A INTRODUCTION

The diffusion of a foreign element in a crystal is the thermally activated motion of an entity involving this element, from which a distribution profile obtained at a given temperature can be fitted to a simple Arrhenius law of the form:

(1)

In silicon, the isolated forms of oxygen are:

1. interstitial oxygen (O _i), an O atom bonded to two nearest neighbour (NN) Si atoms in a near bond-centre location,

2. the oxygen-vacancy centre (OV), where a missing NN of O allows re-bonding to a next nearest neighbour (NNN) Si atom. It is produced by irradiation with high-energy particles.

Below the melting point, as-grown Czochralski (CZ) silicon is supersaturated with O _i. The bond-centre location of O _i increases the distance between the two NN Si atoms from 0.236 to ~0.32 nm, resulting in an expansion of the lattice in the <111> directions. Thus, precipitation of SiO ₂ reduces the O _i concentration and allows some lattice relaxation. Points to remember are that diffusion of O _i is already detected near 400 C and that an O atom can form complexes with defects, dopants, foreign atoms and, presumably, with another O atom.

The diffusion coefficient D _oxy of O in silicon has been measured by different methods and a good account of this complex subject is given in the review by Newman and Jones [1]. Many diffusion results can...