The effects of excitation frequency (10 kHz–25 MHz) on plasma etching, voltage‐current characteristics, emission spectra, and ion densities and energies in the sheath of chlorine plasmas, have been studied at 0.3 Torr using several techniques. Emission spectra and mass spectral analysis of ions extracted from the sheath region show a dramatic increase in the Cl+signal as frequency is lowered through the ion–transit frequency near ∼1 MHz. Concurrently, the voltage at constant power and energy of ions impinging on the electrodes increase dramatically, while the etch rate of poly‐Si increases due to ion‐enhanced reactions. The Cl+2ion density and degree of Cl2dissociation to Cl atoms were found to be roughly frequency independent.