Fringe field theory and experiment for electrostatic chucking of extreme ultraviolet photomasks

Fringe fields during electrostatic chucking depend on a variety of factors including the type and design of the chuck, chucking voltage, the proximity of other hardware and the electrical characteristics of the mask. The effects of uniform target potentials on the degradation of the position and imaging of an electron beam from a mask writer has been reported previously [J. Ruan and J. G. Hartley, Proc. SPIE 5992, 1385 (2005)]. In this article the authors are reporting on our modeling and experimental studies of the asymmetrical field environment induced by the fringe fields from electrostatic chucks. It has been proposed that masks for extreme ultraviolet (EUV) lithography be patterned in an electron beam mask writer equipped with the same style of chuck that will hold the mask in the exposure tool. Modeling of the fringe fields was performed using Munro’s electron beam software (MEBS SW Ltd., 14 Cornwall Eardens, London SW7 4AN, England) (MEBS) and an experimental apparatus was constructed which enabled a direct measurement of the axial electric potential for various styles of EUV masks and chucks in simulated electron beam writer environments. This article examines the fringing fields due to electrostatic chucking of EUV masks on two different chucks and three electron optic column designs as well as masks with a continuous conductive coating and ones with electrical isolation between the top and bottom sides. Specific recommendations are made for an optimal mask patterning strategy when using electrostatic chucks to hold the mask.