Determination of local electrostatic forces for EUVL mask chucks

Determination of local electrostatic forces across the surface of an ultra-planar, pin-structured mask chuck for EUVL is addressed. By measuring the flatness of a thin Si-wafer across the supporting pins at high chucking voltages, local bending values are obtained. Comparing these values with FE calculations based on the wafer parameter and chuck design data, the local electrostatic forces can be derived. Our measurements reveal considerable stochastic bending variation across the surface, but are (on the whole) in good agreement with calculated electrostatic forces from the chuck design and demonstrate the potential of this method for chuck characterization.