Effect of van der Waals forces on Retilce Nonflatness in Extreme Ultraviolet Lithography

Abstract

Due to the increasing cost of the enhancement techniques in current projection lithographic techniques and the required time in developing new technology's as feasible manufacturing technology, EUVL is considered as the leading candidate for production of 45 nm node and less. In EUVL, mask is held electrostatically against chuck. This electrostatic chucking process affects the nonflatness of the mask due to contact interaction and the voltage force between the mask and chuck. A fundamental understanding of chucking phenomenon is required to realize the SEMI P37 and SEMI P40 stringent flatness requirements. The primary challenge is to understand and characterize the ability of electrostatic chucking phenomenon to acheive consistent and reliable shapes of chucked masks. The objective of this thesis is to study the effect of initial nonflatness of mask and chuck, chucking voltage, chuck and mask dimension and gravity on the final nonflatness of the mask A finite element model of the mask and chuck with initial nonflat surface is developed. To predict the final nonflatness of the mask frontside with nm accuracy, the contact interaction between mask and chuck is modeled using van der Waals forces. These results are compared with penalty method for the runtime and accuracy of results