We demonstrate that phase masks can be made from modified fused silica with a period of 180 nm and similar to8 mm long by using immersion interference photolithography. The fabrication process of the phase mask is optimized to generate the largest intensity ratio of diffracted I to 0 order. The phase mask is demonstrated to produce a photoresist pattern with halved period (90 nm) when illuminated with a laser of 157 nm wavelength. The phase masks are also capable of generating two-dimensional patterns of holes and dots and serving as molds for imprint applications. (C) 2003 American Vacuum Society.