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Bird's Beak-Free Full-Rox Isolation Scheme

IP.com Disclosure Number: IPCOM000044413D
Original Publication Date: 1984-Dec-01
Included in the Prior Art Database: 2005-Feb-05
Document File: 2 page(s) / 34K

Publishing Venue

IBM

Related People

Ray, AK: AUTHOR

Abstract

This article relates generally to full ROX (recessed oxide) isolation techniques used in semiconductor devices and more specifically to a plasma oxidation technique wherein the resulting ROX is bird's beak-free and defect formation and impurity migration are substantially eliminated. A full-ROX isolation scheme is preferred to a semi-ROX isolation scheme in FET devices because of improved device performance. However, problems, such as dislocations and bird's beak formation have discouraged the use of full-ROX structures in FET device fabrication. The critical step which gives rise to these problems is the silicon etching process.

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Bird's Beak-Free Full-Rox Isolation Scheme

This article relates generally to full ROX (recessed oxide) isolation techniques used in semiconductor devices and more specifically to a plasma oxidation technique wherein the resulting ROX is bird's beak-free and defect formation and impurity migration are substantially eliminated. A full-ROX isolation scheme is preferred to a semi-ROX isolation scheme in FET devices because of improved device performance. However, problems, such as dislocations and bird's beak formation have discouraged the use of full-ROX structures in FET device fabrication. The critical step which gives rise to these problems is the silicon etching process. Before the isolation oxide is grown, silicon is normally etched to a depth approximately half the desired isolation oxide thickness and a self- aligned ion implantation is carried out to adjust the field threshold. The profile obtained after the silicon etching step is very important for proper device isolation. If the silicon etching is anisotropic as shown in the cross-sectional view of a silicon substrate of Fig. 1, vertical walls and sharp corners near the mask edges are obtained. Then if a high temperature oxidation step is used subsequently to grow field oxides, dislocations and other defects are generated at the sharp corners. Migration of field implant towards active device areas also gives rise to increased junction capacitance. However, if a low temperature-high pressure oxidation process is used to reduce defect formation, then bird's beak length increases and the field implant does not spread out enough...