Measurement of the SEM-beam diameter using a relief structure: Influence of contamination

Abstract

Relief structures on plate surfaces are used to measure the diameter of the scanning electron microscope (SEM) beam. A contaminant film which alters the geometric parameters of the relief structure appears on its surface even in a high-vacuum SEM. It turns out that the film is deposited onto the surface nonuniformly, and there exist such regions of the film that remain almost unchanged after structure scanning for many hours. The discovered phenomenon is explained in this paper. The values of the beam diameter determined using these regions can be used to monitor the stability of a measuring SEM under conditions of relief-structure surface contamination. The beam diameter is determined using two models. In a model with an a priori unchanged beam form, the variation in the effective diameter value is ∼2 nm during long-term scanning. In a model with the recovery of the beam form, the diameter variation is larger; however, the character of the time dependence is similar to that observed for the effective value in the model with the unchanged beam form.