Patent ID: 6890692

Claim:
A method of focus monitoring used for focus monitoring that measures the position of an exposed surface in an optical system in order to adjust the focus of an optical image on the exposed surface at the time of pattern exposure, wherein focus monitoring is carried out by utilizing the characteristics wherein an image of the pattern of a photomask for focus monitoring formed on said photosensitive material surface by irradiating said photomask with the exposure light moves in the direction perpendicular to the optical axis when said photosensitive material surface is moved in the direction of said optical axis, wherein said photomask for focus monitoring comprises a substrate that allows the exposure light to pass through and unit mask structures for focus monitoring, wherein said unit mask structure for focus monitoring has: two patterns for position measurement for measuring the mutual positional relationship formed on the surface of said substrate; and a light blocking film that is formed on the rear surface of said substrate and that has a rear surface pattern for substantially differentiating the incident directions, relative to said substrate, of the exposure light that enters said two patterns for position measurement, and wherein L/λ is 10, or greater, wherein the dimension of said rear surface pattern is L and the wavelength of the exposure light is λ.