Microstructure control of very thin polycrystalline silicon layers on glass substrate by plasma enhanced CVD

Very thin (<100 nm) polycrystalline silicon (poly-Si) thin films were deposited on glass by plasma enhanced chemical vapor deposition (PECVD) using SiF4 and H2 gas mixtures. Film structures, i.e. crystal fraction, nucleus density and/or grain size, were controlled by an alternating deposition and etching technique. By this technique, an improved crystal fraction of 52% was successfully obtained for a 50 nm-thick film with a grain diameter of ∼37 nm. By adopting a two-step-growth (TSG) technique in which these thin layers are used as seeds, larger size grains (220 nm in diameter) were obtained in 290 nm-thick films. Also, preferential orientation was observed in the RHEED pattern of films grown by the TSG.