氧化銦錫(ITO)是一種透明導電氧化物(TCO)，它具有很高的可見光透射率同時又擁有實用的導電率。本研究以ITO作為研究主題主要是因為，即使在這透明導電材料百家爭鳴的世代，ITO仍然是高品質透明導電材料的首選，例如可撓顯示器的透明電極。這要的歸功於它優異的材料性質可利用大面積大量生產方式製造且品質重現度極高。在這篇論文中我們在不同的基板上-PET、矽晶圓、玻璃, 製作ITO薄膜並且鑑定它們的材料結構與光電特性。本研究所有ITO樣品都是以直流磁控濺鍍機製作，採用這個技術主要是因為，相對於其他的成膜技術(例如脈衝雷射法(PLD)，溶膠凝膠法等)，直流磁控濺鍍技術可以大面積生產且品質再現度高，總製造成本相對低廉；而且直流濺鍍技術已經實驗證實可以在常溫下產出高品質的ITO薄膜。
本論文主要區分為兩大研究主題: 第一，在PET基板上以直流磁控濺鍍機製作ITO薄膜的製程分析與最佳化; 第二，以光譜式橢圓偏光儀進行ITO薄膜的不均勻光學與電學性質分析。在第一項主題下，本研究先進行PET基板上濺鍍ITO薄膜 (ITO/PET)的實驗計畫以了解製程參數的變化對薄膜的光學與電學性質的影響趨勢。沉積時間、氬氣流量與靶材基板間隙是這個實驗計畫選定的製程控制參數。其中頗值得一提的是，我們克服了PET的光學非等向性的影響，成功地利用橢圓偏光術取得ITO的光學能隙、光學函數與厚度，藉此確定了影響ITO樣品透射率的主要原因。最終，在這個實驗裡我們不僅獲得了製程參數對光學與電學性質的影響趨勢並且得知薄膜性質對個別參數的敏感程度。接著，我們進行ITO/PET製程最佳化實驗，目標是要在微幅影響透射率的條件下獲得最低的ITO電阻率。在此最佳化實驗中我們提出一個新的概念-累積離子轟擊量,作為製程參數調控的依據以及樣品品質的觀察指標。實務上所謂累積離子轟擊量是以累積濺鍍氣體流量加以描述，它被定義為濺鍍氣體流量與濺鍍時間的乘積。同時, 為探討離子轟擊機制以及ITO光、電性質受基板材質的影響情形，我們選用了硬基板-矽-與軟基板-PET-作為比較對象。透過這個實驗我們不僅找到優化條件同時也以實驗證實其一致性;在最佳條件下ITO薄膜的ITO樣品(含PET)透射率平均值可達77.5%,，電阻率最低可達4.2 × 10-4 Ω cm，此結果與文獻非常接近。
最後,我們運用光譜式橢圓偏光儀探討玻璃基板上濺鍍ITO薄膜的不均勻光學與電學性質隨膜厚變化的情形。運用多層結構模型搭配選定的介電函數模型我們可以用光學量測法-橢圓偏光術-推估薄膜內部的不均勻光學性質，計算結果顯示薄膜內不同深層-表層與裡層-的光學吸收性有所差異性。由於介電函數的特性，我們同時可以用橢圓偏光術推估薄膜內部的不均勻電性 (含電阻率與載子狀態)，其可信度可用霍爾電性量測(Hall measurement)法之結果為基準加以評估。以多層結構模型估算的電性顯示表層與裡層的電阻率差異很明顯，透過自由載子的等效質量模型設定，這差異也反應在載子濃度與載子遷移率上，藉此，我們可以判斷各等效質量模型的適用性。
總結以上說明，這份研究在ITO薄膜研究領域提出幾點值得注意的貢獻:第一,我們發展出一套量測方法可解決PET的光學非等向性造成的干擾，成功的利用橢偏儀量測到ITO的厚度、複數折射率頻譜以及光學能隙，藉此確定了影響ITO樣品透射率的主要原因。
第二，針對ITO磁控濺鍍製程，本研究提出一個新的概念”累積離子轟擊量”作為ITO電阻率變化的觀察指標，並且以累積濺鍍氣體-沉積時間與濺鍍氣體流量的乘積-作為實際控制參數進行電阻率最佳化實驗。本研究成功的找出關鍵的累積濺鍍氣體條件並以重現性實驗證實其可行性並且證實，在這關鍵條件下，在PET基板上以直流濺鍍製作ITO薄膜，可以獲得極低的電阻率並且不致大幅影響透射率。
第三，本研究提出一個新方法，可以利用光學量測技術(橢圓偏光術)估算ITO薄膜內部的不均勻電性。這個新方法不但使我們能夠在霍爾電性量測無法進行的情況下(例如線上量測)獲得ITO薄膜的總電阻率，並且可以獲得薄膜內部不同層的電阻率、載子濃度與載子遷移率。

Tin doped indium oxide (ITO) is a kind of transparent conductive oxide (TCO) which has high transparency in the visible spectrum, combined with useful electrical conductivity. Selection of TCO film for application depends on device performance requirement and reproducibility using commercially feasible, large area processing techniques. ITO was chosen for this study for the reason that among different flavors of TCOs actively applied in recent year, ITO is still the most popular one for high quality application such as smart phone and liquid crystal displayer (LCD). In this dissertation, we present fabrication and characterization of ITO thin film on various types of substrate material, including polyethylene terephthalate (PET), silicon, and glass. The DC magnetic sputtering technique was selected to prepare all of our ITO samples because, among different available techniques for ITO deposition, including sol-gel deposition, pulsed laser deposition (PLD), and so forth, DC magnetron sputtering is commonly preferred due to its large area producible, good reproducibility, and relatively low cost. Moreover, the plastic substrates used in flexible electronics applications have a low thermal resistance, and thus sputtering should be performed at a low temperature in order to avoid thermal damage to the substrate surface. DC magnetic sputtering has been approved to deposit high quality ITO films on plastic substrate at room temperature.
There are two subjects consisted in the present work; the first: process analysis and optimization for ITO films deposited on the PET substrate using DC magnetic sputtering technique. The second: investigation into inhomogeneous optical and electrical properties of ITO thin film using spectroscopic ellipsometry. In the first subject, an experiment of deposition process for sputtered ITO thin film on the PET substrate was first performed to recognize the effects of deposition parameters on the characters of ITO film. The changes induced by changing of the deposition time, the argon flow rate and the target-substrate distance on the optical and electrical properties were identified in this section work. Consequently, for the purpose of process optimization, the electrical and optical properties of the ITO films on the PET substrate were then investigated as a function of the cumulative sputtering gas (CSG); a parameter newly proposed in this study and defined as the product of the gas flow rate and the deposition time. Meanwhile, a silicon based ITO thin film was prepared simultaneously with ITO film on the PET substrate in order to investigate the different ion bombardment condition between soft and hard substrates. In this section work, a critical deposition guideline was proposed and verified to obtain minimized resistivity without any significant reduction in the transmittance of ITO films.
Finally, this work investigated the thickness dependent inhomogeneous electrical and optical properties of ITO thin films deposited on glass substrates using spectroscopic ellipsometry (SE). Given multi-layer optical models and specific dielectric function models, the inhomogeneous optical function inside of ITO film can be measured by SE. Such multi-layer optical properties revealed an apparently different optical absorption between the bulk and transition area of ITO thin films. By the selected dielectric function models and effective mass models, the inhomogeneous electrical properties inside of ITO film can be measured by SE either. A comparison was performed between estimated electrical properties by SE and the values measured by Hall measurement for accuracy checking. The electrical resistivity estimated by the multi-layer model unveils apparent difference between the bulk and transition layer of ITO thin film. The difference on free carrier density and carrier mobility within the multi-layer ITO film can be estimated by modeling the effective mass of a free carrier in the Drude model. Accordingly, we had a feasibility study on effective mass models for ITO films with different thickness.
In summary, this report offers some remarkable contributions to the research on sputtered ITO thin film. The first contribution is that we proposed a method to locate the principle optical axis of anisotropic The PET substrates so that the dielectric function and optical gap obtained by SE measurement is more accurate for ITO films on such PET substrate. The obtained SE measurement results give some reasonable description of the changing of transmittance for our ITO samples.
The second one is: a new concept about “the cumulative ion bombardment” for sputtering technique was proposed and used to observe the variation of resistivity of ITO film. The cumulative sputtering gas defined by the product of the gas flow rate and the deposition time was used to approach the cumulative ion bombardment in practice and adopted as a control parameter in the optimal experiment for resistivity. A critical cumulative sputtering gas condition was discovered and verified by a repeatability experiment. The resistivity of the sputtered ITO/PET thin films can be minimized without any significant reduction in the transmittance following the guideline of critical cumulative sputtering gas condition.
The third one is: a novel method is developed in this study to estimate inhomogeneous electrical properties of ITO films. Such new method enables us to estimate the total resistivity whenever the Hall measurement is not accessible, for example, in-line measurement. Meanwhile, the method is available to obtain the resistivity, carrier density and carrier mobility of every sub-layer within an ITO film.

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