Scatterometry is one of the most promising CD profile metrology technologies for future technology nodes. As critical dimension (CD) continues to decrease, sensitivity of scatterometry needs to be improved to measure even more subtle structures. Sensitivity of a scatterometer highly depends on film stack structure and optical properties of the sample and wavelength, incident angle and polarization implemented by the scatterometer. When measuring different types of sample, scatterometer should be capable of optimizing measuring configurations to get best sensitivity. In this work, we attempt to optimize the measuring sensitivity by introducing a hybrid scatterometer, which is able to measure reflected light from a sample through either an angle-resolved method or a spectroscopic method using two complementary measuring arms. In this setup, improvement of sensitivity can be achieved by choosing better measuring method and adjusting light wavelength, incident angle and polarization.
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.
Diffraction Based Overlay (DBO) is widely evaluated by numerous authors, results show DBO can provide better
performance than Imaging Based Overlay (IBO). However, DBO has its own problems. As well known, Modeling based
DBO (mDBO) faces challenges of low measurement sensitivity and crosstalk between various structure parameters,
which may result in poor accuracy and precision. Meanwhile, main obstacle encountered by empirical DBO (eDBO) is
that a few pads must be employed to gain sufficient information on overlay-induced diffraction signature variations,
which consumes more wafer space and costs more measuring time. Also, eDBO may suffer from mark profile
asymmetry caused by processes.
In this paper, we propose an alternative DBO technology that employs a dedicated overlay mark and takes a rigorous
modeling approach. This technology needs only two or three pads for each direction, which is economic and time saving.
While overlay measurement error induced by mark profile asymmetry being reduced, this technology is expected to be as
accurate and precise as scatterometry technologies.
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