Evolution of wavelength shrinkage in lithography

Optical lithography has driven on-going miniaturization in the microelectronics industry, thereby enabling continuation of 'Moore's Law'. To achieve this, lithographers have steadily reduced the wavelength of the illumination light used in the optical systems. However, as we transition from the visible spectrum, through ultra-violet, and now towards the soft x-ray wavelength regime, a host of new challenges are introduced. The majority of these challenges are related to material properties, as wavelength reduction significantly narrows the field of available materials that are both sufficiently transparent, as well as radiation resistant to the illumination light. We also are limited by the actual wavelengths that can be produced which deliver sufficient power to provide a production-worthy light source. In this paper, we will examine the history of wavelength transition in optical lithography, explaining the key material developments that enabled wavelengths such as 248nm to be highly successful, as well as explain the reasons wavelengths such as 157nm and 126nm were not adopted.