Disclosed herein is an apparatus comprising: a source configured to emit charged particles, an optical system and a stage; wherein the stage is configured to support a sample thereon and configured to move the sample by a first distance in a first direction; wherein the optical system is configured to form probe spots on the sample with the charged particles; wherein the optical system is configured to move the probe spots by the first distance in the first direction and by a second distance in a second direction, simultaneously, while the stage moves the sample by the first distance in the first direction; wherein the optical system is configured to move the probe spots by the first distance less a width of one of the probe spots in an opposite direction of the first direction, after the stage moves the sample by the first distance in the first direction.