Interferometric-spatial-phase imaging for six-axis mask control

Abstract

Articles you may be interested inFast aerial image simulations using one basis mask pattern for optical proximity correctionWe describe a unified approach to measuring alignment and gap with nanometer detectivity between two planar objects ͑e.g., a mask and a substrate͒ in close proximity. The method encodes lateral position in the phase of interference fringes, formed by diffraction from grating and checkerboard alignment marks, designed to enable a wide acquisition range. For gapping, the method incorporates, in the same mark, coarse-gap detection ͑30-300 m͒ and absolute-gap detection at sub-30 m using a chromatic Fabry-Pérot scheme. Fine detection of sub-30 m gaps is inferred from the frequency and phase of fringes, calibrated using the chromatic Fabry-Pérot. Illumination with a variable-bandwidth source enables either ''achromatic'' aligning or ''chromatic'' gapping. Sub-nanometer detection and feedback control of mask position is demonstrated in X, Y, and . Overlay of exposed patterns is demonstrated to be Ͻ3 nm.

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