Characterizing metal-masked silica etch process in a CHF₃/CF₄ inductively couled plasma

A silica etch process conducted using a CHF₃ /CF₄ inductively coupled plasma is characterized. This was accomplished by employing a statistical experimental design in conjunction with neural network process models. As a mask layer, patterned AlSi (1%) metal was used. Parameters varied in the design includes source power, bias power, and gas ratio. Besides those conventional etch responses including etch rate, selectivity, and profile, sidewall roughness of the etched pattern is first modeled. Etch rate and sidewall roughness were found to be predominantly influenced by source power with a trade-off between them. Bias power significantly affected selectivity while controlling a trade-off against etch rate. A decrease in profile angle with increasing bias power was attributed to AlSi (1%) film expansion induced by ion bombardment effects. As gas ratio was varied, profile angle remained almost constant due to nearly same chemical reaction of its plasma on the silica surface. The roughness was little affected by bias power at its low levels, thereby providing an increased degree of freedom to optimizing the process. The gas ratio exerted no noticeable impact on the etch responses.