Participation of nitrogen impurities in the growth of grown-in oxide precipitates in nitrogen-doped Czochralski silicon

For nitrogen-doped Czochralski (NCZ) silicon, it is well known that nitrogen (N) and oxygen (O) impurities can interact to form nitrogen–oxygen shallow thermal donors (N–O STDs); moreover, the N impurities can be involved into heterogeneous nucleation to facilitate the formation of grown-in oxide precipitates. However, how the N impurities participate in the growth of grown-in oxide precipitates during the post-anneal remains unclear. Besides, the correlation between the formation of N–O STDs and the growth of grown-in oxide precipitates is yet to be revealed. In this work, the effects of pre-anneals at temperatures of 900–1200 °C on the formation of N–O STDs at 650 °C in NCZ silicon have been first investigated. Thus, it has been found that the more significant growth of grown-in oxide precipitates during the pre-anneal, which consumes much more N impurities, leads to forming much fewer N–O STDs. This finding stimulates us to explore the mechanism for the participation of N impurities in the growth of grown-in oxide precipitates. To this end, the capture of N impurities by the oxide precipitates, on the one hand, and the release of N impurities from the oxide precipitates, on the other hand, have been investigated by two systematically constructed experiments. The obtained results enable us to reasonably propose that the N impurities participating in the growth of grown-in oxide precipitates predominately reside at the oxide precipitate/Si interfaces, which reduces the interfacial energies, thus favoring the growth of grown-in oxide precipitates. Such a viewpoint is well supported by the density functional theory calculations. In a word, this work has gained an insight into the mechanism for the participation of N impurities in the growth of grown-in oxide precipitates, starting from exploring the correlation between the formation of N–O STDs and the growth of grown-in oxide precipitates.