Behavior of excited argon atoms in inductively driven plasmas

Laser induced fluorescence has been used to measure the spatial distributio n of the two lowest energy argon excited states, 1s(5) and 1s(4), in induct ively driven plasmas containing argon, chlorine and boron trichloride. The behavior of the two energy levels with plasma conditions was significantly different, probably because the 1s(5) level is metastable and the 1s(4) lev el is radiatively coupled to the ground state but is radiation trapped. The argon data are compared with a global model to identify the relative impor tance of processes such as electron collisional mixing and radiation trappi ng. The trends in the data suggest that both processes play a major role in determining the excited state density. At lower rf power and pressure, exc ited state spatial distributions in pure argon were peaked in the center of the discharge, with an approximately Gaussian profile. However, for the hi ghest rf powers and pressures investigated, the spatial distributions tende d to flatten in the center of the discharge while the density at the edge o f the discharge was unaffected. The spatially resolved excited state densit y measurements were combined with previous line integrated measurements in the same discharge geometry to derive spatially resolved, absolute densitie s of the 1s(5) and 1s(4) argon excited states and gas temperature spatial d istributions. Fluorescence lifetime was a strong function of the rf power, pressure, argon fraction and spatial location. Increasing the power or pres sure resulted in a factor of 2 decrease in the fluorescence lifetime while adding Cl-2 or BCl3 increased the fluorescence lifetime. Excited state quen ching rates are derived from the data. When Cl-2 or BCl3 was added to the p lasma, the maximum argon metastable density depended on the gas and ratio. When chlorine was added to the argon plasma, the spatial density profiles w ere independent of chlorine fraction. While it is energetically possible fo r argon excited states to dissociate some of the molecular species present in this discharge, it does not appear to be a significant source of dissoci ation. The major source of interaction between the argon and the molecular species BCl3 and Cl-2 appears to be through modification of the electron de nsity. (C) 2000 American Institute of Physics. [S0021-8979(00)08712-0].