Solid Phase Crystallization of Hydrogenated Amorphous Silicon/Hydrogenated Microcrystalline Silicon Bilayer Deposited by Plasma-Enhanced Chemical Vapor Deposition

Abstract

To reveal the effect of modifications of the top and bottom layers on the crystallization of bilayers deposited by plasma-enhanced chemical vapor deposition (PECVD), we have investigated the solid-phase crystallization of a hydrogenated amorphous silicon/hydrogenated microcrystalline silicon (a-Si:H/mu c-Si:H) bilayer. First, mu c-Si:H films (similar to 50 nm) were deposited on coming 7059 glasses from an Ar-diluted SiH4 gas and subsequently a-Si:H films (similar to 100 nm) were deposited on top of those mu c-Si:H films. Annealing treatment of such bilayers was conducted in a conventional vacuum furnace at 600 degrees C. The density of crystallites in the mu c-Si:H bottom layer was controlled by varying r.f. power while other deposition parameters were kept constant. To control the structural disorder of the a-Si network in the a-Si:H top layer, different deposition temperatures were used. I;rom TEM and Raman analysis, it is found that the density of preexisting crystallites in the bottom layer affects the final grain size of the crystallized bilayer while the structural disorder of the a-Si network in the top layer affects the crystallization time. Under the conditions of low density of crystallites in the bottom layer and low structural disorder of the a-Si network in the top layer, polycrystalline silicon (poly-Si) films with large grain size (similar to 0.6 mu m) an well formed within a short crystallization time (similar to 24 h). (C) 2000 Published by Elsevier Science S.A. All rights reserved.