Browse Prior Art Database

Locating Collector and Subcollector Junctions

IP.com Disclosure Number: IPCOM000075365D
Original Publication Date: 1971-Sep-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Kennedy, DP: AUTHOR

Abstract

In bipolar transistor fabrication, the use of a subcollector has become an accepted method for reducing the extrinsic collector resistance. If in such a structure the collector junction space-charge layer is permitted to penetrate into its subcollector region, the resulting device can be exceedingly sensitive to variations of epitaxial layer thickness. In this method the collector junction can be located, relative to the subcollector, to obtain a reduced extrinsic collector resistance, without making the device excessively sensitive to variations of epitaxial layer thickness.

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Locating Collector and Subcollector Junctions

In bipolar transistor fabrication, the use of a subcollector has become an accepted method for reducing the extrinsic collector resistance. If in such a structure the collector junction space-charge layer is permitted to penetrate into its subcollector region, the resulting device can be exceedingly sensitive to variations of epitaxial layer thickness. In this method the collector junction can be located, relative to the subcollector, to obtain a reduced extrinsic collector resistance, without making the device excessively sensitive to variations of epitaxial layer thickness.

It has been shown that the manufacturing reproducibility of a transistor is dependent upon the degree of subcollector penetration into the collector junction space-charge layer. Shallow penetration (the collector junction penetrates only a small distance into the collector junction space-charge layer) can be tolerated, although extensive process control precautions are required to maintain this type of situation. In contrast, deep penetration (subcollector profile penetrates into the metallurgical collector junction) should be avoided; most transistor manufacturing that involves deep penetration is considered beyond the present state-of-the-art.

Simple space-charge layer interference provides a means whereby the extrinsic collector resistance can be reduced without producing a serious problem of device reproducibility. In the design of such struc...