Intrinsic Diffusion of Boron and Phosphorus in Silicon Free From Surface Effects

Abstract

Boron and phosphorus were diffused in either hydrogen or pure-argon atmosphere into float-zoned, eptiaxial, and oxygen-doped (111) silicon from a 4-12-μ-thick epitaxial doped silicon surface layer. Under intrinsic conditions, the concentration profiles obtained show Fickian behavior at all surface and bulk concentration conditions. Between 1130 and 1405 °C, the intrinsic diffusivities can be described by $D_P=7.4\mathrm{}\times {10}^{-2\mathrm{}}\frac{\exp \left[\frac{(3.30\mathrm{}\pm 0.03 \mathrm{eV})}{\mathrm{kT}}\right]{\mathrm{cm}}^2}{\exp \left[\frac{(-2.85\mathrm{}\pm 0.05 \mathrm{eV})}{\mathrm{kT}}\right] \frac{{\mathrm{cm}}^2}{sec}}$. Compared with earlier studies using $\exp \left[\frac{(-3.30\mathrm{}\pm 0.03 \mathrm{eV})}{\mathrm{kT}}\right]$ ${\mathrm{cm}}^2$ oxide diffusion sources, the diffusion coefficients of both boron and phosphorus are found to be considerably smaller. Moreover, above 1130 °C they are independent of surface concentration (⋜ 3 × ${10}^{19}$ ${\mathrm{cm}}^{-3\mathrm{}}$), bulk conductivity type ($n$ or $p$) and level (6 × ${10}^{13}$-8 × ${10}^{18}$ ${\mathrm{cm}}^{-3\mathrm{}}$), surface face-to-bulk concentration ratio (∼ ${1-3.3\times 10}^5$), and oxygen concentration (to ${10}^{18}$ ${\mathrm{cm}}^{-3\mathrm{}}$). In the light of some related work, the present results are shown to indicate the true bulk-diffusion process in silicon.