Proceedings Article | 5 May 2017
KEYWORDS: Nanoimprint lithography, Photomasks, Stochastic processes, Diffraction, Extreme ultraviolet lithography, Optical lithography, Lithographic illumination, Scanners, Immersion lithography, Stray light, Extreme ultraviolet, Calibration, Fiber optic illuminators, Contamination
As we presented in the last conference, it is much difficult to get down the k1 limit of EUV lithography compared to that of optical lithography especially recent immersion lithography. Even though current 0.33NA NXE3300 tool has enhanced aberration characteristics and variable illumination mode than its predecessor, ADT and NXE3100, still there are limitations related with resolution capability of EUV lithography. First of all, photon shot noise and immature resist performances play an important role in patterning of very fine patterns. As already known, low sensitivity resists have been widely used to reduce shot noise. However, when considering productivity in EUV lithography, high sensitivity resists are inevitable, so it is necessary to increase image contrast by reducing scanner blur like aberration, M3D, stray light et al. We have investigated the impact of aberration and limitation in illumination pupil fill ratio in EUV. In particular, the aberration sensitivity is different by the illumination conditions, this was intensified when using the particular pupil. Because the lens calibration is conducted with standard illumination condition in NXE3300, it is necessary to consider different aberration sensitivity in accordance with pattern and used pupil condition in EUV lithography. To ensure the process margin of tech node close to limit, a flexpupil with low pupil fill ratio (PFR) than 0.2 were required. Hence in order to avoid through-put loss at this condition, the new concept of the illuminator design is required without light loss. Contamination of collector mirror can affect the patterning also. We will also report about the patterning effect of pupil deformation by degraded collector in low PFR condition.
