Thermal donor formation and annihilation at temperatures above 500 °C in Czochralski-grown Si

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Abstract
Thermal donors (TDs) are generated in Czochralski (CZ)-grown silicon by heat treatments around 450 ° C . They form several individual effective-mass-like donors with slightly different ionization energies and act as double donors ( TD x 0 , TD x + ). Heat treatments at elevated temperatures (e.g., >500 ° C ) lead to a competition of the formation and the annihilation of TDs. We studied the formation and the annihilation of TDs in the temperature range between 520 and 700 ° C . CZ-grown Si samples with an initial total TD concentration of ∼5×10 15 cm −3 were employed to study the annihilation of TDs. The number of interstitial oxygen atoms generated per annihilated TD center depends on the temperature and ranges from 4 to 24. For the temperature range investigated the activation energy for thermal annihilation of TDs was determined to be 2.5±0.4 eV. The same CZ-Si material but with an initial TD concentration of ∼2×10 13 cm −3 was used to study the formation of TDs. During annealing, the concentrations of individual TDs reach equilibrium concentrations, which depend on the temperature of the final annealing step and the total oxygen concentration. We demonstrate that a model in which the individual TD x centers are represented by oxygen clusters of different sizes consistently explains our experimental data.