Active lens for thermal aberration compensation in lithography lens

High laser absorption and strong resolution enhancement technology make thermal aberration control of lithography lenses more challenging. We present an active lens that uses four bellows actuators to generate astigmatism (Z5) on the lens surface. The apparatus utilizes optical path difference to compensate the system wavefront. In order to assess the specifications of the compensator, the finite element method and experimental analyses are carried out to obtain and validate the general properties of the apparatus. The results show that the Z5 deformation quantity of lens's upper surface exceeds 600 nm; further, Z5 coefficient accuracy is better than +/- 1 nm. The apparatus can be an efficient compensator for thermal aberration compensation, especially aberration caused by the dipole illumination. (C) 2018 Optical Society of America