定量化準同步差動干涉對比顯微術之研發

Abstract

差分干涉對比(DIC)顯微術是一種解決傳統光學顯微鏡中由於參考光和物體光強度明顯不相等而產生低對比度干涉的方法。DIC技術最初僅用於增強透明試樣對環境的圖像對比度，但定量化測量的能力近年來在工業應用中變得至關重要，為了重建待測物三維形貌，必須獲得兩正交的DIC相位梯度圖。 本研究研發出一套基於同步空間相移與差分干涉對比技術的量測系統，可用於檢驗奈米級反射型態待測物三維形貌量測，由於共光路的特性，所有軸向振動造成的影響皆可以被兩道光自相抵消，因此本系統具有高度的抗振能力。 本研究之技術發展成功整合空間相位移術、雙折射晶體之分光效應、及傅立葉積分方法等原理達成即時三維形貌量測之目標。系統採用兩片Savart稜鏡，簡單地產生兩組橫向剪切波，此外，藉由偏振態相機搭配四分之一波板，可以立即獲得四幅相位相隔45°之干涉影像進行相位移術，取得兩垂直方向的相位梯度資訊，最後使用Frankot-Chellappa 演算法來進行三維形貌重建。 本文對所提出的系統進行了理論描述，且使用70 nm之標準階高塊作為系統量測之驗證，另外，本系統亦量測一工業產品，微透鏡陣列，並成功重建其三維形貌。

Differential interference contrast (DIC) microscopy has been emerging as a solution to overcome the low contrast interference incurred by significantly unequal intensity of reference and object light beams in conventional optical microscopes. Although DIC was originally used to enhance the contrast of transparent sample images, the ability of quantitative measurement has become very important in industrial applications in recent years. In order to reconstruct the 3D profile of the sample, two orthogonal DIC phase gradient maps must be obtained. A measurement system has been developed based on quantitative simultaneous spatial phase-shifting and differential interference contrast (DIC) technique to measure the 3D profile of the nanoscale reflected samples. Due to the characteristics of common optical path, all the effects of axial vibration can be offset by two beams, so the system introduces high anti-vibration ability. The developed measuring methods employ spatial phase-shifting, light splitting by birefringent crystal and Fourier integration method to achieve the simultaneous measurement of 3D profile. The system used two Savart prisms and simply produced two sets of shear waves. In addition, by combining a polarizing camera with a quarter wave plate, four phase-shifting interference images can be obtained for phase-shifting technique, and phase gradient maps in two vertical directions can be obtained. Finally, Frankot-Chellappa algorithm is used to complete 3D profile reconstruction. The proposed system was theoretically described and verified by step height standard of 70 nm, while the system also measured an industrial product, microlens array, and successfully reconstructed its 3D profile.