Development of a wafer positioning system for the Sandia extreme ultraviolet lithography tool
A wafer positioning system was recently developed by Sandia National Laboratories for an Extreme Ultraviolet Lithography (EUVL) tool. The system, which utilizes a magnetically levitated fine stage to provide ultra-precise positioning in all six degrees of freedom, incorporates technological improvements resulting from four years of prototype development. This paper describes the design, implementation, and functional capability of the system. Specifics regarding control system electronics, including software and control algorithm structure, as well as performance design goals and test results are presented. Potential system enhancements, some of which are in process, are also discussed.
EUV engineering test stand
The Engineering Test Stand (ETS) is an EUV laboratory lithography tool. The purpose of the ETS is to demonstrate EUV full-field imaging and provide data required to support production-tool development. The ETS is configured to separate the imaging system and stages from the illumination system. Environmental conditions can be controlled independently in the two modules to maximize EUV throughput and environmental control. A source of 13.4 nm radiation is provided by a laser plasma source in which a YAG laser beam is focused onto a xenon-cluster target. A condenser system, comprised of multilayer-coated mirrors and grazing-incidence mirrors, collects the EUV radiation and directs it onto a reflecting reticle. A four-mirror, ring-field optical system, having a numerical aperture of 0.1, projects a 4x-reduction image onto the wafer plane. This design corresponds to a resolution of 70 nm at a k1 of 0.52. The ETS is designed to produce full- field images in step-and-scan mode using vacuum-compatible, one-dimension-long-travel magnetically levitated stages for both reticle and wafer. Reticle protection is incorporated into the ETS design. This paper provides a system overview of the ETS design and specifications.
Imaging of extreme ultraviolet lithographic masks with programmed substrate defects
Extreme ultraviolet lithographic masks with programmed defects on the mask substrates have been imaged to study substrate defects printability. The imaging was performed with a 2‐aspherical‐mirror system operating at 14 nm wavelength. Results showed that 25 nm thick substrate defects caused observable distortions of resist patterns. Defects of sizes approximately half the minimum resolvable features resulted in 15%–20% variations in resist linewidths. However, since the imaging system was operating at a reduced resolution due to misalignments of the optics, the effect of the defects may have been partially concealed by the phase front distortions caused by mirror misalignments. The defects are difficult to observe under a scanning electron microscope.