- 學位論文
白光干涉儀之尖峰數據消除演算法
Spike Data Removal Algorithm for White-Light Interferometer
摘要
在利用白光干涉儀進行垂直掃描干涉方式進行量測時，有兩種較為普遍的量測方式，其中相移干涉掃描適用於觀察表面的微小變化，而垂直掃描則可做有較大階高變化待測物的量測。在量測未知樣品時，使用相移干涉術時雖有高解析度之優點，卻受限於兩像素點的高度差必須小於四分之一波長之限制；垂直掃描量測則在低於四分之一波長的階高時常會產生蝠翼(bat-wing)現象而誤判其高度值，也容易將凹槽與凸起判斷錯誤。本研究的目的係在透過演算法消除如蝠翼等之尖峰數據並避免階高誤判，此方法亦不受限於相移干涉術之限制，使其結果同時具有兩種量測方法的優點。 為證實本改良演算法的可靠性，首先使用階高標準片進行量測，得到平均值為74.72nm相當接近75nm的階高片。其次使用原子力顯微鏡(AFM)與掃描式電子顯微鏡(SEM)量測未知矽晶圓試片，並與本演算法所得數據相互比較，得線寬最小誤差可達2nm，階高最小誤差小於1nm，因此可證明本演算法能消除尖峰數據並得到正確之表面輪廓。
並列摘要
Generally, there are two operating methods when using white light interferometry (WLI) to measure an object. First, phase shift interferometry (PSI) is applicable to observe small scale of change on the surface of sample. Second, vertical scanning interferometry (VSI) is usable to measure large scale of step height. Although PSI method has the advantage of high resolution, it is limited by the height difference between two pixels must be less than a quarter wavelengths. The weakness of VSI method is the misjudgment of vertical depth of grooves caused by bat-wings, the phenomenon often happens when the step height is less than quarter wavelength. The goal of this study is to develop an algorithm to eliminate the spike data when using VSI technique. The algorithm is not restricted by the weakness of PSI method; on the contrary it integrates the most promising advantages possessed by the PSI method and VSI method. In order to confirm the reliability of the algorithm, there are two experiments were executed in this investigation. First, a standard sheet with a step height of 75 nm was measured based on the proposed algorithm. The measured step height was 74.72 nm which is approximate to the nominal value. Second, a sample with a series of line-width on a silicon wafer was measured with VSI and the surface was reconstructed with the algorithm. The measured result was compared with the data obtained from an atomic force microscope (AFM) and a scanning electron microscope (SEM), an average error of 2 nm was found. This indicates that the spike data encountered in the WLI can be effectively eliminated and the surface morphology can be clearly reconstructed with the proposed technique.