電漿蝕刻在半導體製程的應用上相當重要，蝕刻製程的監測可使用橢圓儀量測薄膜的膜厚、表面粗糙度等變化。橢圓儀為利用光學的非破壞性量測，常用於各式薄膜的量測。我們實驗室在幾年前發展出一套可即時監測蝕刻製程的相位調變式橢圓儀系統，利用了光彈調變器，可以作蝕刻製程的即時監測。當蝕刻薄氧化層時，若進行過蝕刻常會造成表面變粗糙，利用我們實驗室所架設的蝕刻機台做蝕刻的即時量測，發現不同的蝕刻製程所造成的表面粗糙度會有不同，從即時監測的橢圓參數變化可以明顯看出其變化。我們將兩種試片：在矽晶片上成長薄氧化層的樣品，及純矽晶片樣品做蝕刻過程的比較，研究發現有薄氧化層時會使得蝕刻過氧化層後，對矽的蝕刻，表面粗糙度增加較快，對純矽晶片樣品的蝕刻，則經過長時間蝕刻後表面才會開始變粗糙。雖然無法直接從橢圓參數的變化計算出表面的粗糙度(因粗糙度甚大，已接近微米等級)，但可從橢圓參數反映出表面的粗糙度的變化，可了解蝕刻過程中試片表面型貌變化的情況。同時我們亦用AFM及SEM對不同階段的蝕刻結果作檢測，以了解表面形貌的實際變化。

Abstract

Plasma etching is an important etching process in the production of integrated circuits. In the plasma etching process, the ellipsometry can be used to monitor the etching process during the etching process. An in-situ ellipsometer using photo elastic modulator (PEM) was developed in our laboratory for monitoring the plasma etching of polysilicon. In this research, the in-situ ellipsometer was used in investigating the over-etching of silicon oxide thin film. The evolution of the surface roughness can also be monitored by the ellipsometer during the etching process. The etching of thin oxide film (about 30 nm on silicon wafer) was compared with the etching of bare silicon. It is found that the surface roughness begins to increase after the oxide layer is etched out. The surface roughness continues to increase rapidly as indicated by the ellipsometer signals. As for the etching of bare silicon, the surface remains smooth in the beginning of the etching for sometime, then it starts to become rough and the roughness also increases rapidly. Eventually the surface becomes needle-like as revealed by SEM. Although it is impossible to determine the magnitude of the surface roughness from the ellipsometry data, it is still very useful to use the ellipsometer to monitor the changes in the surface roughness during the over-etch of silicon oxides.

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