SENSAT-a practical tool for estimation of the IC layout sensitivity to spot defects

A practical interactive tool, SENSAT, is presented for IC layout optimization based on the concept of sensitive area. Since reduction of the layout sensitivity to shorts may increase its sensitivity to opens and vice versa, a practical tool must determine sensitive areas for both. The main function of SENSAT is to extract and display the sensitive areas in the IC masks. Crucial algorithms in SENSAT are the algorithms which determine shapes of the sensitive areas for shorts and opens in the actual layout. In this work we focus our attention on the sensitive area for opens. We demonstrate that in the case of arbitrary mask geometry there are qualitative differences between the concepts of the sensitive areas for shorts and for opens, and a more complex algorithm is needed to find the sensitive areas for opens. We propose such an algorithm. This algorithm has been implemented in SENSAT together with a known algorithm which determines the sensitive areas for shorts. A practical example of optimization of an analog CMOS cell layout shows how our tool can be used to reduce the sensitivity of a layout to spot defects