基于相关度的白光干涉信号解调算法

White Light Interference Signal Demodulation Algorithm Based on Correlation

超精密的微纳器件是制造领域的核心器件,随着超精密加工技术的迅猛发展,对相应的微纳检测技术要求越来越高。微纳检测技术是保证超精密加工技术精确稳定的重要手段,是超精密加工技术进一步发展的前提。现有的微纳器件表面轮廓检测方法按是否使用光学原理可以分为光学类和非光学类,非光学类检测通常为点扫描、接触检测的方式,检测效率低,容易破坏待测器件的表面形貌。光学类的检测方式多为面扫描,非接触式测量,不会划伤待测器件,检测效率高。在光学检测中,白光干涉技术由于其相干长度短的特点,可实现微纳器件三维形貌的高精度测量,受到国内外研究人员的广泛关注。在白光干涉检测技术中,信号解调算法对整个检测系统至关重要,传统的白光干涉信号解调算法只采用了干涉信号的部分信息,解调精度较低,而高精度的相移解调算法又依赖于粗定位的精度,无法直接实现高精度的三维形貌恢复。为了解决以上问题,提出以相关度为基础的信号解调算法,该算法通过三级滑动窗口计算相关度,利用了白光干涉信号的全部信息,无需粗定位,就可直接确定待测物体的表面三维形貌信息。为验证该算法的性能,对其进行了模拟仿真和实验验证。模拟仿真结果表明该方法具有可行性,可准确恢复仿真待测三维结构形貌,采用三级滑动窗的设置可有效提高运算效率。同时,搭建了白光干涉垂直扫描实验系统,并对光栅结构和微透镜结构进行了测量,将实验结果与传统的重心法和相移法进行了比较。实验结果表明该方法能准确恢复出不同物体的三维形貌,精度及鲁棒性均优于改进的重心法,接近相移法,光栅高度的恢复结果表明该方法与相移法的误差小于0.5 nm。仿真和实验结果表明,所提出的基于相关度的白光干涉信号解调方法是可行的,无需粗定位便可实现待测物体表面三维形貌的高精度恢复,具有高精度、高鲁棒性的特点。

Ultra precision micro nano devices are the core devices in the manufacturing field.With the rapid development of ultra-precision machining technology,the corresponding micro nano detection technology is required to be higher and higher.Micro nano measurement technology is an important means to ensure the accuracy and stability of ultra-precision machining technology and is the premise for further development.The surface profile detection methods for micro/nanodevices can be divided into optical and non-optical types according to whether optical principles are used.Non-optical detection usually adopts point scanning and contact detection,which is inefficient and easy to damages the surface morphology of the device to be tested.Optical detection methods are mostly surface scanning,and non-contact measurement,which will not scratch the device to be tested,and the detection efficiency is high.In optical detection,white light interferometry has been widely concerned by researchers at home and abroad because of its short coherence length,which can achieve high-precision measurement of three-dimensional morphology of micro-nano devices.In white light interference detection technology,the signal demodulation algorithm is very important to the entire detection system.Traditional white light interference signal demodulation algorithm only uses part of the information of the interference signal,which has low demodulation accuracy.However,high-precision phase shift demodulation algorithm depends on the accuracy of rough positioning,which cannot directly achieve the high-precision three-dimensional shape recovery.In order to solve the above problems,this paper proposes a signal demodulation algorithm based on the correlation.This algorithm calculates the correlation through a three-level sliding window and uses all the white light interference signal information.Without rough positioning,it can directly determine the three-dimensional surface topography information of the object to be measured.In order to verify the performance of the algorithm,this paper has carried out simulation and experimental verification.The simulation results show that the method is feasible and can accurately restore the 3D structure morphology to be measured.The setting of a three-stage sliding window can effectively improve the calculation efficiency.At the same time,the white light interference vertical scanning experimental system is built,and the grating structure and microlens structure are measured.The experimental results are compared with the traditional gravity center and phase shift methods.The experimental results show that this method can accurately restore the three-dimensional topography of different objects,and its accuracy and robustness are better than the improved barycenter method,which is close to the phase-shifting method.The grating height recovery results show that the error between this and phase-shifting methods is less than 0.5 nm.The simulation and experimental results show that the white light interference signal demodulation method based on the correlation proposed in this paper is feasible.It can achieve high-precision recovery of the three-dimensional surface topography of the object to be measured without rough positioning and has the characteristics of high precision and high robustness.