Impact of the absorber thickness variation on the imaging performance of ArF immersion lithography

摘要

As the feature sizes on the wafer continue to shrink, the dimensions on the mask also scale down, which makes the mask topography more important. The impact of the absorber thickness of a Binary Intensity Mask (BIM) and an Alternating Aperture Phase-Shifting Mask (AAPSM) on the imaging performance of ArF lithography is investigated by using a rigorous electro-magnetic field simulator, an NA0.85 immersion scanner, and an NA0.93 conventional scanner. The simulation at NA0.85 dipole illumination for BIM shows that the mask-error enhancement factor (MEEF) for 130-nm-pitch lines and spaces increases to 3.1 from 2.5 by reducing the absorber thickness from 104 nm to 56 nm. Lower aerial-image contrast at the thinner absorber, which causes the larger MEEF, is attributed to the lower interference efficiency due to increase of transverse-magnetic component and decrease of the intensity balance between Oth- and 1 storder diffracted light. In AAPSM, the image-placement errors caused by intensity imbalance between 0 and π phase-shifting spaces are influenced by the absorber thickness. It was demonstrated by the increase of dose sensitivity from 5.2 to 6.5 nm/(mJ/cm~2) and line edge roughness increase from 7.1 to 8.2 nm of 150-nm-pitch lines and spaces made by using immersion process that thinning the BIM absorber from 103 to 59 nm degraded the aerial image of NA0.85 annular illumination. The conventional dry exposures by using NA0.93 dipole lithography supported the image degradation due to thinning the BIM absorber by showing that the line edge roughness of 125-nm-pitch lines and spaces increased by 1.2 nm using un-polarized illumination. The aerial-image contrast of the thicker absorber keeps better up to NA1.40, which suggests that we need to balance the merits and demerits of using the thinner absorber by giving attention to the mask topography effects.