Patent ID: 6277531
Filing Date: 2001-08-21
Classification: B82Y,H01J

Abstract:
In a charged-particle-beam (CPB) microlithography projection-exposure method in which a pattern, defined by a reticle, is projection-transferred onto a sensitive substrate using a CPB projection-optical system, the reticle pattern being divided into multiple exposure units that are individually and sequentially transferred to corresponding respective locations on the substrate where images of the exposure units are stitched together to form a complete pattern on the substrate, an improvement comprising:providing a focal-point-correcting lens in the CPB projection-optical system, the focal-point-correcting lens being selectively energizable as required to change a focal point of an image of an exposure unit being exposed onto the sensitive substrate using the CPB projection-optical system:dividing an exposure unit into multiple subregions;calculating a respective feature surface area within each subregion so as to determine a minimal feature surface area greater than zero and a maximal feature surface area for the exposure unit;calculating, from the minimal and maximal feature surface areas for the subregions of the exposure unit, an average feature surface area for the exposure unit; andenergizing the focal-point-correcting lens according to the calculated average feature surface area so as to adjust a focal point of the CPB projection-optical system.