【作者】 周小为；

【导师】 付绍军；

【作者基本信息】 中国科学技术大学 ， 同歩辐射及应用， 2010， 博士

【摘要】 衍射光学元件广泛应用于红外成像系统、光谱分析以及其他现代光学系统。随着激光技术的发展，激光器中的重要元件——大口径衍射光学元件的制作成了重要的究课题。现在大口径衍射光学元件的制作主要采用全息曝光和离子束刻蚀相结合的方法。表征大口径衍射光学元件性能的主要因素包括均匀性、衍射效率以及激光损伤阈值。如何通过离子束刻蚀技术提高大口径衍射光学元件的性能，得到均匀性更好、衍射效率更高以及高激光损伤阈值的光栅是制作工艺中的重点研究内容。本文的研究内容定位于离子束刻蚀技术，重点关注的是刻蚀的均匀性以及多层介质膜脉冲压缩光栅（PCG）的离子束刻蚀情况。近来，随着高功率激光器的不断发展，衍射光学元件的口径不断增大，对离子束刻蚀提出了更高的要求。目前，国内大口径元件的制作已经取得了重要进展，基于大口径光学元件的大型激光器也已建成出光。大口径衍射光学元件的离子束刻蚀课题受到了国家863课题重大项目的资助，作者在导师组的指导下从事了课题的研究工作。作者的主要工作有以下几个方面：1.提高离子束刻蚀均匀性对于大尺寸衍射光学元件而言，尺寸的增加给全面积均匀性带来了更大的挑战。整个工艺流程中都对均匀性有着很高的要求。我们使用的离子源束流密度均匀性在需要的工作尺度范围内达不到要求，而样品所处的工作台又只在短轴方向（即横向）扫描，所以，离子束流密度沿着长轴方向（即纵向）的均匀性修正显得极为重要。离子束流的均匀性主要和气体流量分布、离子源参数设置以及束阑形状有关系。本文的工作重点在于调整束阑形状改变束流均匀性。首先是制作整体束阑，其次是制作分离式石墨条束阑，最后通过样品的纵向平移来提高离子束刻蚀的均匀性。具体修正内容包括纵向束流密度分布的测量与定位、横向束流密度分布曲线的测量以及积分、纵向束流密度分布的修正。2.多层介质膜脉冲压缩光栅的离子束刻蚀多层介质膜脉冲压缩光栅的离子束刻蚀包括两个部分：初始光刻胶掩模的定性判断与修正；离子束刻蚀中的图形转移情况。首先，由于全息曝光得到的光刻胶掩模的部分区域可能有残余底膜存在，残余底膜不仅影响图形转移精度而且影响刻蚀均匀性，故而需要判断掩模情况，并对可以修正的掩模进行等离子体灰化修正掩模形状。本论文中的等离子体灰化实验是在我室自行研制的大尺寸衍射光栅灰化装置上进行的。初始光刻胶掩模到底情况，主要通过光学显微镜和原子力显微镜的观察结果进行判断。实验中对于小尺寸的实验片还采用了扫描电镜(肖特基场发射扫描电子显微镜)看其断面轮廓的方法，来了解掩模具体情况。通过大量的统计结果，得到定性的判断，即要求掩模高度>300nm，占空比>0.3，全面积衍射效率>80%且均匀。本论文中，基于现有的测量仪器，设计了一个新的光路来更精确的测量脉冲压缩光栅的衍射效率。该光路消除了激光器中808 nm光源的影响，并削弱了光源中TM偏振的影响，减少了探测器疲劳以及光源波动带来的衍射效率测量误差。其次，为了得到更好的刻蚀选择比，以降低光刻胶掩模加工难度，选用对光刻胶具有保护作用的CHF3作为工作气体。我们通过对小样品刻蚀前后的扫描电镜照片进行统计，得到了离子束刻蚀中的图形转移情况的定性结论。更多还原

【Abstract】 The diffractiive optical components are widely used in many applications,including IR Imaging Systems , spectrometer and other modern optical system. Withthe development of the laser technique, the using of large aperture diffractive opticalcomponents which are a important part of the laser are more and more abroad. It ismade by lithography and ion beam etching. The reasearch of how to get betteruniformity of the diffraction efficiency in whole aperture, high diffraction efficiencyand high laser damage threshold is very important problem. How to improve theperformance of the large aperture diffractive optical elements by ion beam etchingprocess is a important research too.The main contents of this paper is the research of ion beam etching technology,which focuses on the etching uniformity and pulse compression gratings diffractionefficiency measurements and others. Recently, with the continuous development ofhigh power laser, the aperture of diffractive optical element is also need to beimproved and a more hard requirements of ion beam etching is needed. How toimprove the uniformity and diffraction efficiency of the large aperture opticalcomponents is urgently needed. Until now, a important progress of the manufacturefor large aperture diffraction optical components has been made, and high powerlaser used these optical components has been built. The object of the ion beametching of the large aperture diffractive optical elements is supported by of the 863national project funding, The author’s work is done under the guidance of the teachergroup. The main work is shown following:1. Improve the uniformity of ion beam etchingFor large-aperture diffraction optical components, the increased size broughtgreater challenges to the entire area uniformity of the components. The wholemanufacture process has a very high requirement on uniformity too. The ion sourcewe used has no good uniformity, and the sample plate is scanning on the minor axisonly. So, ion beam current uniformity along the major axis is important parametersfor the type of ion source usce in this paper.The relationship between ion beam current density uniformity and gas flowdistribution, the ion source parameter and the shape of ion beam channel is studiedin this paper. This paper mainly focuses on the relationship between ion beam current density uniformity and the shape of the beam channel. The modificationinclude the measurement of longitudinal beam density and orientation, themeasurement of transverse beam density distribution curve and integration,modification of longitudinal beam density distribution.First, a whole beam channel was made; Second, production of a separategraphite beam channel; third, moving the sample in the long axis to get a much moregood etching uniformity.2. Etching of the Multilayer Dielectric Gratings for Pulse CompressorThe etching of the Multilayer Dielectric Gratings for Pulse Compressor consiststwo parts: the judgments of initial photoresist mask and the modification; the graphictransfers during the ion beam etching.First, the photoresist mask is produced by holographic exposure, and someresidual photoresist is existed in the bottom of groove. So we need to judge thesituation of the mask, and to modify the the shape of the mask by plasma ashing. Theexperiment of plasma ashing used in this paper is done on the photoresist descumsystem for by large diffraction grating which is developed by our team. We use theoptical microscope to check the residual photoresist film both before and afterashingt. Atomic Force Microscopy is used to detect the height and duty cycle of thephotoresist mask. Sample with mall size can also uses Schottky Field EmissionScanning Electron Microscope to see the section and received the results of theashing .Through a large number of statistical results, a qualitative judgments is received,which called mask a high degree of > 300nm, duty cycle > 0.3, the whole area of thediffraction efficiency > 80% and uniform. This paper used the existed measuringinstruments, designed a new system to get more accurate measurement of thediffraction efficiency. This optical system eliminate the stray light such as the lightwith wavelength 808nm, reduce the TM polarization in the laser , eliminate theeffect of light source fluctuations and also reduce the effect of photodetector fatigueduring a long time irradiation.Second, In order to reduce the Difficulty of photoresist mask processing, we useCHF3which has a good Etching selectivity to photoresist and the SiO2film as thework gas. A qualitative judgments for graphic transfer of ion beam etching isreceived through the picture before and after etching which is get from the SchottkyField Emission Scanning Electron Microscope.更多还原