噴射式大氣電漿鍍製鎵摻雜氧化鋅薄膜之性質研究及均勻度改善

Characteristics and Uniformity Improvement of Ga-doped ZnO Thin Films Deposited by Atmospheric Pressure Plasma Jet

周東陞(Tung-Sheng Chou)

指導教授 ： 莊嘉揚

國立臺灣大學/工學院/機械工程學研究所/碩士(2014年)

https://doi.org/10.6342/NTU.2014.02389

摘要

目前透明導電膜材料以銦錫氧化物薄膜(Indium Tin Oxide, ITO)為主流，ITO具有相當低的電阻率(約10-4 Ω∙cm)、良好的可見光穿透率(>80%)等優良特性，但礙於銦的價格日益攀升，研究人員正積極地尋找替代材料。其中，又以氧化鋅相關的研究最為蓬勃發展，透過摻雜不同的金屬，目前以濺鍍法沉積的鎵摻雜氧化鋅(Ga-doped ZnO, GZO)薄膜已經能與ITO薄膜相抗衡。濺鍍法雖然有諸多優點，但是其操作環境必須在真空下進行，因此機台造價不低，且無法與其他製程進行連續製造。本研究使用噴射式大氣電漿(Atmospheric Pressure Plasma Jet, APPJ)進行GZO薄膜的鍍製，其優點是在大氣環境下進行鍍膜，免去高昂的真空腔體費用，且透過小面積漸進式掃描的方式可以在大面積基板上成膜。
本研究使用直流脈衝電源產生之噴射式大氣電漿，以柵形掃描(Raster Scan)軌跡在玻璃基板上沉積鎵摻雜之氧化鋅薄膜，分別在50 mm × 50 mm的小面積基板探討製程參數對氧化鋅薄膜品質的影響，以及在185 mm × 117 mm的大面積基板探討掃描路徑及外部氣流對電性均勻度的影響。在小面積基板方面，藉著控制包含掃描參數、前驅物鎵濃度、基板溫度、工作距離、主氣流量和混合載氣比例等，來了解其與薄膜光電性質的關聯性，進而找出一最佳組合。
在小面積基板，透過各參數的調配，將膜厚控制在150 nm左右能得到最好的光電特性。從調整大面積的掃描路徑我們發現，單次掃描的試片其片電阻隨著各區域大氣退火時間的上升而上升，且二次掃描比單次掃描路徑擁有較佳的電性均勻度，但是卻也造成中間區域有較高的片電阻。在外部氣流對均勻度影響的實驗中，抽風氣流會造成片電阻最大值的移動，產生一往抽風端的位移。我們透過膜厚量測、等效電路模型、X光繞射儀、掃描式電子顯微鏡、應力量測及霍爾量測來分析造成其電性分布不均的原因。

關鍵字

鎵摻雜氧化鋅 ； 噴射式大氣電漿 ； 片電阻 ； 均勻度 ； 軌跡效應

並列摘要

Indium tin oxide (ITO) is one of the most widely used transparent conductive oxide (TCO) materials owing to its low resistivity (about 10-4 Ω∙cm) and excellent transmittance at visible light range (over 80%). However, its principal component, indium, is scarce and expensive. Many researchers are searching for substitutive materials for ITO aggressively. Polycrystalline ZnO films on glass have been extensively developed. By doping different metal atoms, Ga doped ZnO (GZO) deposited by sputtering can now compete with ITO both in cost and quality. Althrough sputtering has many advantedges, it must work in vacuum and, hence, raises the cost. In addition, it is not suitable for mass production when integrating with other processes is required. In this study we use atmospheric pressure plasma jet (APPJ) to deposit GZO thin films in atmospheric pressure environment without a vacuum chamber. Deposition of thin films on large area substrate is achieved by moving the nozzle with respect to the substrate, and the material is continuously sprayed during the scanning process.
In this thesis we use APPJ generated by a DC pulse source to deposit GZO thin films on the glass substrate with a raster scanning trajectory. We discuss the effects of several key process parameters on the film deposited on smaller substrate with a dimension of 50 mm × 50 mm × 0.5 mm, and study the effects of electrical properties and uniformity of GZO thin films influenced by different trajectories and external flows on larger substrate, 185 mm × 117 mm × 0.5 mm in dimension. For the smaller sample, we adjust the parameters, including scanning recipe, Ga concentration, substrate temperature, gap, main gas flow rate and mixed carrier gas ratio, to understand the correlations between those parameters and photoelectric properties of the films, and as a result, obtain optimized recipes.
In small samples, the films with about 150 nm thickness have better optoelectronic properties. By adjusting scanning repcipe on large area samples, we find that the sheet resistance is proportional to the air annealing time for samples experiencing single scan (refered as single-pass sample); Two-pass samples, in which the scan begins from one edge to the opposite edge and returns to the original edge so that the entire film enssentially consist of two layers, exhibit better uniformity in general, but show highest sheet resistance near the center of the substrate. In the external flow experiments, the pumping flow, caused by a fan designed to remove undeposited materials, alters the sheet resistance distribution, in particular the region with the highest sheet resistance. We apply α-step, equivalent circuit models, XRD, SEM, residual stress measurement and Hall measurement to analyze the reason of nonuniform electrical properties.

並列關鍵字

Ga doped ZnO (GZO) ； atmospheric pressure plasma jet (APPJ) ； large area substrate ； uniformity ； trajectory effect

參考文獻

[24] 陳偉強, “藉由大氣電漿沉積氧化鋅摻雜鎵薄膜其光電特性與材料分析之研究,” 國立交通大學, 2010.

[42] 許耀文, “利用常壓式噴射式電漿沉積氧化鋅薄膜及其特性之研究,” 國立台灣大學, 2010.

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