DE1191921B - Induction heating element for zone melting or cleaning device and process for the production of the same - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Int. Cl .:

H05b

German class: 21h-29/03

Number: 1191 921

File number: M 58927 VIII d / 21 h

Filing date: November 15, 1963

Opening day: April 29, 1965

The invention relates to an improved induction heating element for a zone melting or cleaning device and a method of manufacturing the element.

The zone cleaning device is used in the semiconductor industry to remove a rod or the like. Made of a semiconductor material, such as silicon, to be cleaned or converted into a single crystal. In order to heat the material to be cleaned, the device usually contains an induction heating element, which consists of a winding which surround a body made of a semiconductor material and pass a small portion of the material through Induction currents are intended to heat the generated by a high-frequency current flowing through the winding be generated. Since most - if not all - semiconductors have one at their melting point have considerable vapor pressure, part of the semiconductor material to be cleaned normally evaporates and condenses on the induction heating element if not isolated therefrom. This would not in itself be a disadvantage if the condensed semiconductor substance did not tend to peeled off the heating element and in large part near the melted portion of the Body made of the semiconductor material to be held in place by the magnetic field generated by the High frequency winding is generated. The leaflets coming out of the heating element often get there back into the body of the semiconductor material near the interface of liquid and solid state and form crystallization nuclei. So if you look at the body of the semiconductor material want to transform into a single crystal, the crystallization nuclei that arise from the flakes prevent which get back from the heating element into the body of the semiconductor material that the desired results can be achieved, so that the body of the semiconductor material is a polycrystalline Mass remains.

According to the invention it has now been found that a coil with less tendency to release can be obtained of particles or flakes of semiconductor material can be obtained by making a winding from a Manufactures electrically conductive base material and then on a point of the winding on the Usually the condensation of semiconductor material occurs, an adherent, coarse-grained deposit applied from an electrically conductive material. According to a preferred embodiment of the invention, the adherence of the coarse-grained Deposition on the base material

Induction heating element for zone melting resp.
cleaning device and method
for making the same

Applicant:

Monsanto Company, St. Louis, Mo. (V. St. A.)

Representative:

Dr.-Ing. H. Ruschke and Dipl.-Ing. H. Agular,

Patent Attorneys, Munich 27, Pienzenauer Str. 2

Named as inventor:
Harry Milton Stevens,
Crystal Lake, Mo. (V. St. A.)

Claimed priority:
V. St. v. America November 16, 1962
(238 203)

strengthens by adding a fine-grained deposit from an electrically over the coarse-grained deposit conductive material is applied such that the contact surface of the body of the first deposition with the base material is effectively increased without altering the gritty nature of the surface of the heating element get lost.

In detail, an induction heating element for a zone cleaning device is according to the invention proposed that consists of a winding made of an electrically conductive base material and that characterized in that on at least a portion of the outer surface of the base material a firmly adhering coarse-grained deposit made of an electrically conductive metal is applied. Another preferred embodiment of the induction heating element is that a fine-grained Deposition of an electrically conductive material applied to the coarse-grained deposit has been.

According to the invention, a method for producing an induction heating element is also proposed, that consists in making a winding

an electrically conductive metallic base material, ζ. Β. Silver or copper, made in such a way that they are around a rod of semiconductor material

509 567/235

3 4

A semiconductor material can be placed on the winding or debossed near the same Deposition from an electrical conductor is gradually practically its entire length Tending metal applies and then the coarse-grained one. At the beginning of the first or one Deposition binds to the base material. later zone melting process one melts normally

A preferred embodiment of the invention 5 times the rod made of semiconductor material on the

according to the method is that one on the lower end to a seed crystal, so that at the

coarse-grained deposit a fine-grained migration of the zone upwards the rod of poly-

separation of an electrically conductive material from crystalline semiconductor material into a single crystal

brings up. is converted. The rod from the single crystal

A heating element according to the invention can then be cut into wafers for each xo made of semiconductor material

Type of zone cleaning device can be used and for the production of electronic prep

den, but the new heating element is used in the intended directions.

most moderate in connection with a vacuum zone die for the production of an inventive Melting device used. This is because heating elements are used for a zone melter this type of device the deposits xs turned base can be arranged in of semiconductor material on the heating element and the construction of a common winding for the largest Cause difficulties. Difficulties particular type of zone melter for which occur with this type of device in particular it is used to match. In most When used for zone cleaning of silicon of the cases, the ground winding can be expediently made Conductivity type "n" can be used because ao consists of a tubular element that has a to This material is necessary, the single crystal in ten turns in the form of a spiral or one the smallest possible number of melt-through screw, which contains a rod of semiconductor threads Manufacture to enclose the evaporation of the material tightly. At least that Limit doping to a minimum. outer surface of the winding should consist of one

In the drawing, a part of a zone clean material is made up of a high-frequency current

Generation device shown, in which an invention is able to easily conduct, with silver being preferred.

proper improved winding is used. In most cases the basic winding is in

Number 10 denotes a rotating, with a cross-section that is chemically uniform, but

Threaded guide shaft on which the basic winding can, if necessary, be an outer one

the thread engaging, winding holding surface of a metal such as silver, the

Block 12 is located. The block 12 is supported by one of a different metal or material

suitable device, not shown, is attached, because in the conduction of high-frequency currents

tends to rotate with the guide shaft 10, so the chemical nature of the surface layers of the

that the holder 12 largely changes its conductivity properties when the shaft 10 is rotated

moves up or down, depending on the turn. Instead of silver, you can

direction of the wave. use any material that is a satisfactory one

At a distance from the guide shaft 10 and the high-frequency current conductor and that is not an un-

substantially parallel to this is a desired contamination of the to be cleaned

Rod made of a semiconductor material 14, which evokes zonal semiconductor material, such. B. copper, gold

should be cleaned. The rod is on one or 40 and iron in some cases.

at both ends by the usual (not shown) the coarse-grained deposition, the invention mounts worn, which is normally applied to the ground winding accordingly, are creating that at least one of the brackets can be made of the same material as the Grundam End can be rotated so that at least one winding or another consist before one Part of the rod is made of semiconductor material 14 but is made of a metal that is a good conductor for rend of the zone cleaning around its longitudinal axis is high-frequency currents because, as is well known, high-speed will. frequency currents largely in the surface

A heating element that is transported from a winding 16 to coat a conductor. Further stands, is carried by a support block 12 and the deposition is preferably such that it extends around the rod of semiconductor material 50 does not allow any impurities to evaporate, which can 14 around. The winding 16, the semiconductor material cleaning from the holder 12 in an undesirable manner is electrically isolated, is through lines 18 and contaminate. For these reasons, this is before -20 with a suitable source of high-frequency drawn material for making the coarse-grained electricity connected and intended to provide a schma- Separation in most cases elementary ensiling Section of rod 14 between the two 55 ber; other suitable metals are e.g. B. copper or To melt the ends of the same. As in the drawing gold. The coarse-grained deposit can be applied to any indicated, the surfaces of the winding are made in a suitable manner, the gal-16 at least partially with a granular metallic or electrolytic and the flame mixing Coated material so that spray process leaflets are preferred. When working in Condensed semiconductor material rarely of the 60 smaller scale is usually the electrolytic one Surface of the winding are released. Application is most expedient. Anyone can do it

During operation, a polycrystalline rod from standard galvanic processes is used, Semiconductor material attached in the device and which leads to a coarse-grained deposition, e.g. B. the coil 16 near the lower end of the rod can be used to make coarse-grained silver. The winding 16 is then deposited by 65 deposition from silver nitrate solution or passing through high-frequency current operated and the one for the deposition of coarse-grained copper Rotate guide shaft 10 slowly so that a copper sulphate solution is used. It goes without saying molten zone, which is first at the lower end of the nature of the for the purposes of the invention

Deposition is important and not the process used to make it.

The mean grain size of the coarse-grained deposit can vary within wide limits, however, the deposit should preferably have a clearly recognizable granular nature, if viewed under low magnification. For most purposes, it has a coarse-grained deposit a preferred mean grain size of about 10 to 50 μ, it should be such in almost all cases have from 5 to 200 μ. The grain size range of the coarse-grained deposit is of little importance and in some cases it can advantageously be quite large, because the smaller grains are the firm ones Increase the connection of the larger grains to the metal base on which they are deposited. Satisfactory results can be achieved if the grain size range is between 200 μ and submicroscopic particles as long as the mean grain size is within the range given above lies.

The coarse-grained deposit applied according to the invention to the metal winding as a base can be any strength desired, but for most purposes the greatest strength should not be essential be larger than the largest grain size of the deposit, so that you can get the base metal through the Can recognize deposition through it. This makes it possible to make the deposition easier on the To anchor base. However, this is only a matter of expediency, satisfactory results can also be achieved with an extremely strong deposit if it is solid is sufficiently bonded to the substrate and if it is not so strong that the spaces between the turns must be chosen too large to avoid a short circuit. In most Cases, however, it is hardly useful if the coarse-grained deposit has a greatest strength of more than has about 200 μ.

Virtually all methods of producing a coarse-grained deposit on a metal base lead to a deposit that adheres so little that it can easily be at least partially with one Soft toothbrush or the like. Can be wiped off, but according to the invention, if you get the best possible Want to achieve results, the coarse-grained deposit will adhere so firmly that it can be removed by once or twice Brushing with such a brush does not noticeably wipe off. So it is normally necessary to close the winding further following the production of the coarse-grained deposit edit to ensure better adhesion of the coarse-grained deposit. A preferred method this consists in applying a fine-grain metal deposit over the first, the contact surface of the larger grains of the first deposit with the metal base enlarged. Apart from its grain size, the second deposit can usually be of the same nature as the be first and also be made of any suitable material that is a good conductor for high frequency currents is. Silver is preferred, but e.g. B. also suitable for gold and copper. The fine-grain deposit can be applied by vapor deposition or in any other suitable manner but preferably applied electrolytically. Electrolytic deposition method of fine-grain deposits on metal substrates are known and all suitable. if If the fine-grain deposit is to be produced from silver, there is a preferred electroplating Process in which an aqueous solution of silver cyanide is used. The fine-grain deposit may conveniently be of almost any strength desired provided it is not so strong that they the coarse-grained nature of the deposit over which

ίο she is upset, obscured and that she is strong is enough to anchor the coarse-grained deposit firmly enough to the substrate. In most In some cases, the fine-grained deposit is about 2 to 15 μ thick and has an average grain size of not more than about 5 to 10 μ, preferably no more than 3 μ.

The invention is explained in more detail with the aid of the following examples.

example 1

10 parts by weight of silver nitrate are placed in a suitable container, which is then approximately 400 parts by volume can be dissolved in double distilled water. A clean zone cleaner winding, cleaned with the sandblasting fan, which has been made from a tube of pure silver is then put into the bath brought and brought into connection with the negative pole of a direct current source. An anode that preferably consists of a rod of pure silver, is then immersed in the solution and is preferred mounted so that it passes axially through the center of the winding. The silver anode is then over a Ammeter connected to the positive pole of the DC power source. Then a current of 30 to 140 mA passed through the solution for a total of 3 to 4 minutes. The winding is then double-distilled Washed with water, taking care that the coarse-grained deposit, obtained by the galvanic treatment in the silver nitrate solution is removed. A zone cleaner winding with a first coarse-grain silver deposit, as described above has been applied, is immersed in a container containing 10 parts by weight of silver cyanide, 10 parts by weight Contains sodium cyanide and 10 parts by weight of potassium perchlorate and so much water that 400 parts by volume and connected to the positive pole of a DC power source as above. A silver anode is fed axially through the winding and 20 to 50 mA is passed through the winding for about 3 minutes Solution sent. The winding is then rinsed thoroughly with double-distilled water and with acetone dried. This second galvanic treatment leads to the fact that the coarse-grained deposit is deposited a very fine-grain deposit is applied so that the coarse-grain deposit adheres firmly to the silver winding tied so that it does not become disrupted by walking over it once or twice with a can be removed with a soft brush.

The winding with the outer fine-grain deposit of elemental silver is in the holding block given a vacuum zone melting device from Siemens and used in the usual way Zone cleaning of silicon used. The number of rods of semiconductor material passing through less than four zone melting passes are converted into silicon monocrystals, is usually more than 300% compared to the usual method

device, in which a silver winding with a conventional mirror-smooth surface is used.

Example 2

A coarse-grained deposit of elemental silver is deposited on a zone melting coil made of silver deposited as a base from silver nitrate solution as in Example 1. The winding is then with Washed double distilled water, dried with acetone and 2 to 10 minutes on weak red heat heated to anchor the coarse silver grains on the metal base. After this sintering treatment The coarse-grained silver crystals adhere so tightly that they cannot easily be attached by walking over them once or twice remove with a soft brush.

The sintered winding is attached as in Example 1 in a zone cleaning device and also provides beneficial results

The procedure for metals other than silver can be general as well as the procedures described only need to make appropriate changes to the chemical nature of the anode and of the salts that are used to produce the galvanic baths.

Claims (14)

Patent claims: 1. Induction heating element for zone melting or cleaning device, consisting of a Winding made from an electrically conductive base material, characterized in that at least on part of the outer surface of the base material a firmly adhering, coarse-grained surface Deposition from an electrically conductive metal has been applied. 2. Heating element according to claim 1, characterized in that a fine-grain deposit of an electrically conductive metal has been applied over the coarse-grained deposit. 3. Heating element according to claim 2, characterized in that the mean grain size of the coarse-grained metal deposition between about 10 and 50 μ and the mean grain size of the fine-grain deposit is smaller than about 10 μ. 4. Heating element according to one of claims 1 to 3, characterized in that the coarse-grained Deposition is elemental silver. 5. Heating element according to claim 2, 3 or 4, characterized in that the fine-grain deposit metallic silver is. 6. Heating element according to one of claims 1 to 5, characterized in that the base material Is copper or silver. 7. induction heating coil according to claim 1, characterized in that it consists of a tubular Base consists of metallic silver, on which a coarse-grained deposit of Silver crystals and an overlying fine-grain silver deposit has been applied. 8. heating coil according to claim 7, characterized in that the fine-grain silver deposit has an average thickness of about 2 to 15 μ. 9. A method for producing an induction heating element according to claim 1, characterized in that that a winding made of an electrically conductive metallic base material, z. B. silver or copper, which is suitable for attachment around a rod of semiconductor material is, produces, on the winding a coarse-grained deposit of an electrically conductive Applies metal and then firmly connects the coarse-grained deposit with the base material. 10. The method according to claim 9, characterized in that the connection by tempering the winding is effected. 11. The method according to claim 9, characterized in that the connection is effected by making a fine-grained deposit from an electrically on the coarse-grained deposit applies conductive metal. 12. The method according to claim 9 or 10, characterized in that the coarse-grained Deposition applies electrolytically. 13. The method according to claim 11 and 12, characterized in that the coarse-grained deposit consists of crystals of elemental silver and the fine-grained deposit on it Is produced electrolytically and consists of a silver layer, which is a middle Has a thickness of about 2 to 15 μ. 14. The method according to claim 9, characterized in that at least part of the Surface of the winding electrolytically from silver nitrate solution with a coarse-grained Deposition from crystals coated by elemental silver and then these coarse-grained Electrolytic deposition from a solution of silver cyanide with a fine-grained Plated silver deposit. 1 sheet of drawings 509 567/235 4.65 © Bundesdruckerei Berlin