化學機械研磨移除厚度之批片雙模式自適應控制

Abstract

化學機械研磨(Chemical-Mechanical Polish, CMP)是一個極為複雜的製程，因為牽涉到物理、化學及機械的領域[1]；對於一種輸出參數(例如移除率)而言，影響它的原因可能不只一種，甚至是極為複雜；而在一般的半導體廠裡，大多採用批次(Run-to-Run)製程控制來控制想要的輸出如均勻度或移除率等；所謂批次，就是由前一製程的資料來預測下一製程所需輸入的參數值，以控制輸出更能符合目標需求。 本研究參考批次的概念提出了兩種批片(Wafer–to -Wafer)之控制架構：指數加權移動平均(Exponentially Weighted Moving Average, EWMA) [1]以及雙模式自適應控制(Dual Mode Adaptive Control, DMAC) [2][3]，再進而比較這兩種控制器之優缺點及特性。實驗條件為不作修整(conditioning)研磨墊，最終控制目標為研磨厚度控制，輸入變數為時間，藉由輸入時間來控制輸出研磨厚度之SISO (Single-Input-Single-Output)系統。 實驗結果證明兩種控制系統都能達成研磨厚度控制目標。DMAC的控制成果較好並且能監聽及預測在線薄膜移除率的變化，作為預防性維修設備的參考，在機台移除率到達軟性下限的時候，才作修整研磨墊的動作，可以省去每作一片就修整研磨墊所浪費的時間；故建議使用DMAC達成CMP製程的厚度控制。

Chemical-Mechanical Polish is an extreme complicated process because it involves physical, chemical, and mechanical field [1]. There are many complicated factors which may affect its output parameters such as removal rate. In semiconductor industry, run-to-run process control is used extensively to control process outputs, e.g. uniformity and removal rate, etc.. Run-to-run process control uses the previous run process data to predict the next run process inputs to make the next run process outputs converge to the target outputs. This thesis uses the run-to-run idea to design two type of wafer-to-wafer control system : Exponentially Weighted Moving Average control [1] and Dual Mode Adaptive Control [2][3], and proceed to compare the performances of this two controllers. The experiment is conducted under no conditioning of the pad, and the objective is removal thickness control of CMP process, the input is time, and it’s a Single–Input–Single–Output system that uses input of time to control output of removal thickness. Experiment data prove both control systems can achieve design objective of removal thickness control. However, DMAC has better performance and provides on-line monitoring and estimate of removal rate as basis of preventive maintenance of CMP equipment, and it can save lots of time by conditioning the pad when removal rate reaches soft lower limit instead of wafer-to-wafer conditioning. Therefore, we recommend DMAC over EWMA for removal thickness control of CMP process.