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Prevention of Birdsbeak Formation

IP.com Disclosure Number: IPCOM000051953D
Original Publication Date: 1981-Apr-01
Included in the Prior Art Database: 2005-Feb-11
Document File: 2 page(s) / 88K

Publishing Venue

IBM

Related People

Antipov, I: AUTHOR

Abstract

To achieve greatest density in integrated bipolar technology, the isolation regions between devices must be made as narrow as possible. Generally, this is accomplished by reactive ion etching (RIE) of deep narrow trenches and their subsequent refill with silicon oxide deposited by chemical vapor deposition (CVD) after thin thermal oxidation. However, even the densest chips have isolation regions that are comparatively wide. These wide isolation regions cannot be easily refilled with CVD silicon oxide and birdsbeak-shaped structures can be formed at the device side of the trenches, when these wide areas are oxidized.

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Prevention of Birdsbeak Formation

To achieve greatest density in integrated bipolar technology, the isolation regions between devices must be made as narrow as possible. Generally, this is accomplished by reactive ion etching (RIE) of deep narrow trenches and their subsequent refill with silicon oxide deposited by chemical vapor deposition (CVD) after thin thermal oxidation. However, even the densest chips have isolation regions that are comparatively wide. These wide isolation regions cannot be easily refilled with CVD silicon oxide and birdsbeak-shaped structures can be formed at the device side of the trenches, when these wide areas are oxidized.

The technique described below prevents birdsbeak formation adjacent to deep trenches and also helps in the elimination of weak spots in the middle of deep trenches filled with silicon oxide. Fig. 1 shows the wide isolation region between two devices after deep trenches 3 and 4 were refilled with silicon oxide by CVD and planarized. This structure was arrived at by a number of process steps: Nsubcollector 1 was diffused into a P- substrate. An N- epitaxial layer 2 was then deposited and oxidized. Deep narrow trenches 3 and 4 were then formed by RIE, oxidized and implanted with Pchannel stoppers 5, 6. Subsequently, the deep trenches 3 and 4 were refilled with CVD silicon oxide 7 and planarized by RIE. It is known that the middle of CVD-refilled deep trenches have weak spots 8 and 9, where two sidewall oxides meet. The weak spots are more easily etched...