Kinetics study of the evolution of oxygen-related defects in mono-crystalline silicon subjected to electron-irradiation and thermal treatment

The diffusion and dissociation mechanisms governing the evolution of oxygen and vacancy-oxygen defects in Czochralski-grown Si samples have been studied. The samples were irradiated at (i) room temperature or (ii) elevated temperature (350 °C) by MeV electrons and then isothermally annealed at 8 different temperatures in the range of 300 °C to 500 °C. The evolution of the concentrations of oxygen complexes (On, n ≤ 3) and mono-vacancy-oxygen defects (VOn, n ≤ 4) have been followed by infrared absorption measurements of local vibrational modes originating from the individual defects. The experimental kinetics data have been compared with simulation results based on the theory for diffusion limited reactions, assuming a model where sequential build-up of the VOn defects is a key ingredient. A close quantitative agreement is obtained for both sets of samples despite quite different initial conditions prior to the annealing, which adds evidence to the validity of the model. Values for the diffusivity and dissociation rates of VOn (n ≤ 4) and On (n ≤ 3) have been deduced and in general, the mobility and stability of VOn decrease and increase with n, respectively. For all the defects, partial dissociation appears as a prevailing process during diffusion, while full dissociation of VOn is limited by an energy barrier identical to that of interstitial oxygen (Oi) diffusion (∼2.55 eV). The oxygen dimer and trimer are fast diffusers but slower than substitutional oxygen, i.e., VO; VO is found to be the most mobile species, whilst Oi is the slowest one with a difference in diffusivity of up to 7 orders of magnitude in the studied temperature range.