SPIE NEWS: SEMATECH, Carl Zeiss finalize design for DP photomask metrology system

Feb. 26, 2008 – Carl Zeiss and SEMATECH say they have completed final design for a next-generation photomask registration and overlay metrology system, dubbed “Prove,” that will enable production of advanced photomasks “with substantially improved image placement accuracy,” eyeing in particular the tighter placement control required for double-patterning technology.

The new system ascertains the accuracy of mask pattern alignment, and registration for 32nm half-pitch and beyond photomasks, they say in a statement. The metrology technology also forms part of the critical infrastructure of EUV. SEMATECH indicated the work has led to completion of design for quantifying image placement errors as small as 2.4nm. The tool itself is expected to be in production in 2009, targeting primarily mask manufacturers.

A key component of the system, the companies indicated, is a diffraction-limited, high-resolution imaging optics operating at 193nm corresponding to at-wavelength metrology for the majority of current and futures photomask applications. They also point to a “reasonable working distance” that allows through-pellicle measurements. Two illumination paths offer measurements both in transmission and reflection (e.g. for EUV), providing flexible illumination for maximum contrast imaging. The photomask resides on an ultra-precision stage, being the only movable part in the imaging path.

“Future lithographic scaling places a high reliance on very tight overlay control of the various device levels, and the photomask is a key component of the overlay error budget,” stated Michael Lercel, SEMATECH director of lithography and chairman of the ITRS Litho Working Group. “This new system will get us past several previously ‘no known solution’ challenges.”


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