Improvement of focused ion-beam optics in single-ion implantation for higher aiming precision of one-by-one doping of impurity atoms into nano-scale semiconductor devices

Focused ion-beam (FIB) optics in single-ion implantation (SII), which enables us to implant dopant ions one-by-one into a fine semiconductor region until the necessary number is reached, has been modified in order to improve the controllability of dopant atom position to within 100 nm. The lateral magnification of the objective lens (OL) was remodeled to 1/19 from the original value of 1/6 before modification. Scanning ion microscope (SIM) images at a high magnification of 75,000 were taken using a 60 keV focused Si ion beam with a current of 1 pA to evaluate the resolution of secondary electron images. A diameter of the ion beam less than of 20 nm was obtained. One-by-one, 60 keV Si ions were implanted by means of SII into CR-39 which is a fission track detector for investigating the aiming precision. Deviation of the single ion incident site from the target position was evaluated using atomic force microscopy (AFM) and compared with that before modification of FIB optics. The average aiming precision in SII was improved to be 60 nm which was 1/3 of that before modification.