Patent ID: 8057972

Claim:
A method for forming a pattern on a surface of a target by means of a beam of electrically charged particles in a number of exposure steps, each step comprising: producing said particle beam; directing said particle beam through a pattern definition means and producing a number of beamlets using an aperture array of the pattern definition means having a plurality of regularly arranged apertures of identical shape defining the shape and relative position of said beamlets, and using an electrically controllable blanking means of the pattern definition means to effectively switch off the passage of selected beamlets towards the target, the remaining beamlets forming, as a whole, a patterned particle beam; projecting said patterned particle beam by means of an optical column comprising controllable particle optical means onto said substrate surface to form an image of those apertures which are switched on, each aperture corresponding to an image element on the substrate surface during respective uniformly timed exposure steps; where there is a relative motion between the target and the pattern definition means according to the movement of the beamlets over a sequence of adjacent image elements on the substrate surface, resulting in an effective overall motion of the patterned particle beam over the target surface and exposing said image elements on the surface in each exposure step, wherein the image elements on the target are exposed to the beamlets multiply, namely several times during a number of exposure steps according to a specific sequence, wherein the sequence of exposure steps of the image elements is arranged on the time axis in a non-linear manner according to a specific rule in order to reduce the current variations in the optical column of the multi-beam exposure apparatus during the exposure of the pattern.