Patterns of lines and trenches with nominal linewidths of 50 nm have been proposed for use as an overlay target appropriate for placement inside the patterned wafer die. The NIST Scatterfield Targets feature groupings of eight lines and/or trenches which are not resolvable using visible bright-field microscopy. However, these repetitive patterns do yield a zero-order reflectivity which can be imaged; as our lines and trenches are formed in different photolithographic steps, the overlay offset can be derived from the relative displacement of these zero-order responses. Modeling of this phenomenon will require a thorough knowledge of the transmissivity of light throughout the microscope as a function of polarization, as unpolarized light entering the illumination train may become polarized before exiting the objective. Linear polarization parallel and perpendicular to these lines and trenches is investigated as a possible enhancer of overlay offset measurement repeatability. In our particular case, nominally unpolarized light performed proved most repeatable.
Proceedings Title: Proceedings of SPIE
Conference Dates: February 26, 2007
Conference Location: San Jose, CA
Conference Title: Metrology, Inspection, and Process Control for Microlithography XXI
Pub Type: Conferences
microscopy, overlay metrology, polarization, scatterfield microscopy, semiconductor manufacturing