COLLISIONAL ELECTRON HEATING IN A RF DISCHARGE

The question of how far the concept of reflection of electrons at the oscillating sheath can be applied to the collisional situation is inve stigated. A radiofrequency discharge between two parallel plates is co nsidered. Model calculations on the basis of the transport equations r esult in two contributions to the collisional sheath oscillation heati ng. The first contribution represents heating in an expanding sheath a nd cooling in a contracting sheath due to reflection at the sheath edg e. The second contribution describes Joule heating within the sheath r ange and is of the same order of magnitude as the corresponding bulk h eating. In the experiment a 300 kHz discharge is operated by a non-sin usoidal voltage with a steep rise and fall to a plateau. Optical emiss ion spectroscopy resolved in time and space is applied. Owing to the s pecial voltage shape, emission caused by radiofrequency heating can be separated from emission caused by secondary electrons from the cathod e. The experimental results confirm the predictions of the model.