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

Highly efficient atomic force microscopy (AFM) cantilevers and an near-field scanning optical microscopy (NSOM) aperture array were fabricated using the functional Si3N4 and SiO2 thin films for the micro electro mechanical systems (MEMS) and NEMS applications. In order to generate the cantilevers and array, a silicon nitride (Si3N4) thin film with a stress below 100 MPa was deposited using NH3 and SiCl2H2 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 Si3N4 thin films. Photolithography and magnetically enhanced reactive ion etching (MERIE) techniques were employed for patterning the Si3N4 thin films and selective bulk etching of Si was carried out using a strong alkaline solution of tetramethylammoniumhyroxide (TMAH) to generate the Si3N4-based cantilevers with 3D shapes. In addition, we also successfully fabricated an array of SiO2 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.