Patent ID: 7295315
Filing Date: 2007-11-13
Classification: B41J,G02B,G03F

Abstract:
1. An alignment sensor for use with a reference grating disposed on a substrate, the alignment sensor comprising: first, second, third, and fourth sensor gratings; and an optical detector; said first, second, third, and fourth sensor gratings and said optical detector being disposed relative to one another such that: said first and second sensor gratings are laterally spaced on opposite sides of said detector along a first axis; said first and second sensor gratings have lines that extend in directions that are perpendicular to said first axis; said third and fourth sensor gratings are laterally spaced on opposite sides of said detector along a second axis that is perpendicular to said first axis; said third and fourth sensor gratings have lines that extend in directions that are perpendicular to said second axis; when said first and second sensor gratings receive illumination, each of said first and second sensor gratings diffracts at least some of the illumination into at least one obliquely transmitted beam directed at the reference grating; the reference grating receives two transmitted beams, one from each sensor grating, and diffracts the transmitted beams into a combined reflected beam; and said detector receives the reflected beam and produces an optical interference signal that is sensitive to the reference grating's lateral position relative to the alignment sensor.