Design requirements for a stand alone EUV Interferometer

摘要

EUV lithography is expected to be inserted for the 32/22 nm nodes with possible extension below. EUV resist availability remains one of the main issues to be resolved. There is an urgent need to provide suitable tools toaccelerate resist development and to achieve resolution, LER and sensitivity specifications simultaneously. An interferometer lithography tool offers advantages regarding conventional EUV exposure tool. It allows the evaluationof resists, free from the deficiencies of optics and mask which are limiting the achieved resolution. Traditionally, a dedicated beam line from a synchrotron, with limited access, is used as a light source in EUVinterference lithography. This paper identifies the technology locks to develop a stand alone EUV interferometer using a compact EUV source. Itwill describe the theoretical solutions adopted and especially look at the feasibility according to available technologies. EUV sources available on the market have been evaluated in terms of power level, source size, spatial coherency, doseuniformity, accuracy, stability and reproducibility. According to the EUV source characteristics, several optic designswere studied (simple or double gratings). For each of these solutions, the source and collimation optic specificationshave been determined.To reduce the exposure time, a new grating technology will also be presented allowing to significantly increasing thetransmission system efficiency. The optical grating designs were studied to allow multi-pitch resolution print on thesame exposure without any focus adjustment. Finally micro mechanical system supporting the gratings was studied integrating the issues due to vacuum environment,alignment capability, motion precision, automation and metrology to ensure the needed placement control betweengratings and wafer. A similar study was carried out for the collimation-optics mechanical support which depends on thesource characteristics.