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Patterning of 25 nm Contact Holes at 90 nm Pitch: Combination of Line/Space Double Exposure Immersion Lithography and Plasma-Assisted Shrink Technology

In this work, two methods are combined in order to provide 25 nm contact holes at 90 nm pitch: the line/space double exposure immersion lithography and the plasma-assisted shrink technology. We first present the line/space imaging method with negative tone development to create directly 45 nm CH at 90 nm pitch. Then, we discuss plasma-assisted shrink technology and how it applies to these small contacts. Plasma-assisted shrink technology relies on running a fast cyclic process, where plasma polymers are deposited on the photoresist mask, then subsequently redistributed over the features sidewalls, allowing in final a diameter reduction of approximatively 50%. Finally, for the metal-hard-mask patterning approach, the dielectric etch challenges driven by the dimensional scaling are analysed and discussed.