Poly-Si films prepared by rapid thermal CVD on boron and phosphorus silicate glass coated ceramic substrates

Abstract

This study investigates the crystallographic properties of polycrystalline silicon films formed on doped (boron or phosphorus) or undoped silicate glass coated ceramic substrates using the chemical vapor deposition method at high temperatures (> 1000 °C). First, FT-IR analysis of the silicate oxide layers is presented in order to monitor the presence of the Si–O, B–O and/or P–O bonds in the layers prior to deposition. Then, the average grain size, crystalline orientation and boundary defects of these poly-Si films on silicate coated mullite and alumina were evaluated as a function of deposition parameters and boron/phosphorus content. The results show a significant increase of the grain size and narrower size distribution after CVD on BSG or PSG intermediate layers, whatever is the substrate. Large grains up to 7 μm are observed for 9 μm thick films. The enhancement in grain size is attributed to the nucleation change by defects or impurities rather due to the flowability of the silicate glass during the silicon deposition at high temperature. The open-circuit voltage measurements of these fine-grained poly-silicon films before hydrogenation shows a dependence on the grain size through the choice of the substrate. The open-circuit voltage increases substantially from 250 mV to 410 mV after 1 h plasma hydrogenation, despite partial etching of the emitter by the hydrogen atoms.