A method of electrostatically clamping a dielectric wafer to a processing table during plasma processing is described. The table has interdigitated electrodes embedded therein. The method comprises applying respective voltages of opposite first and second polarities to adjacent electrodes wherein polarization charges are induced in the wafer with opposite polarity to the respective underlying electrodes thereby electrostatically clamping the wafer to the table; and, after a predetermined time (ton), reversing the polarities of the voltages so that the polarization charges and electrostatic clamping continues. The on time (ton) of each of the first and second polarities is preselected to be a) greater than the time (T1) required to generate sufficient polarization charge in the wafer such that the wafer is held with a required pressure for at least 2 seconds after withdrawing of clamping voltages, b) less than the time (T2) for the wafer to separate from the table by a first predetermined amount while in the presence of a steady voltage and a plasma, and c) less than the time (T3) for the wafer to separate from the substrate by a second predetermined amount in the absence of a plasma, after an applied voltage has been applied. The time (ts) for switching between the first and second polarities is less than the time (T1) and less than 2 seconds.