Patent ID: 7772574

Claim:
A method of controlling the positioning of an image of a pattern in a particle-beam projection processing apparatus during exposure of a target with said image wherein said pattern is formed in a pattern defining means and is, by means of a beam of electrically charged particles, imaged through a particle-optical projecting system onto said target, said method comprising the following steps: imaging a number of reference marks provided in said pattern defining means through the same projecting system onto a corresponding number of registering means positioned at locations of desired positions of images of the reference marks, detecting images of said reference marks at said registering means generating corresponding signals, processing said signals in a control means and deriving control signals for adjusting the imaging properties of said projecting system and bringing said reference mark images into coincidence with said desired positions, the imaging of said pattern being done by means of at least two consecutive projector stages of said projecting system, namely, at least one non-final projector stage and one final projector stage, the latter producing said image of the pattern, wherein the detection of reference marks images is done at the location of an intermediary image of a non-final projector stage, the registering means being positioned at locations of nominal positions of an intermediary imaging plane.