JP3160956B2 - Cold wall melting equipment using ceramic crucible - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to 1) high-purity metals or alloys known as materials for semiconductors and the like, 2) oxygen (O), nitrogen (N) or carbon (C) such as titanium or zirconium (Zr). Metals or alloys that are difficult to melt as high-purity products because they easily react with 3) Dissolution of metals treated as special metals such as W, Mo, Ta, Nb with extremely high melting temperatures and their alloys A melting crucible furnace called a cold wall induction melting crucible furnace, and more specifically, the entire furnace body including the crucible furnace side wall and bottom wall or at least the side wall is made of an electrically conductive material such as AlN. The present invention relates to a cold wall induction melting furnace made of a ceramic material having a low rate and a high thermal conductivity.

[0002]

2. Description of the Related Art As described above, high-purity metals known as materials for semiconductors, metals or alloys which easily react with oxygen, nitrogen or carbon such as titanium or zirconium, W, Mo, Ta, Nb and the like having extremely high melting temperatures. For melting special metals and their alloys, an electron beam melting furnace, a non-consumable arc furnace and the like have been used. However, since these furnaces are melted in a furnace body or crucible made of a metal oxide refractory material such as alumina, magnesia, zirconia, and beryllia as described later, at a high temperature, the refractory material and the molten metal ( (Hereinafter abbreviated as molten metal), there is a problem that a reaction product is taken into the molten metal as an impurity and the quality is degraded, and as a furnace body or a crucible using no metal oxide refractory material, there is a problem of water cooling. A cold wall induction melting method (also called a cold crucible melting method or an induction skull melting method) using a copper crucible has been adopted.

As shown in FIGS. 4A and 4B, an induction crucible furnace generally referred to as a cold wall crucible furnace generally used to date has a good copper conductivity and good thermal conductivity. A crucible body having a bottom and a hollow cylindrical shape as a whole, and an induction heating coil 8 disposed on the outer periphery thereof, and a portion from the side wall or the side wall to a part of the bottom of the crucible has a plurality of portions. This is a metal crucible melting furnace for induction melting in which a plurality of strip-shaped segments 3 are divided by a narrow slit 2 and the inside 11 of each of the segments 3 is cooled by a coolant such as cooling water. When the melting of the metal to be melted proceeds by the induction heating coil 8,
The molten metal 9 in contact with the inner wall of the water-cooled strip-shaped segment 3 is solidified to form a skin-like skull 5, and the molten metal in contact with the side wall of the metal crucible melting furnace adheres to the side wall or enters the slit portion and is removed. Serves to prevent difficulties. On the other hand, the function of floating the molten metal from the side wall at the upper part of the crucible by electromagnetic induction to prevent a short circuit between the water-cooled strip-shaped segments 3 of copper is also achieved.

As described above, the crucible body of the cold wall type crucible furnace is made of copper, and is made of a refractory made of a simple substance or a mixture of metal oxides such as alumina, magnesia, beryllia, silica or zirconia as in a conventional melting furnace. No materials are used. The metals and alloys to be melted by the cold-wall crucible furnace have a high melting temperature, whereas the above-mentioned refractory materials constituting the crucible body as a container for housing the molten metal and alloy are all thermally conductive. , The temperature of the crucible body also reaches almost the same high temperature as the temperature of the molten metal inside as the melting proceeds. As a result, a chemical reaction proceeds between the elements constituting the metal and the alloy and the elements constituting the refractory material of the crucible body, and the elements in the refractory material are taken into the molten metal as impurities to lower the quality of the metal and the alloy. Therefore, general ceramic refractory materials could not be adopted.

[0005]

The above-mentioned copper has been used as an alternative to general refractory materials. Copper has high thermal conductivity, so the furnace wall of a crucible furnace can be cooled with a cooling medium such as water to keep it at a much lower temperature than the molten metal inside, but as a common property of metal,
Conductivity and thermal conductivity have the same tendency, typically copper, silver,
Those having high thermal conductivity, such as aluminum, have good conductivity. However, good conductivity is a drawback in terms of induction heating, but by dividing the furnace wall vertically into strips, the continuous hollow tubular furnace wall itself forms a secondary coil for the induction heating coil. However, since the strip-shaped copper segment itself is a conductor, it is still heated to some extent by the induction heating coil, like the material to be melted.
According to the measurement results, when the amount of electric power used for the material to be melted was set to 1, the amount for the crucible was 1.3, and the power was used for the material to be melted, excluding the loss of the path and the coil primary side. Only about 40% of the electric power is effectively used. Also, to compensate for the power lost in the crucible, it is necessary to increase the coil voltage.However, when vacuum melting is required, the applied voltage must be several hundreds because the higher the voltage in vacuum, the easier the plasma discharge will occur. It is limited to about volts, and the input power is also limited. Also, in induction lysis,
If the frequency is low, the molten metal inside the crucible will be stirred vigorously and vigorously, and the surface of the molten metal will not be stable.In some cases, part of the molten metal will jump out of the crucible and adhere to the outer wall of the crucible, reducing the amount of molten metal. This leads to inconveniences such as a reduced yield. When the frequency is increased, the flow of the molten metal is reduced, and the applied electromagnetic force acts in a direction to stably preserve the surface shape of the molten metal, thereby enabling stable melting. However, in a conventional cold wall type crucible furnace having strip-shaped copper segments, it is necessary to increase the coil voltage in order to compensate for the loss in the crucible furnace. Since the coil voltage is further increased proportionally, there is a problem that the upper limit of the voltage required in the case of vacuum melting is exceeded, and from this point, the heating that the crucible receives by the induction heating coil has a segment. It has been an object to provide a melting crucible that is negligible or considerably less than a conventional copper cold wall crucible.

[0006]

As a crucible capable of solving the above-mentioned problems, 1) The crucible itself does not form a coil which is heated by an induction heating coil as a heating means or a conductor which is a heated object. 2) Even if the temperature of the material to be melted inside the crucible rises, the temperature of the crucible itself can be reduced by means such as water cooling. Lower than the temperature and high in thermal conductivity so that no chemical reaction occurs between the crucible and the molten metal. 3) The crucible withstands thermal stress due to repeated heating and cooling during melting. The problem can be solved if a material that satisfies the above three conditions (1) to (3) can be selected by using a heat-resistant material having the obtained strength and having an appropriate structure. Sex is extreme Nothing satisfies the condition of low thermal conductivity. Therefore, as the material of the cold wall crucible, the use of copper was fixedly used until now, but as a material of the crucible, the inventors have found that the electric conductivity is extremely low in ceramics and the thermal conductivity is high. An appropriate material that satisfies the condition was selected.

[0007] Recent advances in ceramic-related technology have led to the development of ceramic materials that can satisfy the above three conditions. Among them, the industrial products include aluminum nitride (AlN), cubic boron nitride (abbreviated as cBN), beryllium oxide (BeO), and the like. It is unsuitable for a large member such as a crucible.
Aluminum nitride has a wurtzite-type crystal structure, and has extremely high mechanical properties such as Hv1200, high compressive strength and bending strength, and does not decrease in strength even at high temperatures. In terms of thermal properties, the thermal conductivity is about half that of copper,
The coefficient of thermal expansion is slightly larger than that of copper, and is electrically equivalent to an insulator and has a low dielectric constant. In addition, it is stable even at high temperatures, has excellent corrosion resistance to molten metal, and has low wettability to molten metal, making it difficult for molten metal to adhere to inner walls such as crucibles. ,
In particular, aluminum nitride was selected as the optimum crucible material because it is extremely suitable as a material for cold wall crucibles. Made of aluminum nitride, basically
As shown in FIG. 1, the side wall is a hollow cylindrical shape, a copper block is inserted as a bottom wall, and a copper pipe serving as an induction heating coil and a pipe for cooling water is arranged on the outer periphery of the side wall of the crucible. Or, the side wall and the bottom wall are integrally formed with a hollow cylinder with a bottom, and a hollow block dedicated to cooling is provided immediately below the bottom wall, or inside a hollow cylindrical shape of a crucible with a copper block inserted as a bottom wall The problem was solved by embedding copper pipes that also served as cooling water pipes.

[0008]

The refractory material constituting the cold wall crucible is made of aluminum nitride, which has very low conductivity and also serves as an insulating material, so that the side wall of the crucible is heated as a secondary coil for the induction heating coil. And it has about half the thermal conductivity of copper, almost the same as aluminum, and is superior to structural metal materials such as zinc, iron and other alloys. The furnace body of the crucible is kept at the same temperature as the water-cooled copper crucible by the usual cooling method of performing heat exchange by passing through, and like the water-cooled copper crucible, the thin skull called the skull is between the molten metal and the crucible. A solidified layer is formed, and apparently a thin solidified layer of this molten metal constitutes the inner wall of the crucible and is melted, avoiding the contamination of impurities due to a chemical reaction with the crucible of ordinary refractory material and melting. Ukoto is possible.

[0009]

FIG. 1 is a front view showing a first embodiment,
Reference numeral 10 denotes the entirety of the cold wall crucible of the present invention, 12 is a side wall made of aluminum nitride, 13 is a copper pipe arranged on the outer periphery of the side wall and serving as an induction heating coil and a pipe for cooling water, 14 is The copper block wall inserted as the bottom wall, as shown by the dotted line in this copper block wall,
In order to prevent a short circuit, a plurality of slits 15 are circumferentially spaced and cut in the axial direction. The induction heating coils arranged on the outer periphery of the side wall are arranged at appropriate intervals to improve insulation, and an insulating material is inserted between the coils. The outer periphery of the side wall 12 made of aluminum nitride is preferably metallized to join a copper pipe, but the joining is preferably continued without a gap, and if the crucible wall is sufficiently cooled, the joining is performed in the circumferential direction. It may be joined at a predetermined angle, or a material for improving heat transfer may be inserted between the outer periphery of the side wall 12 and the copper pipe. Reference numeral 16 denotes a coil holder. If the coil and the outer periphery of the crucible are tightly joined, coil holding is not necessarily required. However, when a substance that improves heat transfer is used, a structure for holding the coil is required.

FIG. 2 is a schematic view showing a second embodiment. Similar to the embodiment shown in FIG. 1, a copper block 2 is formed at the bottom of a hollow cylindrical aluminum nitride side wall 22 as a bottom wall.
4 is inserted, and a copper pipe 23 serving also as a pipe for cooling water is embedded in the side wall 22. Although not shown, a coil retainer is provided as needed.

FIG. 3 is a schematic view showing a third embodiment, in which a crucible body is formed of a cylindrical side wall 3 made of aluminum nitride.
2 and a bottom wall 32a are integrally formed, and a hollow copper block 36 dedicated to a cooling device in close contact with the back surface of the bottom wall 32a.
Is arranged. Reference numeral 33 denotes a copper pipe arranged on the outer periphery of the side wall and serving also as a pipe for the induction heating coil and cooling water. Although not shown, a coil retainer is provided as needed.

[0012]

In the crucible made of aluminum nitride according to the present invention, the electric power for induction heating is not used to heat the crucible unlike the copper crucible, but is supplied only to the heating of the melting inside the crucible. Power consumption can be reduced. Since the power consumption can be reduced, the coil voltage can be reduced as compared with the copper crucible, so the frequency can be increased correspondingly, and the advantage is that the molten metal does not shake and stable melting is possible, and the molten metal is moderately stirred. Can be made uniform.

[Brief description of the drawings]

FIG. 1 is a front view showing a cold wall crucible made of aluminum nitride according to a first embodiment of the present invention.

FIG. 2 is a schematic view showing a cold wall crucible made of aluminum nitride according to a second embodiment of the present invention.

FIG. 3 is a schematic view showing a cold wall crucible made of aluminum nitride according to a third embodiment of the present invention.

FIG. 4 is a schematic side sectional view and a plan view showing a conventional cold wall crucible furnace.

[Explanation of symbols]

 10, 20, 30 Crucible body 12, 22, 32 Side wall 13, 23, 33 Cooling tube serving as coil 14 Copper bottom wall 15 Slit 16 Coil presser 32a Integrated bottom wall 36 Water-cooled hollow block

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Masahiro Tadokoro 150, Motoyashiki, Miyako-cho, Toyohashi-shi, Aichi Prefecture Shinko Electric Co., Ltd. Toyohashi Mfg. Co., Ltd. (58) Field surveyed (Int. Cl. ⁷ , DB name) F27B 14 / 06 F27D 11/06 H05B 6 / 24,6 / 32

Claims (6)

(57) [Claims] 1. A furnace chamber is formed by a side wall that stands substantially vertically and a bottom wall that seals the bottom and forms a furnace bottom.
A crucible body whose top is released and the material to be melted is accommodated in the furnace chamber, an induction heating coil disposed in close contact with the side wall to heat and melt the material to be melted in the furnace chamber, and induction heating is performed. A cold wall melting apparatus comprising: a supply / discharge pipe for a cooling medium such as water for cooling the crucible body during the operation; at least a side wall of the crucible is made of aluminum nitride
A cold wall melting apparatus using a ceramic crucible, wherein the induction heating coil is formed of a ceramic material and is disposed on a side wall of the crucible, also serving as a supply / discharge pipe for the cooling medium. 2. The cold wall melting apparatus according to claim 1, wherein said crucible body is made of aluminum nitride.
A furnace chamber is defined by a hollow cylindrical crucible side wall formed of a ceramic material to be formed, and a copper bottom wall inserted into the bottom of the side wall, and the induction heating coil has a water supply / drainage pipe for water as the cooling medium. A cold wall melting apparatus using a ceramic crucible, which is also disposed on the outer periphery of the side wall. 3. The cold wall melting apparatus using a ceramic crucible according to claim 2, wherein said induction heating coil serving also as said water supply / drainage pipe is embedded in said side wall. . 4. The cold wall melting apparatus according to claim 2, wherein the bottom wall further has a predetermined width along an axis of the crucible at a predetermined interval circumferentially on an inner periphery thereof. A cold wall melting apparatus using a ceramic crucible, characterized in that a slit having a depth and a slit is provided. 5. The cold wall melting apparatus according to claim 1, wherein said crucible body has a side wall and a bottom wall formed by nitrogen.
The induction heating coil, which is integrally formed in a hollow cylindrical shape with a bottom with a ceramic material made of aluminum halide and also serves as a supply / discharge pipe for a cooling medium, is disposed in close contact with an outer periphery of the side wall, and further includes a crucible. A cold wall melting apparatus using a ceramic crucible, wherein a hollow block for cooling the bottom wall portion is provided in close contact with the back surface of the bottom wall portion. 6. The cold wall melting device according to claim 1, wherein an induction heating coil serving also as the side wall and a supply / discharge pipe for the cooling medium is provided on a back surface of the bottom wall portion. A cold wall melting apparatus using a ceramic crucible, wherein the hollow block is continuously or intermittently joined via a metallized layer provided on a wall surface of the crucible body.