A simple method of photomask yield optimization by defect inspection

The quality of the photomask set decides to a large extent the quality and quantity of the device that will be produced. In order to ensure the quality of the photomasks, several sophisticated instruments are commercially available. However, in a research type of environment, the cost of such equipment can be prohibitive. In this paper, we propose a simple method of multiple master mask preparation with subsequent matching of defective die locations to optimize the master mask set. The advantage here is that a very good master mask set can be chosen so that minimum number of dies on the photomask set itself contribute to low wafer yield. The method is based on manual inspection of individual dies on photomasks and can be practically used for a complexity of up to 500 components.