Real‐time observations of extreme‐ultraviolet aerial images by fluorescence microimaging

A new technique, fluorescence microimaging (FMI), using single‐crystal phosphors was used to look directly at aerial images produced by an extreme‐ultraviolet (EUV) camera operating at a wavelength of 139 A. The achieved spatial resolution was estimated to be ∼0.2 μm. A comparison of this technique with the usual resist‐exposure scanning electron microscopy inspection technique as a means of focusing a 20×EUV Schwarzschild camera was performed. FMI could in principle be improved to view fluorescent images with features as small as 0.07 μm, in real time.