International Business Machines Corporation

Eva Horner

Hans-Joachim Trumpp

Reinhold Muhl

A method of making via holes in a double-layer insulation of nitride and polyimide. The via holes are made with one photomask only by applying a photoresist process with double exposure, and a multi-step dry etching process. The double exposure, which includes an image-wise exposure followed by blanket irradiation, achieves an edge angle in the photoresist between approx. 60.degree. and 70.degree., depending on the exposure time ratios. This angle is transferred into the polyimide layer in a dry etching process. In a first etching step with CF.sub.4 as etching gas the greater part of the polyimide is removed. For removing the residual polyimide in the via holes there now follows an etching step in O.sub.2. Etch bias is thus kept on a very low level. The nitride layer is then etched with CF.sub.4 as etching gas, with the etching process being executed in two steps, each followed by an etching step in O.sub.2 for laterally shifting the photoresist and the polyimide via the resist angle. By softening the step height a softer profile of the via holes is ensured, which permits very good covering by a second layer of metallurgy.

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Holzerlingen, Germany

Eva Horner