Diffusivity analysis of POCl3 emitter SIMS profiles for semi empirical parametrization in sentaurus process

Abstract

The diffusion of phosphorus mediated by phosphorus oxychloride (POCl3) is extensively used in photovoltaics due to its higher controllability over phosphine. However, the POCl3 decomposition in the gas phase as well as the subsequent oxidation reaction between silicon and the resulting phosphorus oxide are not very well documented and increase the complexity of a realistic simulation of the POCl3 diffusion. This paper examines the possibility of modeling the POCl3 diffusion only by modifying the diffusion constants of a standard phosphine mediated diffusion simulation implemented in Sentaurus process. To this aim, the Boltzmann-Mattano Analysis (BMA) is applied to experimental SIMS profiles in order to extract a concentration dependent effective phosphorus diffusivity. The fitting of diffusivity profiles is then performed to determine the specific diffusion constants of the diffusion mechanisms believed to be responsible for the phosphorus diffusion in silicon. Through the study of specific artifacts appearing in the diffusivity profile because of the non ideal conditions for application of the BMA, it is believed that at low POCl3 flow, the surface concentration during the pre-deposition phase is low enough to induce an enhanced diffusivity at the early stage of the diffusion. Finally, the assumptions of this diffusivity fitting are reviewed and a model matching these assumptions is identified in Sentaurus Process for a direct implementation of the BMA results into Sentaurus Process.