Rapid Thermal Processing-based Internal Gettering For Czochralski Silicon Wafers

The internal gettering (IG) of Czochralski (CZ) silicon wafers enables the surface metal contaminants to be removed by the bulk microdefects (BMDs) including oxygen precipitates and the induced secondary defects which are generated by appropriate annealing process. High temperature rapid thermal process (RTP) can introduce vacancies with well-defined depth profile of concentration into CZ silicon wafers, thus playing a role in controlling oxygen precipitation (OP). Around the year of 2000, the former MEMC Company in America developed a so-called MDZ process that is an IG process based on the high temperature RTP. Since the MDZ process features low thermal-budget and well reproducibility, it has received intensive attention over the years. In this thesis, on one hand, the MDZ process for the<100> silicon wafers widely used to fabricate integrated circuits (ICs) has been modified; on the other hand, the MDZ process for<311> silicon wafers possibly used to fabricate ICs has been explored. The main results achieved in this thesis are described as follows.The MDZ process for<100> silicon wafers is generally composed of RTP@1250℃+800℃/4h+1000℃/16h under Ar ambient. It is found that a 1200℃/30 min anneal under Ar ambient prior to the MDZ process can significantly enhance the nucleation of oxide precipitates at 800℃ and, therefore, accerlerating OP at 1000℃. The glowing discharge mass spectroscopy (GD-MS) and deep level transient spectroscopy (DLTS) indicate that the 1200℃/30min pre-anneal introduces no substantial metal contamination into silicon wafers. Accordingly, it can be reasonably excluded that the metal contaminants enhance OP in CZ silicon wafers during the MDZ process. During the conventional MDZ process, the vacancies introduced by the RTP@1250℃ are substantially consumed by the growth of grown-in oxide precipitates rather than by the formation of fresh oxide precipitate nuclei. With the 1200℃/30min pre-anneal, the grown-in oxide precipitates have been substantially dissolved.In this context, the vacancies introduced by the RTP@1250℃ are actively involved into the oxide precipitate nuclecation at 800 ℃. The resulting oxide precipitate nuclei are much more than the grown-in oxide precipitates, thus leading to the enhanced OP at 1000℃during the MDZ process. Consequently, the application of 1200℃/30min pre-anneal can reduce the annealing time at 1000℃ in the MDZ process, without deteriorating the IG capability of CZ silicon wafers.<311> CZ silicon wafers possess better oxide breakdown characteristics than <100> counterparts. Hence, the <311> CZ silicon wafers may be employed to fabricate ICs. However, the OP behavior and the related IG process of the <311> CZ silicon wafers have not yet been investigated. By comparison on the OP behaviors of <311> and<100> CZ silicon wafers subjected to low-high two-step anneal or MDZ process, it is found that the OP rate of <311> CZ silicon wafer is larger than that of <100> counterpart. Moreover, it is verified that the oxygen diffusivities at 1000℃ in such two kinds of silicon wafers are almost the same. It is believed that both the nucleation and growth of oxide precipitates are much more favorable in the <311> CZ silicon wafer than in the<100> counterpart since the ejection of silicon self-interstitials is more readily in the <311> CZ silicon wafer. With the same MDZ process, the BMD density in the <311> CZ silicon wafer is much higher than that in the<100> conterpart, indicating the better IG capablity of <311> CZ silicon wafer.