Patent ID: 8508715

Claim:
A system, comprising: a projection system configured to project a beam of radiation onto a substrate as an array of sub-beams of radiation; a modulator configured to modulate the sub-beams of radiation to substantially form a requested dose pattern on the substrate, the requested dose pattern being built up over time from an array of spot exposures, each of the spot exposures being produced by one of the sub-beams of radiation at a given time; a rasterizer configured to convert data defining the requested dose pattern to a sequence of data representing the requested dose at a corresponding sequence of points within the pattern; a controller configured to receive the sequence of data and generate a control signal therefrom, the control signal being used to control the modulator; and a focus determination unit configured to measure a position of at least a portion of the substrate relative to a plane of best focus, wherein the controller comprises a focus compensation unit, the focus compensation unit configured to change the control signal based on measured deviations of the position of at least the portion of the substrate relative to the plane of best focus.