High refractive index liquid medium used in
immersion lithography that replaces the air gap between the lens and the
resist surface in conventional
photolithography.
Source:
PAC, 2020, 92, 1861. 'Terminology of polymers in advanced lithography (IUPAC Recommendations 2020)' on page 1876 (https://doi.org/10.1515/pac-2018-1215)