A INTRODUCTION

Carbon impurity atoms occupying substitutional lattice sites are commonly found in single crystal silicon grown from either the melt (e.g. Czochralski (CZ) and floating-zone (FZ) silicon) or from the vapour phase (e.g. chemical vapour phase epitaxy and molecular beam epitaxy). The diffusion coefficient (D _c) and the diffusion mechanism of carbon control the rate and type of defects formed during the high temperature heat treatments required for device processing. Diffusion coefficient data are available for the temperature range from 800 C to 1400 C and, in general, independent investigations using different techniques are in good agreement. Published data have been obtained for dislocation-free Si, plastically deformed Si, CZ material and FZ crystals, but these variations do not lead to changes in D _c for the temperature range quoted. However, diffusion in a phosphorus ambient enhances D _c, while there is an indication that a nitrogen ambient reduces D _c.

Substitutional carbon atoms are ejected into bonded interstitial sites (C _i) when they capture a rapidly diffusing self-interstitial (I-atom) produced by the displacement of lattice atoms by high energy irradiation (e.g. electron irradiation, neutron irradiation or ion implantation, etc.) or by the precipitation of SiO ₂ particles in CZ Si. The carbon interstitial may be present in a negative, neutral or positive charge state, depending upon the position of the Fermi level. These centres are highly mobile above room temperature and form...