Dependence of Intrinsic Stress in Hydrogenated Amorphous-Silicon on Excitation-Frequency in a Plasma-Enhanced Chemical Vapor-Deposition Process
Intrinsic stress measurements were carried out on hydrogenated amorphous silicon (a-Si:H) films deposited with different excitation frequencies (13.56-70 MHz), by plasma-enhanced chemical vapor deposition. It was observed that films deposited at 70 MHz have one order of magnitude smaller intrinsic stress than those deposited at 13.56 MHz. These results have been linked to the estimated variation of the ion impact energy as a function of excitation frequency, deduced from the measured variation of the peak-to-peak voltage between the electrodes. The observation of diminished ion energy at higher excitation frequencies has been interpreted as the cause, both of the decrease in intrinsic stress as well as of the measured increase in surface roughness, of films prepared at higher frequencies.