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Nanostructure analysis and laser damage mechanism of ultra-precision polished surface of calcium fluoride single crystals for high-power DUV applications.

高功率 DUV 应用氟化钙单晶超精密抛光表面的纳米结构分析和激光损伤机制。

基本信息

批准号：
14350077
负责人：
OHNISHI Naoyuki
金额：
$ 9.66万
依托单位：
Chubu University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
2002
资助国家：
日本
起止时间：
2002 至 2004
项目状态：
已结题

项目摘要

High power, Deep Ultra Violet (DUV) lasers are expected to be light sources for optical lithography, laser microprocessing, and laser fusion. High purity, DUV-grade calcium fluoride (CaF_2) single crystal material is the only candidate for such optics. The requirements for the CaF_2 surface are to have a high precision figure and an ultra-smooth surface, even though the CaF_2 crystal is difficult to polish because it is soft and has a relatively high thermal expansion coefficient. In order to increase the laser induced damage threshold, the polished surface must be extremely smooth and without subsurface damage caused by finishing. In this research, high purity calcium fluoride (111) single crystals have been float polished in order to obtain the highest quality surfaces. Float polishing is a means of obtaining the smoothest surfaces without introducing subsurface damage. The finished surfaces were observed with a Nomarski differential interference contrast microscope, two optical profilers, a scanning probe microscope and two transmission electron microscopes. The following conclusions can be drawn from the results of this research project.1. A flatness of 31.9 nm p -v and 6.03 nm rms were obtained on 90-mm-diameter area samples by 80 min of float polishing after optical polishing.2. It is clear from high resolution transmission electron microscope images, scanning probe microscope and Nomarski differential interference contrast microscope observations that there is no subsurface damage in the float-polished CaF_2 single crystal sample.3. The float-polished surface is formed from a perfect (111) lattice with small atomic steps, so that the polished surface roughness depends on the mismatch between the sample surface and the (111) planes.4. A surface roughness of 0.059 nm Ra, 0.077 nm rms, and 0.72 nm Ry was obtained by the float polishing process, as measured on a 1 x 1 □m area with an SPM.

高功率、深紫外（DUV）激光器有望成为光学光刻、激光微处理和激光聚变的光源。高纯度，duv级氟化钙（CaF_2）单晶材料是这种光学器件的唯一候选材料。对CaF_2表面的要求是具有高精度的图形和超光滑的表面，尽管CaF_2晶体由于其柔软和具有较高的热膨胀系数而难以抛光。为了提高激光诱导损伤阈值，抛光表面必须非常光滑，并且没有精加工造成的亚表面损伤。本研究对高纯氟化钙（111）单晶进行浮法抛光，以获得最高质量的表面。浮子抛光是一种获得最光滑表面而不引入亚表面损伤的方法。用诺马斯基差示干涉对比显微镜、2台光学剖面仪、1台扫描探针显微镜和2台透射电子显微镜对加工后的表面进行观察。从这个研究项目的结果可以得出以下结论：光学抛光后，经过80 min浮子抛光，在直径90 mm的样品表面获得了31.9 nm的p -v和6.03 nm的rms平面度。高分辨透射电子显微镜、扫描探针显微镜和诺玛斯基差干涉对比显微镜观察表明，浮磨后的CaF_2单晶样品无亚表面损伤。漂浮物抛光表面是由一个完美的（111）晶格以小的原子步骤形成的，因此抛光表面的粗糙度取决于样品表面和（111）平面之间的不匹配。用SPM在1 × 1□m的面积上测量，浮子抛光工艺获得了0.059 nm Ra， 0.077 nm rms和0.72 nm Ry的表面粗糙度。