晶圆定位标记光学成像的自适应聚焦评价
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Adaptive focusing evaluation algorithm for optical imaging of wafer positioning marks
YANG Jin ， ZHANG Hangying 1，2，3* ，MENG Kai 1，2，3 ， LOU Peihuang1 （1. College ofMechanical and Electrical Engineering， Nanjing University of Aeronautics and Astronautics，Nanjing 2lOol6，China; 2. National Key Laboratory ofMicrowave Photonics，Nanjing 2lool6，China; 3.Key Laboratory of Aerospace Integrated Circuits and Microsystem， Ministry of Industry and Information Technology，Nanjing 21Oo16，China） * Corresponding author， E -mail： markzhang@nuaa. edu. cn
Abstract：The wafer positioning mark is characterized by its small size and diverse shapes. Traditional fo cus evaluation functions exhibit limitations，including poor stability and low sensitivity during computation. To address these challnges，an adaptive focus evaluation algorithm based on multi-directional gradient variance was proposed in this paper. Initially，feature edge pixel points of the mark image were adap tively sampled and extracted. Subsequently，a multi-directional gradient function，tailored for wafer positioning marks，was developed by integrating the Brenner function and the Roberts function.The sampled pixel points were then evaluated to derive the initial focus evaluation function value.Finally，the variance of the initial focus evaluation function values across the image set was computed，thereby enhancing the robustness of the function against noise and yielding the final focus evaluation function value.Experimental results indicate that the proposed algorithm reduces fluctuations in flat areas by 61.49% and enhances sensitivity by a factor of 2.56 compared to traditional evaluation algorithms. This innovative approach proo vides a superior calculation strategy for achieving high-sensitivity automatic focusing of wafer positioning marks and other micro-nano mark images characterized by distinct edge feature structures.
Key words： imaging system; image quality assessment； fringe analysis； auto-focusing； focus function
1引言
晶圆的高精定位与对准是半导体先进制造与封装工艺的必然需求，其主流技术往往依赖于对各类晶圆定位标记的光学成像与处理，其中，自动聚焦技术是获取高质量标记图像的关键[1]。（剩余14128字）