A statistical method for fast and accurate capacitance extraction in the presence of floating dummy fills

Dummy fills are being extensively used to enhance CMP planarity. However presence of these fills can have a significant impact on the values of interconnect capacitances. Accurate capacitance extraction accounting for these dummies is CPU intensive and cumbersome. For one, there are typically hundreds to thousands of dummy fills in a small layout region, which stress the general purpose capacitance extractor. Second, since these dummy fills are not introduced by the designers, it is of no interest for them to see the capacitances to dummy fills in the extraction reports; they are interested in equivalent capacitances associated with signal power and ground nets. Hence extracting equivalent capacitances across nets of interest in the presence of large number of dummy fills is an important and challenging problem. We present a novel extension to the widely popular Monte-Carlo capacitance extraction technique. Our extension handles the dummy fills efficiently. We demonstrate the accuracy and scalability of our approach by two methods: (i) classical and golden technique of finding equivalent interconnect capacitances by eliminating dummy fills through the network reduction method and (ii) comparing extracted capacitances with measurement data from a test chip.