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Behavior of nitrogen-doped Czochralski monocrystalline silicon oxygen precipitation induced defects

Author: WangHongJie
Tutor: YangDeRen；ZuoDuanZuo
School: Zhejiang University
Course: Materials Physics and Chemistry
Keywords: Czochralski silicon nitrogen doping oxygen precipitates RTP OSFs Cu gettering
CLC: TB39
Type: Master's thesis
Year: 2004
Downloads: 157
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Abstract

In recent years, it has been proved that nitrogen-doping can be employed to manipulate the formation of grown-in void defects and oxygen precipitates in Czochralski (CZ) silicon. Consequently, the defects in nitrogen-doped CZ (NCZ) silicon have been extensively investigated. In this thesis, the oxygen precipitates and their induced defects in NCZ silicon have been investigated by means of FTIR, TEM, SRP, EBIC and OM. Listed below are the primary results achieved in this thesis.1. Effects of nitrogen-doping on oxygen precipitation in CZ silicon.The oxygen precipitation behavior at 800 C and 1000 C in NCZ silicon was intensively investigated. It was found that, compared to the control sample of CZ silicon, in the NCZ silicon oxygen precipitates with higher density but smaller size were generated, thus leading to larger amount of precipitated oxygen atoms, which definitely implied that the nitrogen-doping could significantly enhance oxygen precipitation in CZ silicon at medium and high temperature. Moreover, it was revealed that the nitrogen-doping would modify the morphology of oxygen precipitates generated at 1000 C, that is, the polyhedral precipitate existed in the NCZ silicon besides the platelet precipitate which was only the case in CZ silicon.2. Effects of nitrogen-doping on the thermal stability of oxygen precipitates and their induced defects.The thermal stability of oxygen precipitates in the CZ and NCZ silicon generated by prolonged anneals at 800 C and 1000 C has been investigated. It was found that the dissolution behavior of oxygen precipitates existing in the CZ and NCZ silicon manifested a remarkable difference, that is, the existing oxygen precipitates in the NCZ silicon were to a large extent dissolved by the conventional furnace annealing (CFA) and rapid thermal processing (RTP) at 1200 C and 1250 C, while those in the CZ silicon were only dissolved by the CFA and RTP at 1250 C, the root cause for which was a large quantity of smaller oxygen precipitates generated in the NCZ silicon due to the nitrogen doping that provided considerable amount of heterogeneous nucleation sites. Moreover, it was proved that a short period of RTP had nearly the same effect of a long time CFA on the dissolution of oxygen precipitates, suggesting that the dissolution of oxygen precipitates is primarily dependent on the annealing temperature, rather than the oxygen precipitation being strongly dependent on both the annealing temperature and time.3. The formation of oxidation induced stacking faults (OSFs) on the annealed CZ and NCZ silicon wafer.The generation of OSFs on the CZ and NCZ silicon wafers subjected to single-step anneals at temperature in the range of 650 C-1150 C and low-high two-step anneals (650 C anneal plus 1050 C anneal) prior to the wet oxidation was respectively investigated. The purpose of this investigation aimed to understand the dependence of OSFs on oxygen precipitates.As for the CZ samples subjected to single-step anneal at temperatures not higherthan 850 C, in which the oxygen precipitation were not significant, the OSFs were hardly generated. It was also the case for the NCZ sample subjected to 650 C anneals even for 64 hours. For the NCZ samples, the OSFs occurred if they had received prior anneals at 750 C for longer than 16 hours or at 850 C for longer than 8 hours, which generated oxygen precipitates as the nucleation centers for OSFs. With prior anneals at 1050 C and 1150 C, for both CZ and NCZ samples, the generated OSFs reached a highest density as the prior anneal lasted for 32 hours, afterwards, the OSFs density reduced instead, the reason for which is that with prolonged anneals at the two temperatures mentioned above, the oxygen precipitate punched out dislocations would generate, these dislocations would absorb the silicon interstitials(Sii) arising from the oxidation, thus suppressed the formation of OSFs.As for the CZ and NCZ silicon subjected to two-step anneal prior to wet oxidation, (l).In the case with low temperature anneal at 650 C, the density of OS

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