The effect of pre-annealing at 400 to 800C, and of C atoms, upon the formation of O aggregates and new donors during prolonged annealing at 650C was investigated. It was found that the suppression of both O aggregation and of new donor formation occurred, even in material with a high C content, which was pre-annealed at 700C for long periods. Enhancement occurred in material which was pre-annealed at 500C, regardless of the C concentration. The suppression and enhancement were attributed to the absence and presence of agglomerations of Si self-interstitials, respectively. The absence of agglomerations of Si self-interstitials was due to a lower excess of Si self-interstitials which had been emitted from a small number of large O aggregates that formed at 700C. Thus, the emission of Si self-interstitials, and O aggregation, were suppressed to the extent that they did not increase the energy due to Si self-interstitial formation. Hence, the large O aggregates transformed into plate-like O precipitates during prolonged annealing at 650C in order to decrease the strain energy. The agglomeration of Si self-interstitials was due to the greater excess of Si self-interstitials which was emitted from a number of small O aggregates that formed at 500C. The further emission of Si self-interstitials could proceed during annealing at 650C. Thus, O aggregation was enhanced, and agglomerates of Si self-interstitials developed into rod-like defects and dislocation dipoles.

H.Yamanaka, N.Miyamoto: Japanese Journal of Applied Physics, 1995, 34[I-9A], 4606-20