고 개구수 극자외선 노광 기술용 위상 변위 흡수체 구조의 설계

Abstract

Increasing the numerical aperture (NA) of an optical system is considered as a resolution enhancing technology. In extreme ultraviolet (EUV) lithography, however, it is hard to use optics with a NA value higher than 0.45 without interference between the incident and reflected light cones at the mask. To avoid this, the incident angle must be increased from 6° to 9°, but the resulting imbalance in reflected EUV light with the different incidence angle, in addition to the mask shadowing effect, can deteriorate the imaging performance of the mask. In this paper, a phase-shifting absorber stack is proposed for high-NA EUVL applications. Aerial image simulation was performed at 0.45NA, an incident angle of 9° and 6× demagnification to compare the imaging properties of a TaBN binary intensity mask with the new TaBN/Mo phase shift mask. The mask 3D effect was mitigated by adopting the phase shifting absorber stack. As a result, image contrast and normalized image log-slope were improved and horizontal-vertical critical dimension bias was significantly decreased.