High accuracy measurement of pattern linewidth is particularly important in Very Large Scale Integrated Circuits (VLSI) manufacturing.
The measurement of pattern linewidth has been done by optical methods. However, the optical methods have several problems: as the measured value depends on slope angle at pattern edge, thickness and optical property of film and also substrate, there exists a large difference in size (0.3 μm) between the defined edge and the true edge in case of photoresist linewidth measurements. Especially, the optical methods have severe problems to measure bottom of pattern edge and are unsuitable to measure pattern linewidth in VLSI's manufacturing.
The secondary electron signal obtained by electron beam irradiation can be used to measure pattern linewidth with high accuracy. In order to avoid radiation damage and contamination during in-process measurement, low primary electron energy (1 keV) and low dosage of primary electrons (1X1020electrons/cm2) are used.
As secondary electron signal includes much random noise, signal averaging and smoothing methods for random noise reduction are utilized.
The automatic detection of bottom edge from secondary electron profile is achieved by detecting the increasing point of line profile which corresponds to the cross point of the average line and the slope line.
The linewidths obtained by this method agree with the linewidths calculated from the pattern pitch of cross section image obtained by scanning electron microscopy(SEM) within the error of 0.04μm.
Yamaji, H.; Miyoshi, M.; Kano, M.; and Okumura, K.
"High Accuracy and Automatic Measurement of the Pattern Linewidth on Very Large Scale Integrated Circuits,"
Scanning Electron Microscopy: Vol. 1985
, Article 9.
Available at: https://digitalcommons.usu.edu/electron/vol1985/iss1/9