Optical Systems for Lithography

One of the cornerstones for the tremendous success of microelectronics is the continuous advancement of optical lithography. Optical systems for illumination and projection of IC patterns have been developed to meet several reductions of projection wavelength, increases in numerical aperture, and the introduction of immersion optics. Today techniques like double patterning are being used to reduce the dimensions of electronic devices to below the optical resolution limit. These techniques further increase the demand on optics regarding wavefront control, image placement, and illumination variability. Currently the leading IC companies are preparing the transition to mirror based EUV systems, which is the largest change in the history of lithography optics. A stream of innovations enables optical lithography to meet those demands and to maintain its position as the predominant structuring technology for the foreseeable future. The innovations involve several areas like e.g. system layout, optical and mechanical design, as well as optical metrology, optics production, and coating technology. We will sketch the development of optical systems for lithography and observe how increasing demands are driving new design principles, all the way from DUV optics to high NA EUV projection systems.