EUV phase mask engineering based on image optimisation

A phase mask concept is used in extreme UV (EUV) lithography to enhance the image resolution of structure nodes. Since an EUV resist model has not been developed yet, optimising the image of the intensity profile is applied here as an alternative for using the optical proximity correction to tailor a phase mask structure. Our optimised results show spaces corresponding to the structure nodes in 30.2 nm size for an attenuated phase mask and 9.7 nm for a chromeless phase mask, with less varying profiles for through-focus calculations. Optimised images have been obtained for application in negative and positive resists.