Novel Design Enables Double-Patterning-Lithography

In a potential boost to advance lithography, engineers at SEMATECH and Carl Zeiss SMT today announced the completion of their final design for the next generation Photomask Registration and Overlay Metrology system – called PROVE. The successful final system design release is a major milestone within the project. PROVE will allow for the production of more advanced photomasks with substantially improved image placement accuracy. Double patterning lithography, in particular, requires tighter image placement control for photomasks, but the new system will also enhance photomask production in general.

The new metrology system PROVE™, developed by a team of more than 40 Carl Zeiss SMT engineers and supported by SEMATECH, ascertains the accuracy of mask pattern alignment, and registration for 32nm half-pitch and beyond photomasks. Double patterning is a technology for enhancing feature density by using standard 193nm wavelength technology. The newly developed metrology technology also forms part of the critical infrastructure of extreme ultraviolet (EUV) lithography.

“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,” said 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.”

“Exploiting the core competencies of Carl Zeiss SMT and our long-term experience in 193nm lithography optics and metrology enabled us to create a revolutionary new system design which will close the technology gap for overlay metrology at 32nm and beyond. Additionally, the broad presence of ZEISS products within the mask industry will be most beneficial for our customers in providing them an increased on-site applications and service support,” said Oliver Kienzle, Member of the Board of Carl Zeiss SMT’s Semiconductor Metrology Systems Division.

“With double patterning coming on strong as an optical extension, registration tolerances are getting even smaller,” said Patricia Gabella, SEMATECH project engineer and manager of the joint project. “Working with Carl Zeiss SMT we have completed a design for quantifying image placement errors as small as 2.4 nm according to the ITRS roadmap. This is a major milestone towards making double patterning a commercially viable technology.”

Gabella said the tool itself is targeted for production in 2009, with mask manufacturers being the primary customers.

Carl Zeiss was chosen to develop the system in April 2007 by an evaluation team of mask makers and SEMATECH member companies, which reviewed proposals from several suppliers. Zeiss’ proposal included a novel design allowing mask manufacturers to measure position deviation of photomask features with high precision and accuracy. Since that time Carl Zeiss SMT and SEMATECH engineers have partnered to develop the concept into a working metrology tool. “The mask pattern placement metrology tool project builds upon an already successful partnership between Carl Zeiss SMT and SEMATECH on the immersion AIMS™ tool,” added Lercel.

Key component of PROVE™ is the diffraction limited, high resolution imaging optics operating at 193nm corresponding to at-wavelength metrology for the majority of current and futures photomask applications. An additional benefit is the reasonable working distance which 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. The project is well on track and will reach 32nm high performance capability by the end of 2009.

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