Poly-silicon films with low impurity concentration made by hot wire chemical vapour deposition

Analyses of various impurities (O, C, W, Fe, Ni and Cr) in the poly-Si mate rial (both in layers as well as in cell configurations) made by HWCVD have been carried out to judge the quality of this material for application in d evices. SIMS analysis showed that the oxygen concentration in the bulk of a poly-Si film made at a low hydrogen dilution (Poly2) is 3 x 10(18) cm(-3) and the oxygen content drops to this value within a depth of only 50 nm fro m the surface. On the other hand, a poly-Si film made at a high hydrogen di lution (Poly1) has a high and homogeneous oxygen content of more than 2 x 1 0(21) cm(-3). However, in a double-layer structure (Poly2 on top of Poly1), the oxygen content of the bottom layer (Poly1) is significantly smaller th an the bare Poly1 film, though this oxygen concentration is still much high er than that in the top Poly? layer. We attribute this behaviour to the str uctural difference between these two films (2000 cm(-1) Si-H IR vibration i n low-dilution material and 2100 cm(-1) vibration in the high-dilution mate rial). We propose that the oxygen penetration in Poly1 occurs by two proces ses: (1) oxygen incorporation during growth: (2) post-deposition oxygen int rusion. The first process occurs at a low deposition rate and is dependent on the type of growth process. The second process is due to the intrusion o f water vapour into the film through the voids, which increases the conduct ivity of the film depending on the amount of intrusion. We have shown that our device quality compact poly-Si:H (Poly2) resists oxygen incorporation e ven when deposited in an oxygen-rich atmosphere. (C) 2001 Elsevier Science B.V. All rights reserved.