ASML Inc., Veldhoven, The Netherlands
Microlithography is used to define patterns of integrated circuits (ICs). The workhorse of lithography is optical projection lithography, whereby a pattern on a mask is imaged on a wafer with a 4:1 reduction ratio.
Using water immersion objectives, a production-worthy lithography system using the 193 nm wavelength and a numerical aperture NA = 1.2 has been shipped in early 2006.1 This system is capable of printing lines and spaces below 45 nm. The next step will be a water-based immersion system with NA = 1.35, capable of printing lines and spaces below 40 nm. Several options are currently being pursued to extend the lithography roadmap down to 32 nm dense lines and spaces. Leading candidates are extreme ultraviolet (EUV) lithography and double patterning using water-based and non-water-based immersion. Opportunities and challenges of these technologies will be discussed in this chapter.
The resolution R of optical lithography, defined as the half-pitch of a dense lines and spaces pattern, is determined by:
where λ is the wavelength of light in vacuum, NA is the numerical aperture of the lens given by the refractive index (of the surrounding medium) multiplied by the sine of the angular semi-aperture of the lens, and k1 is an imaging enhancement-dependent ...