氧化鎳薄膜之原子層沉積研究

Abstract

本研究運用鎳烯(nickelocene) 和臭氧分別做為原子層沉積技術(Atomic layer deposition, ALD)之反應前驅物來成長氧化鎳薄膜，並對薄膜基本特性進行分析。由研究結果顯示，ALD氧化鎳薄膜之製程溫度視窗範圍在150~250℃，於此範圍內其沉積速率約為0.7(A/cycle)。我們利用XPS分析測得ALD NiO薄膜中之殘碳量低(<4%)，且鎳原子與氧原子的比例接近化學計量比。同時在GIXRD、SEM和AFM的觀察下，可以發現ALD NiO是具有立方晶體結構排列且平坦的表面。此外，ALD NiO薄膜能有效阻擋氦氣氣體滲透，其阻氣性質的表現如同其他結晶材料之ALD薄膜，如氧化鋅和氧化鉿。在光學穿透度的表現上，ALD NiO薄膜在可見光波段中的穿透率均超過65%，由此估計ALD NiO的能隙為3.47eV。在電性方面，ALD NiO薄膜具有極低之載子濃度與極低之導電度，此乃因ALD NiO薄膜之元素組成接近化學計量比，使其鎳空缺或氧間隙原子等微結構缺陷產生的Ni3+陽離子含量極少所致。本研究所開發之ALD NiO薄膜將於下階段研究中應用於有機光電元件上。

This study develops an atomic layer deposition (ALD) process to deposit NiO thin films, using ozone as an oxidizing source and nickelocene (Ni(Cp)2) as a Ni-containing precursor. The ALD process window was found to be 150~250℃ with a deposition rate of ~0.7 A per cycle. XPS analysis revealed that the films were composed of nearly stoichiometric, Ni/O ratio = 0.95, with < 4% carbon content, indicating thorough reaction and low level of Ni vacancies which are typical of NiO films. GIXRD, SEM and AFM analyses show that the films were cubic polycrystalline, with NaCl-type structure, with ~12 nm crystal size and smooth surface. Additionally, the ALD NiO films were found to be effective gas-diffusion barriers when deposited on polymer substrates, with similar gas permeability to those of other crystalline metal oxide films by ALD, such as ZnO and HfO2. In terms of optical transparency, the ALD NiO films with 70nm thickness showed > 65% light transmittance across the visible light wavelength. From the visible light spectrum, the optical band gap of the ALD NiO was estimated to be 3.47eV. In terms of electrical properties, the ALD NiO films contained very low level of carrier (hole) concentration and thus were highly electrically insulating. This was attributed to the nearly stoichiometric Ni/O ratio of the films, which minimized the amount of holes associated with Ni vacancies or interstitial O atoms.