A non-delta-chrome OPC methodology for process models with three-dimensional mask effects

Abstract

Delta-chrome optical proximity correction (OPC) has been widely adopted in lithographic patterning for semiconductor manufacturing. During the delta-chrome OPC iteration, a predetermined amount of chrome is added or subtracted from the mask pattern. With this chrome change, the change of exposure intensity error (IE) or the change of edge placement error (EPE) between the printed contour and the target pattern is then calculated based on standard Kirchhoff approximation. Linear approximation is used to predict the amount of the proper chrome change to remove the correction error. This approximation can be very fast and effective, but must be performed iteratively to capture interactions between chrome changes. As integrated circuit (IC) design shrinks to the deep sub-wavelength regime, previously ignored nonlinear process effects, such as three-dimensional (3D) mask effects and resist development effects, become significant for accurate prediction and correction of proximity effects. These nonlinearities challenge the deltachrome OPC methodology. The model response to mask pattern perturbation by linear approximation can be readily computed but inaccurate. In fact, computation of the mask perturbation response becomes complex and expensive. A non-delta-chrome OPC methodology with IE-based feedback compensation is proposed. It determines the amount of the proper chrome change based on IE without intensive computation of mask perturbation response. Its effectiveness in improving patterning fidelity and runtime is examined on a 50-nm practical circuit layout. Despite the presence and the absence of nonlinear 3D mask effects, our results show the proposed non-delta-chrome OPC outperforms the deltachrome one in terms of patterning fidelity and runtime. The results also demonstrate that process models with 3D mask effects limit the use of delta-chrome OPC methodology.