Surface morphology of poly-Si films made by aluminium-induced crystallisation on glass substrates

Abstract

The surface morphology of polycrystalline silicon (poly-Si) films made at low temperature (∼500°C) by the aluminium-induced crystallisation (AIC) bi-layer process on glass substrates was investigated. The excess of amorphous silicon (a-Si), the substrate preparation process and the native aluminium (Al) oxide thickness were all found to strongly influence the surface morphology. The AIC bi-layer process produces a continuous poly-Si film on the glass with protruding Si islands. The Si islands have vertical sidewalls with a smooth upper surface, due to the high interfacial energy of the incoherent interface between the Al matrix and the Si islands. A coalescence of nanosized crystalline Si clusters is suggested as the growth mode of the Si islands. Transmission electron microscopy and Raman analysis show that the crystalline quality of the Si island is comparable with that of the poly-Si film. Furthermore, an activation energy estimation indicates that the overall thermal mechanism behind the formation of the continuous poly-Si film and the Si islands is the same. A feedback process consisting of a dynamic interaction between the Al and the a-Si layers in the bi-layer structure is suggested. However, the crucial role of the Al oxide interface layer needs to be further investigated before a complete physical model of the glass/Al/a-Si AIC bi-layer process can be suggested.