In-vacuo growth studies and thermal oxidation of ZrO2 thin films

ZrO2 thin films might be used as capping layers for protecting extreme ultraviolet (EUV) optics against chemical degradation processes. These coatings should form a homogeneous closed layer that does not degrade the underneath layers, while the thickness is restricted to a few nanometres to keep good reflection of the mirror. The initial growth of ZrO2 films by reactive magnetron sputtering on top of amorphous Si, SiNx and SiO2 was monitored by in vacuo low-energy ion scattering (LEIS). This technique is selectively sensitive to the outermost atomic layer, such that it can be determined for which deposited thickness a closed layer was formed and how deposition parameters and surface passivation affect the sharpness of the ZrO2/Si interface. In-vacuo X-ray photoelectron spectroscopy (XPS) was used to study the oxidation state of both ZrO2 and underlying Si. Additionally, XPS was used ex-situ for probing oxygen diffusion through the capping layer after thermal oxidation in ambient.