Chemical Imaging in EUV

Semiconductor Engineering publishes a nice article on photoresist operation in EUV photolithography systems used in advanced processes. It shows how far the chemical imaging, the predecessor of image sensors, can go:

"In the early days of EUV development, supporters of the technology argued that it was “still based on photons,” as opposed to alternatives like electron beam lithography. While that’s technically true, even a casual glance at EUV optics shows that these photons interact with matter differently.

An incoming EUV photon has so much energy that it doesn’t interact with the molecular orbitals to any significant degree. John Petersen, principal scientist at Imec, explained that it ejects one of an atom’s core electrons.

...the photoelectron recombines with the material, ejecting another electron. This cascade of absorption/emission events, with energy dissipating at each step, continues until the electron energy drops below about 30 eV.

Once the electron energy is in the 10 to 20 eV range, Petersen said, researchers see the formation of quantized plasma oscillations, known as plasmons. The plasmons in turn create an electric field, with effects on further interactions that are not yet understood.

Only after energy falls below 5 to 10 eV, where electrons have quantum resonance with molecular orbitals, does the familiar resist chemistry of older technologies emerge. At this level, molecular structure and angular momentum drive further interactions."