On the Initialization of Threaded Run-to-Run Control of Semiconductor Manufacturing

Run-to-run control is a major tool used in semiconductor manufacturing to keep the unit processes within the required manufacturing constraints. Typically, the difference or bias between the desired and actual result of processing a particular wafer is affected by not only the particular product being produced, but also the prior processing path. Each unique combination of effects is called a thread, and in threaded run-to-run control a separate exponentially weighted moving average controller is applied for each thread. One of the challenges of threaded control is the initialization of the bias estimate for a new thread. Automated initialization methods prevent the cost of manual initialization or utilizing a pilot run, but at the risk of producing outliers in the initialized runs. On the other hand, the manual initialization or using pilot runs incur an extra expense. In this paper, we study a new approach for initialization of the threads by combining the threaded and nonthreaded control strategies. This method avoids the cost associated with manual initialization methods and improves the efficiency of automated methods. Finally, the simulation results will demonstrate the efficiency of the proposed method in comparison with other techniques.