A multi-variable analysis of the influence of process parameters on VHF PECVD deposition process for amorphous silicon

It is reported about the influence of the parameters gas flow, gas pressure and RF power on a PECVD (plasma enhanced chemical vapor deposition) process of amorphous silicon (a-Si:H) in the excitation frequency range from 40 to 80 MHz. In contrast to the usual method, the process parameters are varied by a special experimental design in order to study the principal effect and contribution ratio of each process parameter separately with respect to the a-Si:H film deposition rate and the characteristic dark conductivity and photo conductivity. The analyzed principal influence of the process parameters RF power and excitation frequency on the PECVD process is explained by the distribution of the electric field on the surfaces of planar plasma electrodes. As a result it is shown that the geometry of the plasma electrodes strongly influences the PECVD process and a new definition of the commonly applied value for power density in the discharge volume should be introduced, since this parameter depends on the excitation frequency as well as on the given plasma electrode system.