Electromagnetic modeling of phase - Shifting contact lithography by broadband ultraviolet illumination

Experiments have recently indicated that phase-shifting contact lithography (PSCL) could provide sub-wave-length resolution by using broadband ultraviolet sources of illumination. Electromagnetic modeling of PSCL is performed to characterize absorption features of the photoresist layer one of whose faces is in contact with a quartz binary phase-shift mask. The electromagnetic field of the broadband ultraviolet source is represented as a spectrum of normally incident plane waves, and a rigorous coupled-wave analysis is performed to determine spectral absorption in the photoresist layer. The specific absorption rate in the photoresist layer is calculated and examined in relation to the geometric parameters of experimental samples. As illustrated by the modeling, columnar features are formed in the photoresist layer due to the localization of absorption. Feature resolution and profile are noticeably affected by the phase-shift mask's thickness. Ideally, the feature linewidth can be less than 200 nm for transverse-magnetic mode illumination.