Precipitation Behaviors of Rapid Thermal Annealing Treated Silicon Wafers under Various Thermal Cycles
In this report, we demonstrate that a 2-step Rapid Thermal Annealing (RTA) treatment in NH3 and Ar gas is capable of producing a high density of precipitates in an extremely uniform profile in the 300mm silicon wafers under CMOS-like thermal cycles. The RTA treatment is a special variant of MDZ® that has been widely adopted in the industry for >10 years [1, 3]. Figure 1 shows typical depth profiles of precipitates in the high oxygen material after through a CMOS thermal simulation and after a subsequent extra growth cycle. Adding the extra growth cycle was necessary for the sake of ensuring all the existing precipitates to be detectable as the metrology tool (laser scattering tomography) would otherwise miss those sub-threshold size in the count, especially in the case of the lower oxygen concentration material. Quite a uniform density of precipitates is formed at the depth of around 7 microns and extended to the entire thickness of the wafers with the maximum density around 8x109/cm3 and 7x109/cm3 in the cases of higher and lower oxygen concentration materials, respectively. It can also be seen that in the case of higher oxygen material the full cycle of the D simulation has effectively grown the precipitates so about 70% of the precipitate distribution was detectable without going through a growth cycle (the D2 curve). These results are pretty consistent with the previous work reported by co-authors, where the uniform density of precipitates is explained as a result of the nitride layer blocking vacancy sinking to the wafer surface . The precipitation sites are created by vacancy aggregation in the course of fast post-RTA cooling.
The radial distribution of oxygen precipitates is remarkably uniform, as shown in Fig. 2 (a) and (c). In comparison, the as-grown wafers (b and d) resulted in a large variation, especially in the high oxygen material, which is due to the inhomogeneous distribution of point defects formed during crystal growth. The result clearly demonstrates that the 2-step RTA eliminated the crystal originated variability, very effectively.
In summary, adding a 2-step RTA treatment produces a high density precipitates near surface, uniformly both vertically and laterally, guaranteeing a <20um thick layer of IG sinks to be retained even after through wafer thinning to 30um.
 K. Bae, .J. Kim, Y. Hong, S. So, S. Lee, S. Kim, S. Ha, C. Koh, S. Pyi and D.M. Lee, ECS Proc. Vol. 2 “Semiconductor Si,”. Eds. H. Huff et al, 786 (2002)
 T. Ono, W. Sugimura, T. Takayuki and M. Hourai, ECS Trans. 2, 109 (2006).
 R. Falster, Future Fab International, 12, 240, (2002)
 V. Voronkov, R. Falster, T. Kim, S. Park, T. Torack,, J. Appl. Phys. 114, 043520 (2013) (1999).