Scanning techniques in particle beam devices for reducing the effects of surface charge accumulation

摘要

Improved scanning methods for use in a scanning particle beam microscop reduce the effects of surface charge accumulation, increasing linearity and precision. More particularly, signal distortion is reduced by scanning across an object along a line in a first direction to produce a first signal, scanning across the object along the identical line in an opposite, anti-parallel, direction to produce a second signal, and combining the first and second signals. This technique is referred to as scan reversal. Baseline drift is substantially canceled out of the resulting signal. According to another technique imaging of a general circular high-aspect-ratio structure is enhanced by identifying approximately the center of the structure, electrostatically scanning a particle beam along a multiplicity of radii of the structure, detecting particles emitted from the surface of the structure being examined to generate a detection signal, and using the detection signal to form an enhanced image of the generally circular high-aspect-ratio structure. This technique is referred to as radial scanning. According to a further technique, the effects of surface charging are reduced by identifying features of an object in a low magnification image and scanning a particle beam across the object discontinuously, only in portions of an image field containing the features of interest. The "background" of the image field is therefore not charged, improving imaging of the features of interest. This technique is referred to as structured scanning.