Uniformity of Etching in Parallel Plate Plasma Reactors

A two‐dimensional transport and reaction model of a high pressure (∼1 torr) high frequency (13.56 MHz) single‐wafer parallel plate plasma reactor was developed. The chemical etching uniformity was studied as a function of reactor operating conditions. The ratio of the reactivity of the surrounding electrode surface as compared to that of the wafer surface, , critically affected uniformity. A bullseye clearing pattern was predicted for , and the reverse pattern for , while etching was uniform for . In the case of , and for the parameter range studied, the absolute uniformity was found to improve by surrounding the wafer with a material of similar reactivity, by increasing the flow rate, or by decreasing the reactor pressure or power. However, such actions also served to decrease the etch rate. The oxygen plasma was used as a model experimental system to test the theoretical predictions. An experimental technique based on spatially resolved optical emission spectroscopy in concert with actinometry and the Abel transform was developed to obtain a three‐dimensional mapping of the reactant (O atom) concentration profile in the plasma reactor. When a reactive film was covering part of the substrate electrode, a profound decrease in the reactant concentration was observed over the film. At the same time, large concentration gradients developed, especially at the boundary of the reactive film with the surrounding electrode. Good quantitative agreement was found between the model predictions and the experimental reactant concentration data for the range of pressure, power, flow rate, and reactive film radius examined.