Precipitation processes in silicon at 465 degrees C
The defect structure and thermal donor activity in n-type Czochralski-grown silicon are studied after annealing at 465 degrees C. Using high-voltage electron microscopy, rod-like defects (RLDs) are found as the dominating defect type after annealing for more than 700 h. Diffusion and agglomeration processes of silicon self-interstitials (Si1) are shown to be more probable at this low temperature than those processes of interstitial oxygen; the formation of RLDs is therefore described as a clustering of Si1. FTIR spectroscopy reveals a splitting-up of the nu 3 vibration mode at 10 K as a function of the annealing time, which is explained by the formation of donor complexes. Electrical measurements have shown that (i) the annealing behaviour of thermal donors depends on the doping type, and that (ii) the sample surface essentially influences the formation kinetics of thermal donors. Moreover, DLTS measurements indicate different annealing kinetics of the E(0.07 eV) and E(0.15 eV) levels, too. This observation is contrary to the double donor concept. Based on these experiments it is supposed that the primary (electrically active) thermal donors represent Si/O complexes in interstitial-like positions, produced mainly by the agglomeration of Si1 on interstitial oxygen atoms. The incorporation of oxygen into the primary donor centres after prolonged annealing initiates a further growth of the centres, thus reducing their electrical activity. The correlation is discussed between the formation of thermal donors and the nucleation and growth of rod-like detects or oxygen precipitates at higher temperatures.