Objective Photolithography is a crucial technology in integrated circuit manufacturing. With the critical dimension of photolithography becoming smaller, integrated circuits are becoming more and more compact. For this reason, a variety of resolution enhancement techniques, such as off-axis illumination, have been proposed. The influence of pupil performance on the quality of exposure pattern and overlay accuracy is prominent with the application of this technology. Off-axis illumination modes are generated by the illumination system of the photolithography machine. The generally used illumination modes include conventional, annular, 0° quadrupole (Q₀), 45° quadrupole (Q₄₅), dipole in X direction (D_X), and dipole in Y direction (D_Y). In the working process of the photolithography machine, the lenses are exposed to deep ultraviolet light. Thus, the transmittance of their optical materials and coating films gradually deteriorate, which may affect the pupil performance. It is necessary to adopt the pupil correction technology for illumination system to improve the pupil performance.

Recently, various pupil correction methods or devices have been proposed. However, these methods have not produced a specific correction process. Energy loss during pupil correction affects production rate of photolithography machine. To solve these problems, a high energy efficiency pupil correction method is proposed in this paper. This method can improve the performance of a corrected pupil while energy efficiency is increased maximally. As a result, production rate of photolithography machine is improved while ensuring quality of exposure pattern.

Methods The main goal of the pupil correction method is to correct an unqualified pupil to a full-field pupil correction target. In traditional correction method, the theoretical limit (zero) is set as the target. However, the reference energy value for the correction method proposed in this paper is changed. The reference energy value is selected by considering the process and assembly errors of the pupil corrector. The deviations of pupil correction results at different fields of view are also considered. In this way, the performance of the corrected pupil can meet the requirements while the energy loss during the correction is minimized. Furthermore, considering the correction requirements of different illumination modes, a pupil correction plate suitable for many illumination modes is designed by the multi-ring partition method.

To verify the feasibility of this method, a pupil correction analysis is conducted. The pupils, including three annular illumination modes and three different quadrupole illumination modes, are measured in the illumination system of a KrF step-and-scan photolithography machine with NA=0.82. These annular (quadrupole) illumination modes are corrected by a correction plate, for which the transmittances are calculated by the multi-ring partition pupil correction method. The pupils of these annular (quadrupole) illumination modes are divided into three rings ([0, 0.5), [0.5, 0.75), and [0.75, 1]) along the radial direction. According to the manufacturing and assembling errors of the pupil corrector, Δ₁ is set to 0.3%. Δ₂ is set to 0.2% for the difference of pupil correction results at different fields of view.

Results and Discussions For a comparison study, the traditional correction method and the method proposed in this paper (Fig. 6) are used to correct the measured three annular (quadrupole) illumination modes. The correction results of the two correction methods can meet the full-field pupil correction target (Fig. 9 and Fig. 10). The transmittance of the correction plate designed by the multi-ring partition pupil correction method is significantly improved (Table 2 and Table 4), and is applicable to the three annular (quadrupole) illumination modes. Compared with the traditional correction method, the multi-ring partition pupil correction method can reduce the maximum energy loss after correction from 4.54%, 5.54%, and 5.52% to 1.98%, 2.06%, and 2.21% for the three annular illumination modes (Table 3), and the maximum energy loss after correction from 3.06% to 0.93% for the quadrupole illumination mode Q₃ (Table 5).

Conclusions In this paper, the high-energy efficiency pupil correction method based on multi-ring partition is proposed. The multi-ring partition method is adopted, and the selection method of the reference energy value is changed. In this way, one pupil correction plate is suitable for several illumination modes. The energy loss caused by pupil correction can be reduced, and the performance of the corrected pupil meets the requirements. The results of pupil correction indicate that the maximum energy loss of annular and quadrupole corrected pupils can be reduced from 5.54% and 3.06% to 2.06% and 0.93% respectively, in comparison with the traditional pupil correction method. This method is of great significance to improve the production rate of the photolithography machine.