Internal Gettering And Copper Precipitation In Czochralski Silicon

With the rapid development of ultra large-scale integrated circuits (IC), the requirements on silicon materials have become increasingly stringent. And with the ever-decreasing feature size of integrated circuits, the elimination of metal contamination by internal gettering has become a key issue in the fabrication of IC device. Not only the rapid thermal processing (RTP) technology, but also the intentionally impurity doping has been adopted to improve the gettering capability. Previous studies have shown that proper germanium doping in CZ silicon can control the microdefects and improve the internal gettering capability. So far many studies still concentrate on the germanium co-doped lightly doped CZ silicon. In this paper, the internal gettering effects in germanium co-doped heavily phosphorus-doped CZ silicon and germanium co-doped lightly phosphorus-doped CZ silicon as well as the Cu precipitation in germanium co-doped heavily phosphorus-doped CZ silicon have been investigated. Listed below are the most important results achieved in this work.(1) The internal gettering effect in germanium co-doped heavily phosphorus-doped CZ silicon has been investigated. It is found that both a good quality defect-free denuded zone (DZ) with a suitable width in the sub-surface area and a high density bulk micro-defect (BMD) region in bulk can be formed by conventional furnace anneal (CFA) and RTP based denudation processing and that the gettering capability can be improved by germanium doping. It also shows that the BMD density and DZ are slightly affected by changing the oxygen precipitation nucleation temperature in high-low-high conventional furnace anneal. Moreover, the germanium doping does not improve the thermal stability of gettering at high temperature in heavily phosphorus-doped CZ silicon.(2) The internal gettering effect in germanium co-doped lightly phosphorus-doped CZ silicon has been investigated. It is found that the behaviors of the denuded zones formed by conventional high-low-high IG process and RTP based magic denuded zone (MDZ) process are different after Cu contamination. The DZ disappears in conventional IG wafers but remains in MDZ wafers, which means that the gettering capability of MDZ process is superior to that of the conventional IG process. Furthermore, it is suggested that the conventional IG process results in an apparent DZ which means the oxygen related defects in fact may still exist, while the DZ generated in MDZ wafers is a real one. Moreover, it is revealed that when the doping content reaches a certain level, the effect of germanium doping on internal gettering is limited by comparing the germanium doping concentration of 1019 and 1020cm-3 silicon.(3) The Cu precipitation behavior in germanium co-doped heavily phosphorus-doped CZ silicon has been investigated. It is found that the Cu precipitates are revealed as rod-like Cu precipitate colonies with low density and large size when the sample cooled down from 1000℃with a rate of 30℃/s, which is different from the silicon without germanium doping. It is revealed that the germanium doping has a significant effect on Cu precipitation. Furthermore, the annealing temperature or cooling rate can exerts effects on Cu precipitation in germanium co-doped heavily phosphorus-doped CZ silicon, which is related to the driving force of Cu precipitation. Moreover, the size of Cu precipitate colonies decreases and the density increases when the sample injected with an amount of vacancies by prior RTP. This is due to that the vacancies can significantly enhance Cu precipitation by recombination with the Si interstitial atoms released by Cu precipitation.In addition, the Cu precipitate colonies can be dissolved by 1000℃annealing, revealing that the germanium doping does not improve the thermal stability of Cu precipitates in heavily phosphorus-doped CZ silicon.