Optimization of Plasma Polymerized Methylsilane process for 248 and 193 nm lithography applications

Abstract

Optical lithography continues to be investigated as the most interesting approach for achieving sub 0.18 μm design rules. Currently an important effort is going on for single layer resist optimization at 193 nm, while some work is also performed to investigate the potential of top surface imaging schemes. A CVD photoresist currently known as Plasma Polymerized Methylsilane (PPMS) can provide a completely dry photolithographic process, useful at 248 and 193 nm. Negative tone patterns can be developed using Cl 2 -based plasma development allowing the resulting PPMSO patterns to be used as SiO 2 patterns. Up to now, PPMS film deposition and development have been achieved using single step recipes. A single step CVD deposition process provides a film whose composition is identical through out the all thickness whereas the photo-oxidation process induces a gradient of oxidation in the PPMSO film. In this work, we show that a significant improvement of the development can be achieved using a multi-step etching recipe which takes into account the oxidation gradient (and therefore etching resistance) throughout the PPMSO film thickness. Similarly, a significant improvement is performed using a two step CVD recipe. A very photosensitive PPMS film can be deposited on top of a non photosensitive PPMS film, allowing the oxygen incorporation to be limited to the photosensitive film, and therefore limiting the partial oxidation between dense lines in the top photosensitive layer. Comparison between single and bi-layer CVD processes and single and multi-step etching recipes will be presented at 248 nm.