【作者】 盛斌；

【导师】 付绍军； 徐向东； 刘颖； 洪义麟；

【作者基本信息】 中国科学技术大学 ， 核技术及应用， 2009， 博士

【摘要】 本文首先概括了闪耀光栅的历史,特点与分类;介绍了制作非对称锯齿形闪耀光栅的各种方法,突出介绍了近些年出现的新技术、新工艺和一些振奋人心的成果;着重介绍了基于硅各向异性刻蚀制作闪耀光栅的原理、最新进展和相比其他技术所独有的特点,这个方法展现了良好的应用前景。闪耀光栅的最大特点就是将入射光的大部分能量衍射到某一个非零衍射级次上,非对称锯齿槽形是闪耀光栅的主要轮廓形式.随着科学技术的发展,真空紫外和软X射线波段上的应用和研究越来越重要,同时对非对称锯齿槽形闪耀光栅的制作也提出了更高要求,包括超低粗糙度的闪耀面和通常方法难以做到的小闪耀角,这几点恰巧是硅各向异性刻蚀制作光栅的优势所在,所以掌握这项技术显得尤为重要。论文就是依托于本实验室良好的实验条件,针对真空紫外波段,对在单晶硅上利用湿法各向异性刻蚀制作闪耀光栅的方法进行了系统的研究,取得了一些有意义的结果。单晶硅是我们制作光栅的基础,因此对单晶硅的质量、硅片的精确切割、硅片的抛光以及硅片的清洁提出了很高的要求,需要对这些参数进行严格的检测,最终得到符合我们制作要求的带5度偏角的单晶硅片。接着是利用热氧化层作为硅各向异性刻蚀掩模的研究。介绍了热氧化层的获得,在理论和实验上对湿法刻蚀中的橫向刻蚀做了详细的研究,对热氧化层掩模厚度和光刻胶线条的占宽比之间的关系进行了分析,总结了湿法刻蚀应用在图形转移中的特点,发现了残余光刻胶对图形转移的影响,得到了初步的光栅样品,对光刻胶掩模的质量和氧化层掩模的厚度提出了明确的要求。然后是利用天然氧化层作为硅各向异性刻蚀掩模的研究。为了消除重力的影响,在倒置状态下对光刻胶掩模进行高于其玻璃转变温度以上的烘烤,尽量保证光刻胶线条高度的同时得到了光滑的光刻胶掩模,再结合光刻胶灰化技术,进一步得到小占宽比、平直而且干净的光刻胶掩模。从理沦上分析了对于我们要制作的用于真空紫外波段的光栅来说,天然氧化层作为硅各向异性刻蚀掩模是完全可行的。在得到高质量光刻胶掩模的基础上,第一次在实验上利用天然氧化层作为硅各向异性刻蚀的掩模,成功制作出接近于理想锯齿槽形的闪耀光栅,其闪耀角为5度,线密度为1200线/毫米,闪耀面的均方根粗糙度约为0.2nm,其闪耀波长在140nm附近.最后是对光栅样品的效率测量。首先分析了在115nm～140nm波段硅表面氧化层厚度对反射率的影响,仔细测量了具有良好闪耀光栅轮廓的光栅样品S27的在s偏振下的衍射效率,发现其绝大部分入射光的能量都被集中衍射到-1衍射级次上,显示出优良的闪耀特性。通过原子力显微镜测得精确的光栅轮廓,利用PC-Grate2000(MLT)计算了光栅样品S27在s偏振下的-1衍射级次的绝对效率和槽形效率,计算的绝对效率与实测数据吻合良好。在135nm波长处测得的绝对效率为53.7%,其相应的槽形效率为83 2%.如果改进工艺条件进一步得到更小占宽比而且平直的光刻胶掩模,就很有希望制作出槽形顶端缺陷更小的锯齿状闪耀光栅。对于制作极紫外和软X射线波段的闪耀光栅而言,天然氧化膜作为湿法刻蚀掩模的方法容易制作出具有较高槽形效率和光滑闪耀面的闪耀光栅,需要做的只是减小切割硅片时的切偏角度或者适当增加光栅线密度。本文介绍的方法对设备要求不高,步骤相对简单,在获得高槽形效率的同时,还可以大大降低工艺难度及制作成本。更多还原

【Abstract】 Blazed gratings with asymmetric sawtooth profiles possess the desirable property of concentrating most of the diffracted light into a single nonzero order.However, accurate control of the sawtooth groove profile is difficult when the groove density is high and the blaze angle is only a few degrees,especially for gratings used at vacuurn ultraviolet and soft x-ray wavelengths.Traditional blazed gratings can be fabricated by diamond scribing with a ruling engine or by ion etching combined with interference lithography.Gratings fabricated by these methods suffer from a number of defects,including high surface roughness and poor groove profile,which lead to large amount of stray light and low diffraction efficiencies.Owing to the anisotropic character of single crystal silicon in the etchants of alkaline ions such as KOH solution,gratings with a controllable blaze angle and smooth blaze facets can be fabricated by anisotropic etching of an off-cut（111） silicon wafer under a mask of thermal-oxidation-grown SiO₂ or deposited Si₃N₄.A systemic research was carried out on fabrication of blazed gratings in the vacuum ultraviolet wavelength range on silicon crystal silicon substrates by anisotropic wet etching.According to the severe demands,the qualities of good single crystalline precise cutting,fine polishing and good cleaning were tested.Well-qualified silicon wafers with an off-cut angle of 5°were obtained.Using thermal-oxidation-grown SiO₂ layer as the mask of anisotropic etdhing,we studied the under-cutting of the wet etching of SiO₂ layer theoretically and experimentally.The character of the transferring of photoresist mask into the SiO₂ layer was summarized,the influence of remainder photoresist was observed and the preparatory sample of grating was obtained.Straight and clean photoresist mask with small line-to-period ratio are required and the thickness of the SiO₂ layer should be as thin as possible.Photoresist becomes viscous when heated above its glass transition temperature, so the line of photoresist mask can be smoothened.In order to avoid the influence of gravity,we heated the photoresist mask with the substrate back side up to maintain the thickness of photoresist lines.To reduce line edge roughness and clean the remainder photoresist,between the grating lines,we performed photoresist ashing by O₂ plasma reactive ion etching,which can etch the photoresist lines isotropically.As a result,straight,smooth and clean photoresist masks with small line-to-period ratio were obtained.The desirable blazed grating had a blaze angle of 5°,groove density of 1200 g/mm and a blaze wavelength of about 140 nm.On the surface of a silicon substrate, the thickness of native oxide layer generally ranges from 1 to 2 nm.First we analysed the feasibility of using the native oxide layer as the mask of anisotropic etching,then realized it experimentally.Then we present a simple and convenient method of controlling the profile of a blazed grating that consists of using patterned native oxide layer as the mask of anisotropic etching to obtain near-ideal grooves of sawtooth.With the blazed grating profile well controlled by this technique,a 1200g/mm blazed grating was fabricated,which had a blaze angle of 5.0°and smooth blaze facets of surface roughness about 0.2 nm rms.Efficiency measurements were made at the Spectral Radiation Standard and Metrology Beamline of the National Synchrotron Radiation Laboratory of China.It was found that the most of the incident radiation was diffracted into the -1 order.The grating sample was measured to blaze at the wavelength of 135 nm,where the peak measured absolute efficiency was 53.7%and the corresponding calculated groove diffraction efficiency was 83.2%in s polarization.更多还原