MEASUREMENT OF ION IMPACT ENERGY AND ION FLUX AT THE RF ELECTRODE OF A PARALLEL PLATE REACTIVE ION ETCHER

An experimental study on the ion impact energy distribution and the total ion flux at the driven electrode of a parallel plate reactive ion etcher is presented. Results are shown for 13.56 MHz discharges in Ar, Ar/H-2, N2, O2, Cl2, and SF6/He over a pressure range of 0.3-40 Pa. The ion impact energy distribution consists of a collision-free part and a collision-induced part. It is observed that in Ar, N2, O2, and Cl2 the collision-induced part contains single and double peaks at regular energy intervals. This peaked structure is attributed to charge exchange processes in the sheath. Both the collision-free part and the collision-induced part of the ion impact energy distribution are well described by a model based on a constant sheath width, a sinusoidal sheath voltage, and a power law for the electric field in the sheath. The only adjustable parameter in the model is the sheath thickness. The sheath thickness has also been determined independently form the total ion current density using the Child-Langmuir law. The obtained values are in good quantitative agreement with each other and with the observed optical sheath thickness, demonstrating the overall consistency of the present approach.