Abstract: Silicon nitride can be etched at a rapid rate selectively against oxide in a gas plasma formed from a gas mixture comprising 10-20 parts NF.sub.3 to 20-35 parts O.sub.2, by volume. Silicon nitride etch rates in the range 55 to 75 milli-microns per minute are obtained at nitride/oxide etch rate ratios of 8-11:1. In contrast to the prior art methods, the invented gas system contains no carbon. Hence, deposition of carbon complexes on the substrate wafers or reactor walls during nitride etching is avoided. The NF.sub.3 +O.sub.2 gas mixture also etches common resists.

Abstract: A polyimide-oxide-polyimide integrated circuit structure is utilized in the process for forming openings having tapered sidewalls and predetermined controlled sizes. At least one opening size is replicated and transferred to an exposed surface in a underlying surface of the structure by first forming a thick layer of oxide over the first cured polyimide layer, anisotropically etching the thick layer of oxide to form an opening of predetermined size therethrough to the surface of the first cured polyimide layer. Next, the first layer of cured polyimide is isotropically etched to form an opening therethrough of substantially said predetermined size and exposing a portion of a thin layer of oxide underlying the first layer of cured polyimide. The thin layer of oxide is then anisotropically etched using the thick layer of oxide as an etch mask to expose an opening of said predetermined size on a surface of a second layer of cured polyimide.