An insulator figure of merit for an electrostatic wafer holder is introduced. A sputtered Ta2O5 membrane has a maximum figure of merit compared to other candidate dielectric coatings, e.g., Al2O3 and SiO2. The breakdown strength of sputtered Ta2O5 coatings can be optimized by controlling working gas pressure and oxygen concentration : a holding pressure that exceeds 30 gF/cm2 (2942 Pa), when 60 V dc is applied in atmosphere. The pressure is not influenced by the duration of the applied voltage. The residual pressure, after voltage is turned off, decreases to 1/50 of initial pressure within 1 s. The breakdown voltage for 60 cm2 area wafer holder exceeds +/- 290 V. A sputtered Ta2O5 coating can also be used to smooth relatively rough ceramic substrates. When a polished Al2O3 mixed with ZrO2 ceramic surface is coated with 10 mum thick sputtered Ta2O5 film, good substrate material for an electrostatic chuck is obtained. The sputter rate for the Ta2O5 is much larger than that for the Al2O3 or SiO2.