According to the ITRS roadmap, semiconductor industry drives the 193nm lithography to its limits, using techniques like
double exposure, double patterning, mask-source optimization and inverse lithography. For photomask metrology this
translates to full in-die measurement capability for registration and critical dimension together with challenging
specifications for repeatability and accuracy. Especially, overlay becomes more and more critical and must be ensured on
every die. For this, Carl Zeiss SMS has developed the next generation photomask registration and overlay metrology tool
PROVE® which serves the 32nm node and below and which is already well established in the market. PROVE® features
highly stable hardware components for the stage and environmental control. To ensure in-die measurement capability,
sophisticated image analysis methods based on 2D correlations have been developed.
In this paper we demonstrate the in-die capability of PROVE® and present corresponding measurement results for shortterm
and long-term measurements as well as the attainable accuracy for feature sizes down to 85nm using different
illumination modes and mask types. Standard measurement methods based on threshold criteria are compared with the
new 2D correlation methods to demonstrate the performance gain of the latter.
In addition, mask-to-mask overlay results of typical box-in-frame structures down to 200nm feature size are presented. It
is shown, that from overlay measurements a reproducibility budget can be derived that takes into account stage, image
analysis and global effects like mask loading and environmental control. The parts of the budget are quantified from
measurement results to identify critical error contributions and to focus on the corresponding improvement strategies.