In situ optical emission and ellipsometry are used to control the etching of titanium nitride/polysilicon gate stacks deposited on 70 Angstrom gate oxide patterned with 0.25-0.35 mu m design rules. Multistep recipes using various chemistries are developed and optimized with a low pressure, high plasma density helicon source in which the goal is to obtain stringent profile control, and high selectivity to the gate oxide. The characteristic real-time optical emission and ellipsometry traces are used as a reference to evaluate reproducibility and to compare the etching rates as a function of the different processing conditions. Optical emission and ellipsometry appear crucial for the rapid development of a multistep etching sequence using various chemistries. Complementary post-process diagnostics using a spectral reflectometer for film thickness measurements and scanning electron microscopy for quantification of profile control are also presented.