IR studies of the oxygen and carbon precipitation processes in electron irradiated tin-doped silicon

Abstract

Oxygen (O) and carbon (C) are key impurities in silicon (Si) and the control of their properties and behavior is an important issue for the microelectronic industry. A number of these properties can be manipulated by isovalent doping. Here we employ Fourier transform infrared (FTIR) spectroscopy to study the evolution of O and C concentration as well as the evolution of the oxygen precipitate bands in electron- irradiated tin (Sn) doped Si, subjected to isochronal anneals up to 950 °C. Special attention was given in connecting infrared absorption bands with certain precipitation morphologies. In this study, bands at 1040, 1060, 1080 and 1170 cm−1 generally attributed to precipitate morphologies were detected. Using arguments from classical theoretical mechanics we have attributed the 1040 cm−1 band to a structure more close to a spherical morphology, although the 1060 and 1080 cm−1 bands were attributed to structures more close to octahedral and polyhedral morphologies, respectively. Additionally the band at 1170 cm−1 was attributed to platelet precipitates. The effect of C and (C, Sn) co-doping Si in the morphologies of the precipitates bands was investigated in detail. It was found that in the irradiated material C suppresses the formation of spheroidal precipitates although it enhances the platelet precipitates, whereas in Si containing C and Sn the opposite behavior was detected. The presence of the two impurities modifies the number of the O precipitates and affects the relative density among the formed morphologies in Si, determining whether the spheroidal or platelet precipitates will prevail. The phenomenon was discussed taking into consideration the effect of the density of the nucleation sites on the interfacial energy of the precipitates. Furthermore, an inverse annealing stage in the evolution curve of C, namely an increase of C concentration prior to its complete disappearance was studied. This recovery stage was determined to be enhanced in (C, Sn) co-doping Si with relatively low Sn content although in Si with high Sn content the increase of C is substantially lower. An explanation was suggested based on the ability of the Sn to temporarily trap vacancies, thus affecting the restoration of the C substitutional atoms in the Si lattice.