Doping in chemically vapour deposited epitaxial silicon

Abstract

The incorporation of phosphorus in silicon has been studied, using PH3 as dopant during epitaxial growth from SiH4 in hydrogen. Interesting variations in doping level ass a function of growth rate (variation of 60 pSiH4). were found: at 1100 °C the concentration of donors increases with silicon growth rate, at 1200 °C the concentration is constant and independent of growth rate, at 1300 °C the donor concentration decreases for higher growth rates.The high temperature results can be explained by a diffusion controlled incorporation of phosphorus giving a constant flux of dopant atoms towards the growing interface. For a constant value of PH3 with increasing growth rate the same amount of phosphorus is incorporated in increasingly thicker silicon layers, leading to the observed results.The increase of dopant concentration with growth rate at lower temperatures is explained by an additional effect, viz. increasing the growth rate of lowering the temperature increases the chance of trapping dopant atoms in the growing layer.The temperature dependence of the gas-solid segregation coefficient for phosphorus also depends on growth rate. Extrapolation to zero growth rate gives a temperature dependence of the equilibrium segregation coefficient of ≈ 0.3 eV.