DEVELOPMENT OF A GATE METAL ETCH PROCESS FOR GALLIUM-ARSENIDE WAFERS

The reactive ion etching of TiWN, which is used as a gate metal on gal lium-arsenide device wafers, was studied in a parallel-plate, single-w afer plasma reactor operating at a frequency of 13.56 MHz. We discuss our experimental program designed to develop a highly uniform TiWN etc h process with low linewidth loss for 100 mm GaAs wafers, using a sulf ur hexafluoride, trifluoromethane, helium chemistry. The effects of di fferent gas compositions, plasma power, inter-electrode gap, chamber p ressure, and electrode temperature on the TiWN etch rate, linewidth lo ss, and etch uniformity were determined. The effects of adding oxygen and/or nitrogen to the above mixture were also studied. In preliminary experiments on Si wafers, standard design of experiments methods were used to narrow the ranges of parameters for further experiments to de velop an optimum process for Si wafers. The results of these experimen ts guided us to the optimum process for GaAs wafers. The optimum condi tions, for both Si and GaAs wafers. are presented.