Fabrication of adaptive mirrors for extreme ultraviolet lithography

Extreme ultraviolet lithography (EUVL) will push the resolution limit of lithography systems to 22 nm and below assisted by the advances in the multilayer mirror technology. At the EUVL wavelength of 13.5 nm, commonly used Mo/Si multilayer mirrors reflect 70% of the incoming radiation and the absorbed 30% may create significant heat load on the mirror, which may introduce wavefront distortions, resulting in a decrease of the overall resolution of the lithography system. The wavefront distortions are usually non-uniform and may change with time. In order to correct these wavefront distortions, and extend the resolution of the EUVL to even smaller dimensions, a novel adaptive optics approach has been developed. The adaptive optics approach enables wavefront correction by integrating dynamically controllable piezo-electric thin films in the multilayer mirror. In order to integrate the piezo-electric thin films in the multilayer mirror, and to make these mirrors compatible with the EUVL requirements in terms of reflectance, surface roughness and figure error, several thin film deposition techniques have been explored including the interaction at each thin film interface. Here, we present evolution of the surface roughness in the deposition process and successful fabrication of the first piezo-electric thin films integrated to the mirrors.