The requirement for state-of-the-art performance by overlay metrology at the 65nm technology node drives the development and design of new optical metrology solutions. The use of measurement modeling is increasing, affecting the tool concepts, tolerances, and calibrations, as well as the overlay target design. In this article, we present our overlay metrology simulation platform, developed in-house, and its central role in optical performance modeling. The simulation validation tests are presented using standard overlay test wafers. The impact of residual optical aberrations with different overlay targets is simulated, emphasizing the degree of control needed to support overlay measurement methodology.