Patent ID: 9136090
Filing Date: 2015-09-15
Classification: H01J

Abstract:
1. A method of scanning a surface of an object using a particle beam, wherein the method comprises: determining an area of the surface of the object to be scanned; determining initial positions of a set of raster points within the area of the surface of the object to be scanned, wherein the initial positions are based at least in part on the shape of the area of the surface of the object to be scanned and on the initial positions of raster points whose initial positions have previously been determined, if any, such that the initial positions of the raster points are not arranged in a regular two-dimensional array; changing the initial positions of at least some raster points of the set of raster points, the changing of the initial positions of the at least some raster points comprising changing positions of centers of the at least some raster points, wherein the changed positions of the centers of the at least some raster points are within the area of the surface of the object to be scanned, wherein the changing of the initial positions of the at least some raster points of the set of raster points is performed such that local deviations of a particle dose from a predetermined target dose occurring when the area of the surface of the object to be scanned is scanned by directing the particle beam to the changed positions are smaller than local deviations of a particle dose from the predetermined target dose occurring when the area of the surface of the object to be scanned was scanned by directing the particle beam to the initial positions of the set of raster points within the area of the surface of the object to be scanned; and, determining final positions of the set of raster points; scanning the area of the surface of the object to be scanned by directing the particle beam to the final positions of the raster points.