Alternating phase-shifting mask with reduced aberration sensitivity: lithography considerations

Abstract

Aberration sensitivity of alternating phase-shifting masks (PSMs) can be reduced by taking advantage of the trim exposure. Rather than a single phase region bordering each edge of a line, the enhanced alternating PSM technique uses multiple phase regions. The number of phase regions and their widths can be optimized for overall process tolerance including aberration sensitivity and exposure latitude. For exposure with a wavelength of 248 nm and a numerical aperture of 0.68, the optimal number of phase regions is two, with widths between 100 nm and 200 nm. These auxiliary phase regions do not affect the final pattern if a light-field trim mask is used. No extra processing step is necessary. With the enhanced alternating PSM technique, isolated lines of average dimension as small as 36 nm can be delineated using 248 urn lithography with a 3o- linewidth control of 13.4 urn. The mean critical dimension of 36 urn corresponds to k1 = 0.1.