ELECTROSTATIC CLAMPING METHOD AND APPARATUS

摘要

The time (t_s) for switching between the first and second polarities is less than the time (T_1) and less than 2 seconds. The present invention relates to a method to electrostatically clamp a dielectric wafer (30) to a processing table (3) during plasma processing. The table (3) has interdigitated electrodes (26, 28) embedded therein. The method includes applying respective voltages of opposite first and second polarities to the adjacent electrodes (26, 28) wherein polarisation charges are induced in the wafer (30) with opposite polarity to a respective underlying electrode thereby electrostatically clamping the wafer to the table; and, after a predetermined time (t_on), reversing the polarities of the voltages so that the polarisation charges and electrostatic clamping continues. (i) The on time (t_on) of each of the first and second polarities is preselected to be: (a) greater than the time (T_1) required to generate sufficient polarization charge in the wafer such that the wafer is held with a required pressure for at least two seconds after withdrawing of clamping the voltages; (b) less than time (T_2) 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 (T_3) for the wafer to separate from the substrate by a second predetermined amount in the absence of a plasma material after an applied voltage has been applied. (ii) The time (t_s) for switching between the first and second polarities is less than time (T_1) and less than two seconds.