Oxygen Precipitation Behaviors In Conventional And Nitrogen-codoped Heavily Arsenic-doped Czochralski Silicon

Heavily arsenic (As) -doped Czochralski (CZ) silicon wafers have been intensively employed as the substrates for silicon epitaxial wafers. The internal getteing capability of silicon epitaxial wafers is substantially dependent on oxygen precipitation in substrate silicon wafers; therefore, the investigation on oxygen precipitation in heavily As-doped silicon wafers is of significance. To date, oxygen precipitation in heavily As-doped CZ silicon have been rarely investigated. Due to the influences of heavy As-doping on lattice stress and point defect concentration in silicon, the oxygen precipitation behavior in heavily As-doped CZ silicon differs significantly from that in lightly doped CZ silicon. In this thesis, the oxygen precipitation behaviors in the conventional and nitrogen-codoped heavily As-doped CZ silicon have been tentatively investigated by means of scanning infrared microscopy as well as the preferential etching in combination optical microscopy. Listed below are the primary results achieved in this thesis.The growth behaviors of grown-in oxygen precipitates in the conventional and nitrogen-codoped heavily As-doped CZ silicon were comparatively investigated. It was found that the grown-in oxygen precipitates in the nitrogen-codoped heavily As-doped CZ silicon were of higher density and smaller size in comparison with those in the conventional heavily As-doped CZ silicon. It is preliminarily believed that the formation of grown-in oxygen precipitates in the nitrogen-codped heavily As-doped CZ silicon occurred at higher temperatures and was enhanced by the nitrogen-vacancy-oxygen complexes, thus the grown-in oxygen precipitates were of higher density and coarsened in a longer period of time.The annihilation of grown-in oxygen precipitates in heavily As-doped CZ silicon by rapid thermal processing (RTP) was investigated. It was revealed that the grown-in oxygen precipitates could be substantially annihilated by three cycles of 1200℃/60s RTP.Through the comparative investigation on oxygen precipitation behaviors in the heavily arsenic-doped and lightly-doped N-type Czochralski (CZ) silicon wafers subjected to the two-step annealing successively at low temperature (450-800℃) and high temperature (1000℃), the effects of low-temperature annealing on oxygen precipitate nucleation in heavily arsenic-doped CZ silicon wafer have been elucidated. It was found that for the heavily arsenic-doped CZ silicon the oxygen precipitate nucleation during the 450 and 650℃annealing was more significant than that during the 800℃annealing, which was contrary to the case for lightly-doped CZ silicon. Moreover, in comparison with the lightly-doped CZ silicon, the oxygen precipitate nucleation at 450 and 650℃was enhanced while that at 800℃was suppressed in the heavily arsenic-doped CZ silicon. It is believed that in the heavily arsenic-doped CZ silicon the As-V-O complexes can be formed during the annealing at 450 and 650℃so as to enhance the oxygen precipitate nucleation; while, during the 800℃annealing the As-V-O complexes are not stable to be as the precursors of nuclei and, moreover, the heavy arsenic-doping leads to compressive lattice stress, therefore the oxygen precipitate nucleation is noticeably suppressed. Furthermore, it is revealed that the nitrogen-doping can facilitate the oxygen precipitate nucleation during the annealing at low temperatures especially at 800℃, which is believed to be ascribed to the heterogeneous nucleation centers induced by nitrogen-doping.