Effects Of Nitrogen And Vacancy On The Oxygen Precipitation In Czochralski Silicon

Oxygen precipitation in Czochralski (CZ) silicon has long been a subject of significance. It has been well established that vacancy and nitrogen can enhance oxygen precipitation. MEMC company, a worldwide leading silicon wafer manufacturer, has developed a rapid-thermal-processing (RTP) based internal gettering (IG) technology named after "magic denuded zone"(MDZ(?)), taking advantage of vacancy enhancement of oxygen precipitation. On the other hand, over the years the nitrogen-doped CZ (NCZ) silicon, which is claimed to possess strong IG capability, had received increasingly intensive attention. Nevertheless, the substantial mechanisms for the enhancement of nitrogen and vacancy on oxygen precipitation have not been completely elucidated. In this thesis, in order to investigate the effects of vacancy and nitrogen on oxygen precipitation, the conventional CZ and NCZ silicon wafers were firstly subjected to RTP that introduced certain concentrations of vacancy, then they were further subjected to one-step annealing at different temperatures or the simulated post-crystal-growth cooling process from a high temperature to a low temperature. List below are the primary results achieved in this thesis.1. The vacancy enhancement effect on oxygen precipitation becomes stronger with higher concentration of vacancy. It is the most significant at around 1000℃, while becomes weaker at higher or lower temperatures. The vacancy enhancement of oxygen precipitation is due to the reduction of critical size for oxygen precipitation by the incorporation of vacancies into CZ silicon and the provision of stain-relief spaces for oxygen precipitation by the vacancies.2. In low-nitrogen-content NCZ silicon, nitrogen exhibits enhancement of oxygen precipitation to some degree in a wide temperature range. It is noteworthy that nitrogen enhancement of oxygen precipitation still operates even at quite high temperatures such as 1100℃. The reason for this is that nitrogen atoms can act as the heterogeneous nuclei for oxygen precipitation at the high temperature at which the super-saturation of interstitial oxygen (Oi) is so small that the homogeneous nucleation of oxygen precipitates is negligible.3. In high-nitrogen-content NCZ silicon, the grown-in oxygen precipitates can not be completely dissolved even by the RTP at 1280℃. The residual grown-in oxygen precipitates exhibit strong impact on oxygen precipitation in the subsequent one-step annealing. The Oi atoms tend to aggregate onto the residual grown-in oxygen precipitates to enable their growth. Therefore, the resulting oxygen precipitate density is nearly independent of annealing temperature, whereas, the sizes of oxygen precipitate increase with the annealing temperature.4. When the vacancy and nitrogen coexist in the silicon, once the vacancy concentration is high while the nitrogen concentration is low, the enhancement of vacancy is superior to that of nitrogen on oxygen precipitation;while the nitrogen concentration is quite high, due to the strong impact of grown-in oxygen precipitates, the vacancy enhancement effect on oxygen precipitation is notsignificant.Once the vacancy concentration of CZ silicon is considerably small, the formation of grown-in oxygen precipitates is determined by the super-saturation of Oi, and its onset temperature is around 900℃;while the vacancy concentration is desirably high, due to the reduction of Oi supersaturation necessary for oxygen precipitation, the onset temperature for the formation of grown-in oxygen precipitates is increased to a certain extent. For example, the vacancies introduced by the RTP at 1280℃ can enable the formation of grown-in oxygen precipitates at the onset temperature around 1100℃. For NCZ silicon, once the vacancy concentration is considerably small, the nitrogen enhancement of oxygen precipitation operates from the high temperature around 1100℃;whereas, once the vacancy concentration is desirably large, the nitrogen enhancement of oxygen precipitation is not remarkable from the temperature around 1050℃;instead, the vacancy enhancement effect is dominant. In the latter case, the nitrogen enhancement effect on oxygen precipitation exhibits at higher temperature.