软X射线光学系统曲面镀膜膜厚测量方法

Period measuring and accuracy analyzing method for soft X-ray optical system

软 X射线光学系统需要在超光滑曲面上均匀镀膜。我们将超光滑曲面看作由若干个小平面拼接而成 ,通过小角衍射仪测量出各个小平面的周期膜厚 ,并拟和出整个曲面的镀膜速率。为提高控制精度 ,我们对同一片多层膜进行等精度多次测量 ,去除其中的粗大误差、系统误差 。

Recent advances in multilayer mirror technology meet many of the stringent demands of soft X ray projection lithography (SXPL). The maximum normal incident reflectivity achieved to data, is 66% for Mo/Si multilayers at 13.4 nm, which is sufficient to satisfy the X ray throughput requirements of SXPL. These high performance coatings must be deposited on figured optics with layer thickness error controled in ~0.5%. Uniform multilayr coatings are required for SXPL imaging optics, so maintaining the surface figure is critical to achieve diffraction limited performance. In this paper, the figured substrate is considered as small super polished planes on the figured curve. By measuring the periods of multilayer on every small plane with small angle diffraction, the deposition speed of the figured substrate can be obtained. For improving the accuracy, every multilayer is measured repeatedly to wipe off the crude and systematic errors, acquire the best value, and calculate limiting error.