Graded reflectance mirror design with unconventional profile for excimer laser

The design of a graded-reflectance mirror (GRM) for KrF-excimer laser has been developed. The mirror consists of three areas of reflectance: (1) a rectangular area in the middle of the substrate with a reflectance R1 about 10 per cent, (2) an outer area with a reflectance R2 about 95 per cent, and (3) a transition area with a defined reflectance increase from R1 to R2. The sandwich type was used to design the GRM with two layers of variable thicknesses and a total of 19 layers. The variable thickness based on the shadowing effect of a fixed non-contact mask with rectangular aperture. For excimer laser applications in particular, the electric field distribution inside the layer system was investigated.