Nucleation and growth of low-temperature fine-crystalline silicon: a scanning probe microscopy and Raman spectroscopy study of the influence of hydrogen and different substrates

Low-temperature fine-crystalline silicon films grown by plasma-enhanced che mical vapour deposition (PECVD) on different substrates are investigated by scanning probe microscopy and Raman spectroscopy. By this, more insight in to nucleation and growth of crystallites is provided. For this purpose depo sition conditions within the transition regime from fine-crystalline to amo rphous growth are chosen leading to the growth of individual crystallites e mbedded in an amorphous matrix. Effects of the type of substrate and of hyd rogen dilution are studied. Films grown on naturally oxidized Si(100) and o n graphite(0001) show a clear correlation between the area density of cryst allites as inspected from surface micrographs and the volume fraction of cr ystalline phase as detected by Raman spectroscopy. Nucleation of crystallit es takes place within a narrow range of film thickness (the first few 10 nm for growth on silicon oxide) whereas the subsequent growth stage exclusive ly promotes the continuous growth of existing crystallites, i.e. nucleation of new crystallites is suppressed. The initial nucleation strongly depends on the type of substrate, for instance purely amorphous films can grow ins tead of two-phase ones if only the oxidized Si(100) substrate is replaced b y Si(100) which has been hydrogen passivated by a HF treatment. A pronounce d influence of hydrogen on crystallite nucleation is observed: if the sourc e gas ratio R = SiH4/(SiH4 + H-2) is reduced by only 0.3% the nucleation de nsity increases by about one order of magnitude. In addition to presently d iscussed kinetic growth models the results indicate the applicability of a thermodynamical concept for explaining the structural evolution. (C) 2000 E lsevier Science S.A. All rights reserved.