METHOD FOR LOCOS ISOLATION OF SEMICONDUCTOR DEVICE

Methods of forming field oxide isolation regions having sloped edges which facilitate uniform step coverage of subsequently patterned metallization, etc. but do not encroach upon semiconductor active regions, include the steps of patterning a first mask on a face of a semiconductor substrate to define an active region thereunder and then forming a pad insulation layer on the face of the substrate and in abutting relation to edges of the first mask. Oxidation resistant spacers are then formed on the edges of the first mask and on the pad insulation layer so that field oxide isolation regions having sloped edges can be formed by growing the pad insulation layer through oxidation so that it extends away from the edges of the first mask and does not undercut the first mask to form parasitic bird's beak oxide extensions. The inclusion of oxidation resistant spacers causes the subsequently formed field oxide isolation regions to have edges which are sloped at low angles of inclination in a direction away from the active region mask instead of being vertical.