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'') tub, a showerhead, and an etch chamb er. The model describes each step of the process in sufficient detail to predict its performance, including ion concentration, wafer etch ra te, and nonuniformity. Model validation was accomplished through compa rison of etch rates and nonuniformity of blanket polysilicon and silic on dioxide wafers in a CDE tool from Matrix Integrated Systems, Inc., using NF3/O-2 gas mixtures at conditions representative of normal tool use. This study is primarily concerned with the effects ol operating parameters on the etch rate and nonuniformity, and thus focuses mainly on etch chamber calculations. The model provides an indication of sys tem performance, predicting from first principles, etch rates to withi n 30% of measured values. Correlation of system performance is obtaine d from calculations of etch rate resulting from changes in pressure, f low rate, plasma power, and system geometry. Correlations of performan ce highlight the importance of controllable parameters and etchant con centration on etch rate and nonuniformity. In addition, the etch chamb er ion concentration is predicted to be less than 10(8) cm(-3).