Monitoring and characterization of metal-over-contact based edge-contour extraction measurement followed by electrical simulation

The aggressive design rules of deep sub-micron technology using Cu metal over Wplugs, makes process monitoring and characterization a real challenge. Lack of metal coverage above contact may cause yield degradation due to un-predicted contact resistance. Due to proximity effects and Optical-Proximity-Correction (OPC) restrictions, different layout configuration of metal-over-contact may results in different contact coverage by the metal. From metrology point-of-view, the ability to control process latitude of two constituent layers in the semiconductor process is critical. The basic way to develop and control Metal over Contact process with a CD-SEM is to measure the contact plugs through the metal trenches. This approach proposes a significant metrological challenge. There is no edge topography, only material contrast, and only part of the Contact can be seen. Hence, innovative algorithms and image processing techniques are required to accurately measure the metal-over-contact area coverage. In this paper, we demonstrate a reliable characterization and monitoring method. A dedicated test chip was designed for this purpose, having ~650 of different layout configurations and dimensions, in one nanometer variation. The methodology flow consists of using systematic Edge-Contour-Extraction (ECE). The physical parameters extracted from the ECE measurements analysis are used for several purposes: (i) identification of design-rule verification, (ii) contact resistance calculation based on the metal-over-contact coverage area, (iii) reliable feedback for OPC correction efficiency.