Extreme Ultraviolet Lithography

Synopsis

Microchips play a central role in our world, from supercomputers to toasters, most objects we build now include them. Fabricating microchips is a very complicated process, with one of the key steps being done by lithography machines, which project a pattern onto a photoresist to build the structure of the device. With ever shrinking device sizes, higher frequencies of light are needed to do this patterning step. Until recently, the leading edge has been deep UV light at 193nm. Recently however, Extreme UV (EUV) has come to market after research began in the early 90s. EUV uses a wavelength of 13.5nm, quite near to the definition of an x-ray. Using this wavelength required a complete redesign of how a lithography system works, from the light source to photoresist. I will talk about some of the incredible systems that have been built to meet these challenges, including mirrors much smoother than those of the James Webb Space Telescope, a light source that works by hitting a stream of tin droplets 50 thousand times per second with a 20 kW laser to generate the light, to the complicated trade-off between the blur caused by electrons emitted at high doses and the stochastic errors that happen at low doses when there are only 10s of photons incident per square nm.