Determination of diffusivities of Si self-diffusion and Si self-interstitials using isotopically enriched single-or multi-³⁰Si epitaxial layers

Self-diffusivity of Si has been obtained over a wide temperature range (867°C-1300°C) using highly isotopically enriched ³⁰Si epi-layers (99.88%) as a diffusion source into natural Si substrates. ³⁰Si epi-layers were grown on both CZ-Si substrates and non-doped epi-layers grown on CZ-Si substrates using low pressure CVD with ³⁰SiH₄. Diffusion was performed in resistance-heated furnaces under a pure Ar atmosphere. After annealing, the concentrations of the respective Si isotopes were measured with secondary ion mass spectroscopy (SIMS). Diffusivity of ³⁰Si (called Si self-diffusivity, D _SD) was determined using a numerical fitting process with ³⁰Si SIMS profiles. We found no major differences in self-diffusivity between bulk Si and epi-Si. Within the 867°C-1300°C range investigated, D_SD can be described by an Arrhenius equation with one single activation enthalpy: D_SD =14 exp (-4.37 eV/kT) cm²/s. The present result is in good agreement with that of Bracht et. al. Diffusivity and thermal equilibrium concentration of Si self-interstitials have been determined using multi-³⁰Si epi-layers consisting of alternative layers with isotopically pure ³⁰Si and natural Si. The sample surface was oxidized and the Si self-interstitials were introduced from the surface. Spreading of ³⁰Si spikes of each layer due to the diffusion of Si self-interstitials generated at the surface was measured with SIMS analysis. The diffusivity of Si self-interstitials, D _I, is obtained by fitting with experimental results. In the temperature range between 820 920°C, D_I and thermal equilibrium concentration of Si self-interstitials, C_Ii, are described by the Arrhenius equations D_I =3.48 × 10⁴ exp(-3.82eV/W) cm²/s and C_Ii = 9.62 × 10¹⁸ exp(- 0.475eV/kT) cm^-3, respectively.