Fabrication of field emission Si-tip array using reduced submicron masks generated by isotropic etching of mask patterns

Abstract

We have developed a novel technique for fabricating submicron size mask patterns using a wet etching technique of SiO 2 . The overetching of the SiO 2 mask layer would present reduction of the diameters of the mask. The reduction of 2 μm SiO 2 mask down to 0.5 μm diameter will be presented and utilized for the fabrication of nano-size Si-tip array. The 4 inch Si (100) wafer was thermally oxidized and followed by the pattern transfer of original mask patterns on the thermally grown oxide using conventional photographic contact printing method. The coated photoresist (PR) layer with 2 μm thickness was exploited as an etch mask layer for following mask reduction procedure. The mask reduction procedure was performed using 7:1 buffered hydrofluoric acid (BHF). Initially, the patterned PR mask layer was dipped into BHF solution for about 300 seconds in order to remove the SiO 2 layer until the Si substrate would be exposed. Additional ∼ 300 second extra-dipping in BHF solution created considerable overetching and resulted in the smaller diameter than that of the original one. The repetition of the dipping process with precise control provided proper size of mask layers. The shape of the mask layer is found to have smaller diameter at the top and greater diameter at the bottom of the mask layer. Further experiments resulted in the various submicron size SiO 2 mask patterns. The diameters of the reduced masks were measured by scanning electron microscopy (SEM) and observed, for example, to be 0.3, ∼ 0.2 μm on the top and 0.7, 0.5 μm at the bottom, respectively. The isotropic and anisotropic Si reactive ion etching (RIE) was performed with this patterned wafer in order to provide sharp Si tip on the ∼ 2 μm height Si-post arrays with the post diameter down to ∼ 0.2 μm. The sharpening oxidation followed by oxide etching resulted in the successful fabrication of the nanosize Si-tip arrays.