Fabrication of sub-10nm Si-tip array coated with Si 3N 4 thin film for potential NSOM and liquid metal ion source applications

Abstract

A nanosize Si tip array for various purposes has been fabricated on the n-type (100) low resistive (0.05 ohm-cm) Si wafers using electron beam direct writing method. The Si pillars with diameter less than 0.1 μm can be potentially utilized for a near field optical microscope tip or a liquid metal ion source application. SiO 2 layers with different thicknesses of 500nm and 1.5μm were initially thermally grown and followed by the fabrication of the 500nm dot array pattern with an electron beam(EB) resist SAL60. The oxide etch-mask layers with two different thicknesses of 500nm and 1.5μm were patterned with a magnetic field enhanced reactive ion etcher. The 500nm EB resist layer (SAL601) was used as an etch-mask for pattern formation during oxide etching. The complete removal of the EB resist and the erosion of the 1.5μm thick oxide dot-patterns resulted from the ∼270 second etching period was observed. On the other hand, no erosion of the oxide mask with the EB resist remaining was found after 90 sec. oxide etching by scanning electron microscope. The two step RIE processes on the sample with a 500nm oxide etch mask were carried out with an isotropic SF 6 etching followed by the anisotropic (Cl 2 + He) etching in order to fabricate tall Si-pillar arrays with ∼4 μm height. Finally, the 35nm Si 3N 4 coated Si-tip array using a low pressure chemical vapor deposition (LPCVD) was fabricated. The LPCVD Si 3N 4 coated Si-tip array will be micromachined into sub-100nm metal aperture for the potential near field optical sensor or into a sub-10nm Si or Si 3N 4 aperture for liquid metal ion source.