Electron beam dose control for scanning electron microscopy and critical dimension measurement instruments

摘要

A system and method for controlling electron exposure on image specimens by adjusting a raster scan area in-between scan frame cycles. A small, zoomed-in, scan area and the surrounding area are flooded with positive charge for a number of frame cycles between scan frames to reduce the voltage differential between the scan area and surrounding area, thereby reducing the positive charge buildup which tends to obscure small features in scanned images. The peak current into a pixel element on the specimen is reduced by scanning the beam with a line period that is very short compared to regular video. Frames of image data may further be acquired non-sequentially, in arbitrarily programmable patterns. Alternatively, an inert gas can be injected into the scanning electron microscope at the point where the electron beam impinges the specimen to neutralize a charge build-up on the specimen by the ionization of the inert gas by the electron beam.