Improving Imaging Contrast of Non-Contacted Plasmonic Lens by Off-Axis Illumination with High Numerical Aperture

Off-axis illumination plasmonic lens (OAIPL) is proposed and demonstrated to improve the imaging contrast in non-contacted application manner. The spatial Fourier components of light transmitted through the nano-patterns are greatly enhanced in the imaging process by shifting the wave vectors with high numerical aperture off-axis illumination. On the other hand, a reflector in the image area helps to tailor the ratio between electric field components in the tangential and normal directions. These two effects resultantly deliver significant improvement of imaging performance, including enhanced resolution, imaging contrast, and elongation of air gap thickness. In comparison to the case of normal illumination, the air gap thickness for 30 and 60 nm half-pitch resolution is extended to 25 and 100 nm by OAIPL with numerical aperture (NA) = 1.55, respectively.