Spatially and temporally resolved absolute O-atom concentrations in etching plasmas

The detection of atomic O by two-photon-allowed laser-induced fluorescence is implemented to obtain the spatial distribution and the temporal evolution of oxygen atoms in a 10 MHz parallel-plate rf discharge. Absolute concentrations are determined via a titration technique for intensities typically found in 20–100 W, 0.1–3 Torr O2 discharges, and are in the range 4–30×1014 atoms/cm3. The spatial O distribution after initial turn on of the discharge is rather uniform, indicative of a uniform production of O atoms throughout the interelectrode space. Furthermore, the decay of the O concentration reveals information about the reaction of O atoms with surface materials in the plasma environment, while the rise of the population indicates a time-dependent production rate. The dependence of the O-concentration rise and decay rates on discharge pressure, power, and gas composition is explored.