Contrast in the evanescent near field of lambda/20 period gratings for photolithography

Light propagation through gratings with periods as small, as lambda/20 is i nvestigated computationally by use of the multiple multipole method in two dimensions. High image contrast: is evident close to the grating. Strong ev anescent decay of the high spatial frequency components is observed with th e region of high contrast shrinking linearly as the period of the grating i s decreased. Simulations were performed for TE and TM polarizations with th e TM polarization providing the dominant contrast compared with TE, which i s strongly attenuated owing to the polarizing effect of the gratings. These results show good promise for optical contact lithography in the evanescen t near field of a shadow mask to attain feature sizes smaller than lambda/2 0. (C) 2000 Optical Society of America OCIS codes: 050.1940, 050.1950, 220. 3740, 220.4000, 220.4610, 260.5430.