| Silicon wafers are fundamental material for the microelectronic industry. With the ever smaller feature size of integrated circuits, the requirement on the control of defects and impurities in Czochralski (CZ) silicon. Oxygen is the most important unintentional doped impurity in CZ silicon, thus its related oxygen precipitation and internal gettering (IG) technique have long been the subjects of research interests. In this thesis, the effects of high temperature hydrogen annealing on oxygen precipitation, formation of denuded zone (DZ) and oxygen thermal donor (OTD) formation in CZ silicon have been tentatively investigated. Listed below are the primary results achieved in this thesis.The oxygen precipitation behavior and formation of DZ in CZ, germanium-doped CZ (GCZ) and nitrogen-doped CZ (NCZ) silicon wafers subjected to a ramping annealing from 800℃ to 1050℃ or 1150℃ with a rate of 1℃/min and with a terminal isothermal annealing for 4 h in argon or hydrogen ambient were investigated. It was found that the ramping annealing in hydrogen ambient led to a higher density of bulk microdefects (BMDs) induced by oxygen precipitation in the above-mentioned silicon wafers, due to the formation of more oxygen precipitate nuclei enhanced by the incorporated hydrogen atoms. With the ramping annealing terminated at 1150℃, the DZ was formed within the silicon wafers, while it was not the case for the ramping annealing terminated at 1050℃. This indicated that only at temperatures 1150℃ and above, the oxygen precipitates existing in the near surface region of silicon wafers could be substantially dissolved. Moreover, it was revealed that the ramping annealing in the hydrogen ambient led to a wider DZ within the silicon wafers due to the hydrogen enhanced oxygen out-diffusion.The oxygen precipitation behavior and formation of DZ in CZ, GCZ, and NCZ silicon wafers subjected to 800℃/4h+1050℃/16h annealing following the high temperature annealing at 1200℃ for 2 h in hydrogen or argon ambient were investigated. It was found that the high temperature annealing in hydrogen ambientresulted in a higher density of BDDs generated in the following L-H two step annealing, which was due to enhanced formation of oxygen precipitate nuclei by the hydrogen incorporated during the high temperature annealing. Moreover, the hydrogen annealing led to a narrower DZ in CZ silicon wafer while a wider DZ in GCZ and NCZ silicon wafers in comparison with the argon annealing. The mechanism related to this phenomenon has been tentatively presented.The effect of high temperature annealing at 1200℃ for 1 h in hydrogen and argon ambient on the dissolution of oxygen precipitates in CZ and GCZ silicon wafers formed by the ramping annealing from 300 to 750℃ with a rate of 1℃/min. It was found that a high density of oxygen precipitates were generated by the ramping annealing, moreover, the dissolution of oxygen precipitates in the bulk of silicon wafer differed slightly by the hydrogen annealing from that by the argon annealing. However, the 1200℃/1 h hydrogen annealing led to a wider DZ within the silicon wafer, because the incorporated hydrogen enhanced the out-diffusion of oxygen and therefore the dissolution of oxygen precipitates. Therefore, it can be believed that the ramping annealing in the low temperature range followed with a high temperature annealing can serve as a new IG process for CZ silicon wafers, which features lower thermal budgets in comparison with the conventional high-low-high IG process.The OTD formation by 450 ℃ annealing in CZ and GCZ silicon wafers subjected to prior annealing at 1150℃ for 2 h in hydrogen or argon ambient was investigated. It was revealed that the enhancement of OTD formation by the prior hydrogen annealing occurred in CZ silicon other than GCZ silicon. It is preliminarily believed that in GCZ silicon the oxygen diffusion is suppressed due to the large amount of Ge-0 complexes, and the concentration of incorporated hydrogen is not high enough to enhance the OTD formation. |
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