The prehistory of EUV

Viewed historically, EUV lithography can be considered a descendant of soft x-ray proximity lithography (SXPL), the first lithographic technique to use x-ray radiation. In SXPL, a mask is held just above the wafer and illuminated, so that the mask structures are transferred at a one-to-one scale. This technique came into use in the early 1980s and would continue to be researched for many years, side by side with EUV lithography. It wasn’t until the turn of the century that science and industry gave up their attempts to make SXPL work for commercial chip production.

The terms soft x-ray and extreme ultraviolet aren’t well defined, but indicate roughly the same wavelength range of a few to a few dozen nanometres. The term EUV was introduced to distinguish between SXPL, which uses a mask as large as the wafer itself, and projection lithography in the same wavelength range, which places the mask much farther from the wafer and prints the mask structures field by field.