Improving the predictive power of modeling the emitter diffusion by fully including the phosphsilicate glass (PSG) layer

Presently, the PV industry is switching to the selective emitter design, where the phosphorus density is significantly reduced between the front metal fingers. Current diffusion models simply adjust the peak phosphorus density at the Si surface to match the measured profiles, and therefore they are unable to predict the necessary gas flows and the temperatures during predeposition and drive-in to realize an optimum emitter profile. In order to achieve better prediction capabilities, we implement a model for the phosphosilicate glass (PSG) layer and for its coupling to silicon. We combine this model with coupled dopant/defect diffusion models in Si to calculate the resulting dopant profiles. With our improvements, we reproduce the profile measurements for a range of POCl₃ flows at temperatures typically chosen in industrial fabrication.