Immersion lithography is a photolithography resolution enhancement technique that replaces the usual air gap between the final lens and the wafer surface with a liquid medium that has a refractive index greater than one. The resolution is increased by a factor equal to the refractive index of the liquid. Current immersion lithography tools use highly purified water for this liquid, achieving feature sizes below 37 nanometers. ASML Holding, Nikon and Canon are currently the only manufacturers of immersion lithography systems. An enhancement is hydrolith immersion technology which allows a "measure dry, expose wet" process.

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