An infrared and neutron scattering analysis of the precipitation of oxygen in dislocation-free silicon

Abstract

The precipitation of oxygen in silicon has been studied in the temperature range 650 to 1050 degrees C using the techniques of chemical etching, IR absorption applied to the 9 mu m band (4.2K), and small-angle neutron scattering (SANS). The IR data and etch pit counts, relating to the number densities of precipitate particles, have been fitted to Ham's theoretical model for the diffusion limited growth of randomly distributed particles. Full allowance is made for the increase in size of the precipitates with increasing time and good agreement is found over the complete period starting from zero time. Values of the diffusion coefficient of oxygen so determined are in excellent agreement with other data obtained by different methods, including SANS measurements at 750 degrees C described in the present work. The combined data give D=0.11 exp(-2.51 eV/kT) cm²s^-1. The SANS data also indicate that the precipitates are not spherical in shape after a short initial period, and they show that the initial concentration of particles nucleated decreases with annealing time. The solid solubility c_s(T) is determined at each temperature and compared with previous measurements. The authors conclude that the best combination of results leads to c_s(T)=2.6*10²² exp(-1.4 eV/kT) down to 850 degrees C. At lower temperatures c_s decreases more slowly with decreasing temperature, indicating a possible change in the structure or the form of the precipitated SiO₂ phase.