Low-temperature diffusion of phosphorus in silicon

Abstract

Nontrivial mechanisms of low-temperature diffusion of impurities in solids have been discovered recently. We studied accelerated diffusion of phosphorus in a single crystal of silicon, which takes place during decomposition of an over-saturated inhomogeneous solid solution. A thin (1.5–2 μm) doped layer was formed by low-temperature diffusion from the gas phase. The distribution profile, which was determined by the method of differential conductivity, shows that heat treatment at 550°C leads to a decrease in the donor concentration in the subsurface region and to the impurity movement into the bulk of the sample. The diffusion coefficient has been calculated on the computer using experimental data, and in the range between 400°C and 700°C has been represented by the Arrhenius equation. The value of the frequency term is equal to 3.7·10−6 cm2/sec, and the value of the activation energy is 1.81 eV. The presented results have been analyzed, as well as the data obtained from the measurements on carrier mobility (using the Hall effect) and the parameters of the crystal lattice (using the method of asymmetric double crystal x-ray spectrometer). A physical model for the dissociation diffusion is proposed, which is controlled by the decay, and analytical expressions are obtained which describe the main characteristics of the process.