Mechanisms involved in the formation of phosphosilicate glass by dehydration of sprayed phosphoric acid in an in-line diffusion furnace

This work studies phosphosilicate glass (PSG) formation from a thin sprayed-on dopant source layer in order to increase the ability of controlling the emitter doping profile. The dopant source contains DI water, 2.5 wt% H3PO4 and a small quantity of surfactants. Most of the layer volume evaporates at the height of the furnace entrance. The further evolution of the dopant source layer composition is described through the dehydrative condensation of H3PO4 and through the reactions between the sprayed-on layer and the Si wafer. The final PSG composition is characterized by means of X-ray photoelectron spectroscopy (XPS). Furthermore, ellipsometry measurements of PSG thickness show that faster heating rates lead to thicker PSG. Finally, it is shown that a thinner dopant source layer results in a lower P surface concentration Cs and, at least in the case of fast heating rates, to a deeper emitter.