Optical mosaic method for orthogonally crossed gratings by utilizing information about both main periodic directions simultaneously

We present a method to make optical mosaic orthogonally crossed gratings by utilizing information about both main periodic directions simultaneously. The whole mosaic system for orthogonally crossed gratings is set up based on the dual Lloyd's mirror interferometer that fabricates orthogonally crossed gratings through a single exposure. The interference fringes formed by the diffractions of the exposure beams from the exposed grating areas are used as the reference to fine tune the position and attitude of the exposure beams relative to the substrates during consecutive exposures. A procedure to make mosaic for two main periodic directions simultaneously is proposed based on the presupposition that the angle between two sets of main lattice lines is constant during the mosaic. Experimentally we made a 2×1 mosaic crossed grating with a period of 574 nm in (30+30) mm ×35 mm area. The peak-valley errors of the (−1, 0)th- and (0, −1)st-order diffraction wavefronts over the whole mosaic grating area are 0.104λ and 0.163λ, respectively.