Effect Of Rapid Thermal Process On Oxygen Precipitates In Heavily Doped Silicon Wafers

Rapid thermal process (RTP) was performed to heavily doped silicon wafers in Ar and N2 ambient. The influence of the RTP temperature, the cooling rate and the RTP time on oxygen precipitates was investigated.RTP was performed to the wafers instead of the first step in conventional intrinsic gettering, oxygen precipitates with higher density and good denuded zone (DZ) were formed easily. The experimental results showed that high density oxygen precipitates were found in heavily B- and Sb-doped wafers annealed both in Ar and N2 ambient, the density of oxygen precipitates formed in N2 was higher than that in Ar, and the quality of DZ in N2 was better. Oxygen precipitates were not found in heavily As-doped silicon wafer. Then ramping annealing was performed to the heavily As-doped silicon wafer after RTP, high-density oxygen precipitates were found. The RTP temperature, the RTP time, the cooling rate, the ambient and the dopant atoms influenced the density and distribution of point defects in wafers, and then affected oxygen precipitates.The formation of oxygen precipitates not only had relation to point defects, but also the dopant atoms. In the bulk of heavily B-doped wafer, because the radius of the B atom was smaller than that of Si, a great deal of vacancies were produced in the bulk of heavily B-doped wafer, and then the B atoms combined with oxygen atomes to form complex which acted as the nucleus of oxygen precipitates and enhanced the formation of oxygen precipitates. In heavily Sb-doped wafer, the interstitials were introduced because the radius of Sb was larger than that of Si. But those interstitials were annihilated by the vacancies produced by RTP, and the residual vacancies acted as the nucleus promoting the formation of oxygen precipitates. Whereas the formation of oxygen precipitates was retarded due to the reaction of the As atoms and the vacancies in heavily As-doped wafer. A ramping annealing was performed to heavily As-dopedsilicon wafer, the radius of oxygen precipitates nuclei were always larger than the critical radius, so oxygen precipitates formed.RTP had many virtues, such as precise control of the temperature, short process time and less diffusion distance of heavy metal impurties. It has a wide application in the defect engineering of wafer in ultra large-scale integration (ULSI).