US2858199A - Crystal production - Google Patents

Description

Oct. 28, 1958 c. c. LARSON CRYSTAL PRODUCTION Filed Oct. 15. 1954 IN VE N TOR. CHRIS T/A N C. L A RSON BY United States Patent CRYSTAL PRODUCTION Christian Charles Larson,

Fort Wayne, Ind., assignor to International Telephone The present invention relates to crystal production, and more particularly to a method for manufacturing crystals which may be used as elements of transistors.

Conventional techniques for fabricating crystals from such materials as germanium, silicon and the like is to melt the basic material in a crucible and then touch the molten material with a seed crystal and draw the latter upwardly and away from the molten material at a sufiicient rate to continuously draw or grow a crystal. Such methods have been used successfully in the past, but are attended with considerable difiiculties in the cases where in silicon materials are used to produce the crystals.

Melted silicon in particular is of such high temperature that the usual crucibles are damaged or destroyed. No known crucible materials have yet been developed which will reliably withstand the high temperatures of molten silicon.

An object of the present invention is to provide a method for producing crystals without the need of a crucible.

It is another object of this invention to produce crystals from molten material in such a manner that the solid raw material constitutes the crucible for the molten material.

It is still a further object of this invention to utilize electron bombardment for melting a predetermined portion of a block of raw crystal material from which a finished crystal may be drawn.

Other objects will become apparent as the description proceeds.

To the accomplishment of the above and related objects, the invention may be embodied in the forms illustrated in the accompanying drawings, attention being called to the fact, however, that the drawings are illustrative only, and that specific change may be made in the specific constructions illustrated and described, so long as the scope of the appended claims is not violated.

In the drawings:

Fig. 1 is a vertical sectional elevation of an embodiment of this invention;

Fig. 2 is a top plan View thereof;

Fig. 3 is a diagrammatic illustration of an electron gun used in the apparatus of Fig. 1; and

Fig. 4 is a perspective illustration showing one step of the method of drawing a crystal.

Referring to the drawings, the apparatus comprises an evacuated bell jar 1 which is hermetically sealed to a metallic base 2. A shaft or rod 3 is reciprocably mounted in the top portion of the bell jar by means of a suitable threaded connection with a hermetically sealed coupling 4. Suitable constructions for reciprocating the rod 3 from a position outside of the bell jar 1 are wellknown to the art and in particular are described in a publication entitled Vacuum Equipment and Techniques by Guthrie and Wakerling, published by the McGraw-Hill Book Company and copyrighted in 1949.

A plurality of suitable electron guns 5 are circumferentially mounted on the top portion of the bell jar in 2,858,199 Patented Oct. 28, 1958 such a manner as to direct high density electron beams along the paths indicated by the dashed lines 6. These electron guns 5 may be of conventional construction and correspond to the electron gun arrangement disclosed in Gardner Patent 2,128,581. A suitable gun construction is diagrammatically illustrated in Fig. 3 wherein electrons emitted by a cathode 7 are concentrated into a pencil-like beam by an anode 8 and accelerated by both this anode 8 and another anode 9. As will become apparent from the following description, this pencil-like beam must be of high density.

On the base 2 of the bell jar 1 is placed a block 10 of silicon, germanium, or the like material in such position that the central portion thereof will be bombarded by the respective electron beams 6. These beams 6 are of such high density as to melt the central portion of the block 10. The beams are so controlled that only the central portion of the block is melted, whereby the block serves as a crucible for the melted portion.

A seed crystal of the type which is to be finally produced is clamped by some suitable means in the lower end of the reciprocable rod 3, and such a starter or seed crystal is indicated in Figs. 1 and 4 by the reference numeral 11. The rod 3 is lowered until the seed crystal 11 just touches the molten material, and is then withdrawn upwardly at a slow rate which will allow the molten material to continuously form on the lower end of the seed crystal. Continued withdrawal of the seed crystal thereby ostensibly draws or pulls a suitable crystal structure from the solid block. During this pulling operation, the beams 6 are trained onto the areas surrounding the drawn crystal, whereupon the operation may be continued until the block 10 is substantially consumed.

Since the block 10 acquires an electrostatic charge from the electron beams 6, it is desirable to provide a conductive return path for current fiowfrom the base 10 to one of the gun anodes, such as the anode 9. A wire 12 is shown as providing this conductive path. While there has been shown a plurality of individual electron guns 5, it is possible to utilize a single electron gun of annular configuration which will produce a tapered, hollow electron beam for melting the block 10 in the vicinity surrounding the seed crystal 11.

By performing the operation in a vacuum, impurities are prevented from entering the finished crystal. By withdrawing the crystal from the central portion of a solid block, the latter also serves as the crucible, thereby avoiding the prior art problem of preventing destruction of crucibles when materials, such as silicon, are melted.

What is claimed is:

1. The method of fabricating crystals comprising born barding a portion of a block of material from which a crystal is to be made with electrons, said bombardment serving to melt said portion, said portion being disposed in one block surface inside the perimeter thereof, and drawing a seed crystal from said melted portion, the unmelted portion of said block serving as a crucible for the melted portion.

2. The method of fabricating crystals comprising selective melting a central portion of a block of material from which a crystal is to be made, said portion being disposed in one surface between the lateral block sides, drawing a seed crystal from said melted portion, the unmelted portion of said block serving as a crucible for the melted portion, and continuing to melt said block in the perimetral vicinity of the crystal being drawn.

3. The method of fabricating crystals from a block of material from which a crystal is to be made, said method comprising positioning a self-supporting block of said material in an evacuated container focusing an electron beam on the upper surface of said block, increasing the energy in said beam until a pool of said material meltsv in said upper surface within the perimeter of said upper surface of the block whereby said block serve as a crucible for the pool of melted material, partly immersing in said pool a seed crystal of said material, and lifting the seed crystal from thepool at the rate of solidification ofthe material uplifted from the pool.

References Cited inthe file of this patent NITED STATES PATENTS Kjellgren May 3, 1949 4 Malone June 7, 1949 Sparks et al. Mar. 17. 1953 Imber July 28, 1953 Sobek Apr. 6, 1954 Little et al. July 13, 1954 FOREIGN PATENTS France Mar. 10, 1954 OTHER REFERENCES Bell Tel, Lab. Inc. and Western Electric Co. Inc., Transistor Technology, part II, chapter 7, July 1952.

Claims (1)

1. THE METHOD OF FABRICATING CRYSTALS COMPRISING BOMBARDING A PORTION OF A BLOCK OF MATERIAL FROM WHICH A CYRSTAL IS TO BE MADE WITH ELECTRONS, AND BOMBARDMENT SERVING TO MELT SAID PORTION, SAID PORTION BEING DISPOSED IN ONE BLOCK SURFACE INSIDE THE PERIMETER THEREOF, AND DRAWING A SEED CRYSTAL FROM SAID MELTED PORTION, THE UNMELTED PORTION OF SAID BLOCK SERVING AS CRUCIBLE FOR THE MELTED PORTION.

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