Patent ID: 8222621

Claim:
A method for forming a pattern on a surface of a target by means of a beam of electrically charged particles, the method comprising: producing said particle beam; directing said particle beam through a pattern definition means comprising an aperture array having a plurality of regularly arranged apertures of identical shape, thus producing a number of beamlets by means of said apertures which define the shape and relative position of said beamlets, and modifying selected beamlets by means of a blanking array means of the pattern definition means towards respective paths which do not meet the target, thus effectively switching off the passage of said selected beamlets, the remaining beamlets forming, as a whole, a patterned particle beam; projecting said patterned particle beam by means of an optical column comprising a controllable deflection means onto said target surface to form a beam image composed of the images of the apertures whose beamlets are not switched off, each aperture corresponding to an image element on the target surface, while the target is moving relative to the pattern definition means along a scanning direction within an image plane in which the images of apertures are formed, wherein during a sequence of uniformly timed exposure steps the location of said beam image is, by means of said controllable deflection means, moved along with the target at least with respect to the relative target movement along the scanning direction, and between exposure steps the location of the beam image is changed with respect to the target, the exposure steps having a duration within which the relative movement of the target covers a uniform distance of advance which is greater than the mutual distance of neighboring image elements on the target, wherein at consecutive exposure steps the beam image is located at image positions which each correspond to a position on one of a set of regular placement grids, said placement grids being congruent and identically oriented but each having a different placement offset within the image plane, the placement offset between any two placement grids being not greater than the mutual distance of neighboring image elements on the target, at least some of the placement offsets being oblique or perpendicular to the scanning direction, wherein with each change of location of the beam image between exposure steps, the beam image is shifted to an image position associated with a different placement grid, thus cycling through the set of placement grids, said change of location additionally comprising a longitudinal component which is generally uniform, said longitudinal component being parallel to the scanning direction and having a length which is a fraction of the width of the beam image as measured along the scanning direction and generally compensating the movement of the location of the beam image between consecutive exposure steps with regard to the location of the pattern definition means.