Fabrication of near-field optical probes using advanced functional thin films for MEMS and NEMS applications

Abstract

Highly efficient atomic force microscopy (AFM) cantilevers and an near-field scanning optical microscopy (NSOM) aperture array were fabricated using the functional Si 3N 4 and SiO 2 thin films for the micro electro mechanical systems (MEMS) and NEMS applications. In order to generate the cantilevers and array, a silicon nitride (Si 3N 4) thin film with a stress below 100 MPa was deposited using NH 3 and SiCl 2H 2 gases with a relative ratio of 1:5 at 140 mTorr, and 835 °C by low pressure chemical vapor deposition (LPCVD). Cantilevers of 10–100 μm in length were fabricated with Si 3N 4 thin films. Photolithography and magnetically enhanced reactive ion etching (MERIE) techniques were employed for patterning the Si 3N 4 thin films and selective bulk etching of Si was carried out using a strong alkaline solution of tetramethylammoniumhyroxide (TMAH) to generate the Si 3N 4-based cantilevers with 3D shapes. In addition, we also successfully fabricated an array of SiO 2 apertures with sub-wavelength sizes as near-field optical probe in order to examine the possible light resonance-tunneling phenomenon. Initially, a (50 × 50) array with a dimension of (5 mm × 5 mm) was fabricated on a Si wafer followed by the V-groove formation using alkaline solution Si bulk micromachining technology. The size of the aperture on top of the pyramidal array was carefully controlled with an opening rate of ∼27 nm/min using HF solution diluted by a factor of 50 using water. The Al thin film was thermally evaporated on the (50 × 50) array pattern for the fabrication of apertures with sub-wavelength sizes.