In situ monitoring of uniformity by end point signal during plasma etching

Abstract

A theory describing the etch rate uniformity based on the end point signal during the cleaning phase of etching is formulated for the case where the influence of residence time of the etching products and the loading effect can be neglected. An etch rate distribution function representing the probability density that the layer is etched at a given etch rate is introduced to calculate the relative root mean square of the etch rate across the wafer. The reduction in the size of the etched surface or the reduction of the flux of etching product molecules leaving the surface during the cleaning phase is used to determine the etch rate distribution function. A numerical simulation of the end point signal was used to illustrate possible applications of the theory. It is also shown that the slope of the end point curve itself cannot be used to characterize the etching nonuniformity as it is generally supposed. The theory was formulated with the aim of finding a simplein situ method applicable to statistical process control in semiconductor manufacturing when the nonuniformity of an etch process is characterized by a number (so-called 3σ method).