Re-dissolution of gettered iron impurities in Czochralski-grown silicon

In order to control the degradation of silicon devices by metal impurities, especially transition metals, different gettering techniques were developed in the past decades. The transition metal gettering by oxide precipitates formed in the bulk wafer turns out to be efficient for fast diffusers such as iron. However, the gettered iron impurities can re-dissolve after gettering into the silicon matrix during the thermal cycles and very little is known about this dissolution process. In this paper, we report a systematic study of the re-dissolution behavior of gettered iron impurities in p-type Czochralski-grown silicon with doping level about 2.5x10(14) cm(-3) and oxide precipitates density of 5x10(9) cm(-3). The concentration of interstitial iron and iron-boron pairs is measured by deep level transient spectroscopy (DLTS). It is found that the dependence of the re-dissolved iron concentration on annealing time can be fitted empirically by the function C(t) = C-o (1 - e(-1/tau)), and tau(-1) has an Arrhenius dependence on temperature: tau(-1) = 4.01 x 10(4) x exp(-1.47eV/k(B)T).s(-1).