IN-SITU MEASUREMENTS OF CHANGES IN THE STRUCTURE AND IN THE EXCESS CHARGE-CARRIER KINETICS AT THE SILICON SURFACE DURING HYDROGEN AND HELIUM PLASMA EXPOSURE

The damage induced by hydrogen and helium plasmas at the surface of cr ystalline silicon has been monitored in situ by time-resolved microwav e conductivity and by spectroscopic ellipsometry measurements. Both pl asma treatments increase the decay rate of the optically generated exc ess charge carriers and decrease the amplitude of the microwave reflec tion transients. While for the helium plasma a high density of electro nic defects is created immediately after plasma ignition, a continuous ly increasing number of recombination centers is observed in the case of the hydrogen plasma exposure. In support of the transient microwave measurements, the analysis of the spectroscopic ellipsometry measurem ents reveals the creation of a damaged surface layer, which in the cas e of the helium plasma exposure has a high and in the case of the hydr ogen plasma a low fraction of amorphous silicon. This can be explained by the different nature of the processes involved in the interaction of hydrogen (chemical) and helium (physical) plasmas with the silicon surface. After a constant plasma exposure time the damaged surface lay er is thicker in the case of the hydrogen plasma exposure. Moreover, t he helium plasma treatment produces a more defective overlayer as dedu ced from the faster decay of the transient microwave signals. (C) 1995 American Institute of Physics.