Characterization of charging in CDSEM for 90-nm metrology and beyond

Three parameters, measurement times, charging distances, and charging area, are studied with respect to measurement of the local charging effect. We found that the effects of measurement times and charging distances to the local charging is under observation limit and the measured CD deviation is very small. However, the charging area is found to be the most dominant parameter for local charging. A 7-nm CD deviation from this local charging is observed. After the root.. cause of the local charging is understood and controlled, we use an extra charging area at the opposite side of the measurement site to compensate for the charging effect. The SEM image and CD deviation are greatly improved after this compensation. At last, a novel measurement algorithm is introduced to deal with the actual OPE evaluation. From simulation, the net Coulomb force experienced during the measurement is greatly reduced with the new algorithm compared with that used in the normal measurement sequence. The comparison of the global charging and local charging effects is also discussed in this report.