Designed experiments were employed to characterize a process for etching phosphorus doped polycrystalline silicon with HBr in a close‐coupled electron cyclotron resonance plasma reactor configured for 200 mm wafers. A fractional factorial screening experiment was employed to determine the principal input factors and the main etch effects. Linear models of the process responses indicate rf power, O2flow rate, and the position of the resonance zone (with respect to the wafer) as the three strongest factors influencing process performance. Response surfaces generated using data from a follow‐on response surface methodology experiment predicted an optimum operating region characterized by relatively low rf power, a small O2flow, and a resonance zone position close to the wafer. One operating point in this region demonstrated a polysilicon etch rate of 270 nm/min, an etch rate nonuniformity of 2.2% (1 std. dev.), an etch selectivity to oxide greater than 100:1, and anisotropic profiles. Particle test results for the optimized process indicated that careful selection of the O2fraction is required to avoid residue deposition and particle formation.