The importance of line-width roughness (LWR)/line-edge roughness (LER) in relation with leakage current has
made it a critical process parameter, especially when device downsizes to 32nm era. Critical dimension scanning
electron microscope (SEM) is still the most popular tool to characterize LWR in semiconductor manufacturing.
However, true LWR metrology by SEM has been a challenge because of metrology noise and induced damage. Method
of repeating multi-shot or long scanning time [5-8] on the same field of view have been proposed to effectively eliminate
metrology noise caused by SEM tool variation and image processing. By such method, however, line damage
(non-conformal critical dimension enlargement) caused by charging is found and damage level depends on the property
of surface material, e-beam energy, and total scanning time. In this article, the impact of damage on LWR metrology
and optimal metrology condition are studied. Following the proposed method , polysilicon lines both with and
without oxide mask are investigated under different e-beam energy and number of shot. LWR metrology noise
decreases along with e-beam energy and saturates at 1400eV while damage level is proportional to beam energy. In
similar way, the larger number of repeating shot, the more effective of noise rejection and the more damage of line will
be at the same time. The damage not only increases metrology noise, but also degrades the LWR, that are verified in
both simulation and experiment. In the final, the optimal conditions of true LWR metrology by SEM for both
polysilicon line with and without oxide mask are proposed.