大氣電漿沉積大面積氧化鋅薄膜與材料性質分布

Material Properties Uniformity of Large Area Ga-doped ZnO Thin Films Deposited by Atmospheric Pressure Plasma Jet

林心恬(Hsin-Tien Lin)

指導教授 ： 潘國隆

共同指導教授 ： 莊嘉揚

國立臺灣大學/工學院/機械工程學研究所/碩士(2015年)

https://doi.org/10.6342/NTU.2015.00568

摘要

透明導電氧化物在近年來引起許多人的興趣並且被廣泛的研究,因為其在 光電元件上扮演了重要的角色。目前最常被使用的透明導電材料為銦錫氧化物 (Indium Tin Oxide, ITO),銦錫氧化物擁有高導電性、寬能隙,並且在可見光區 域有良好的穿透度,然而銦的含量稀少,使得銦錫氧化物成本不斷提高。氧化鋅 (Zinc Oxide, ZnO)因其擁有高化學及機械穩定性、含量豐富、無毒性、以及高 電子移動率,便成為氧化銦錫的適合替代物。氧化鋅為 II-VI 型透明半導體,擁 有寬能隙(~3.37 eV)並高結合能(60 meV),氧化鋅摻雜鋁、鎵等金屬能有很 好的傳導性及穿透率。
噴射式大氣電漿法(AtmosphericPressurePlasmaJet,APPJ) 提供了相對簡 易並低成本的鍍膜製氧化鋅薄膜的方式,其操作環境為常壓,並且可以在基板溫 度低於200度的環境下運作,能夠免去抽真空以及將環境加熱的成本,並且透過 噴頭對基板掃描的方式可以進行大面積的鍍膜。
本研究使用大氣電漿在大小為 185 mm × 117 mm 玻璃基板上鍍製摻雜鎵之 氧化鋅薄膜,以不同的軌跡及鍍製參數來探討其對薄膜性質以及阻值均勻度的影 響。鍍膜參數中由不同的鍍膜開始實驗探討大氣電漿鍍膜的穩定性,並且改變基 板溫度及掃描速度來探討其對氧化鋅薄膜的影響。實驗發現大氣電漿鍍膜會隨鍍 膜時間而漸趨穩定,穩定後可以得到較低阻值的薄膜,並且在較高的基板溫度、 較低的掃描速度下有較低的片電阻值,目前可得的最佳結果為平均阻值 49.4 Ω/□、均勻度 7%、穿透度為 86.2%的薄膜。從腔體外氣流的實驗發現環境的流場 會影響薄膜的形成,腔體外氣流會將雜質帶走,形成膜厚較低、電阻率較低的薄 膜,但會影響薄膜片電阻值的分布。另外使用迴旋式軌跡鍍膜可以得到中央阻值 最低的薄膜,本研究中將迴旋式軌跡與柵型往復式軌跡做疊加,使用組合式軌跡可以得到片電阻值均勻度更低的薄膜。

關鍵字

透明導電氧化物 ； 氧化鋅 ； 噴射式大氣電漿法 ； 掃描軌跡 ； 阻值分布

並列摘要

Transparent conductive oxides (TCO) thin films have drawn great interests and have been widely studied in recent years because of their important role as electrodes in various optoelectronic devices. One of the most widely used TCOs is tin-doped indium oxide (ITO) due to its high electrical conductivity, wide band gap, and high transparency in the visible spectral range. However, indium is rare in the Earth’s crust, which increases the production cost of ITO. Owing to its high chemical and mechanical stability, high abundance, nontoxicity, and exceptionally high electron mobility, zinc oxide (ZnO) thin film has become one of the popular alternatives to ITO films. ZnO is a well-known II-VI transparent semiconductor with a wide direct band gap of ~3.37 eV at room temperature, and a high exciton binding energy of 60 meV. ZnO heavily doped with metals, such as Al, Ga and In, shows Fermi level degeneration and thus behaves metallic along with its high transparency.
Atmospheric pressure plasma jet (APPJ) technology provides a relatively simple and cost-effective method to deposit gallium-doped zinc oxide (GZO or ZnO:Ga) films onto large-area glass substrates in atmosphere. APPJ is simple and compatible with a wide range of precursor materials, facilitating the incorporation of suitable dopants without the need of heating the substrate over 200 C.
We prepare GZO thin films on 185 mm × 117 mm glass substrates by APPJ,
and study the effects of deposition parameter and trajectory on film sheet resistance
uniformity. In this study, we find that during the deposition, the plasma jet deposition
becomes more stable over time, and is able to deposit films with lower sheet
resistance. By adjusting the substrate temperature and scanning speed, we find that
films deposited with a higher substrate temperature and a lower scanning speed exhibit lower sheet resistance. The lowest sheet resistance of 49.4 Ω/□ and uniformity
of 7% is obtained. In the external flow experiment, we observe that the flow field
between the plasma jet chamber and the tool enclosure has a significant effect on the
film quality and uniformity. The films near the exhaust of the enclosure tend to exhibit
higher resistivity. The exact mechanism is still unclear and is a topic for future work.
Using the concentric trajectory we can obtain films with the lowest sheet resistance in
the central area. By using a raster scan on top of a concentric scan, we obtain a
two-layer film with better uniformity.

並列關鍵字

Transparent conductive oxides (TCO) ； zinc oxide (ZnO) ； Atmospheric pressure plasma jet (APPJ) ； scanning trajectory ； sheet resistance distribution

參考文獻

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