全場顯微干涉術及其在折射率及表面形貌之量測應用

Abstract

本論文主要描述利用外差干涉術取代目前顯微干涉術中的傳統光干涉方法，進而改良成為全場外差干涉顯微技術。利用此技術可量測微米尺度下的二維相位延遲分佈、折射率分佈、表面形貌分佈等等。將單點量測擴展成為全場時，必須解決參考訊號的取得問題，在此提出兩種可決定全場絕對相位的新方法，利用較低振幅鋸齒波或非對稱三角波做為驅動電光晶體的電壓訊號，使得外差干涉訊號產生斷點而決定出參考相位，進而得到絕對相位。 在二維相位延遲的量測方法中，以共光程干涉儀的架構，使外差光束通過待測樣本與檢偏板，在任一像素位置上擷取到呈現弦波的干涉光訊號，其相位則為相位延遲量。這些取樣數據可經由IEEE 1241標準規範中提到的最小平方弦波擬合法，擬合成一連續弦波，待扣除參考訊號之相位後，則可求得該像素位置的相位延遲，而其他像素亦可藉此方法得到，即可完成全場相位延遲分佈的量測。 在折射率分佈的量測方法中，提出一種垂直入射的方法來進行。利用線性與旋光外差光束依序進入一改良式Twyman-Green干涉儀的光學架構中並得到干涉訊號之相位值，之後由Fresnel公式可推得相位與折射率之間的關係，而解出二維折射率分佈。在表面形貌分佈的量測方法中，將外差光束準直後進入一改良式Linnik顯微鏡的光學架構並得到干涉訊號之相位值，之後由兩臂光程差與相位差值的關係進而解得二維表面形貌分佈。另外為了改良顯微鏡系統之量測區域範圍與角度大小的限制，利用影像縫合技術，將不同位置或不同角度所測得多張影像的重疊區域，經由最佳化的旋轉平移矩陣運算而縫合成一完整影像，進而得到完整的樣本表面形貌。 本論文所提出的量測方法有光學操作簡單、高量測解析度以及高重現性等優點。

The heterodyne interferometry is introduced to the conventional interference microscopy to measure full-field phase retardation, refractive index distribution and surface topography. For determining full-field absolute phases, two different voltage signals, the saw-tooth wave with lower amplitude and the asymmetric triangle wave, are applied to drive the electro-optic modulator. Their break point positions are used to derive the reference phases. A common path heterodyne interferometry is applied to measure the full-field phase retardation. A heterodyne light passes through the sample and an analyzer. The interference intensities recorded at any pixel of camera are the sampling points of a sinusoidal signal. The phase of that pixel can be derived with a least-square sine fitting algorithm on IEEE 1241 standard. Subtracting the reference phase, the phase retardation can be obtained. The retardations at other pixels can be obtained similarly. The full-field phase distributions are measured with a modified Twyman-Green interferometer, in which linearly/circularly polarized heterodyne light beams are used in order. The measured data are substituted into the special equations derived from Fresnel equations, and the full-field refractive index distribution can be obtained. In addition, the height distribution can be calculated from the phase distribution measured by using a modified Linnik microscope with a heterodyne light source. Because the measurable region of a microscope is restricted, the overall topography of measuring larger samples cannot be obtained in a single measurement. It can be improved by measuring at different angles and positions. Then, these data are merged together to form the associated geometrical topography with the image stitching method. The above methods have several merits such as easy operation, high resolution and rapid measurement.