Molecular and polymeric resists for deep UV lithography

Abstract

The fabrication of increasingly smaller feature size for integrated circuits requires advanced lithographic techniques with high resolution. Recently molecular resist materials gain much importance because of their less line edge roughness and high resolution. For the next generation lithography, bilayer resist is promising in the industries due to its high resolution of sub 65 nm. The major advantage of the bilayer resist is that very thin film (~100-200 nm) of photoresist material is used in this process. Because of this reason, even the resist materials with high absorbance can also be used for this purpose. For a resist material, which could be used as a bilayer resist, minimum of 10 wt % of silicon content is one of the major requirements. Polyhedral oligomeric silsesquioxane (POSS) was chosen as the ‘cage’ of the molecular resist to give enough silicon content for the material to be used as a top layer of the bilayer resist system. Moreover, the silsesquioxanes have very low absorbance in the 193 nm and 157 nm wavelengths. Also the silicon content gave good oxygen plasma etch resistance. To give good film-formability, we introduced cholate derivatives. The alicyclic-rich cholate derivatives give good etch resistance also. Various functional derivatives of cholic acid and their corresponding POSS derivatives were synthesized. The thermal properties and lithographic properties of the synthesized molecular resists were evaluated. Among the molecular resists, TBC-POSS and EC-POSS were evaluated for lithographic performance as negative tone resists. These two molecular resist materials show a resolution of 2.5 μm. ATBC-POSS was synthesized to be used as a positive tone resist and it was also showing a resolution of 2.5 μm. Photobleachable molecular resist, CDEOPE-POSS, was synthesized and its lithographic performance was evaluated. This CDEOPE-POSS was found to possess moderate thermal stability, good film formability. Also CDEOPE-POSS was showing positive t...