Preparation of DLC strip targets for the tabletop storage ring synchrotrons MIRRORCLE

Abstract

The tabletop storage ring synchrotrons MIRRORCLE-6X and MIRRORCLE-20SX can generate powerful extreme ultraviolet (EUV) radiation. They are applicable as sources for EUV lithography and for EUV photoemission spectroscopy. EUV radiation is emitted from a strip target consisting of a vertical strip with a width of ∼3 mm mounted on a frame with an inter-arm distance of 10 mm. The highest EUV power is expected to be achieved by using a diamond-like carbon (DLC) strip with a thickness of 55–150 nm. Two technologies were developed for preparation of such DLC strip targets. In the first technology, the DLC strip is backed by a 15-nm-thick formvar layer. Such a strip is floated on a water surface, and lifted from there directly onto an open frame. Since the strip tends to curl around its vertical axis while being lifted from the water, it curls mostly around the inter-arm center, and hence has its smallest width there. In the second technology, the DLC strip is not backed. A temporarily closed frame is constructed using two extra blades, and the foil is attached easily to that frame. Subsequently, the two free strip edges are formed, via cutting with a surgical blade along the edges of the two extra blades. Lastly, the extra blades are released and left to fall. Using these two technologies, strip targets containing a 55 nm DLC+15-nm-thick formvar strip, as well as 85-nm-thick and 150-nm-thick DLC-only strips were prepared.