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Recessed Oxide Process to Reduce Field Doping Encroachment

IP.com Disclosure Number: IPCOM000060771D
Original Publication Date: 1986-May-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 2 page(s) / 38K

Publishing Venue

IBM

Related People

Furukawa, T: AUTHOR [+3]

Abstract

A method is described to very simply create a controlled offset between the field doping and the edge of an active device in a recessed oxide (ROX) process. The method results in reduction of narrow channel effects, reduced device perimeter capacitance, and an increased junction breakdown voltage. Referring to Fig. 1, a thin thermal oxide 2 and a silicon nitride film 4 are first formed on a silicon substrate 6. A photoresist layer 8 is applied and patterned to define the offset field implant regions 9. The silicon nitride 4 is then plasma etched using the photoresist layer 8as an etching mask. Field implant 10 is then performed using the same photoresist 8 as an implant mask.

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Recessed Oxide Process to Reduce Field Doping Encroachment

A method is described to very simply create a controlled offset between the field doping and the edge of an active device in a recessed oxide (ROX) process. The method results in reduction of narrow channel effects, reduced device perimeter capacitance, and an increased junction breakdown voltage. Referring to Fig. 1, a thin thermal oxide 2 and a silicon nitride film 4 are first formed on a silicon substrate 6. A photoresist layer 8 is applied and patterned to define the offset field implant regions 9. The silicon nitride 4 is then plasma etched using the photoresist layer 8as an etching mask. Field implant 10 is then performed using the same photoresist 8 as an implant mask. After stripping the photoresist 8, the oxide layer 2 is etched by ahydrofluoric acid (HF) solution and over-etched by a controlled amount to create an undercut L. This undercut provides the offset of the field implant away from the device perimeter. In the ROX process, the lateral oxidation will start at the intersection between the surface of the exposed silicon 6and the edge of the oxide 2 under the silicon nitride 4. As a result, the edge of the ROX 12 or the tip of the "bird's beak" 14 is shifted towards the remaining thin oxide region 2 by a controlled distance, approximating L, when compared to the conventional ROX process. Note that the field implant regions 9 of Fig. 1 have diffused vertically and laterally, and are shown in...