Hydrogenation of multicrystalline silicon from a backside silicon nitride layer

In order to improve multicrystalline p-type silicon wafers, the authors have used the hydrogenation technique to deposit a Si₃N₄ layer containing hydrogen on a p-type surface. Silicon nitride films have been deposited by the process of mercury-sensitized photochemical vapor deposition (photo-CVD), using a gaseous mixture of SiH₄ and NH under 253.7 nm ultraviolet light irradiation. The main advantages of this technique are the low deposition temperature (100-400°C) and no radiation damage compared to the plasma-enhanced CVD method. Due to the low temperature, the Si ₃N₄ film could be deposited after the metallization of solar cells, provided that the back contact is a grid. On the front surface, the Si₃N₄ layer could constitute an antireflecting coating. A deposition rate of 8 nm/min and a refractive index of about two were achieved