Prevention of Vertical Birds' Beaks During Oxidation of Semiconductor Structures
Original Publication Date: 1987-Aug-01
Included in the Prior Art Database: 2005-Feb-01
Disclosed is a method to avoid the formation of vertical birds' beaks along the sides of isolation trenches under the base region of semiconductor devices. This article suggests providing a source of silicon on top of the exposed trench liner to prevent oxidation of the epi region. During oxidation of some semiconductor structures, vertical birds' beaks are formed at the intersection of shallow and deep trenches. Additionally, during sidewall oxide removal by wet etching, a significant undercut of the thin thermal SiO2 layer covering the npn transistor area is possible. (Image Omitted) In the proposed process, after the formation of the shallow trench 1 (Fig. 1) by reactive ion etching (RIE) a layer of undoped polysilicon (PolySi) 2 is deposited.