CLUSTERED DEFECTS IN IC FABRICATION - IMPACT ON PROCESS-CONTROL CHARTS

A control chart is a graphical record of sample measurements to track a manufacturing process over time. Measurements above or below control limits alert operators and engineers that the process is out-of-control. In IC fabrication, standard process control charts for defects often sound many false alarms, i.e., the chart incorrectly indicates the process is out-of-control. The cause for these false alarms in some cases: defects in IC fabrication tend to cluster, basic assumptions that support the construction of standard control charts for defect data. A method for distinguishing between data from an in-control process that yields clustered defects and data from an out-of-control process is contained. Further, a method for constructing defect control charts for processes that yield clustered defects is presented.