A new approach to the DFM for the metals

Metal layers have some drawbacks in building up model based OPC (MBOPC) because metal layers are mainly composed of 2 dimensional (2D) patterns which show modeling inaccuracy and the difficulty of fragment optimization compared with 1-dimensional patterns. As a result, metal layers have considerable hot spots such as pinch, bridge and insufficient contact overlap. The modeling inaccuracy of 2D patterns results from a few reasons like measurement noise, inaccurate optical simulation and empirical resist modeling etc. The fragment optimization operated by rule does not control automatically corner rounding problems induced by small jogs of 2D patterns. The design for manufacturability (DFM) is known to provide a solution to overcome these problems. One of engines operating the DFM is MBOPC, which is made by an empirical process model and offers the process variation counter map simulated by the MBOPC engine. However, the accuracy of the simulation is quite low because we cannot avoid over-corrected patterns generated inevitably with the empirical model. In order to detect and correct the hot spots caused by the design itself, that is, the inherent function of the DFM, it is necessary to provide the OPC engine of the physical model with the optimized illumination condition to rule out empirical effect. Physical model is more emphasized in case of process window simulation because of its accuracy in the edge boundary of process window. One of important function of DFM for the metal layers is to enhance the contact overlap margin which can be influenced by the lithography process such as line end shortening, corner rounding effect and miss-alignment. Etch process is also a significant parameter of contact overlap. Calibrated process model is very effective to detect the insufficient contact overlap with process window. In this paper, MBOPC of sub-45nm node metal layers is studied to provide the effective DFM engine. The DFM flow with renewed MBOPC engine will show the improved process window and large contact overlap margin and will also make it possible to search and correct just patterns capable of decreasing the process window by only layout defect itself.