Creating an EUV mask microscope for lithography generations reaching 8 NM (2012)

CREATING AN EUV MASK MICROSCOPE FOR LITHOGRAPHY _GENERAT|ONS REACHING 8 NM Kenneth A. Goldberg‘, lacopo Mochi‘, Markus P. Benk‘, Arnaud P. Al|ezy1, Nathan s. Smith‘, Carl w. Cork‘, William Cork‘, James Macdougall‘, Weilun L. Chao‘, Erik H. Anderson‘, Patrick P. NauIleau1, Eric Acomez, Eric Van Everyz, Veljko Milanovic3 and Senajith B. Rekawa‘ ‘Lawrence Berkeley National Laboratory, Berkeley, California, USA 2Advanced Design Consulting USA lnc., 126 Ridge Rd, Lansing NY 14882, USA 3Mirrorcle Technologies, lnc., 2700 Rydin Road, Unit F, Richmond, CA 94804 INTRODUCTION We are creating a synchrotron-based extreme ultraviolet (EUV, 13.5-nm wavelength) micro- scope to support advanced photomask research for the semiconductor industry. The new micro- scope will serve photolithography generations to the year 2020 and beyond, when printed feature sizes are expected to fall below 10 nm. Called SHARP (the SEMATECH High-NA Actinic Reti- cle review Project), the microscope is designed to emulate the optical properties of current and future EUV lithography tools, enabling the study of mask defects, pattern architectures, optical proximity correction, phase—shifting patterns, and more [1]. EUV lithography, a pattern—transfer technology based on 13.5-nm-wavelength light, is a leading contender for the commercial mass-production of several generations of computer chips within this decade. In this wavelength range, all mate- rials are highly absorptive, so optical systems must operate in high vacuum and optical elements are formed from glancing-incidence mirrors, multilayer-coated Bragg reflector mir- rors, or from nano-patterned, diffractive optical elements. Photomasks, which carry integrated- circuit master patterns, are made from an atomi- cally-smooth low-thermal-expansion glass sub- strate (typically 6 x 6 x ‘/4 inches) with a reflective, Mo/Si multilayer coating, topped with a patterned absorber layer. During printing, the image of the photomask pattern is projected onto a photoresist-covered wafer with 4x demagnification. Arguably, the widespread adoption of EUV lithography has been delayed by limited light- source power and the unavailability of defect- free masks. Owing to their highly wavelength- specific optical properties, the creation of pro- duction-quality masks relies upon dedicated EUV-wavelength mask-blank inspection and pattern-imaging tools. Currently, commercial tools are several years from deployment. This delay provides an opportunity for an industry/government partnership—SEMATECH together with Lawrence Berkeley National Labo- ratory (LBNL)—to create and operate the SHARP microscope as a research tool that will begin operations in early 2013. SHARP will be the first short-wavelength micro- scope to combine lossless, customizable coher- ence control [2] with zoneplate-lens imaging; and, it will be the first to use a dynamic, MEMS- based EUV mirror element. The central concept of diffraction-limited EUV imaging with zoneplate lenses has been demonstrated [3]. Ultimately, we seek to measure the detailed properties of mask patterns and features that are as small as 24 nm using objective lenses that emulate mask- side numerical aperture (NA) values up to 0.156. (This is equivalent to 6-nm wafer features and 0.625-NA imaging.) SYSTEM DESCRIPTION The system specifications can be divided into the optics (illuminator, and imaging), and the mechanical systems required to support them. Achieving high signal-to-noise ratios depends on delivering the maximum possible light—f|ux into the small imaging region. To that end, SHARP&#39;s simplified design contains only essential optical elements. Mechanically, the central challenge is to achieve sub-5-nm stability between the mask and the objective lens during 1-5-second expo- sures, a level that is required for accurate pat- tern measurements. The Source and llluminator The SHARP microscope is powered by a syn- chrotron bending-magnet beamline at LBNL’s Advanced Light Source, with a monochromator