Impact of SiO 2 and CaF 2 surface composition on the absolute absorption at 193nm

Significant effort is pursued for the development and optimization of lithography grade materials aiming for ultra-low optical losses. Nowadays, very sophisticated crystal growing techniques are available. The surface finish of these DUV substrates has to be considered in an analogous manner, as the performance of thin film optical coatings may directly be influenced by the surface composition. Using laser calorimetry according to ISO 11551, the treatment-dependent surface contribution to the overall absorption of lithography grade substrate materials is deduced. The sensitivity enhanced test setup allows for a detailed study at ultra-low fluences - typical for current deep ultraviolet lithography applications. The results on absorption measurements are supported by an innovative surface qualification method, deriving both, characteristics on roughness and near surface stoichiometry, which are the footprints of applied polishing methods and, further, handling conditions on the one hand side, and a consequence of cleaning procedures and dose dependent exposure to DUV-radiation on the other side.