Forming Sub-32-nm High-Aspect Plasmonic Spot via Bowtie Aperture Combined with Metal-Insulator-Metal Scheme

We theoretically utilize bowtie aperture combined with metal-insulator-metal (MIM) scheme to obtain sub-32-nm (lambda/12) high-aspect plasmonic spots. The improvement of the depth profile is attributed to the asymmetry electromagnetic mode excitation in MIM structure and the decaying compensation of the reflective Ag layer. A theoretical near-field exposure model has been used to evaluate the exposure depth in the photoresist. It is demonstrated that the exposure depth of the sub-32-nm plasmonic spot is more than 20 nm, which is about four times of the bowtie aperture without MIM scheme. The influences of the air gap tolerance and the ridge gap size of bowtie aperture are also discussed.