Simulation of Al and phosphorus diffusion gettering in Si

Abstract

We present a quantitative computer model (‘Gettering Simulator’) of phosphorus diffusion gettering (PDG) that allows to simulate the PDG process. The model was checked for Au as a typical substitutional metallic impurity elements and for Co as an example of the fast diffusing interstitial 3d metals in Si. Here we will only discuss the gettering of substitutional metals. The ‘Gettering Simulator’ includes a model for P diffusion for phosphorus concentrations [P] up to the solubility limit. In this model, the main contribution to phosphorus diffusion at [P]<2×1019 cm−3 comes from the kick-out mechanism, while at higher P concentrations the diffusion is dominated by phosphorus vacancy complexes. The latter results in the development of the well-known ‘kink-and-tail’ P and specific self-interstitial profiles. The gettering mechanism is described by a combination of three factors: (1) the Fermi level effect; (2) the formation of phosphorus–metal pairs; (3) the high concentration of self-interstitials in the bulk together with nearly equilibrium concentration in the region of high phosphorus concentration near the surface. The third factor was found to be very important for the PDG of substitutional metals. No local equilibrium is assumed in the model. Instead. the calculations are based on the reaction rates between different species.