原子層沉積技術臨場摻鋁氧化鋅薄膜之製備與應用研究

Abstract

我們發展一套新穎的原子層沉積製程，此製程展現了高深寬比與極薄膜披覆的優越能力，並可大幅提升元件之場發特性。首先利用新穎氣流中斷法製程，使得原子層沉積系統可以獲得高品質的氧化鋅磊晶薄膜。在這實驗中，同時使用氣流中斷法與傳統連續氣流法的原子層沉積系統，在成長溫度25 – 260 °C區間，成長氧化鋅薄膜在m面的藍寶石基板上。由此進而得知最佳成長磊晶薄膜的溫度為200 °C。X光繞射的結果得知氣流中斷法確實改善了薄膜的結晶性，此乃歸因於氣流中斷法的步驟增加了前驅物二乙基鋅與水的反應時間。氣流中斷法同時顯著的提升氧化鋅薄膜的結晶性、光性與電遷移性質。 接著以氣流中斷法為基礎，吾人更進一步發展出臨場摻雜之原子層沉積技術，以獲得高品質均勻摻鋁之氧化鋅薄膜。此部分實驗，在成長溫度200-280 °C之間，經由臨場摻雜氣流中斷法的原子層沉積系統成長摻鋁氧化鋅薄膜在玻璃上。當薄膜厚度為110 nm時，成長溫度在260 °C，呈現最低的電阻率。當摻雜比例為 6 :1 時，最低的電阻率~5.7 × 10-4 Ω cm、載子遷移率為8.80 cm2 V-1 s-1 ，400nm - 800nm的光穿透率達到94%.。摻鋁的氧化鋅薄膜成長在m面的藍寶石基板，在X光繞射的結果中，顯示為正交晶系的氧化鋅(110)晶面呈現二軸對稱的磊晶本質。本實驗全部的結果都顯示臨場摻雜氣流中斷法的原子層沉積系統更簡化了控制摻鋁氧化鋅的鋁含量與更能使用在高深寬比結構披覆的應用。 最後的實驗部分展現出一種簡單而有效的方法，製備極薄摻鋁氧化鋅薄膜/氧化鋅奈米線的核殼結構，以獲得最低電阻率與優越的場發性質。摻鋁氧化鋅薄膜/氧化鋅奈米線的核殼結構形成，是經由典型的汽相傳輸法成長奈米柱與臨場摻雜的氣流中斷法原子層沉積系統做成摻鋁氧化鋅薄膜的殼層披覆結構。網型形態的鋁氧化鋅薄膜/氧化鋅奈米線的核殼結構顯示：摻鋁氧化鋅薄膜成長在400週期厚度下，有最低之面電阻~3.3 Ω/cm2 ，相當於純氧化鋅奈米柱電阻的萬分之一。使用新穎原子層沉積製程，成長摻鋁的氧化鋅薄膜提供了一種簡單降低電阻的表面改質方法，此可應用在元件上增強其場發性質。

We developed a novel process for atomic-layer deposition (ALD) that yields ultrathin films of large aspect ratio and superior performance, coated to enhance field emission. We first applied interrupted flow (IF) to obtain high quality epitaxial ZnO films. The thin films of m-plane ZnO were grown on m-plane sapphire substrates by ALD with IF and with a conventional continuous-flow method in a temperature range 25 – 260 °C. The optimal temperature to obtain epitaxial ZnO films was 200 °C. The x-ray diffraction results indicate that the addition of interrupted flow might extend the duration of reaction of diethylzinc and water to improve the crystallographic quality of the films. The IF method showed strongly improved crystalline quality, optical properties and electrical mobility of ZnO films. We further developed in-situ doped-ALD with an interrupted flow to obtain uniform aluminium-doped ZnO films. In-situ Al-doped ZnO (AZO) films were grown on glass substrates with atomic-layer deposition (ALD) and interrupted flow at temperatures in the range 200-280 °C; the optimal temperature, 260 °C, depended on the electrical properties at the same thickness ~ 110 nm. The electrical resistivity was least, 5.7×10-4 Ω cm, for ALD-AZO films with pulse ratio 6:1; the carrier mobility was 8.80 cm2 V-1 s-1 with optical transmittance up to 94 % in a range 400 - 800 nm. The in-situ epitaxial AZO films grown also on m-plane sapphire exhibited the two-fold symmetry of ZnO (110) in the orthorhombic crystal system. All results show that a novel in-situ doping method with an interrupted flow controls the Al content of AZO films more easily, and is more usefully applicable for a structure with a large aspect ratio for an advanced photoelectric device. Finally, we demonstrated a simple yet effective method to fabricate ultrathin AZO/ZnO-nanowire core-shell structures with minute resistance and superior field-emission performance. In this work, an AZO/ZnO-NW core–shell structure was obtained with a traditional vapor-transport and ALD system in-situ. The morphology of the net-like AZO at 400 cycles (~100 nm)/ZnO-NW had sheet resistance 3.3 Ω/cm2, about 1/10,000 the sheet resistance of ZnO-NW as grown. The ALD-AZO film provided a simple method to control the resistance for a surface modification that can be applied also to the field-emission properties. The enhancement of field emission was found to depend strongly on the thickness of the AZO film.