It was shown that energy contamination introduced by ion beam deceleration technology, used to increase the beam currents available for low- energy B implants, could adversely affect fabricated junctions. A 4keV 11B beam was extracted and retarded by a potential of −3.5keV for 0.5keV 11B implantation, or by a potential of −3.8keV for 0.2keV 11B implantation. Intentional beam contamination was introduced by turning off the retarding potential to allow the 4keV 11B ions to bombard Si wafers directly. A percentage of contamination, at levels of 0.1, 0.2 and 0.3%, was introduced. Rapid thermal annealing of all of the implanted samples was performed under an N2 ambient at 1050C for 1s. The dopant tail profiles were themselves insignificant if the contamination levels were low. However, the much higher damage level arising from high-energy contamination more than proportionately increased the transient enhanced diffusion of 11B; resulting in considerable B diffusion. Energy contamination at a level of 0.1% could extend the profile of 0.5keV 11B implants some 10nm deeper after a 1050C spike annealing. The study showed that a highly mono-energetic beam, with an energy contamination of less than 0.1%, was required for sub-micron devices.

The Effects of Energy Non-Monochromaticity of 11B Ion Beams on 11B Diffusion. J.Chen, L.Shao, T.Lin, J.Liu, W.K.Chu: Nuclear Instruments and Methods in Physics Research B, 2005, 237[1-2], 155-9