ELASTIC-DEFORMATION OF X-RAY-LITHOGRAPHY MASKS UNDER EXTERNAL LOADINGS

This paper describes the elastic deformation of x-ray lithography masks due to external loadings using finite element modeling. The design of the mask support structure is critical to achieve 0.25-mu-m device design rules, for which the mask contribution to the total overlay budget must be kept below 50 nm. Therefore the mask deformation due to external loads should be below 10 nm. Several three-dimensional finite element models were constructed to simulate x-ray lithography masks under gravity loading and external in-plane loading (an out-of-plane loading can be related to an equivalent in-plane loading via the Poisson ratio of the material). A figure of merit was developed to evaluate the relative stiffness of mask support structures, and to guide future x-ray lithography mask designs.