Initial generation kinetics of oxygen-related thermal donors at 430 °C in silicon

Abstract

The initial generation kinetics of thermal donors at 430 °C in Czochralski-grown silicon crystals containing (3–10)×1017 interstitial oxygen atoms per cm3 is studied by careful resistivity measurements at room temperature. The density of thermal donors is measured over the range from 1013 to 1016 cm−3. An analysis based on the chemical rate theory is made. For as-grown crystals, the well-known dependence of the initial donor formation rate and the maximum donor density on the initial oxygen concentration is confirmed. However, some irregularities are present in the very initial period of donor generation, probably arising from differences in thermal history of as-grown crystals. These irregularities are completely removed by pre-heating as-grown crystals at 1300 °C for 22 h and rapidly quenching them. In such heat-treated crystals, the initial kinetics of the thermal donor generation process can be described well by the following reaction scheme. The smallest donor species involving five oxygen atoms is preferentially formed, with its density being proportional to the square of the annealing time. Also, the electrically inactive cluster that involves four oxygen atoms and can be converted into the donor by the addition of an oxygen atom is simultaneously generated, while the formation and dissociation reactions for the smaller neutral clusters involving two and three oxygen atoms maintain the equilibrium. In as-grown crystals, the same reaction scheme can also explain the initial kinetics very well only if the initial densities of the smallest donor and the smaller neutral clusters are significantly increased, indicating that the initial irregularities are due to the differences in the densities of preexisting donors and neutral clusters.