Optical Lithography Techniques for 0.25 μm and Below

Lithography has enabled the continuous shrinking of device geometry over many years. Whereas it has been predicted many times that optical lithography would run out of steam, it still is the technology of choice, and this will certainly remain for a considerable time. In this paper various optical lithography techniques for 0.25 μm feature printing will be reviewed. The issues related to deep-UV lithography will be discussed. During the last years, various resolution enhancement techniques, such as phase shifting masks, off-axis illumination and surface imaging have been proposed. In an attempt to indicate the future of optical lithography, a simulation study is presented. Reasonable processing windows are obtained down to 0.12 μm by using 'known' techniques.