Induction Heating Coil For A Zone Heating Process

Abstract

An induction heating coil which is detachably mounted on a holding member of an induction heating device having a chamber receiving at least a portion of the coil, which device is adapted for use in a process of zone melting of a rod of material, characterized by the coil comprising a tube of insulating glass-like material, such as glass or quartz, which is both heat resistant and vacuum-tight, receiving a metal conductor therein. Each end of the coil is provided with an intermediate member of a good conducting material which member is electrically connected to the conductor and is sealed in a vacuum-tight relationship with both the tube of the coil and the holding member of the device. Preferably, a cooling agent such as water is circulated through the tube to cool the metal conductor during a heating operation. To form the seal with the intermediate member, the tube is either provided with a metalized end that is soldered to the intermediate member or the intermediate member is provided with a ring of silicon rubber which is compressed between the tube and intermediate member by an appropriate clamping device.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an induction heating coil having one or more turns for use in an induction heating device used in a zone melting of rods of materials.

2. Prior Art

Non-crucible zone melting processes for semiconductor materials are well known. For example, the process of zone melting utilizes a molten zone produced by an induction heating device having either a copper or silver coil and the molten zone is moved along a rod shaped body of material being treated. In this way, impurities in the molten material are carried to one end of the rod. Frequently, molten zone heating processes are also used to produce monocrystalline growth by a process in which a seed crystal is melted into one end of the rod. The zone heating is started at the end having the seed crystal and then progressively moved along the rod. When employing this method, the rod shaped body is usually arranged in a vertical orientation and has its ends clamped in suitable holding devices. The zone melting process may be carried out in either a vacuum chamber or a chamber of protective atmosphere which may be an inert gas such as argon or may be a reducing atmosphere of hydrogen.

Heating coils for zone melting use a high frequency current and usually consist of a copper or silver tubing through which a coolant water flow. In such a coil, the current conducting part of the coil, such as the silver or copper tube, is not isolated from the atmosphere within the chamber of the device in which the zone process is carried out.

In order to obtain a dislocation free crystalline material, the zone melting chamber is provided with a highly purified protective atmosphere at a superatmosphereic pressure. When the induction heating coil is formed of a material having a good electrical conductivity and has one or more turns which are fed with a high frequency alternating current and when argon is used as the inert gas, electric sparking will occur between the turns or along the coil. Such sparking reduces the crystal quality of the semiconductor rod produced by the zone melting process and may also destroy the high frequency leads. In addition to the above problem, the working life of a coil is often reduced due to impurities being deposited thereon from a vapor phase created during the heating process. Another problem existing in the present coils is achieving a good electrical contact and vacuum-tight connection between the coil and a holding means positioning the coil in the induction heating apparatus.

A coil consisting of an appropriately bent aluminum tube with its outer surface, covered with an anodize layer has been proposed. Such a coil has solved some of the above mentioned problems such as the avoiding of sparking on the coil.

SUMMARY OF THE INVENTION

The present invention is directed to providing an induction heating coil having one or more turns and which coil is detachably mounted on a holding member of an induction heating device which has a chamber receiving at least a portion of the coil and which device is adapted for performing a process of zone melting of a rod of material in a protective atmosphere.

The coil of the present invention meets the above requirements better than the previously used anodized aluminum coil and is more reliable in operation. The coil of the invention comprises a metal conductor formed in at least one turn which conductor is surrounded by heat resistant and vacuum-tight insulation member. Each end of the coil has an intermediate member attached thereto. Each intermediate member has means for forming a vacuum-tight connection with the coil and for forming a vacuum-tight connection with a holding member. Preferably, the insulating member is a tube of glass-like material, such as heat resistant glass or quartz, and the electrical conductor is one or more wires of silver or copper inserted in the tube. To form the vacuum-tight connection between the conductor and the insulation member, the tube may be metalized and then soldered to the intermediate member which is made of a material of a good or high electrical conductivity. Another embodiment of forming the vacuum-tight connection is by using a silicon rubber seal which is compressed into tight engagement with the tube and the intermediate member. Preferably, the wires are soldered onto the intermediate member to form the electrical connection. The tube whether it is glass or quartz is used as a duct for a cooling medium, such as water, to cool the conductor, but due to the poor heat transfer qualities of the tube. The cooling medium does not cool the protective atmosphere and this does not create an adverse temperature gradient in the melt or the adjacent parts of the rod to produce unfavorable crystal quality of the drawn rod.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view, with portions in cross section, of a coil in accordance with the present invention;

FIG. 2 is a cross-sectional view with portions in elevation of an intermediate member interconnecting the end of a coil to a holding member in accordance with the present invention;

FIG. 3 is a cross-sectional view with portions in elevation of an embodiment of an intermediate member interconnecting an end of a coil to a holding member in accordance with the present invention;

FIG. 4 is a partial cross-sectional view of an embodiment of the holding member illustrated in FIG. 3; and

FIG. 5 is a partial cross-sectional view with portions in elevation for purposes of illustration of another embodiment of a connection of the end of the tube to the intermediate member.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The principles of the present invention are particularly useful when utilized to provide a coil which has at least one turn and which is illustrated in FIG. 1 as having two flat turns. The coil 1 has a metal conductor such as a pair of wires 3 which is surrounded by a heat resistant and vacuum-tight insulation member, such as a tube 2.

To form the coil 1, the tube 2 of a glass-like material, such as a high temperature resistant glass or quartz, is bent into the desired configuration of one or more turns. Then the metal conductor 3 which may be a plurality of wires twisted together into a single strand to provide a large conducting surface with a small ohmic resistance for the high frequency current utilized in the heating device are inserted or drawn through the tube.

When the coil 1 is used in an induction heating device, a cooling fluid such as water 5 is passed through the tube in the direction of the arrows 6 and 6' to cool the metal conductor such as wires 3. Due to the poor heat conducting properties of the tube 2, the cooling fluid will not cool the atmosphere adjacent the outer surface of the tube and thus the cooling medium will not create any adverse temperature gradient in the rod of material, such as a semiconductor material, to influence either the growth or quality of the crystal being processed.

In order to provide a good electrical contact with the conducting elements 3 of the coil 1, each end of the coil is connected to a holding member 8 which is a high frequency lead or contact, through an intermediate member 7. As illustrated in FIG. 2, the intermediate member 7 which is formed of a good conducting material, for example silver, is provided with means for forming a vacuum-tight connection with the holding member 8 and the end of the tube 2 of the coil 1. The intermediate member 7 has a bore or passage 13 with a recess 14 at one end which recess forms an internal shoulder 22 and receives an end of the tube 2. The bore 13 is in registry with the corresponding bore or passage 23 in the holding member 8 so that the water 5 can flow through the bores 23 and 13 into the tube 2. The ends of the single or plurality of wires 3 which forms the conductors are soldered to the interior of the bore 13 of the intermediate member at 9 and 10 to provide the necessary electrical connection.

To protect the interior of the tube 2 from the atmosphere and to form a vacuum-tight seal, the recess 14 receives an annular silicon rubber seal 11 which surrounds the tube 2 as it abuts against shoulder 22 and the seal 11 is compressed by means such as a plate 12 which is clamped thereon by machine screws that connect the intermediate member 7 to the holding member 8. To prevent leakage of water between the intermediate member 7 and the holding member 8, an annular sealing ring 15 is clamped between the two members as they are held together by the above mentioned machine screws.

An embodiment of the intermediate member is illustrated in FIG. 3 and indentified at 7' which intermediate member comprises a tube member 17 and a plate member 4. The plate member 4 is provided with a recess 24 in which one end of the tube member 17 is fixed such as by soldering. The tube member 17 and the plate member 4 are of a good electrical conducting material such as silver, copper or silver plated brass.

The plate member 4 has a passage or bore 25 which is in alignment with an axial bore or passage 26 in the tubular member 17. The intermediate member 7' is mounted on the holding member 8 which acts as a high frequency lead with the bores 25 and 26 aligned with the bore 23 and with the interface between the plate member 4 and the holding member 8 provided with an annular sealing ring such as 0-ring 15.

The outer end of the bore 26 is supplied with an enlarged portion 27 such as by a counterbore to form an annular shoulder 28. Adjacent the end, the enlarged portion 27 is provided with internal threads 29. To provide a sealing means of the intermediate member 7', an annular ring 16 of silicon rubber is disposed in the enlarged portion 27 and is clamped or pressed against the shoulder 28 and into engagement with the tube 2 by clamping means which is illustrated as a bushing 18 having external threads 30 which cooperatively engage the internal threads 29 of the portion 27.

The leads or wires 3 can be connected to the intermediate member 7' by being soldered to the interior wall of the bore 26 if desired. As illustrated, a cross-bore 31 extends transverse of the tubular member 17 and intersects the bore 25. The leads or wires 3 extending into the bore 31 and are electrically connected to the exterior portion or surface of the tubular member 17 by a solder 19 which also serves to seal the bore 31. As in the previous embodiment, cooling water is circulated through the tubular member such as in the direction indicated by arrow 20.

Instead of using a bushing 18 for providing the means to compress the silicon rubber sealing ring 16, another embodiment of the device of FIG. 3 is illustrated in FIG. 4. In this embodiment, an intermediate member 7" has a tubular member 17 which is provided with an axial bore 26, having an enlarged portion 27 which is free of threads and which portion 27 forms a shoulder 28 on which an annular ring 16 of silicon rubber is compressed to form a liquid and vacuum-tight seal between the exterior of the tube 2 and the intermediate member 7". Instead of using a bushing 18, a sleeve nut 21 having an inner sleeve 33 and a concentric outer sleeve 34 which outer sleeve has inwardly extending threads is used. The tubular member 17 is provided with external threads which are engaged by the threads on the outer sleeves 34 to enable the sleeve nut 21 to be threaded down into clamping engagement on the sealing ring 16. As compared with the embodiments of FIG. 3, the embodiment of FIG. 4 ensures a better positioning of the sealing device and a more exact adjustment is possible since no threads are present in the enlarged portion 27 to foul the ring 16. As in the previously described embodiment of FIG. 3, the leads or wires 3 are electrically connected by the solder 19 to the external surface of the tubular member 17.

Another embodiment (see FIG. 5) of forming a liquid and vacuum-tight connection between the tube 2 of insulation material of the coil 1 and the intermediate member 7 is by metalizing the end of the tube such as a quartz tube. With the end of the quartz tube having a metalized portion 37 a solder connection 38 can be formed between the metalized portion 37 and the intermediate member 7 to form the desired vacuum-tight connection.

Although various minor modifications might be suggested by those versed in the art, it should be understood that we wish to employ within the scope of the patent granted hereon all such modifications as reasonably and properly come within the scope of our contribution to the art.

Claims

1. An induction heating coil having at least one turn, which coil is adapted for detachably mounting on a coil holding member of an induction heating device which has a chamber receiving at least a portion of the coil, the device being adapted for performing a process of zone melting of a rod of material in a protective atmosphere, the coil comprising a metal conductor of at least one turn and a heat resistant and vacuum-tight insulation member surrounding the metal conductor, said insulation member being a tube of glass-like material bent into the form of the coil and the metal conductor being at least one wire inserted into the bent tube, each end of said coil having a metal intermediate member which is attached to the conductor and the insulating member, each of said metal intermediate members having means for forming a vacuum-tight connection with the coil and forming a vacuum-tight connection with the holding member, and each of said intermediate members having a passage in alignment with the tube to

2. An induction heating coil according to claim 1, wherein the tube of

3. An induction heating coil according to claim 1, wherein the tube of

4. An induction heating coil according to claim 1, wherein the metal

5. An induction heating coil according to claim 4, wherein the plurality of

6. An induction heating coil according to claim 4, wherein the plurality of

7. An induction heating coil according to claim 1, wherein the cooling agent is water, and wherein the means forming a vacuum-tight connection also forms a water-tight connection with both the holding member and the

8. An induction heating coil according to claim 1, wherein each end of the metal conductor is soldered to the intermediate member which is made of a good conducting material and wherein the means forming the vacuum-tight connection between each end of the tube of glass-like material with the

9. An induction heating coil according to claim 8, wherein the intermediate member has a recess for receiving an end of the tube of glass-like material and wherein the silicon rubber seal is disposed between the end of the tube of glass-like material and the recess and wherein the means for forming a vacuum-tight connection includes means for compressing the silicon rubber seal into tight engagement between the recess and the tube

10. An induction heating coil according to claim 9, wherein the recess of the intermediate member is provided with internal threads and wherein the means for compressing comprises a bushing received on the end of the tube

11. An induction heating coil according to claim 9, wherein the external surface of the intermediate member adjacent the recess is provided with external threads and wherein the means for compressing comprises a sleeve nut surrounding the end of the tube having a sleeve portion for applying pressure to the silicon seal and an exterior sleeve which is threadably

12. An induction heating coil according to claim 1, wherein means forming a vacuum-tight seal between the insulation member and the intermediate member comprises the ends of the tube of glass-like material being metalized and the metalized ends being connected to the intermediate member by a solder connection.