顯影後關鍵尺寸之批次預測與控制

Abstract

半導體晶圓尺寸從8吋邁向12吋，線寬從微米縮小至奈米的新世代，晶圓越大線寬越小相對於製程方面也越來越複雜，晶圓製程中微影製程是決定線寬是否能更小的主要因素。 微影製程檢視又可分為三大類，層對層覆蓋誤差檢查（Overlay error）及線與孔的寬度檢查（Critical Dimensions, CD）以及顯影後檢查（After Develop Inspection, ADI），微影製程良率就是取決於這三項參數。

本論文所研究的方向是設計一套應用於微影製程之關鍵尺寸(Critical Dimension，CD)的批次(Run to Run)多輸入單輸出(MISO)先進製程控制方法。利用實驗設計法(Design of Experiment，DOE)找出步進機之輸入變數(製程配方:焦距跟能量)與輸出變數(關鍵尺寸)之間的關係，建立批次控制預測模式，然後利用Recursive Least Squares係數調變方法，作為模型係數的動態調整，以適應製程隨時間變化之變異及干擾，再以調變完成之模型係數更新批次控制器，計算出機台的最佳輸入變數（最佳能量以及最佳焦距），達到我們所設定的CD目標值，提高製程控制能力，增進晶圓的線寬品質。驗證結果發現ADI CD 的 在使用RLS Run to Run控制器後，能夠從沒有ADI CD回饋控制的1.472提升至1.8136，改善約23%。

Semiconductor wafer size has been increased from 8 inch to 12 inch, line width in the IC wafer has been reduced from micrometer to nanometer range. The bigger the wafer size and the smaller the line width, the more complicated the wafer manufacturing process. Photolithography process is the key process in reducing line width in IC wafer. There are three kinds of photolithography process inspection, i.e. overlay error, critical dimension （CD） and after develop Inspection （ADI）, the yield of photolithography process depends on these three parameters.

This research proposes a new run to run (MISO) advances process controller for photolithography process. In this thesis, the run to run control model among input recipes (focus and exposure dose) and output variables (Critical Dimension) are formed by using design of experiment (DOE) method. We then uses on-line recursive least squares (RLS) model identification to update parameters of run to run controller. We can find the best recipe (best focus and best exposure dose) to keep CD on the target, enhance the process control capability and improve the quality of line width on the wafer. According to experimental results， using RLS Run to Run controller, of ADI CD can be improved from 1.472 to 1.8136, a 23% improvement compared with the case of no feedback control of ADI CD.