Micromachined Si3N4-Tip on cantilever for parallel SFM and NSOM applications

Micromachining of a nanoscale Si3N4 tip for near field scanning optical mic roscopy (NSOM) and scanning force microscopy(SFM) has been described. The t apered optical metal-coated fiber is generally used to provide a sub-wavele ngth sized aperture on tip. Several micromachining methods have been perfor med in order to have a metal aperture with radius less than lambda/2. Apert ures provided with less than lambda/2 and hollow tips would provide a suita ble probe for both NSOM and SFM. A Si3N4 tip coated with thin metal film wi ll meet these requirements. The Si tip have been initially fabricated using reactive ion etching (RIE). The SiO2 etch masks with 10 mu m and 0.5 mu m were patterned followed by Si etching. The etched Si post was at least 3 mu m tall and the radius of the tip was found to be 30nm and similar to 10nm depending on the fabrication methods. A Si3N4 thin film was deposited on th e fabricated Si -tip using a low pressure chemical vapor deposition techniq ue in order to provide a capability for atomic force microscope. A Cr metal film was deposited using thermal evaporator. The thick photoresist film wa s coated using two-stage methods in order to cover the tall 5 mu m tip. The PR film was carefully etched to have a metal aperture size with less than lambda/2.