Fabrication of a nanosize metal aperture for a near field scanning optical microscopy sensor using photoresist removal and sputtering techniques

Micromachining of a nanoscale Si3N4 tip for near field scanning optical microscopy (NSOM) and scanning force microscopy (SFM) has been described. The tapered optical metal-coated fiber is generally used to provide a subwavelength sized aperture on the tip. Several micromachining methods have been performed in order to have a metal aperture with a radius less than lambda/2. Apertures provided with less than lambda/2 and hollow tips would provide a suitable probe for both NSOM and SFM. A Si3N4 tip coated with a thin metal film will meet these requirements. The Si tip has been initially fabricated using reactive ion etching. The SiO2 etch masks with 10 and 2 mu m were patterned followed by Si etching. The etched Si post was at least 3 mu m tall and the radii of the tips were found to be 30 and 10 nm depending on the fabrication methods. A Si3N4 thin film was deposited on the fabricated Si tip using a low pressure chemical vapor deposition technique in order to provide a capability for an atomic force microscope. A 30 or 60 nm Cr metal film was deposited using an electron beam evaporator. The thick photoresist (PR) film was coated using a two-stage method in order to cover the tall Si tip. The PR film was carefully etched to have a metal aperture size with less than lambda/2. The removal of the Cr metal at the top of the Si tip has been performed using a Ne sputtering technique. The radius of the sputtered tip has been observed to be similar to 80 nm after 2 h sputter etching. (C) 2000 American Vacuum Society. [S0734-2101(00)17804-2].