High spatial resolution spin-polarized scanning electron microscopy (abstract)

Abstract

Spin-polarized scanning electron microscopy (spin SEM) to observe magnetic domains has the potential for spatial resolution as high as 10 nm. The best resolution from spin SEMs attained so far, however, is around 50 nm. In this talk, we report a newly developed spin SEM with 20 nm resolution. The major factor determining the resolution of a spin SEM is probe diameter. A smaller probe diameter, however, results in lower probe current. This is a serious issue in spin SEM because the efficiency of a spin detector is very low. Thus, to get high resolution with a reasonable signal/noise (S/N) image, higher efficiency in the spin detector and/or higher probe current are needed in addition to get a smaller probe diameter. The higher probe current has been attained by using a thermal assisted field emission cathode in an electron gun. The higher efficiency in the spin detector was achieved by increasing the acceptance angle of electron detectors inside the spin detector and optimizing both a secondary collector and transport optics. Obtaining a smaller probe diameter required a low aberration objective lens and a short working distance. Those were achieved by computer calculation so that there was no interference between the objective lens and the secondary collector. This achieved both a short working distance of 20 mm and high secondary collection efficiency. As a result, magnetic images of 20 nm resolution with a 25 keV and 1 nA probe beam have been attained. We have applied this spin SEM to observing recorded bits of longitudinal thin film media at high recording densities.