Electrostatic chucks for lithography applications

High precision electrostatic chucks with diameters up to 12 inches are being developed at IOF for electron/ion-beam lithography applications. For optimal performance, selection of the appropriate chuck dielectric is crucial. We have tested various materials, including sapphire, quartz and glass-ceramics with respect to chucking force under vacuum conditions. Differences in electrostatic force of more than an order of magnitude were observed and are attributed to Coulomb and Johnsen-Rahbek behaviour. For the former, reasonable agreement with theoretical calculations was obtained when taking the corresponding dielectric constants and a finite gap between wafer and support into account. Time constants for chucking and dechucking were determined for the latter.