光刻物镜非球面镜超精面形检测技术基础研究

In some high-tech areas such as IC lithography, super-smooth aspheric mirrors are demanded in urgent, and a higher accurate measurement of aspheric mirrors, e.g.,hypo-nano rms, is necessary. Although, foreign countries have designed related measurement equipments for themselves, they are not for sale. In our country, we still lack of effective measuring method with such high accuracy. In this project, we put forward a new measuring method to solve this problem which based on point diffraction interferometer and annular sub-aperture stitching technique, and some basic research will be done. The main detection object is optical aspheric surface in lithography projection, and a hypo-nano rms accuracy is expected. The main research contents include two aspects: theory and key technology research on ultra precision measurement of optical surface based on the point diffraction interferometer; theory and key technology research on annular sub-aperture stitching about large aspheric surface based on point diffraction interferometer. .Conventional interferometer, such as Fizeau or Twyman-Green interferometer, can only achieve nano accuracy with restricted by fabricating error of reference spherical lens. In our method, a nearly ideal spherical wavefront with spherical wavefront error less than λ/100000 rms, can be acquired through diffraction of a very small pinhole which diameter is only a few microns. The diffraction spherical wavefront can replace conventional real standard lens, and used as reference spherical wavefront in interferometer. So, an ultra precise measurement interference system can be made, and it's longitudinal test range can be expand through annular sub-aperture stitching technique. Our research can realize ultra precise measurement of aspheric surface with large diameter and deviation, and can provide an ultra precise measuring method for a same kind of aspheric surface. It will lay a strong foundation in theory and technology for our country to develop equipment independently.

IC光刻领域对高精度非球面镜的需求激增，提出亚纳米级超精检测要求，国外相关检测设备均为自制，并不外售，国内缺乏检测手段。本项目提出基于小孔点衍射干涉测量结合环形子孔径拼接技术实现非球面面形超高精度检测的新方法，以光刻机投影物镜中所用非球面为主要检测对象，以实现超高精度检测为目标，主要研究基于小孔点衍射干涉测量的超高精度面形检测理论及关键技术；基于点衍射干涉测量系统的环形子孔径拼接检测大口径非球面理论及技术。.该方法通过微米尺寸小孔的衍射产生大范围、近似理想的球面波作为参考波面，组成超高精度干涉测量系统，摆脱了传统球面干涉仪标准镜头对其检测精度的限制，理论上可达到亚纳米级检测精度，利用环形子孔径拼接技术进一步扩展干涉测量系统的纵向测试范围，从而实现大口径、较大偏离非球面的超高精度检测，为一类非球面的超高精度检测开辟了新的途径，并为我国自主研制超高精度非球面检测设备奠定强有力的理论及技术基础。

光刻领域技术的发展对非球面镜的面形检测提出了纳米甚至亚纳米级的超高精度要求，传统的干涉仪检测精度受到标准镜头制造精度的限制，且国外相关检测设备和关键技术对我国进行技术封锁，国内检测手段不足。本项目研究利用微米级尺寸的小孔衍射产生大范围的近乎理想的球面波代替干涉仪的标准镜头进行干涉测量，并与环形子孔径拼接技术相结合，扩展点衍射干涉系统的纵向测量范围，以实现对大口径较大偏离非球面的超精面形检测。主要研究工作如下：.1. 研究大范围超高精度的衍射球面波的实现及理论。通过建立点衍射理论数学模型，分析小孔直径、衍射波面范围与可测数值孔径的关系；研究影响衍射波面质量的因素，并进行波面误差估计，得出满足PV≤/100的小孔技术指标；研究满足要求的微米级小孔的实现技术。.2. 研究高精度干涉图像处理技术。在研究各种相移算法的基础上，基于扩展平均法提出了误差不敏感的多步相移算法；进行了不同步数算法的误差抑制特性分析；确定了满足纳米以下检测精度的相位提取算法；比较分析了不同相位解包算法和波面拟合方法对精度的影响。.3. 研究高精度的非球面环形子孔径拼接技术。建立环形子孔径划分模型；分析不同的拼接算法、拼接参数对拼接结果的影响；研究环形子孔径拼接检测的误差分析和补偿方法，给出了综合考虑各种误差的拼接流程。.4. 点衍射拼接干涉测量系统研究与实验。研究系统设计方案、光路布置方案、关键器件的选取及光路精确调整的方法与步骤；搭建出2.5微米小孔点衍射干涉测量系统，并实现了球面镜和非球面镜的高精度面形检测，获得了与Zygo干涉仪十分接近的检测结果，重复性精度优于/450(RMS)..5. 点衍射干涉测量系统误差分析。分别研究了硬件条件、环境因素和调整误差对点衍射干涉测量系统误差的影响，给出了系统误差的总体估计，并给出了相应的减小误差影响的措施。.以上研究充分证明了本项目方法解决非球面镜超高精度面形检测的可行性，项目按计划顺利开展，并在上述几个方面取得了理论创新和技术成果。