Standard Cell Printability Grading and Hot Spot Detection

Abstract

Prior to 90nm the main contributor to yield loss was particle contamination. Random particle defects were directly proportional to particle density and chip size. To maximize yield, manufacturing was done in clean rooms where particles were reduced to a minimum. Yield was then directly proportional to the chip size. At 90nm and below, systematic defects play major roles in yield. Two designs of the same size can result in very different yield. This paradigm shift is caused by the printability problems that are inherent to process technologies operating in the sub-wavelength regime. The technology for printing patterns on silicon has not kept up with Moore's law. The wavelength of lithography equipment is as much as 6 times larger than the silicon features. This results in greater variation on silicon, which directly affects yield. How the design is implemented is becoming as important as how small you make it. Even at the standard cell level different solutions can demonstrate increased sensitivity to particles, short, opens, gate leakage and other yield issue. We present in this paper a methodology for grading how well standard cells will print on silicon. Using standard cell layouts, we predict a silicon image under different process conditions and take CD measurements on these images. These measurements are converted into a printability factor for each cell. This printability factor is used to grade cells and identify which cells have the largest impact on printability and which should be optimized. To help with this optimization the measurements are also used to mark printability hot spots in the cell layouts.