Preparation of thick polycrystalline silicon layers on glass by laser irradiation

For polycrystalline silicon thin film solar cells a silicon layer 50 mu m thick is required consisting of grains 100 mu m in diameter deposited on low cost glass substrate. We report on a preparation method combining plasma enhanced CVD of amorphous silicon and laser crystallization. We start from a-Si:H thin films 200 nm thick which are deposited on glass (Corning 7059) by a rf-CVD process. These films are irradiated by scanning with an Ar+ laser to result in crystals of several 10 mu m in diameter. In order to increase the film thickness on this crystalline seed layer further amorphous silicon is deposited by the same CVD process at a rate of 20 nm/min. During the deposition the growing layer is irradiated by excimer laser pulses with about 300 mJ/cm(2) at a repetition rate of less than 0.1 Hz. Each laser pulse melts the newly deposited amorphous layer down to the crystalline interface which acts as a homoepitactic substrate during resolidification. In this way the whole growing amorphous layer is converted to a polycrystal. (C) 1998 Elsevier Science S.A.