Abstract
The performance and packing density of silicon integrated circuits can be increased by the use of thermally grown silicon dioxide for the dielectric isolation of the active components of the circuit and by employing fabrication procedures which yield devices with flat surfaces. Using Si3N4 masking, anisotropic etching of the silicon substrate, and thermal oxidation, structures were fabricated in which the SiO2 was recessed below the original surface. Because of the lateral oxidation under the edge of the Si3N4 mask, a so-called bird's beak shaped structure is formed at the Si-SiO2 and SiO2-Si3N4 interfaces. Factors which influence the surface planarity due to the bird's beak formation have been studied experimentally. This investigation studies the minimization of the bird's beak by using a combination of a thick Si3N4 film, a thin SiO2 pad, and a suitable thickness of recessed oxide (ROX). Uniform anisotropic etching and parallel alignment to <110> are also required to maintain dimensional control. © 1976, The Electrochemical Society, Inc. All rights reserved.