Electrostatic clamping with an EUVL mask chuck: Particle issues

Particle and defect issues related to electrostatic chucking with an ultra-planar, pin-structured mask chuck for EUVL application were addressed. By mapping particles/defects on the backside of 8 inch Si-wafers before and after chucking, particle transport from the chuck to the wafer was studied at application relevant electrostatic forces. Particles were detected by analysis of stray light intensities on the wafer side. Investigations were performed under ambient conditions at high chucking voltages on a bipolar chuck. Particle transport from the chuck surface to the wafer surface was mapped and found to concentrate at the pin sites. Successively lower particle counts with increasing number of chucked wafers were observed, indicating a "cleaning effect" on the chuck's surface induced by the electrostatic chucking procedure. No influence of electric field direction (polarity) on particle count was discernable.