Exploring acidic functionalities in the design and development of high performance 193nm photoresist polymers

Abstract

The combination of immersion lithography and reticle enhancement techniques (RETs) has extended 193nm lithography into the 45nm node and possibly beyond. In order to fulfill the tight pitch and small critical dimension requirements of these future technology nodes, the performance of 193nm resist materials needs to further improve. In this paper, we have systematically studied a variety of acidic functionalities in an effort to improve the dissolution properties of 193nm resists. The hexafluoroalcohol (HFA) and fluorosulfonamide (FSM) are found to be most effective in eliminating the swelling behavior associated with typical 193nm methacrylate resists. The HFA and FSM groups are highly transparent at 193nm. High performance 193nm resists are developed with the HFA and FSM acidic groups. Compared to the HFA group, the trifluoromethyl sulfonamide (TFSM) functionality has a lower pKa value and contains less fluorine atoms. Polymers containing the TFSM functionality have exhibited improved dissolution properties and better etch resistance than their HFA counterparts. Resists based on the FSM-containing polymers have shown superior lithographic performance for line, trench and contact hole levels under the 45nm node exposure conditions. In addition, FSM resists have also demonstrated excellent bright field and dark field compatibility and thereby make it possible to use one resist for both bright field and dark field level applications. Finally, to alleviate the adverse impact of the fluorine content in the etch resistance of the 193nm resists, we have also evaluated a non-fluorinated acidic functional alternative - naphthol. ©2007TAPJ.