Extending Moore’s Law Continuing to Shrink Features with Optical lithography As chipmakers continue to reduce feature sizes and shrink CDs on the wafer, they require advanced lithography tools to enable patterning of the most critical layers.

The feature resolution, R, is defined by the Rayleigh’s criterion;
Where lambda is the exposure wavelength, NA is the lens numerical aperture and k₁ is a lithography process factor.

The resolution of an imaging system can therefore be improved by increasing numerical aperture, reducing wavelength and reducing process k₁ factor. In single-exposure lithography, the theoretical lower limit for k₁ is 0.25.

By introducing highly purified water to the imaging medium, chipmakers are able to increase numerical aperture (NA) greater than 1. The most advanced ArF immersion scanners have a numerical aperture of 1.35.