With optical lithography driving device-manufacturing capability to subwavelength dimensions, complicated phenomena that were once safely ignored art playing a crucial role in determining process quality. One such critical effect result from the consideration of mask topography. As low k1 processes are entering pilot production, we as an industry are finding that we can no longer simply treat the mask as a simple planar surface and therefore consideration of reticle topography is becoming as important as pre-CMP wafer topography once was. The use of advanced masks in a low-k1 process is far from straightforward however, because any image model describing these processes must now predict the effects of light scatter from the mask that lead to a loss in already low process tolerance we have. In this paper we will discuss the extraction of mask topography information, using advanced atomic force microscopy (AFM), and the resultant structures simulated through the use of electro-magnetic field simulation. We will also verify the accuracy of these simulations by examining the correlation between data gathered on an Aerial Image Measurement System and the simulations. We will further show how we have transferred these EMF simulated masks to a conventional lithography simulator to estimate the effects in the resultant photoresist image. This data will be compared to the actual performance of the masks when exposed using state-of-the-art processing.