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Multiwafer-Multisegment Coil Design for Plasma Processing

IP.com Disclosure Number: IPCOM000043361D
Original Publication Date: 1984-Aug-01
Included in the Prior Art Database: 2005-Feb-04
Document File: 3 page(s) / 40K

Publishing Venue

IBM

Related People

Berkenblit, M: AUTHOR [+4]

Abstract

It is known that silicon wafers can be oxidized in a pure oxygen plasma on the side of the silicon wafer facing away from the plasma at temperatures ranging from a few hundred degrees centigrade to conventional thermal oxidation temperatures (1000-1100ŒC). In complete distinction to previously known techniques for plasma oxidation, no intentional electrical bias is applied to the wafer to be oxidized and, as mentioned, the desired oxide grows on the wafer surface facing away from the plasma. The resultant oxides are uniform in thickness and of comparable quality to those grown by thermal means. In semiconductor device applications these plasma oxides, because they are obtainable at much lower temperatures, offer distinct advantages.

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Multiwafer-Multisegment Coil Design for Plasma Processing

It is known that silicon wafers can be oxidized in a pure oxygen plasma on the side of the silicon wafer facing away from the plasma at temperatures ranging from a few hundred degrees centigrade to conventional thermal oxidation temperatures (1000-1100OEC). In complete distinction to previously known techniques for plasma oxidation, no intentional electrical bias is applied to the wafer to be oxidized and, as mentioned, the desired oxide grows on the wafer surface facing away from the plasma. The resultant oxides are uniform in thickness and of comparable quality to those grown by thermal means. In semiconductor device applications these plasma oxides, because they are obtainable at much lower temperatures, offer distinct advantages. They exhibit lower compressive stress, do not, result in impurity depletion from the underlying silicon, do not in forming, cause the generation of oxidation- induced silicon defects, and are free of associated "bird's beak" phenomena in regions in which oxidation masking is employed. The process enables oxidations to be effected at rates less than, equal to or greater than achievable using conventional thermal means. As practiced, the known processes are limited to oxidation of only two wafers at a time, one on each side of the RF coil which is used to generate the pure oxygen plasma. From a practical point of view, it would be highly desirable to be able to oxidize larger numbers of wafers at the same time. The present article describes a unique RF coil design which enables the oxidation of more than two wafers at a time, obtaining good thickness uniformity. Using the unique coil design, up to 16 wafers may be oxidized simultaneously. If, instead of a single RF coil, a multisegment coil is employed, two immediate problems are encountered: 1) a discharge cannot be sustained in pure oxygen at the system pressure required, (10-60 mm), and 2) the discharge cannot be ignited simultaneously in all coil segments. The result of the second effect is that the power is directed to that segment (or segments) in which ignition occurs, causing initial overheating of the wafers surrounding the segment (or segments) in which ignition occurs. This is highly undesirable. It was discovered that if a discharge is initiated in a pure argon plasma and oxygen is subsequently introduced in the ratio of 1 part or less of oxygen to: 20-30 parts of argon, a discharge can be sustained in a preferred pressure range of 45-60 mm without t...