Ostwald Ripening Of Oxygen Precipitation In Czochralski Silicon

Oxygen is the most important impurity unintentionally doped into Czochralski (CZ)silicon,its related oxygen precipitation in CZ silicon has long been the subject of importance.At a certain temperature,the so-called Ostwald ripening of oxygen precipitates will occur after the equilibrium of oxygen precipitation is reached. However,this phenomenon has not been systematically investigated to date. Moreover,the effect of nitrogen-doping on the Ostwald ripening of oxygen precipitates is yet to be revealed.In this thesis,based on Fourier transformation infrared(FTIR)spectroscopy and optical microscopy following preferential etching, the scanning infrared microscopy(SIRM)was employed to comparatively investigate the Ostwald ripening of oxygen precipitates in CZ and nitrogen-doped CZ(NCZ) silicon wafers subjected to the two-step annealing successively at low and high temperatures.In the following,the primary results achieved in this thesis are described.The oxygen precipitation behaviors in CZ and NCZ silicon wafers subjected to a two-step annealing of 800℃/8 h followed with 1000℃annealing for 4-256 h were comparatively investigated.It was found that the Ostwald ripening of oxygen precipitates occurred in CZ silicon after 64 h annealing at 1000℃,while,it happened in NCZ silicon after 32 h annealing at 1000℃.Therefore,the Ostwald ripening of oxygen precipitates is believed to be accelerated by nitrogen-doping which facilitates the formation of oxygen precipitate nuclei during the low temperature annealing and, furthermore,results in a shorter time to the equilibrium of oxygen precipitation followed by the Ostwald ripening process occurring during the high temperature annealing.The SIRM characterization definitely revealed that during the Ostwald ripening of oxygen precipitation,the large-sized oxygen precipitates coarsened further at a price of the dissolution of small-sized ones.The reduction in oxygen precipitates/silicon matrix interracial energy is believed to be the driving force for the Ostwald ripening of oxygen precipitates.The oxygen precipitation behaviors in the conventional and nitrogen-codoped heavily arsenic(As)-doped silicon wafers subjected to a two-step annealing of 650℃/8 h followed with 1000℃annealing for 4-256 h were comparatively investigated.It was found that the oxygen precipitates in the nitrogen-codoped heavily As-doped silicon were of higher density and smaller size and,moreover,experienced Ostwald ripening 16 h earlier in comparison with those in the conventional heavily As-doped silicon.Furthermore,the size distribution of oxygen precipitates was more uniform in the nitrogen-codoped heavily As-doped silicon than in the conventional heavily As-doped silicon.It is believed that during the 650℃annealing the nitrogen-oxygen complexes were formed in the nitrogen-codoped heavily As-doped silicon,acting as the heterogeneous nucleation centers thus leading to a higher density of oxygen precipitate nuclei,which further accelerated the oxygen precipitation and its Ostwald ripening during the annealing at 1000℃.