摘要
为了实现极紫外光刻光源驱动激光光斑位置的高精度、宽范围、快响应检测,设计了一种高重复频率窄脉冲信号多通道同步采集处理电路,并提出了基于高斯光斑模型的二级扩展误差补偿算法,可以为极紫外光刻光源驱动激光指向控制提供高精度反馈调节量。首先,介绍了光斑位置检测系统的结构组成与四象限探测器的基本检测原理;然后在考虑探测器半径、光斑半径以及沟道宽度等因素影响的前提下对误差补偿函数进行改进,并对改进的二阶扩展误差补偿算法进行了仿真分析;接着介绍了用于高重复频率窄脉宽信号的多通道同步高速采集电路;最后搭建了实验平台,对改进的算法进行验证。实验结果显示,二阶扩展误差补偿算法的均方根误差为0.0042,最大绝对误差为0.0092 mm,绝对误差的平均值为0.0034 mm;与二阶误差补偿算法相比,二阶扩展误差补偿算法的均方根误差、最大绝对误差和绝对误差的平均值分别降低了83.06%、85.28%和83.50%。表明二阶扩展误差补偿算法与二阶误差补偿算法相比,具有明显的优越性及实用性,在扩展了光斑位置检测范围的同时,光斑位置的检测精度也得到了明显的提升,解决了传统算法无法兼顾计算速度与检测精度的问题。
Objective Currently,the laser induced plasma(LPP)technology is the best method to obtain high quality extreme ultraviolet(EUV)light source,whereby a high-power,high-frequency,short-pulse CO_2 laser under the main oscillation power amplification technology is used to bombard a droplet tin target to obtain high-quality extreme ultraviolet signals.In an EUV lithography light source system,the laser beam direction is significantly affected by the cascade when the laser beam passes through the four-stage amplification system.During the amplification process,the optical components in the optical path between the amplifiers feature different thermal distortions under different laser powers;all the four-stage amplifiers used are high-power laser amplifiers,and the vibrations caused by the cooling device during operation are unavoidable.These factors cause the center of the laser beam to deviate from the optical axis and affect the EUV conversion efficiency.Therefore,for EUV lithography light source systems,the further research on beam pointing stability is necessary to achieve a certain EUV conversion efficiency.At present,four-quadrant detectors are widely used in high-precision laser measurements owing to their fast response,high position resolution,high measurement accuracy,and simple data processing.However,a high-precision spot location algorithm based on a four-quadrant detector is generally complex.Thus,during high-repetition-frequency pulse signal detection,the real-time requirements of spot location calculations cannot be met.Therefore,it is necessary to develop a new algorithm that considers the accuracy of spot location detection and its real-time performance.Methods In this study,we first obtain the four-quadrant detector output signal under the Gaussian distribution model for spot energy distribution and subsequently calculate the initial solution for the spot position under the influence of the detector radius and dead zone using the normalization and difference algorithm.The initial spot position solution is a transcendental equation,and its analytical solution cannot be derived using a mathematical method.The expression for the actual position of the spot centroid is then obtained using the approximate decomposition method,which compensates for the influence of the spot radius,detector radius,and dead zone width on the actual position of the spot centroid.Finally,to improve the solution accuracy,a correction factor is established,and the error characteristics of the correction factor are used to correct the actual position of the spot.This can help improve the spot position detection accuracy and detection range,without increasing the complexity of the algorithm.According to the detection principle of the four-quadrant detector,electrical signals from the four quadrants of the detector should be obtained simultaneously;if the acquisition of the electrical signals from each quadrant is not synchronized,the accuracy of the spot position solution is affected.Therefore,a multi-channel synchronous acquisition and processing circuit is designed for the acquisition of detector output signals,to ensure the accuracy and real-time acquisition of the signals.Results and Discussions According to the analysis of the simulation results,the root mean square error of the secondorder error compensation algorithm is 0.0115;after improvement,the root mean square error is reduced to 0.003,which is 73.91%lower.The maximum error of the second-order error compensation algorithm is 0.0372 mm;after improvement,the maximum error is reduced to 0.0076 mm,which is 79.56%lower,and the absolute error is less than0.005 mm.The detection range of the spot position is expanded from-0.12 mm≤x≤0.12 mm to-0.59 mm≤x≤0.59 mm,which is approximately five times larger.The average absolute error value in the absolute error range of less than 0.005 mm is reduced from 0.0025 mm to 0.0019 mm,which is approximately 24%lower(Fig.4).The spot position detection results are analyzed.It is shown that the root mean square error of the second-order error compensation algorithm is 0.0248,and the root mean square error of the second-order extended error compensation algorithm is0.0042,i.e.,a reduction of 83.06%.The maximum absolute error of the second-order error compensation algorithm is0.0625 mm,and the maximum absolute error of the second-order extended error compensation algorithm is 0.0092 mm,i.e.,a reduction of 85.28%.The average absolute error of the second-order error compensation algorithm is 0.0206 mm,and the average absolute error of the second-order extended error compensation algorithm is 0.0034 mm,a reduction of approximately 83.50%.Notably,the spot position detection accuracy is better than 19μrad in the detection range of-0.5 mm≤x≤0.5 mm(Fig.8).Conclusions The simulation analysis and experimental results reveal that the detection range of the second-order extended error compensation algorithm is considerably larger than that of the second-order error compensation algorithm under the same detection accuracy.Compared with the traditional polynomial algorithm,the second-order extended error compensation algorithm offers clear advantages and practicability,significantly improving the detection accuracy of the spot position over a wide detection range.Based on the abovementioned discussion,the results of this work are expected to help realize the wide-range,real-time,and high-precision detection of the spot position for an ultraviolet lithography source driven by a high-repetition-frequency narrow-pulse CO_2 laser.
作者
李鑫鹏
于德洋
郭劲
陈飞
潘其坤
Li Xinpeng;Yu Deyang;Guo Jin;Chen Fei;Pan Qikun(State Key Laboratory of Laser Interaction with Matter,Changchun Institute of Optics,Fine Mechanics and Physics,Chinese Academy of Sciences,Changchun 130033,Jilin,China;University of Chinese Academy of Sciences,Beijing 100049,China)
出处
《中国激光》
EI
CAS
CSCD
北大核心
2023年第2期64-71,共8页
Chinese Journal of Lasers
基金
国家重点研发计划(2018YFE0203200)
国家自然科学基金(62104223)。
关键词
测量
光斑位置检测
极紫外光刻光源
高重复频率窄脉冲
CO_(2)激光
四象限探测器
measurements
spot position detection
extreme ultraviolet lithography light source
high repetition rate narrow pulse
CO_(2)laser
four quadrant detector
