With semiconductor technology moving to smaller patterns after the 45nm hp node, introduction of high-NA immersion
lithography progresses, and with it, the challenge of decreasing process latitude. The decreasing lithography tool focus
margin is mentioned as one of the key problems of a high-NA immersion lithography process. Tool focus fluctuation
has an impact on resist pattern shape and not only does CD change, pattern height also decreases. As a result of
previous studies , it is understood that the resist loss influences pattern formation after etch, and it was confirmed
that resist loss is important for CD control. We observe correlation between the resist top roughness and the resist loss,
and evaluate the resist loss measurement function by quantifying the resist top roughness. This principle of resist loss
detection by measuring roughness is that a changing roughness of resist pattern top is detected as a fluctuation in image
brightness on the CD-SEM. A measurement idea was proposed and performance evaluation has already been performed
by using one kind of sample. In this study, we demonstrate the validity of resist loss detection by investigating various
wafer conditions which contain the dependency by looking at two types of resist and different exposure tool
illumination settings. Furthermore, we have confirmed the sensitivity limit of resist loss detection which is
approximately above 10nm. Finally, we have discussed improving the resist loss detection sensitivity and considered the applicability of resist loss detection for the litho process monitor.
The model-based library (MBL) matching technique was applied to measurements of photoresist patterns exposed with a
leading-edge ArF immersion lithography tool. This technique estimates the dimensions and shape of a target pattern by
comparing a measured SEM image profile to a library of simulated line scans. In this study, a double trapezoid model
was introduced into MBL library, which was suitable for precise approximation of a photoresist profile. To evaluate
variously-shaped patterns, focus-exposure matrix wafers were exposed under three-illuminations. The geometric
parameters such as bottom critical dimension (CD), top and bottom sidewall angles were estimated by MBL matching.
Lithography simulation results were employed as a reference data in this evaluation. As a result, the trends of the
estimated sidewall angles are consistent with the litho-simulation results. MBL bottom CD and threshold method 50%
CD are also in a very good agreement. MBL detected wide-SWA variation in a focus series which were determined as in
a process window by CD values. The trend of SWA variation, which is potentiality to undergo CD shift at later-etch step,
agreed with litho-simulation results. These results suggest that MBL approach can achieve the efficient measurements for process development and control in advanced lithography.