Precise thickness distribution control of soft X-ray multilayers using a speed programmahle shutter and application to aspherics fabrication

在离子束溅射沉积中，离子枪的时间稳定性是厚度控制精度的主要因素。Mo/Si多层凹面镜在13.5rim处的反射峰值波长需要在2%的误差内，而由于我们的沉积设备的溅射速率的变化，它已经达到10%。因此，离子枪稳定运行以将溅射速率变化降低到2%以下是重要的。离子枪的主要参数是氩气流量、加速器电压和引出电压。详细研究了这些因素对离子束输出的影响。获得最大离子束输出的条件为：Ar流量为1.4sccm，加速器电压为-1.4kV，引出电压为+300V。然后，时间的稳定性依赖于Ar流量进行了研究。当Ar流量增加时，离子束输出在较低的水平上变得更稳定。最佳Ar流量在1.7 ~ 2.0sccm之间。此外，在总离子流和离子密度中，分别通过提取器和射束快门处的电极来监测离子束输出。发现室温和离子流之间以及源电压和离子流之间存在很强的相关性，这意味着如何提高稳定性。在我们的用于厚度分布控制的可编程快门的原始技术中，重新推导了最小经过时间的计算方法，并重新检查了延长机械行程的快门形状。在KEK的光子工厂制作了曲率半径为50、270和300 mm的Mo/Si多层凹面镜，并利用正入射软X射线反射仪对它们的厚度分布进行了评价。

In ion beam sputtering deposition, the temporal stability of ion guns is a dominant factor for the accuracy of thickness control. Mo/Si multilayer concave mirrors for use at 13.5 rim need a reflectance peak wavelength within an error of 2%, while it has been 10% owing to the variation of the sputtering rate of our deposition apparatus. Therefore a stable run of ion guns to decrease the sputtering rate variation under 2% has been significant. Main parameters of an ion gun are Ar flow rate, accelerator voltage and extractor voltage. Ion beam output dependence on these factors has been investigated in detail. The condition for maximum ion beam output was found to be 1.4 sccm Ar flow rate, -1.4 kV accelerator voltage and +300 V extractor voltage. Then the temporal stability dependence on the Ar flow rate was investigated. The ion beam output was found to become more stable at a lower level when the Ar flow rate increases. The optimum Ar flow rate lies in the range between 1.7 and 2.0 sccm as a conclusion. Furthermore the ion beam output was monitored in the total ion flow and in the ion density by electrodes at the extractor and at the beam shutter, respectively. Strong correlations between the room temperature and the ion flow and between the source voltage and the ion flow were found, which implies how to improve the stability.In our original technique of the programmable shutter for thickness distribution control, the calculation method of the minimum elapsed time was newly derived and the shutter shape to extend the mechanical stroke was reexamined. Mo/Si multilayer concave mirrors of radii of curvature of 50, 270 and 300 mm were fabricated and their thickness distributions were evaluated by normal incidence soft X-ray reflectometry at the Photon Factory, KEK.