The Interaction of Photoresists with Metals and Oxides during RF Sputter-Etching

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Abstract
When photoresists are used as masks for rf sputter‐etching of various materials, interactions between the material being etched and the photoresist occur as a result of backscattering of some of the ejected material. We have studied these interactions in a variety of ways. Most of the interactions are similar to the interactions of the materials with carbon, and the intrinsic sputter‐etch rate of photoresists is the same as that of carbon. When metals and photoresists are etched simultaneously, both materials are eroded at the same rate because backscattering converts the surface to a uniform mixture of all materials present. The etch rate of the composite surface increases over the intrinsic etch rate of the photoresist if metal carbide intermetallics can form. When only solid solutions can form, the composite etch rate decreases with decreasing solubility of carbon in the metal. Wnen oxides are backscattered onto photoresists, the etch rate of the composite surface varies in a way which we cannot explain, and the photoresist is etched preferentially because of oxide decomposition followed by “chemical sputtering” The ability of a photoresist to mask oxides varies from one photoresist material to another. It is not possible to correlate the performance of a sputter‐etch resist to its structure at this time, but it is clear that different materials behave differently in every respect.

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