A novel self-aligned process between a nano-aperture and a solid immersion lens for a near-field optical system

Abstract

For near-field optical systems, an aperture in nano-size and a solid immersion lens (SIL) are two popular methods to overcome the diffraction limit and reduce the optical spot size. In previous research, combining a nano-aperture and SIL has been proposed to provide high throughput and ultra-high resolution. However, alignment between the nano-aperture and SIL is very critical in the fabrication process, and no effective alignment technique has been investigated yet. In this research, a novel self-alignment technique is proposed for the combination of the nano-aperture and SIL, where the nano-aperture is fabricated with the focused ion beam (FIB) system and the SIL is formed by the thermal reflowing process. The self-alignment technique is based on the backside exposure and the surface tension self-modulation technique during the thermal reflowing process. The maximum deviation of the fabricated SIL is less than 3% in comparison with the designed values. A SIL of 15 µm diameter has been measured with 65.2% transmission efficiency. The polymer SIL combined with the circular aperture of 329 nm diameter has 1.68 times enhancement on throughput compared with the circular aperture of 329 nm alone. This result shows that the SIL can effectively enhance the throughput of the nano-aperture, and the feasibility of the proposed self-alignment method is also verified.