Abstract
A new technique for achieving electrically isolated, closely spaced, and self‐aligned metalization patterns on thin insulating films for integrated circuit applications is described. This scheme takes advantage of the shadowing effect of an undercut area etched in a two‐layer insulator sandwich. A pattern first etched in the upper insulator delineates and acts as an etch mask for undercutting and thinning down the second insulator on the semiconductor substrate. The major requirement is that the first insulator be weakly or not at all affected by the etch for the second insulator. Because of the masking effect of undercutting, a thin metal evaporation will be discontinuous at all undercut edges resulting in electrically isolated metalization patterns with virtually zero lateral spacing between them. The silicon dioxide‐alumina double insulator system with titanium‐palladium‐gold metalization was used and the details of the technique, including methods of selectively connecting isolated metal patterns, are described. Experimental data are presented to show that undercut isolation can be achieved with high reliability, undercut edges several centimeters in length being typically observed between unintentional shorts. Advantages and utility of the technique are illustrated by describing the design of a charge‐coupled device.