Browse Prior Art Database

Reduced Bird's Beak ROI Process

IP.com Disclosure Number: IPCOM000061360D
Original Publication Date: 1986-Jul-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 2 page(s) / 52K

Publishing Venue

IBM

Related People

Chu, SF: AUTHOR [+3]

Abstract

Disclosed is a process for reducing the length of "bird's beak" associated with a recessed oxide isolation (ROI) region of semiconductor devices. The process uses phosphorous-doped polysilicon to achieve a rapid oxidation which lends itself to a reduced bird's beak. Referring to Fig. 1, starting with an N-Si, a thin layer of thermal oxide 2 and a layer of silicon nitride 3 are formed. The device region in the form of pedestal 1 is defined by reactive ion etching a trench. Then, another oxide layer 2' is grown in the trench. This oxide 2' will prevent any dopant in the subsequently deposited doped polysilicon layer from diffusing into the silicon. Silicon nitride 3 serves as an oxidation mask. Referring to Fig.

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Reduced Bird's Beak ROI Process

Disclosed is a process for reducing the length of "bird's beak" associated with a recessed oxide isolation (ROI) region of semiconductor devices. The process uses phosphorous-doped polysilicon to achieve a rapid oxidation which lends itself to a reduced bird's beak. Referring to Fig. 1, starting with an N-Si, a thin layer of thermal oxide 2 and a layer of silicon nitride 3 are formed. The device region in the form of pedestal 1 is defined by reactive ion etching a trench. Then, another oxide layer 2' is grown in the trench. This oxide 2' will prevent any dopant in the subsequently deposited doped polysilicon layer from diffusing into the silicon. Silicon nitride 3 serves as an oxidation mask. Referring to Fig. 2, next, phosphorous-doped polysilicon 4 having a N+ content equal to or exceeding the solid solubility limit is deposited. The thickness of the polysilicon 4 is controlled to be equal to or thicker than the step height: Tpoly = Tox + Tnitride + Tsi etch The wafer surface is next planarized as shown in Fig. 3. The nitride layer 3 on the silicon pedestal 1 serves as a polish stop. The remaining polysilicon is then thermally oxidized in steam to form the recessed oxide having a bird's beak 5 (Fig. 4) of a length dictated by the oxidation temperature, as indicated in the table below. The nitride 3 and oxide 2 are removed to expose the Si surface for further processing. Bird's Beak Length As Related To Oxidation Temperature(1,2)...