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FORMATION KINETICS OF THERMAL DONORS IN SILICON JEFFREY T. BORENSTEIN(a), DAVID PEAK(b) and JAMES W. CORBETT(a) (a) Physics Department, SUNY/Albany, Albany NY 12222, USA. (b) Physics Dept., Union College, Schenectady NY 12308, USA. ABSTRACT The kinetics of thermal donor formation in Czochralski-silicon at ca. 4500 C are explained by a simple model based on the work of Suezawa and Sumino which derives forward and reverse reaction rates for each electrically active species from the general features of the infrared electronic absorption spectra. The model, which is independent of the chemical nature of the thermal donor core, assumes that all thermal donors beyond the first donor species are chemically stable at the donor formation temperature, and approximates the reactions for species smaller than the first thermal donor as being in chemical equilibrium. The model is shown to be consistent with both sets of the available IR spectra of thermal donors (Oeder-Wagner and Suezawa-Sumino) when differences in the annealing temperature and initial oxygen concentration are taken into account. INTRODUCTION The discovery of oxygen-related donor states in Czochralski-silicon annealed at 400-500o C [11 has led to thirty years of efforts to model the formation kinetics of these defects. In 1958 Kaiser, Frisch and Reiss (KFR) [2] proposed a model which was capable of explaining many of the experimental results concerning these defects, and they argued that the dominant thermal donor species was a four-oxygen complex of unspecified configuration. The KFR model required a forward reaction rate for donors which is orders of magnitude above the value expected from the now known diffusion coefficient of oxygen in dispersed silicon [3]. Recent infrared absorption measurements [4-7] have revealed that the thermal donors comprise a hierarchy of at least nine divalent defects with successively shallower ground states. Therefore, it has become necessary to provide more sophisticated kinetic models which are capable of explaining the formation rates of each distinct species. One such model is that of Ourmazd, Schr6ter and Bourret (OSB) [8], which is capable of fitting the IR annealing data of Oeder and Wagner [6]. Like the KFR model, their theory also requires a diffusion coefficient for oxygen which is much higher than the experimental value. OSB argued on the basis of their best-fit that the thermal donor core, or first electrically active species, contains five oxygen atoms. In this paper we introduce a kinetic model based upon an approximate scheme proposed by Suezawa and Sumino (S+S) [7], and successfully apply it to the IR data of both Oeder and Wagner [6] and S+S [7]. The present formulat'i-n differs

Mat. Res. Soc. Symp. Proc. Vol. 59. 1986 Materials Research Society

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from the aforementioned models in that the kinetic fitting yields rate constants for the thermal donor formation reactions without defining a specific chemical structure for The number of free parameters in our each donor species. model is reduced by making certai