Arbitrary trapezoidal illumination generation method based on variable slits for optical lithography.

Trapezoidal illumination is an effective approach to improve the integrated uniformity of light intensity in a step-and-scan lithographic system. When different laser pulses are utilized, the optimal trapezoidal illumination varies. In addition, if the coherence factor takes different values, the outline of the trapezoidal illumination varies as well, directly affecting the integrated uniformity of light intensity. To reduce the impact of variations in trapezoidal illumination, a newly designed method for generating arbitrary trapezoidal illuminations using variable slits is proposed. The performance of our method after adjusting the trapezoidal outline for different coherence factors in different illumination modes was verified through optical simulations. Compared to the traditional method, the proposed strategy to realize arbitrary trapezoidal illuminations based on variable slits can obtain the best outlines for illumination, calculated by balancing pulse quantization error and energy losses. Furthermore, when different coherence factors are applied, the outline of the generated trapezoidal illumination can always be maintained by simply moving the blades an appropriate distance.