Low energy ion beam machining of ULE® substrates: Evaluation of surface roughness

Low Energy Xe+ Ion Beam Machining of the Ultralow Expansion Glass Substrates for Aspherical Extreme Ultraviolet Lithography Projection Optics

“…[19][20][21][22] In the case of the ULE Ò surface, the 0.2-10.0 keV Xe þ ion beam energy used to machine the substrate is lower than that for the Ar þ ion beam. [23][24][25] When a high energy (3.0-10.0 keV) Xe þ ion beam is used for figure error correction of the ULE Ò substrate, the HSFR at a machined depth of 50 nm (this value is greater than the figure error after mechanical polishing) becomes 0.18 nm rms. Moreover, the HSFR of the ULE Ò substrate machined by a Xe þ ion beam with energy below 0.7 keV at a machined depth of less than 50 nm become less than 0.08 nm rms.…”