Apparatus and its principle for thermal aberration compensation.

Abstract

Thermal aberrations caused by absorption of laser beams degrade the image quality of exposure tools during the working process. Many compensators, such as lens movement or lens deformation, are used to compensate for low-order thermal aberrations of optical systems. In this paper, an apparatus with higher-order aberration correction capability is presented. The main principle of the apparatus is to actively heat and cool the lens near the pupil to generate a desired temperature profile to compensate for thermal aberrations. We first introduce the basic concept of the apparatus. Then we establish an analytical model to describe the lens temperature of the apparatus based on its working principle and demonstrate its compensation capability. Finally, an algorithm for dynamic thermal aberrations compensation is proposed to overcome the time lag effects of a thermally controlled lens.