新型EWMA變動折扣因子控制器及其於半導體微影製程實際應用之研究

Abstract

由於半導體製程的特性，為使製程維持於一定的輸出水準。線上需使用到批次回饋控制。批次回饋控制的主要工作在於根據量測值與預先建立的輸入/輸出模型，改變系統的輸入值，以迫使下一批次的輸出值符合目標值。在控制的設計上必須注意兩點，一是控制的穩定性（Stability），一是控制的靈敏性（Sensitivity）。穩定性是指控制技術不會對製程產生不必要的過度控制，使得製程變異增加。而靈敏性指的是當製程發生異常時，控制法則能儘快地調整製程。而傳統上所使用的EWMA控制器其所使用的折扣因子通常為一固定常數，很難同時兼顧到對偏差調整的效率及減少因控制所造成不必要的變異。本文將介紹兩種非固定折扣因子的EWMA控制器，分別為利用偏差量來決定折扣因子的大小，以及結合統計製程管制觀念來決定折扣因子的的大小，並利用統計模擬方式探討此兩種方式與傳統固定折扣因子的優劣。最後並將新型控制器實際運用到半導體微影製程中確認新型控制器的效能。

The purpose of run-by-run controller is to fine tune the input parameters according to the process model setup from experiment to guarantee the output value can always meet the target. Due to the batch to batch variation property of the semiconductor manufacture process, the exponentially weighted moving average (EWMA) run-by-run controller is widely utilized through the front-end and back-end processes to improve the process yield. An ideal controller should be both sensitive and stable. For the stability, the controller should not over-control that will enlarge the variation of the process. And for the sensitivity, a good controller should be able to bring the process back to normal state within few runs when it has deviations due to different causes. The traditional EWMA controller with fixed discount factor can hardly meet both the stable and sensitive requirements. Thus in this study we will introduce two innovative EWMA controllers with variable discount factor. One is the deviation functional EWMA controller, and the other is to combine the statistical process control (SPC) with the EWMA controller. To evaluate the performance of these two controllers, we employ statistical simulation in different conditions, and implement these two controllers in the lithography process for critical dimension (CD) control.