Experimental Investigation on the Sputtering Process for Tantalum Oxynitride Thin Films

Chuan Li,Jang-Hsing Hsieh,Y R Chuang

doi:10.3390/photonics8020053

Abstract

Metal oxynitrides are compounds between nitrides and oxides with a certain level of photocatalytic functions. The purpose of this study is to investigate an appropriate range of oxygen flow rate during sputtering for depositing tantalum oxynitride films. The sputtering process was carried out under fixed nitrogen but variable oxygen flow rates. Post rapid thermal annealing was conducted at 800 °C for 5 min to transform the as-deposited amorphous films into crystalline phases. The material characterizations of annealed films include X-ray diffraction and Raman spectroscopy for identifying crystal structures; scanning electron microscope for examining surface morphology; energy-dispersive X-ray spectroscopy to determine surface elemental compositions; four-point probe and Hall effect analysis to evaluate electrical resistivity; UV-visible-NIR spectroscopy for quantifying optical properties and optical bandgaps. To assess the photocatalytic function of oxynitride films, the degradation of methyl orange in de-ionized water was examined under continuous irradiation by a simulated solar light source for six hours. Results indicate that crystalline tantalum oxynitride films can be obtained if the O2 flow rate is chosen to be 0.25–1.5 sccm along with 10 sccm of N2 and 20 sccm of Ar. In particular, films deposited between 0.25 and 1.5 sccm O2 flow have higher efficiency in photodegradation on methyl orange due to a more comprehensive formation of oxynitrides.

Highlights

Certain transition metal oxynitrides are known photocatalysts capable of water splitting by the energy of photons in the range of visible light [1,2,3]
The purpose of various material characterizations in this study is to provide us an optimal window of deposition parameters for the fabrication of tantalum oxynitride films with appropriate microstructures, enabling photocatalytic function
Combining results from all the above assessments, we suggest that annealed tantalum oxynitride films deposited under ~0.25–1.5 sccm O2 supply should be capable of photocatalysis in our current setups for magnetron sputtering

Summary

Introduction

Certain transition metal oxynitrides are known photocatalysts capable of water splitting by the energy of photons in the range of visible light [1,2,3]. Much more like doping processes, these intra-bands provide alternative paths for electrons to change their states and serve as stepstones to the conduction band. If prudently articulating this mechanism, the electron-hole pair can be effectively separated and followed by further immediately available proximate photochemical reactions. From an engineering point of view, transition metal oxynitrides can be apt photocatalysts only under given optimal compositions and microstructures Another feature of transition metal oxynitrides is their good corrosive resistance because of the stable microstructures maintained by the coexistence of nitrides and oxides [1,2,3]. Metal oxynitrides are mechanically stronger than pure oxides because of denser structures packed by nitrides [4,5,6]

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