【作者】 林慧；

【导师】 李立峰；

【作者基本信息】 清华大学 ， 光学工程， 2009， 博士

【摘要】 多层膜光栅是集衍射光栅的高光谱分辨率及多层膜的高反射率于一身的光学元件,在极紫外空间光谱探测、极紫外光刻等领域有着重要用途。衍射效率是衡量多层膜光栅性能的重要指标,它很大程度上取决于光栅的槽形质量。矩形光栅槽形控制精度高,已达到实用化水平。闪耀光栅较矩形光栅具有更高的理论衍射效率,但由于极紫外闪耀光栅的闪耀角通常小于3°,其槽形难以精确控制,制约了实际衍射效率的提高。如何改进制作工艺,提高闪耀光栅的衍射效率是目前极紫外多层膜光栅研究中的一个重点。本论文围绕衍射效率这个核心问题,从理论计算、制作工艺和实验测试等方面对极紫外多层膜闪耀光栅进行了较为系统的研究。同时考虑到制作实用化器件的技术储备需要,对其他类型的极紫外光栅也进行了研究。理论计算方面,编写了一套基于微分法的能模拟光栅实际槽形和粗糙度因素的衍射效率计算程序。该程序的计算结果与测试结果良好符合,为理论分析光栅槽形参数与衍射效率之间的关系提供了可靠手段。工艺制作方面,提出了基于矩形掩模的Ar+-O+混合离子束刻蚀闪耀光栅的工艺方法和理论模型,验证了该方法的便捷性和模型的有效性。该方法的特色是O2和矩形掩模的使用。O2有利于获得0.5-3°的小闪耀角,基于矩形掩模的刻蚀模型简单实用,工艺过程易于精确控制。采用该工艺能重复制作出槽形近似为三角形的闪耀光栅,闪耀角的控制精度达到±10%。实验测试方面,测得多层膜闪耀光栅样品的衍射效率达30%以上,达到甚至略高于国际上报道的最佳结果。通过比较闪耀光栅对照组的衍射效率测量结果,结合理论分析,定量评价了各项槽形参数对衍射效率的影响,给出了它们的误差容许范围,有利于指导闪耀光栅的实用化制作。其他研究方面,制作得到了衍射效率在20%以上的多层膜矩形光栅,与国际上实用化的矩形光栅相当。提出并制作了宽带多层膜光栅,在保证衍射效率约为10%的前提下,光谱范围达2.8nm,较普通多层膜光栅增大近三倍。更多还原

【Abstract】 Multilayer-coated gratings realize the high spectral resolution of diffraction gratings and the high normal-incidence reflectivity of multilayer coatings in a single optical element, so they are widely used in extreme-ultraviolet (EUV) astronomical spectrometers, EUV lithography systems, and so on. Diffraction efficiency, which is the key performance parameter of a grating, depends largely on the grating’s groove shape. Gratings with a rectangular groove shape (laminar gratings) have been used in most EUV applications, for the rectangular groove shape can be accurately controlled. A blazed grating with a triangular groove shape has higher theoretical diffraction efficiency than a laminar grating. However, the required blaze angle of a EUV blazed grating is so small (typically < 3°) that it is difficult to control precisely the groove profile. As a result, the measured efficiency of a blazed grating is much less than the theoretical prediction. Researchers are now focusing on improving the fabrication technique so as to get higher efficiency. This dissertation mainly reports our investigation on EUV blazed gratings, which includes efficiency calculation, grating fabrication, and efficiency measurement and analysis. Some other types of EUV gratings are also studied.For efficiency calculation, a computer code based on the differential theory was written, which takes the actual groove shape and the surface and interface roughness into account. The calculated results are in good agreement with the measured results. This computation program is useful for analyzing the relationship between diffraction efficiency and groove parameters.A simple and practical method to make high-quality EUV blazed gratings is developed. This method uses an argon and oxygen mixed-gas ion-beam to directly etch the fused silica substrate through a rectangular-profile photoresist mask. A corresponding theoretical model is built to analyze the etching process. This method is characterized by its use of rectangular photoresist masks and oxygen as an etchant ingredient. With oxygen added, it is easy to obtain small blaze angles of 0.5-3°. The etch model based on rectangular mask is concise, and the etch process can be precisely controlled. Experimental results confirm the convenience of the method and the effectiveness of the model. With this fabrication technique, blazed gratings with sharp edges can be reproducibly fabricated, and the control precision of the blaze angle is±10%.A typical multilayer-coated blazed grating was measured with synchrotron radiation and has a peak efficiency more than 30%, which approaches or is even slightly higher than the best results published to date. Besides, a group of blazed gratings with different groove parameters were fabricated and measured for comparing their measured efficiencies and with theoretical calculation. The influences of different groove parameters on the efficiency are quantitatively assessed. The error margins of all parameters are found, which might be a guide for making EUV blazed gratings.In addition, a multilayer-coated laminar grating was made; its peak efficiency is larger than 20%, which is comparable with the efficiencies of pratical laminar gratings. Besides, a grating with broad wavelength bandwidth was designed and fabricated. Its efficiency is ~10% in a 2.8 nm-wide wavelength range that is almost 3 times more than that of a multilayer grating not designed for broad band applications.更多还原