Device Photolithography: An Overview of the New Mask-Making System

The Electronic Materials and Components Development Area of Bell Telephone Laboratories has made the development of hybridintegrated electronics, combining semiconductor and thin-film technologies, its major general field of activity for several years. Silicon integrated circuits provide the active elements for both digital and analog systems, and passive components can be incorporated if tolerances are not too tight. Thin-film circuits based on tantalum can provide stable resistors and capacitors which can be trimmed to precise values, while other thin-metal films can be used advantageously for conductors. Thus silicon and thin-film technologies together provide a sufficient set of elementary components for most systems functions. Equally important, the choice of silicon circuits made in the beam1997 1998 T H E BELL SYSTEM TECHNICAL JOURNAL, NOVEMBER 1970 leaded, sealed-junction form and thin-film elements on ceramic or similar substrates give us complementary technologies which are physically compatible. Both parts of this hybrid-device technology have come to depend primarily on photolithographic methods for delineating the areas in which material will be added, removed, or modified as the original substrate is successively transformed into the final circuit. Both parts of this technology have grown in volume of activity and in sophistication of technique. In doing so they have put increasing demands on maskmaking laboratories for more masks per year and for more complex mask patterns.