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As lithography mask process moves toward 45nm and 32nm node, phase control is becoming more important than ever.
Both attenuated and alternating Phase Shifting Masks (PSM) need precise control of phase as a function of both pitch
and target sizes. However conventional interferometer-based phase shift measurements are limited to large CD targets
and require custom designed patterns in order to function properly, which limits phase measurement Zeiss is currently
developing an optical phase measurement tool (PhameTM), providing the capability of extending process control from
large CD test features to in-die phase shifting features with high spatial resolution. The necessity of designing this
optical metrology tool according to the optical setup of a lithographic exposure tool (scanner) has been researched to be
fundamental for the acquisition of phase information generated from features close to the size of the used wavelength. It
was found by simulation that the image phase of a scanner depends on polarization and the angle of incidence of the
illumination light due to rigorous effects. Additionally, for small features the phase value is strongly influenced by the
imaging NA of the scanner due to the loss of phase information in the imaging pupil.
Simulations show that the resulting scanner phase in the image plane only coincides with the etch-depth equivalent
phase for large test features, exceeding the size of the in-die feature by an order of magnitude.
In this paper we introduce the PhameTM phase metrology tool, which enables the industry to perform in-die phase
control for Alternating PSM, Attenuated PSM and CPL masks. The PhameTM uses a 193nm light source with the optical
capability of phase measurement at scanner NA up to the equivalent of a NA1.6 immersion scanner, under varying,
scanner relevant angle of incidence for Attenuated PSMs and CPLs, and with the possibility of polarizing the
illuminating light. New options for phase shifting mask process control on in-die features will be outlined with first
phase measurement results for varying states of polarization.
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