In this paper we perform a fundamental study on the impact of mask absorber in ArF immersions lithography: the mask 3D effects. From simulations and analysis of diffraction coefficients we could identify a range of relevant features and imaging and placement phenomena. For these features, experimental results were obtained to pinpoint the mask 3D effects. We will demonstrate how to model and understand the mask 3D effects and give solutions to counteract the mask 3D effects.© (2011) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.