US 4,347,431 AGranted

Diffusion furnace

AssigneesBell Telephone Laboratories, Incorporated, Western Electric Company, Inc.

InventorsCharles W. Pearce, Paul F. Schmidt

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Abstract

A diffusion furnace (11) includes a typical process tube (12) and an outer envelope (26) which forms an annular chamber (37) with the process tube. A heating element (29) of high purity graphite substantially surrounds the process tube within the chamber (37). Inner surfaces of the chamber (37) are made of materials such as, for example, silicon, pyrolytic graphite or quartz. Such materials are essentially free of harmful impurity elements such as iron, nickel, copper calcium or gold, which have an energy level about halfway between the valence and the conduction band of a semiconductor material to be processed within the process tube. A nonoxidizing gas within the heater chamber protects the graphite elements therein from oxidation. A small gas flow within the chamber (37) is preferred to purge such harmful impurity elements as may penetrate into the chamber during the operation of the furnace.

Claims6

Dependent claims

A diffusion furnace which comprises:

a central process tube of a material taken from the group of silicon and quartz;
a resistance heating element of a high purity graphite material having an ash content of no more than 100 parts per million, said element being disposed about said process tube;
and
an insulative envelope substantially enclosing the process tube and forming with said process tube an annular heater chamber for housing the heating element, said envelope having an inner wall of a material taken from the group of high purity graphite having an ash content of no more than 100 parts per million and quartz, such that the combination of the heating element and said envelope and process tube are capable of heating the space within said process tube to a temperature range including temperatures of 700.degree. C. and 1250.degree. C. substantially without contaminating transfer of undesirable impurities from such heater chamber toward the space within the process tube.

1 more element

Dependencies are inferred from the claim text.