光彈調變式影像橢圓偏光儀

Abstract

本文介紹一利用光彈調變器的快速相位調變機制來量測二維橢圓偏極參數之影像式橢圓偏光儀。 本文量測一樣品厚度的二維分佈，並與單點量測的結果比較。 由於光彈調變器之調變速度遠快於二維偵測之電荷耦合元件(CCD)之影像傳輸速度，所以我們利用光彈調變器之方波參考訊號為時間對準的基礎，進而利用觸發脈波產生器 (pulse generator) 來對雷射二極體光源進行時間相位的調變，此系統需將時間相位確實調為0°, 30°, 90°以及210°； 故至少須取四張像方能換算二維橢圓偏光參數。 本系統的曝光時間則視亮度須要幾個脈衝波而決定。我們利用鉑 (Pt) 試片來確認時間相位起始點，並且將脈波量測結果與其檢波波型比較以校正此系統之架構。最後利用兩已知薄膜的厚度來驗證此系統二維量測之正確性。

A short pulse illumination method is proposed to measure the two-dimensional ellipsometric parameters by using CCD as the detector in a PEM ellipsometry. The time reference of the system is provided by the photoelastic modulator. The laser diode (□=660 nm) is modulated by a programmable pulse generator, the width of the pulse is 85 ns, and is generated exactly at the temporal phase angle is 0°, 30°, 90°, and 210°, respectively. Therefore, at least four image frames have to be recorded for ellipsometric parameters deduction in the modulation period (□20□s ) of PEM The exposure time of each CCD image is chosen for how many pulses are needed for its integrated flux. We use the platinum thin film to determine the temporal phase shift; and calibrate the system by comparing its oscilloscope waveform to the intensity measured through the modulated laser pulse. Finally, two optical thin films with different thickness were measured to demonstrate the results of two-dimensional ellipsometric parameters.