The effects of energy non-monochromaticity of 11B ion beams on 11B diffusion

We have shown that energy contamination introduced by ion beam deceleration technology that is used to increase the beam currents available for low energy boron implants, can affect fabricated junctions adversely. A 4 keV 11B beam is extracted and retarded by a potential of −3.5 keV for 0.5 keV 11B implantation, or by a potential of −3.8 keV for 0.2 keV 11B implantation. Intentional beam contamination was introduced by turning off the retarding potential to allow the 4 keV 11B ions to irradiate Si wafers directly. The percentage of contamination, at levels of 0.1%, 0.2% and 0.3% was introduced. Rapid thermal annealing of all the implanted samples was performed under N2 ambient at 1050 °C for 1 s. The dopant tail profiles themselves are not significant if the contamination levels are low. However, the much higher damage level coming from high energy contamination increases the transient enhanced diffusion of 11B more than proportionately, resulting in considerable boron diffusion. Energy contamination at a level of 0.1% can extend the profile of 0.5 keV 11B implants 10 nm deeper after a 1050 °C spike annealing. The study shows a highly monoenergetic beam with energy contamination less than 0.1% is required for sub-micron devices.