DUV vs. EUV

DUV (Deep Ultraviolet) and EUV (Extreme Ultraviolet) are not fundamentally different exposure methods, but two wavelength regimes of the same basic idea: reduction projection exposure, as described in the chapter on exposure methods. The jump from 193 nm (DUV) to 13.5 nm (EUV) sounds like a small numerical difference, but technically reinvents almost everything – from the optics and the mask to the operating environment of the entire system.

DUV systems mostly use ArF excimer lasers at 193 nm, often as immersion lithography: a thin water film between the final lens and the wafer increases the effective refractive index and thus the resolution. The optics are transmissive – light passes through a system of fused-silica lenses, and the mask is transparent like a photographic slide.

EUV radiation at 13.5 nm, by contrast, is absorbed by practically every material, including air and glass. The entire system must therefore operate in high vacuum, and lenses are useless – imaging instead relies on a system of molybdenum-silicon multilayer mirrors, which reflect a fraction of the radiation through destructive/constructive interference. The mask itself is also not a transparency but a structured mirror.