多波長光彈調變式橢圓偏光術

Abstract

摘要 多波長光彈調變式橢圓偏光術已可用於線上校正與即時量測。將偏光片/析光片轉動式引入光彈調變器可發展成一多波長光彈調變式橢圓偏光術。為了線上量測的封閉系統，本論文介紹一固定入射角線上校正法,將偏光片，析光片及光彈調變器一一根據待測物的反射面作零點的校正：首先，在偏光片-待測物-析光片的架構下,使用兩個事先設計的標準片或兩個適當的波長，可先根據入射面校正偏光片及析光片的方位角；隨後，再置入光彈調變器，透過方位角的轉動測得光彈調變器的方位角。 多倍頻亮度比技術可利用資料擷取系統校正光彈調變器的相位調變振幅。 經由反射式及穿透式架構判斷相位調變振幅,可證明不受頻率影響，甚至經由數位化波形確認。除了相位調變振幅之外，在632.8奈米波長下,我們也校正靜態殘餘相位延遲。既然光彈調變器的幾何尺寸固定，我們設定相位調變振幅為針對波長 568.2奈米的0.383個波長，並用於多波長相位調變振幅。線上即時的多波長光彈調變式橢圓偏光術之時間解析度已可至40微秒，此橢圓儀也已安裝在清華大學工科系電漿實驗室，用於監控電漿蝕刻製程。

Abstract Multi-wavelength Photoelastic Modulation ellipsometry has been used for in situ/ real time measurement. However, comparing to the rotating polarizer/analyzer ellipsometry, Photoelastic Modulation (PEM) ellipsometry introduces a wavelength-dependent element, the photoelastic modulator. The multi-wavelength PEM ellipsometry needs precise knowledge of the polarization of light emerging from the modulator. In this thesis, in situ azimuth alignment and real time phase calibration of the PEM ellipsometry has been achieved in multi-wavelength . The fixed incident angle azimuthal alignment technique is proposed to determine the azimuthal orientations of the polarizer and the analyzer to the incident plane by using two pre-designed testing samples or two probing wavelengths under a Polarizer-Sample-Analyzer (PSA) ellipsometric setup. Then, the azimuth of photoelastic modulator is directly obtained from the measurement of azimuthal rotation the PEM. A multiple harmonic intensity ratio technique is introduced to real time calibrate the modulation amplitude (do) of a photoelastic modulator by using a data acquisition system. The modulation amplitude do of PEM determined by this technique is proved to be frequency independent by the reflection and transmission setups, and further confirmed by the digitized oscilloscope waveform. In addition to its modulation amplitude do, we also calibrated its static phase retardation (Di) at 632.8 nm. Since the physical size of PEM is constant, we calibrated the do at multiple wavelengths by setting the Do (i.e. do / 2p) value at 0.383λ for 568.2 nm. An in situ/real time multi-wavelength PEM ellipsometry has be realized with a time resolution of 40ms. The practical system has been installed in NTHU for monitoring the plasma etching process.