摘要
提出一种同时出射3个波前的复合三相位计算全息图(CGH),并将其应用于波前误差校正.通过6次组合测量标定出CGH基底制造误差和图形位置误差,并在检测结果中予以消除.所测试的极紫外光刻(EUVL)非球面光学元件峰谷(PV)值和均方根(RMS)误差分别为31.6 nm和4.88nm.此外,对同一非球面光学元件进行基于折射零位补偿的检测实验,其PV值和RMS误差分别为38.6 nm和5.14 nm.所提出的复合三相位CGH具有实现亚纳米量级的EUVL非球面光学元件面形检测潜力.
Abstract
Objective Aspherical surface testing plays an important role in projection optics for extreme ultraviolet lithography(EUVL)systems and determines the resolution and overlay accuracy of the lithography system.The substrate transmission wavefront error and the pattern placement error are the main factors influencing the accuracy in the metrology of aspherical surface based on computer-generated hologram(CGH),which remains a great challenge to the traditional calibration methods.To this end,a new method for calibrating the wavefront error introduced by pattern placement error based on a triple complex phase is proposed and experimentally studied.Methods We propose a triple complex CGH that simultaneously emits three wavefronts for aspheric surface testing,and apply it to wavefront error calibration.By conducting six combined measurements,the manufacturing error and graphic position error of the CGH substrate can be calibrated,and they can also be eliminated in the measurement results.The first measurement is for interferometer TF and RF verification,and with the calibrating method,the surface form of TF and RF can be known.The second measurement is adopted for calibrating the first-order diffraction wavefront of CGH in the+X direction.The third measurement is employed for calibrating the first-order diffraction wavefront of CGH in the-X direction.The fourth measurement is for calibrating the first-order diffraction wavefront of CGH in the+Y direction.The fifth measurement is for calibrating the first-order diffraction wavefront of CGH in the-Y direction and the sixth measurement is to utilize TF and CGH for testing the aspheric surface.Results and Discussions Based on the measurement results of test 1-6,TF and RF surface form and tested aspheric surface form can be calculated.The peak-to-valley(PV)value of TF surface form is 74.2 nm and root mean square(RMS)error is 13.9 nm.The PV value of RF surface formform is 53.3 nm and RMS error is 6.6 nm.The PV value of surface form of the tested aspheric surface is 31.6 nm and RMS error is 4.88 nm.The same tested aspheric surface is also measured by refraction null compensation test,and the tested PV value is 38.6 nm and RMS error is 5.14 nm.The comparison between the two results indicates that the proposed method has subnanometer RMS accuracy.Conclusions Aspherical surface testing plays a vital role in projection optics for EUVL systems,and determines the resolution and overlay accuracy of the lithography system.The substrate transmission wavefront error and the pattern placement error are the main factors that influence the accuracy in the metrology of aspherical surface based on CGH,which remains a great challenge to traditional calibration methods.Therefore,we propose a triple complex CGH that simultaneously emits three wavefronts for aspheric surface testing and apply it to wavefront error calibration.By carrying out six combined measurements,the manufacturing error and graphic position error of the CGH substrate can be calibrated,and they can be eliminated in the measurement results.The PV value and RMS error are 31.6 nm and 4.88 nm for a tested aspheric surface respectively.Furthermore,the same aspheric surface is also measured by a refractive aspherical null testing system,with the corresponding PV value and RMS error being 38.6 nm and 5.1 nm respectively.This method intrinsically has the subnanometer accuracy necessary for EUVL aspherical optical components.
基金项目
国家自然科学基金(62375281)
应用光学国家重点实验室开放基金(SKLAO2021001A05)
NETL
NSTL
万方数据