charged - particle - beam microlithography methods and apparatus are disclosed that employ a segmented reticle and provide high - accuracy pattern transfer even under conditions of drift of the charged particle beam . beam - drift test patterns are defined on a reticle at the termini of deflection fields at one or both lengthwise ends of certain reticle stripes . corresponding beam - test marks are situated on or at the wafer . a charged particle beam passing through a beam - test pattern on the reticle is a “ detection beam ” that is directed to and scanned over the corresponding beam - test mark on the wafer . before performing actual pattern transfer , the beam - test marks on the wafer are scanned by the detection beam passing through the corresponding beam - drift test patterns on the reticle , and electrons emitted by impingement of the detection beam on the wafer beam - test marks are detected . the positions of the beam - test marks are detected multiple times and the corresponding data is used to measure beam drift . the beam - drift measurements provide data usable to perform a correction of the beam position so as to reduce or eliminate effects of beam drift .