Method of manufacturing a semiconductor integrated circuit device having a trench

Abstract

A semiconductor integrated circuit device and a method of manufacturing the same. The surface of a substrate of an active region surrounded by an element isolation trench is horizontally flat in the center portion of the active region but falls toward the side wall of the element isolation trench in the shoulder portion of the active region. This inclined surface contains two inclined surfaces having different inclination angles. The first inclined surface near the center portion of the active region is relatively steep and the second inclined surface near the side wall of the element isolation trench is gentler than the first inclined surface. The surface of the substrate in the shoulder portion of the active region is wholly rounded and has no angular portion.

1 . A method of manufacturing a semiconductor integrated circuit device comprising steps of:
 (a) forming a first silicon oxide film over a surface of a semiconductor substrate by thermally oxidizing said substrate and then forming an oxidation resistant film over said first silicon oxide film, and selectively exposing said surface of said substrate for an element isolation region by removing said oxidation resistant film and said first silicon oxide film;   (b) after said step (a), recessing an end of said first silicon oxide film inward more than an end of said oxidation resistant film;   (c) forming a second silicon oxide film, having a thickness larger than that of said first silicon oxide film, on said surface of said substrate which is exposed after said step (b) by thermally oxidizing said exposed substrate surface including a silicon surface extending from an edge of said first silicon oxide film and under said oxidation resistant film, said second silicon oxide film including a bird's beak that extends inwardly from the end of said oxidation resistant film;   (d) exposing said surface of said semiconductor substrate in said element isolation region by etching said second silicon oxide film, including said bird's beak, to form an inclined surface of said substrate at an edge of said element isolation region, wherein said edge of said element isolation region extends inwardly from the end of said oxidation resistant film;   (e) forming a trench in said substrate of said element isolation region by etching said substrate exposed in said step (d) to form a concave surface at said edge of said element isolation region, using said oxidation resistant film as a mask;   (f) after said step (e), rounding said edge of said element isolation region by thermal treatment; and   (g) after said step (f), burying said trench with a silicon oxide film by polishing a silicon oxide film formed over said oxidation resistant film and said trench.   
   
   
       2 . A method according to  claim 1 , wherein said concave surface is formed by a recessing of an intermediate portion of said inclined surface in said step (d). 
   
   
       3 . A method according to  claim 1 , wherein a third silicon oxide film is formed on an inner wall of said trench by said thermal treatment in said step (f). 
   
   
       4 . A method according to  claim 1 , wherein said substrate is over-etched in said removing of said step (a).