Development of direct deep reactive ion etching process using laser interference lithographed etch barrier without intermediate layer

Laser interference lithography (LIL) is a technique that allows maskless patterning of large areal periodic nano/micro structures. The LIL pattern is often used as an etch barrier to pattern SiO2 intermediate layer in the fabrication process of high aspect ratio silicon nano/micro structures by deep reactive ion etching process (DRIE) with SiO2 etch barrier. In this study, a method to fabricate high aspect ratio nanograting structures by direct DRIE process of silicon substrate using LIL pattern without intermediate layer was developed as a simple and cost-effective fabrication process. To fabricate high aspect ratio silicon nanograting with high pattern fidelity, a simulation method to predict the cross sectional profile of photoresist (PR) pattern after exposure and development processes was investigated, and the LIL processing conditions were selected to obtain optimized cross sectional profile of PR pattern without residual layer based on the simulation results. To minimize the side wall defects during the DRIE process due to the deterioration of LIL pattern etch barrier, the processing conditions of DRIE process including etching gas, etching gas ratio, passivation time and power were optimized. Finally, a silicon nanograting with a grating pitch of 780nm and height of 2.42 μm (aspect ratio: 6) was fabricated via the developed direct DRIE process with LIL pattern.