Dopant and carrier concentration in Si in equilibrium with monoclinic SiP precipitates

The behavior of silicon slices very heavily implanted (1.5\ifmmode\times\else\texttimes\fi{}${10}^{17}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}2}$) with phosphorus was investigated by transmission electron microscopy and secondary neutral mass spectrometry (SNMS) after annealing at 800, 850, 900, and 1000 \ifmmode^\circ\else\textdegree\fi{}C. Precipitation of large monoclinic, and partially orthorhombic, SiP particles takes place in the most heavily doped region. From the shape of the SNMS profiles in the dissolution stage of these precipitates, we determined the concentration ${\mathit{C}}_{\mathrm{sat}}$ of P in equilibrium with the conjugate phase: ${\mathit{C}}_{\mathrm{sat}}$=2.45\ifmmode\times\else\texttimes\fi{}${10}^{23}$exp(-0.62/kT) ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$. This concentration has to be compared with the equilibrium concentration ${\mathit{n}}_{\mathit{e}}$ of the electrically active dopant. To this end, more accurate determinations of ${\mathit{n}}_{\mathit{e}}$ were performed on heavily P-doped polysilicon films. It was found that ${\mathit{n}}_{\mathit{e}}$=1.3\ifmmode\times\else\texttimes\fi{}${10}^{22}$exp(-0.37/kT) ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$. Hence for T\ensuremath{\gtrsim}750 \ifmmode^\circ\else\textdegree\fi{}C, ${\mathit{C}}_{\mathrm{sat}}$ exceeds ${\mathit{n}}_{\mathit{e}}$ and the concentration (${\mathit{C}}_{\mathrm{sat}}$-${\mathit{n}}_{\mathit{e}}$) of inactive mobile P increases with temperature. The formation and the diffusion behavior of this inactive dopant are in keeping with a preprecipitation phenomenon. \textcopyright{} 1996 The American Physical Society.