Analysis of the mechanical response of extreme ultraviolet lithography masks during electrostatic chucking

Stringent flatness requirements have been imposed for the front and back surfaces of Extreme Ultraviolet Lithography (EUVL) masks to ensure successful pattern transfer that satisfies the image placement error budget. During exposure an electrostatic chuck will be used to support and flatten the mask. The EUVL Mask and Chucking Standards, SEMI P-37 and SEMI P-40, specify the flatness of the two mask surfaces as well as the chucking surface to be within about 50 nm peak-to-valley. It is critical that the electrostatic chucking process and its effect on mask flatness be well-understood. The principal objective of this thesis is to develop a model that predicts the electrostatic chucking response of masks and the resulting flatness of the pattern surface using FE techniques and to validate this model with chucking experiments.; Studies are performed to evaluate the definition of flatness as given in the SEMI standards and a more efficient representation is suggested. Classical plate theory is used to illustrate the effect of chuck thickness and stiffness on the chucking response of masks. A basic FE model is developed to demonstrate that the sum of the chuck shape and thickness variation of the mask are crucial to the response of the mask during chucking.; FE models are also developed to model clamping using a bipolar Coulombic pin chuck used for this research. The initial geometry of the mask and chuck surfaces are created using interferometric flatness data. Chucking is simulated by the application of forces between the mask backside and the chuck surface. The final pattern surface shape is compared with experimental electrostatic chucking results.; An experimental set-up is developed to validate the FE model predictions. This consists of a Zygo interferometer mounted on top of an optical table, inside a cleanroom, with the chuck and mask placed inside a vacuum chamber. Once the voltage is turned on, the pattern surface nonflatness is measured using the interferometer. The results from the FE model and chucking experiments are compared for two masks with different shapes to establish the validity of the models.