Simulation of chemical downstream etch systems : Correlation of the effects of operating conditions on wafer etch rate and uniformity

A detailed chemically reacting flow model has been used to predict the performance and operating characteristics of chemical downstream etch (CDE) tools. In CDE systems, wafer etching is accomplished by neutral reactive gases. In practice CDE systems consist of a plasma source, a chemically inert (transport) tube, a showerhead, and an etch chamber. The model describes each step of the process in sufficient detail to predict its performance, including ion concentration, wafer etch rate, and nonuniformity. Model validation was accomplished through comparison of etch rates and nonuniformity of blanket polysilicon and silicon dioxide wafers in a CDE tool from Matrix Integrated Systems, Inc., using NF{sub 3}/O{sub 2} gas mixtures at conditions representative of normal tool use. This study is primarily concerned with the effects of operating parameters on the etch rate and nonuniformity, and thus focuses mainly on etch chamber calculations. The model provides an indication of system performance, predicting, from first principles, etch rates to within 30% of measured values. Correlation of system performance is obtained from calculations of etch rate resulting from changes in pressure, flow rate, plasma power, and system geometry. Correlations of performance highlight the importance of controllable parameters and etchant concentration on etch rate and nonuniformity. In addition, the etch chamber ion concentration if predicted to be less than 10{sup 8} cm{sup {minus}3}.