Lower wavelength - deep UV (193nm emitted by ArF laser and 248 nm emitted by KrF laser), thus smaller structures can be obtained (resolution is linear proportional with the wavelength)
The reaction that takes place in the laser is: Xe* + Cl2 → XeCl* + Cl
What happens in a laser?
there is a large population of metastable (for a longer time than usual) excited Xe* atoms (or other atoms)
if a photon passes with the right frequency (same as the photon which will be emitted in the deexcitation process), the excited atoms will emit photons, all of them with the same phase and frequency, creating the laser light
the name excimer comes from the fact that excited dimers (F2 for example) are used in the laser
Problem: excimer laser has poor spatial coherence (broader beams)
Advantages: lower wavelength and higher intensity (five times higher than mercury lamp)
Reticles are used instead of masks made of glass, in order to avoid absorbtion of photons in the transparent glass
EUV
EUV (5 - 50 nm) uses mirrors instead of lenses - lenses absorb these wavelengths quite well, thus mirrors with multilayers of Mo and Si (Bragg reflecting layers) that refelect 70% of the light are used for the optical system in order to collimate and project light over the wafer
The whole system is placed in vacuum, beacuse even air absorbs the photons with these wavelengths
Substrate preparation
