Dual-masked field isolation

摘要

A field isolation process utilizes two or more isolation formation steps to form active areas on a semiconductor substrate. Each field isolation step forms a portion of the field isolation in a manner which reduces field oxide encroachment, in particular, by forming field oxide islands. The superposition of field isolation configurations define the desired active areas. A presently preferred dual-mask process may be carried out using a single masking stack, or more preferably using a masking stack for each isolation mask. The present isolation process further allows isolation features to be optimized for a variety of isolation requirements on the same integrated circuit.