Methods of forming isolated semiconductor device active regions

Abstract

Methods of forming semiconductor device active regions include the steps of forming a buffer layer containing a material susceptible to oxidation, such as polycrystalline or amorphous silicon, on a semiconductor substrate. To inhibit any native oxide film on the buffer layer from facilitating the formation of field oxide isolation regions having bird's beaks, the native oxide film is converted to a nitrogen containing film, such as silicon oxynitride, by nitrating the native oxide film. The silicon oxynitride film can be formed by exposing the oxide film to a nitrogen containing plasma, implanting nitrogen ions into the oxide film or annealing the oxide film in a nitrogen containing atmosphere, for example. During the nitrating step, chemically active oxygen in the native oxide film becomes bound to the nitrogen incorporated therein. A top oxidation resistant layer containing silicon nitride can then be formed on the nitrated surface of the buffer layer and used as an oxidation mask during a subsequent step of oxidizing the buffer layer to form field oxide isolation regions. By binding chemically active oxygen to nitrogen during the nitrating step, lateral oxidation under the top oxidation resistant layer is inhibited by limiting the lateral transport of chemically active oxygen. The masking properties of the top oxidation resistant layer can therefore be enhanced and utilized to form field oxide isolation regions having short or nonexistent bird beak's.