Abstract
The patterning performance of 3Xnm half pitch contact hole for 2Xnm DRAM was achieved from NXE3100, EUV pre-production tool last year. The local CD uniformity of EUV was comparable to that of immersion DPT (Double Patterning Technology), so the EUV patterning performance of 3Xnm half pitch is ready for mass production. But productivity progress of EUV source power is behind the plan and EUV shot noise is still problematic, so EUV resist process need to be improved for sub 3Xnm half pitch contact hole patterning. And also the patterning of sub 20nm half pitch line and space was gathered from NXE3100 but LWR and collapse are critical issues to be improved. Recently we introduced negative tone development (NTD) in immersion lithography for mass production and achieved excellent patterning performance compared to positive tone development (PTD) because negative tone development (NTD) showed better optical contrast on contact hole patterning and swelling-free property of resist film against developer. In this paper, we describe necessity of negative tone development (NTD) on EUV, optimization of mask cell size, upgrade status of resist and resolution limit between positive (PTD) and negative tone development (NTD).
