Conduit for high temperature transfer of molten semiconductor crystalline material

• US 4,396,824 A
• Filed: 10/09/1979
• Issued: 08/02/1983
• Est. Priority Date: 10/09/1979
• Status: Expired due to Term

• Current Assignee: Siltec Corporation
• Original Assignee: Siltec Corporation
• Inventors: Fiegl, George, Torbet, Walter
• Primary Examiner(s): Bartis, A.
• Application Number:
  US06/082,640
• Time in Patent Office: 1,393 Days
• Field of Search: 219/300, 219/301, 219/421, 219/535, 138/140, 138/141, 138/149, 138/153, 138/177, 428/36, 428/408, 156/617 SP, 156/623, 156/604, 156/608, 137/341, 222/146 R, 222/146 H, 222/146 HE, 222/590-593, 13/33, 422/248, 422/249, 164/337
• US Class Current: 392/480
• CPC Class Codes: B22D 41/50 Pouring-nozzles
• CPC Class Codes: C01B 33/02 Silicon forming single crystals or homogeneous polycrystalline material with defined structure C30B
• CPC Class Codes: C30B 15/00 Single-crystal growth by pulling from a melt, e.g. Czochralski method under a protective fluid C30B27/00
• CPC Class Codes: Y10T 137/6606 With electric heating element
• CPC Class Codes: Y10T 428/30 Self-sustaining carbon mass or layer with impregnant or other layer

Abstract

A conduit for high temperature transfer of molten semiconductor crystalline material consists of a composite structure incorporating a quartz transfer tube as the innermost member, with an outer thermally insulating layer designed to serve the dual purposes of minimizing heat losses from the quartz tube and maintaining mechanical strength and rigidity of the conduit at the elevated temperatures encountered. The composite structure ensures that the molten semiconductor material only comes in contact with a material (quartz) with which it is compatible, while the outer layer structure reinforces the quartz tube, which becomes somewhat soft at molten semiconductor temperatures. To further aid in preventing cooling of the molten semiconductor, a distributed, electric resistance heater is in contact with the surface of the quartz tube over most of its length. The quartz tube has short end portions which extend through the surface of the semiconductor melt and which are lef bare of the thermal insulation. The heater is designed to provide an increased heat input per unit area in the region adjacent these end portions.

Claims

1. A conduit for conducting a fluid stream of a molten material at a high temperature comprising:

a. a transfer tube through which said stream is to be conducted, which tube is made of a material which is substantially non-contaminating to said molten material;

b. a reinforcing structure more structurally rigid than said transfer tube encompassing the exterior of said tube and extending substantially the full length thereof but terminating short of the ends of said transfer tube to leave the exposed end portions of said transfer tube for immersion into a body of said molten material without requiring contact between said reinforcing structure and said molten material;

c. a heater extending over the surface of said transfer tube and substantially surrounding said transfer tube interiorly of said reinforcing structure, said heater being substantially coterminous with said reinforcing structure at said ends and arranged to provide to said tube a greater heat input per unit length in a region of said tube proximate said ends than at other regions thereof remote from said ends; and

d. a layer of thermal insulating material interposed between said transfer tube and said reinforcing structure to transmit the structural rigidity of said insulating structure to said tube, said heater being disposed between said insulating material and said transfer tube.

2. The conduit of claim 1 wherein said molten material is silicon, said material of said transfer tube is quartz, and said reinforcing structure is graphite.

3. The conduit of claim 1 wherein said thermal insulating material is graphite felt.

4. A conduit for conducting a fluid stream of a molten material at a high temperature comprising:

a. a transfer tube through which said stream is to be conducted, which tube is made of a material which is substantially non-contaminating to said molten material;

b. a reinforcing structure more structurally rigid than said transfer tube encompassing the exterior of said tube and extending substantially the full length thereof but terminating short of the ends of said transfer tube to leave the exposed end portion of said transfer tube for immersion into a body of said molten material without requiring contact between said reinforcing structure and said molten material;

c. a heater extending over the surface of said transfer tube and substantially surrounding said transfer tube interiorly of said reinforcing structure, said heater being substantially coterminous with said reinforcing structure at said ends and arranged to provide to said tube a greater heat input per unit length in a region of said tube proximate said ends than at other regions thereof remote from said ends; and

d. said heater is an electrically resistive surface heater in substantial contact with the surface of said transfer tube, comprising three longitudinally extending circumferentially spaced resistive strips extending along the length of said tranfer tube, a first circumferentially extending resistive link electrically interconnecting a pair of said strips at one end thereof, and a second circumferentially extending resistive link at the other end of said strips electrically interconnecting one of said pair of strips with a third strip and forming said series circuit loop with said strips and said first link.

5. A conduit for conducting a fluid stream of a molten material at a high temperature comprising:

a. a transfer tube through which said stream is to be conducted, which tube is made of a material which is substantially non-contaminating to said molten material;

b. a reinforcing structure more structurally rigid than said transfer tube encompassing the exterior of said tube and extending substantially the full length thereof but terminating short of the ends of said transfer tube to leave the exposed end portions of said transfer tube for immersion into a body of said molten material without requiring contact between said reinforcing structure and said molten material;

c. a heater extending over the surface of said transfer tube and substantially surrounding said transfer tube interiorly of said reinforcing structure, said heater being substantially coterminous with said reinforcing structure at said ends and arranged to provide to said tube a greater heat input per unit length in a region of said tube proximate said ends than at other regions thereof remote from said ends; and

d. wherein said heater comprises four resistive strips and four resistive links, said strips being oriented to extend axially along said transfer tube, said resistive links being oriented to circumferentially extend between, and electrically interconnect the ends, of said strips so as to form a single series circuit loop including said strips and said links.

6. The conduit of claim 5 wherein said heater is formed from flexible graphite sheet.