Electrical and Computer Engineering Publications
Comparison of phase diagrams for vhf and if plasma-enhanced chemical vapor deposition of Si:H films
Document Type
Conference Proceeding
Publication Date
12-1-2004
Volume
808
Journal
Materials Research Society Symposium Proceedings
First Page
215
Last Page
220
Abstract
Deposition phase diagrams are convenient for categorizing the evolution of the surface microstructure and phase with accumulated thickness for hydrogenated silicon (Si:H) films during plasma-enhanced chemical vapor deposition (PECVD). They can also be used to assess the electronic quality and device suitability of Si:H, based on previous correlations. In this study, phase diagrams have been applied in a comparison of Si:H PECVD using two different plasma excitation frequencies (rf: 13.56 MHz; and vhf: 60 MHz). Smooth crystalline Si (c-Si) wafer substrates have been used to obtain the surface roughness evolution with maximum sensitivity in the amorphous silicon (a-Si:H) growth regime. This study has shown that under all explored conditions of plasma power, frequency, and gas pressure, yielding deposition rates of 0.5-20 Å/s, a-Si:H exhibits improved microstructural characteristics with increasing H2-to-SiH4 flow ratio R right up to the amorphous-to-(mixed-phase microcrystalline) [a→(a+μc)] boundary of the phase diagram. For depositions at R values much lower than the a→(a+μc) transition for a thick film, vhf PECVD can provide a significant improvement in microstructural evolution over rf PECVD, for a given deposition rate. For optimum R just below the a→(a+(ic) transition, however, vhf and rf a-Si:H films exhibit remarkably similar structural evolution for a given rate.