Determination of Diffusivities of Si Self-Diffusion and Si Self-Interstitials using Isotopically Enriched Single-or Mult
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E8.4.1
Determination of Diffusivities of Si Self-Diffusion and Si Self-Interstitials using Isotopically Enriched Single-or Multi-30Si Epitaxial Layers
S. Matsumoto1, S.R. Aid1*, T.Sakaguchi1, K.Toyonaga1, Y.Nakabayashi1, M.Sakuraba2, Y.Shimamune2, Y.Hashiba2, J.Murota2, K.Wada3, T.Abe4 1 Department of Electronics and Electrical Engineering, Keio University, Hiyoshi, Yokohama 223-8522, Japan 2 Research Institute of Electrical Communication, Tohoku University, Sendai 980-8577, Japan 3 Department of Materials Science, University of Tokyo, Tokyo 113-8656, Japan 4 Shin-Etsu Handoutai, Isobe, Gunma 379-01, Japan
ABSTRACT 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, DSD) 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, DSD can be described by an Arrhenius equation with one single activation enthalpy: DSD =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, DI, is obtained by fitting with experimental results. In the temperature range between 820 920 °C , DI and thermal equilibrium concentration of Si self-interstitials, CIi, are described by the Arrhenius equations D I = 3.48 × 10 4 exp(− 3.82eV kT ) cm2/s and -3 18 C Ii = 9.62 × 10 exp(− 0.475eV kT ) cm , respectively. INTRODUCTION As device dimensions shrink with increasing degree of integration, accurate prediction and precise control of dopant profiles in Si become very important. Since dopant atoms in Si diffuse by their interaction with point defects [vacancies (V) and Si self-interstitials (I)], it is important to understand the properties of point defects. Si self-diffusion is considered to be a limiting case of dopant diffusion, in which the diffusing atoms are mediated via only the intrinsic point defects without the effect of charge states and strain due to dopant atoms. Thus, the study of Si self-diffusion is of fundamental significance for investigating t
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