Reactive Ion Etching of Benzocyclobutene Polymer Films

Reactive ion etching is a widely-used technique for fabricating via holes in polymer-metal multilayer interconnect structures. Reactive ion etching of thin film polymers was studied using Benzocyclobutene polymer and photoresist etch mask, in O2 and SF6 plasma. A design of experiments (DOE) was carried out with rf power, pressure, and SF6 concentration as the design variables, with a constant total gas flow rate. The responses measured in this study were dc bias, etch rate, via angle, uniformity, selectivity, lateral etch rate, and etch cleanliness. The DOE revealed some complex relationships between variables. DC bias was a very important parameter for explaining the observed effects on etch rate, via angle, selectivity, and lateral etching. A simple model was formulated to explain the dependence of via angle on design variables. The etching characteristics of the photoresist mask affected not only the selectivity, but also the via angle and lateral etch rate. Due to conflicting requirements posed by the responses, optimization of the reactive ion etch (RIE) process involves many trade-offs which depend on the particular application.