Amorphous-crystalline phase transition during the growth of thin films: The case of microcrystalline silicon - art. no. 085402

Thin silicon films of varying thickness were deposited on foreign substrate s by electron-cyclotron resonance chemical vapor deposition from SiH4-H-2 m ixtures at 600 K. Optical thickness measurements, Rutherford backscattering , and transmission electron microscopy reveal that a thin amorphous interla yer of some 10 nm thickness has formed upon the substrate, before the growt h of a microcrystal line layer begins. The amorphous layer is found to be d eposited with a higher rate than the crystalline phase, Since similar effec ts have been observed for a large variety of deposition techniques, the amo rphous-crystalline phase transition is considered as an inherent property o f the growth of thin silicon films on foreign substrates at low homologous temperatures. The change in growth mode is interpreted in terms of Ostwald' s rule of stages, which predicts the evolution of film growth to proceed vi a a set of phases of descending metastability and nucleation rate. In apply ing capillarity theory a criterion is derived from the ratio of amorphous-p hase and crystalline-phase nucleation rates J(a)/J(c). This ratio is develo ped into basic thermodynamic functions and is shown to govern the formation of either the stable or metastable phase. The approach is of general valid ity for thin-film deposition processes. In the case of microcrystalline sil icon, experimental measures can be derived from the developed model to dire ctly design the evolution of film structure.