US Patent 7317606 Particle trap for electrostatic chuck

Wafer supporting apparatus, including an electrostatic chuck for supporting the wafer. The apparatus further includes an electrostatic shield which is positioned in proximity to the chuck and the wafer, and a voltage source which is coupled to apply an electric field between the chuck and the wafer. The voltage source applies one or more potentials to the electrostatic shield so as to prevent penetration of particles to the wafer.