Extension of Practical K1 Limit in EUV Lithography

Sub 0.3k1 regime has been widely adopted for high volume manufacturing (HVM) of optical lithography due to various resolution enhancement technologies (RETs). It is not certain when such low kl is feasible in EUV, though most technologies are available in EUV also. In this paper, experimental results on patterning performance of line space (L/S) and contact hole (C/H) in EUV lithography will be presented. First, practical kl value with 0.33NA EUV lithography was investigated through experiment by using NXE3300 EUV tool. Patterning limit, as defined by local critical dimension uniformity (LCDU) for C/H array pattern were measured with respect to various design rules. It was evaluated that the effect of off axis illumination (OAI) mode with various illumination conditions to improve the patterning performance and to reduce kl limit. Then the experimental results of LCDU were compared with normalized image log slope (NILS) values from simulation. EUV source mask optimization (SMO) technologies to increase the NILS with FlexPupil option of EUV scanner were evaluated and possibility of further improvement was also discussed.