Fabrication of ultra-high precision optics by selective deposition through a multiple aperture mask

A technique for fabricating ultra-high precision optics is presented. The technique employs a thin multiple aperture mask positioned in front of the substrate during sputter deposition to selectively occlude the beam. The apertures are small in regions where low material deposition is required and correspondingly larger in regions requiring more. During deposition, the substrate is slowly moved back and forth behind the mask over a distance equal to the pitch of the apertures (typically around 2 - 4 mm). This smoothes out any residual patterning of the substrate due to the aperture design of the mask. Using this technique, a transmission optic having an rms physical thickness uniformity less than 0.5 nm, or λ/1000 (measured at 632.8nm) has been produced from a lithium niobate substrate. We believe that this technique will enable the production of the next generation optics for semiconductor fabrication.