High-resolution tri-level process by downstream-microwave rf-biased etching

In this paper we discuss some properties of a novel dry etching system for high resolution transfer of e-beam generated pattern for a viable submicron lithography. In order to achieve pattern transfer by an e-beam lithography a tn-layer system has been used. The submicron pattern which has been generated in a 300 nm PBS-layer (imaging layer) was transfered into a 300 nm anorganic intermediate layer (Si3N4) by RIE with a CHF3-plasma. The underlayer of 1 micron polyimid was etched in a microwave downstream RF-biased etching system developed by Plasma Technology Ltd (UK). E-beam lithography generated structures of 75 nm size with very low image size bias were etched in Si3N4. After patterning in the polyimid layer structures with very high aspect ratio (10) could be achieved. It was observed that anisotropy is enhanced by crack-products that originate from the microwave downstream oxygen plasma and the CHF3+CH4 mixture in the space between the parallel-plate electrodes.