Spin-on-glass coatings for the generation of superpolished substrates for use in the extreme-ultraviolet region

Substrates intended for use as extreme-ultraviolet (EUV) optics have extremely stringent requirements in terms of finish. These requirements can dramatically increase the cost and fabrication time, especially when nonconventional shapes, such as toroids, are required. Here we present a spin-on-glass resist process capable of generating superpolished parts from inexpensive substrates. The method has been used to render diamond-turned substrates compatible for use as EUV optics. Toroidal diamond-turned optics with starting rms roughness in the 3.3-3.7 nm range have been smoothed to the 0.4-0.6 nm range. EUV reflectometry characterization of these optics has demonstrated reflectivities of approximately 65%.