A simple model for the etching of photoresist with plasma-generated reactants

Abstract

The neutral heterogeneous chemistry between reactive species formed in a glow discharge plasma and a polymer surface is investigated. Oxygen and fluorine atom concentrations in an O2/CF4 plasma afterglow are measured by gas phase electron resonance spectroscopy. These atom concentrations are correlated to etch rate data via a simple heterogeneous model which divides the etching process into three steps: initiation, etching, and passivation. The model predicts etch rate data well using measured atom concentrations. When the substrate temperature is changed, the etching step is affected most, presumably limited by product desorption. Dilution of the discharge with argon enhances the etch rate in two ways. First, the homogeneous chemistry is altered, most notably affecting the fluorine atom concentration. The homogeneous effects are taken into account through measured atom concentrations. Second, the argon metastables play a role in the heterogeneous chemistry, enhancing the etching step. From an estimation of this enhancement based on the shift in etch rate maximum, the magnitude of etching in an argon diluted discharge can be predicted.