Patent ID: 6187149
Filing Date: 2001-02-13
Classification: B01J,G01N,H02N,Y10S,Y10T

Abstract:
An electrostatic chuck for attracting charged grains to a bead collection zone on a bead contact surface comprising:a bead electrode for selectively establishing a grain attracting field to the bead collection zone, the bead electrode shaped and configured in such a manner so that when an AC waveform potential is applied thereto, the grains are influenced by it and guided to selective retention by the bead electrode to the bead collection zone; andan electronic driver programmed to deliver the AC waveform potential configured to provide a repeated effective grain attraction potential at the bead collection zone, wherein the AC waveform potential comprises a grain-attracting potential pulse followed by a recovery period wherein(a) the recovery period is adapted to allow, in the case where the bead collection zone is formed on a substrate with a resistivity below 10.sup.11 .OMEGA.-cm, an effective grain attraction field at the bead collection zone on activation of a subsequent grain-attracting potential pulse, wherein the AC waveform potential has a frequency of 100 Hz or less, or(b) the AC waveform potential corresponds to applied voltages and time periods effective so that the voltage at the bead collection zone resulting from the grain-attracting potentials following a grain-attracting potential (other than an initial grain-attracting potential) is at least 10% of an initial voltage at the bead collection zone, or(c) the AC waveform potential corresponds to applied voltages and time periods effective so that the integrated voltage at the bead collection zone integrated over the pulse period (other than an initial pulse period) during which a grain-attracting voltage is applied voltage at the bead collection zone is at least 20% of an initial integrated voltage.