing apparatus according to any one of claims 1 to 4,

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