Solid-phase crystallization of hydrogenated amorphous silicon/hydrogenated microcrystalline silicon bilayers 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/ μc-Si:H) bilayer. First, μc-Si:H films (~50 nm) were deposited on corning 7059 glasses from an Ar-diluted SiH 4 gas and subsequently a-Si:H films (~100 nm) were deposited on top of those μc-Si:H films. Annealing treatment of such bilayers was conducted in a conventional vacuum furnace at 600°C. The density of crystallites in the μc-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. From 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 (~0.6 μm) are well formed within a short crystallization time (~24 h).