The fluctuation of high-order aberration's sensitivity in ArF immersion lithography

Abstract

To achieve smaller and smaller feature sizes in the semiconductor industry, extreme demands are placed on the lithographic optics, specifically the projection lens. Higher numerical aperture (NA) is adopted to obtain higher resolution. However, higher NA scales the impact of geometrical aberrations on lithography performance. Thus, a detailed understanding of the effect of geometrical aberrations on the lithographic process is indispensable. In this paper, we consider some of the surprising phenomena that occur at such high NA. We discuss the impact of flare, polarization state and MSD on higher-order aberration's sensitivity using ArF immersion lithography to print elbow pattern exposed features in photo resist on 65nm node. The higher-order aberration's sensitivity is analyzed when the annular illumination (NA=1.2, sigma out=0.76, sigma in=0.52) is employed. The 3rd, 5th, 7th, 9th geometrical aberrations according to the Fringe convention are discussed. The sensitivities to individual geometrical aberrations are calculated by introducing a fixed amount of aberration for each Zernike coefficient with all other aberrations being zero. On 65nm node, with annular illumination, the high-order aberration's sensitivity is calculated respectively according to the variation of flare, polarization state, and MSD. The results show that flare, polarization state, and MSD can contribute to the high-order aberration's sensitivity. The aberration sensitivities are increasing with the MSD and flare's value rising. The aberration sensitivities can be decreased when the horizontal linear polarized light is adopted. The merits of adjusting polarization state to choke back the aberration sensitivities are presented.