Characterization of electrostatic chucks for extreme ultraviolet lithography

Abstract

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.

Electrostatic chucking of EUVL masks: coefficients of friction

“…Dynamic friction was found to be only marginally smaller than static friction and values in the range from 0.27 to 0.33 were obtained for the static friction coefficient under vacuum conditions. These values are a bit lower, but not far from previous friction results for an Alumina pin chuck on a CrN metallised mask blank 6 were static coefficients of friction around 0.35 were observed. The difference might well be related to the different material and surface conditions.…”

Role of wafer geometry in wafer chucking

“…The development of EUV lithography systems has driven increased interest in characterization of different electrostatic chucking mechanisms and their capabilities, but previous reports have largely focused on mask chucking. [5][6][7] As a result, there is a critical need to better understand the mechanics of the wafer chucking process and the role of wafer geometry in chuck performance.…”