As feature sizes decrease, requirements on critical dimension uniformity have become very strict. To monitor variations
in lithography process and perform advanced process control it is important to establish a fast and accurate measurement
technique for characterizing critical dimension, sidewall angle and height of the resist profile. Various techniques for
feature measurement such as CD-SEM, AFM, FE-SEM, and scatterometry have been developed. Among these
techniques, scatterometry has both high accuracy and a non-deconstructive measurement modality. It thus provides
advantages of low-cost, high throughput, and robustness. Angle-resolved scatterometry has already been shown to
provide in-line feedback information necessary for tight process control.
In present paper, we introduce a novel angle-resolved scatterometer with pupil optimization. The intensity distribution of
the incident light in the pupil plane is optimized considering the feature and the image sensor response properties, which
improve the measurement performance of the scatterometer. A first order analysis of measurement sensitivity at different
polarization conditions is carried out on resist-coated wafers with 45nm and 22nm features using Rigorous Coupled-
Wave analysis (RCWA). Based on the criteria defined as the sum of the absolute difference of the relative intensity
values between the nominal and varied conditions in the pupil, the sensitivity of the new technique and traditional
scatterometer is compared. Simulation results show that, for 45nm feature, the sensitivity in s and p-polarization is
increased by 400% and 300% respectively. While for 22nm feature, the sensitivity is increased by 200% and 130%.
Reproducibility of measurement is also analyzed on 45nm and 22nm features using a Monte Carlo method and models
for detector noise. Comparison of reproducibility for CD, sidewall angle, and resist height measurement is demonstrated.