In order to respond to shrinking circuit line widths of semiconductor devices, it is necessary to reduce the wavelength of the light source in exposure equipment or increase the numerical aperture (NA) of the projection lens. Because NA is proportional to the refraction index (n), when using ultrapure water (n = 1.44), for example, light at the same angle would yield an NA that is 1.44-times greater. Immersion exposure technology exploits this principle, whereby the gap between the semiconductor exposure equipment's projection lens and the wafer is filled with ultrapure water. When combined with an ArF excimer laser (193-nm wavelength), which provides the shortest wavelength available for lens optics today, immersion lithography can shrink circuit line widths from 65 nm — previously believed to be the limit — to 45 nm. Immersion exposure technology would allow even higher-density circuit patterns using current facilities and equipment,significantly reducing capital investment and other costs.

Canon is actively working to develop ArF immersion exposure technology and focusing on practical applications of liquid film immersion methods and a projection lens (ultrahigh-NA catadioptric lens). As work progresses on liquids with high refractive indexes and the means to apply them, coupled with advances in projection lenses, we may eventually draw closer to light sources in the EUV (Extreme Ultra Violet) region, enabling circuit patterning with line widths of 30 nm.