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In photolithography, immersion lithography is a variant technique that interposes a liquid medium between the optics and the wafer surface, replacing the usual air gap. With the 193 nm wavelength, the typical liquid used is ultra-pure, degassed water. Immersion lithography increases the effective depth-of-focus for a given numerical aperture and permits the use of optics with numerical apertures above 1.0, thus raising the maximum resolution potential of 193 nm technology. Immersion techniques may help extend the use of the 193 nm wavelength to the 45 nm feature size node and beyond.
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