Achievement of sub nanometer reproducibility in line scale measurements with the nanometer comparator

Abstract

Due to the discussed introduction of double patterning techniques the overlay and registration metrology requirements in advanced lithography will drastically increase so that reference metrology tools need to be developed further to be able to follow the resulting tightening of the specifications. Therefore, the PTB further develops the Nanometer Comparator, a 1D vacuum comparator, which already has proven its performance during the measurements of incremental encoders. The implementation of the angular control loops decreases the angle deviations of the measurement carriages down to 0.15 μrad, which led to a reduction of the contribution of the Abbe errors to the measurement uncertainty to insignificant levels. Changes in the illumination and alignment of its optical microscope resulted in an improved defocus behaviour, which consecutively reduced the reproducibility (1 σ) of measurements of high quality scales in the order of 1 nm. Therefore an expanded measurement uncertainty of below 5 nm has been achieved.