The Mask 3D Effect on 2D Pattern Shape Fidelity, a Simulation Study

Abstract

Mask 3D effect has been viewed as a drawback to the pattern fidelity with major characteristics in higher mask error factor (MEF), lower image contrast, or exposure latitude (EL), and reduced common depth of focus (DOF) between dense and semi-dense patterns. Recently, we found that the mask 3D scattering can also result in pattern shape variation, which can make optical proximity correction (OPC) less difficult. We use both thin mask simulation and the 3D mask simulation tools on a regular proximity test pattern of contact holes and found that the holes are usually elliptical and the degree of ellipse is primarily dependent on the relative image contrast values in the mutually orthogonal dimensions, or X and Y directions. And we found through simulation that the mask 3D scattering can reduce the imaging contrast in the relatively speaking denser dimension, which will make the contact look more round.