Patent ID: 9581434
Date: 2017-02-28
CPC Classifications: G01B

Claim:
1. An apparatus for measuring pattern of a grating device, the apparatus comprising: a light source unit to irradiate to a surface of the grating device; an image unit for acquiring images with respect to the grating device, the image unit comprising: an image sensing device; a microscopic device, optically coupled to the image sensing device; and an optical device comprising a beam splitter, wherein the microscopic device receives beams through the optical device; a processing unit, coupled to the image unit, for controlling the image unit to acquire the images; and a movement unit for producing relative movements between the image unit and the grating device; wherein the image unit acquires a plurality of first digital images including an image on the surface of the grating device and images due to Talbot effect between the surface and a first position with respect to the grating device; the processing unit determines a second position based on the first digital images; the image unit acquires a plurality of second digital images due to the Talbot effect at the second position with respect to the grating device when the movement unit produces a relative movement between the image unit and the grating device; the image unit acquires the first digital images due to the Talbot effect with respect to the grating device when the image unit focuses on the surface of the grating device and while the image unit focuses on a plurality of different positions which are away from the surface and between the surface and the first position; the movement unit produces the relative movement in a direction perpendicular to fringes of the grating device in order for the image unit to acquire the second digital images.