Flexible pupil correction technology for photolithography machine

The resolution limit is one of the key performance specifications of photolithography machine. And off axis illumination is one of the important resolution enhanced technologies. The generally used illumination modes include conventional, annular, quadrupole and dipole. And their performance is expressed by the characteristic parameters. To guarantee these parameters, the pupil correction unit should be adopted. Therefore, it is necessary to study the pupil correction technology for photolithography. In order to achieve flexible pupil correction, a method with correction finger is studied, which could change the regional energy by partial blocking effect. It is available to reduce regional energy by adjusting the width and length of correction finger. As a contrast, a method with grayscale filter is also analyzed. The grayscale filter has uniform transmission distribution in every region. The higher energy region corresponds to lower transmission distribution to achieve the energy balance. The comparison of the two pupil correction methods are analyzed firstly. The analysis results show that the two methods could improve pupil performance significantly and achieve the same correction results. Furthermore, the photolithography performance simulation is implemented. The results indicate that the critical dimension (CD) and H-V bias of the corrected pupils are improved consistently compared with the uncorrected pupils. In the application perspective, the method with correction finger is more flexible because its length could be adjusted to change relative blocked energy. However, the grayscale filter has to be replaced to change its correction effect.