Fabrication of High-Verticality Grating Nanostructures Using Twice-Deposited Etching Mask Layers

Abstract

To study the influence of twice-deposited mask layers on the verticality of side wall and the aspect ratios of silicon-based nanostructures, the performance of focused ion beam (FIB) and CF4-based inductive coupled plasma reactive ion etching (ICP-RIE) processes was realized. The first etching mask of chromium (Cr) was deposited by radiofrequency (RF) magnetron sputtering as the conductive and etching barrier layers. Next, the Cr layer was directly patterned by a dual-beam FIB system to form nanograting patterns. Thereafter, a secondary mask layer of oxide (SiO2) with a thickness of 50 nm was deposited by sputtering. In order to study the influence of various deep etching parameters on verticality and aspect ratios, we examined argon flow rates, coil powers, platen powers, and chamber pressures. The SiO2 barrier layer on the side wall could be retained to maintain a high verticality contour and reduce the line-width shrinking ratio to surmount over etching during the use of fluorine-based gas. The residual Cr and SiO2 layers were dissolved and removed using a wet etching process consisting of a Cr-etching solution (CR-7). Measurements show that the verticality and aspect ratios of the grating nanostructures were 92.1° and 5.63, respectively.