Method for manufacturing semiconductor device having isolating groove

Abstract

A semiconductor device having a LOCOS region formed on a Si substrate comprises a minute groove filled with non-oxidizable isolation film provided at the boundary between the LOCOS region and an IC area to be formed on the Si substrate. The non-oxidizable isolation film prevents the intrusion of thermal oxidation for the LOCOS region into the IC region, and is of silicon nitride 1000-10000 .ANG. width. A method of manufacturing a semiconductor device having a LOCOS region formed on a Si substrate comprises the steps of depositing a silicon nitride film on the substrate; etching a minute width region at the boundary between an area to be the LOCOS region and an area to be an IC region on the substrate by anisotropic etching with a reactive ion etching mode, thereby to form a groove thereat thermal-oxidizing the Si substrate to form a thin SiO.sub.2 film on an area to be covered with silicon nitride; filling the groove with silicon nitride; thermal-oxidizing a part of the Si substrate other than the area covered with silicon nitride films formed previously; and removing the silicon nitride film deposited at the first step to flatten the surface of the Si substrate.