FORMATION OF SELECTIVE MASK

PURPOSE:To form a selective mask simply and accurately by a method wherein an aperture is drilled in two insulating films laminated on a semiconductor surface so as to have a step-shape cross-section and a high melting point metal layer is applied only to the part of the semiconductor surface inside the aperture and the lower insulating layer is selectively removed by anisotropic dry etching. CONSTITUTION:The first insulating film 12, for instance made of silicon oxide, and the second insulating film 14, for instance made of silicon nitride, are successively formed on a semiconductor substrate 10, for instance made of silicon, into laminated layers. An aperture 16, which has a step-shape cross-section, is drilled in the first and second insulating films 12 and 14 by selective etching. Then a high melting point metal layer 18 is selectively applied only to the part of the substrate surface inside the aperture 16. Then, the first insulating layer 12 is selectively etched by anisotropic dry etching with the second insulating film 14 and the high melting point metal layer 18 as masks to form an aperture 16A. With the selective mask obtained with the above-mentioned processes, the substrate surface is selectively subjected to anisotropic dry etching to form a groove 20 for isolation.