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Published on: October 11, 2016
Measurement of large low-order aberrations by using a series of through-focus Ronchigrams
Hisanao Akima1, Takaho Yoshida2
1Central Research Laboratory, Hitachi, Ltd, 1-280 Higashi-Koigakubo, Kokubunji-shi, Tokyo 185-8601, Japan Research Institute of Electrical Communication, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan.
Abstract:
A method for measuring large aberrations up to second order (defocus, 2-fold astigmatism and axial coma), which uses a through-focus series of Ronchigrams, is proposed. The method is based on the principle that line-focus conditions in Ronchigrams can be locally detected and low-order aberrations can thereby be measured. The proposed method provides auto-tuning of large low-order aberration; in particular, iterative aberration measurement and correction reduce low-order aberrations from several thousand nanometers to less than a few hundred nanometers, which can be handled by conventional fine-aberration tuning methods.
