Controlled undercut microwave devices

The paper illustrates a new technique to define narrow windows in SiO2layers by means of a carefully controlled undercut in SiO2/Si3N4flims, The method described takes advantage of the etching propertie of the silicon nitride and of its action as a mask against oxygen diffusion. Stripe Widths less than 1µ were obtained with good definition and uniformity on the whole wafer and without the difficulties normally encountered in micron-line photoengraving. The technique gives reproducible results, requires one masking operation only and seems to be suitable as a production process.