Investigation of various factors' influence on charging effects in linewidth metrology

The charging effects has been investigated quantitatively using Monte Carlo (MC) simulation when the linewidth of the insulator is measured by Scanning Electron Microscope (SEM) in secondary electron (SE) detection mode and with the low accelerating voltage around 1 kV. The yield of the electron generation is near the unity for most materials under low voltage condition, and is slightly different from unity depending on the material and geometry of the pattern. For insulators, however, such a yield difference leads to locally different charge accumulation that influences on the measured linewidth. In this paper, we set reference operating and shape conditions for isolated and array pattern of PMMA/Si wafer, and calculated the influence of charging effects on linewidth metrology according to change of each condition. We have used 50% threshold and linear regression algorithm for the edge determination and calculated the offset in those conditions. The most critical factor in the linewidth measurement is the charging in the edge, which results in large offsets from the linewidth to be measured in normal state. We also calculated the influence on the linewidth measurement of the variation of charging state with elapse of time.