Study of Si deposition in a batch-type LPCVD-system for industrial thin-film crystalline Si solar cells

We study Si deposition in a low pressure chemical vapour deposition (LPCVD) system as a possible technique for the industrial production of thin-film Si solar cells. More specifically, a cost goal below 40$/m² for the Si-deposition was aimed at. The system consists of a lamp-heated quartz tube connected to a pump system at one end and closed with a quartz door at the other (the thermal insulation between door and reaction volume is realised by a vacuum-pumped quartz bell jar). Si layers can be grown on 20 wafers simultaneously, using a system which allows removal of the unwanted Si-deposition on the reactor walls by using a quartz insert which can be easily removed from the system. Two deposition processes have been investigated, with dichlorosilane in the range of 900-1050°C and with silane between 750 and 900°C. A growth rate of 0.2-0.3 μm/min has been achieved with a small H₂-consumption/wafer. High quality epitaxial layers have been obtained, a fact illustrated by solar cells produced in layers grown on p⁺ monocrystalline Si substrates. Homogeneous layers have also been deposited on ceramic substrates. In spite of the small grain size, the first solar cells processed in these layers show low leakage currents