Characterization of Electrostatic Chucks for Extreme Ultraviolet Lithography

The use of an electrostatic chuck to support and flatten an extreme ultraviolet (EUV) mask during scanning exposure will be a critical component to meet the stringent requirements on image placement errors in the sub-30-nm regime. Consequently, the ability to predict the response of the mask during e-chucking is necessary for the design and implementation of the e-chuck system. This research focuses on characterizing the coefficient of friction between the EUV reticle and the dielectric material of the chuck. A customized tool was constructed to test chuck and reticle samples both in air and in a vacuum chamber. Studies were conducted to identify the friction coefficient at various chucking pressures and to examine the effects of wear caused by repeated measurements on the same location of the reticle surface. All experiments were performed in a cleanroom environment. Results of the friction testing illustrate the range of values to expect for typical EUV reticles and chucks. Finite element (FE) modeling was then used to illustrate the effects of friction on the overall capability of the chuck to flatten the mask. Additional FE simulations demonstrated the magnitude of the friction force needed to ensure that the reticle would not slip during the acceleration/deceleration loading seen in the scanning exposure process.