By Vincent Wiaux, Eric Hendrickx, Geert Vandenberghe, IMEC, Leuven, Belgium
OVERVIEW 193nm immersion lithography has become the industry’s prime choice for printing critical layers in 45nm node processes. In a research facility, through-pitch imaging solutions for 65nm lines and 80nm contact holes were explored using a preproduction 193nm immersion scanner with a numerical aperture (NA) of 0.85. Imaging solutions for lines down to a pitch of 140nm have been obtained, and 170nm pitch contact holes have been resolved with an acceptable process, together with isolated contact holes. Current resist process and mask critical dimension (CD) uniformity have been identified as the main imaging constraints.
After just a few years of development, immersion lithography has now become the leading exposure technology for printing the critical layers at the 45nm process node. The semiconductor industry has recognized the merits of replacing water between the final imaging lens and the wafer. This immersion concept has a twofold effect. First, it allows for lens designs with higher numerical aperture (NA) in comparison with its dry counterpart, resulting in enhanced resolution. Secondly, for a given NA, a significant depth-of-focus (DOF) improvement can be obtained. Earlier investigations already confirmed the expected superior imaging performance of 193nm immersion lithography. Experimental 0.75NA ArF dry imaging data have been compared to those of a 0.75NA ArF immersion scanner, using optimized illumination and mask conditions. A substantial gain in DOF at a wide range of pitches was seen when printing lines and contact holes with the immersion scanner .
Julie MacShane, Managing Editor, SST at email: [email protected]