Preparation And Characterization Of Copper Nitride Films By Reactive Radio-frequency Magnetron Sputtering

In recent years, there has been much interest in studying the properties of Cu₃N films. Cu₃N is a promising material which has potential applications in the electronic industry, such as high-speed integrated circuits. Its low decomposition temperature and nature of non-toxic could be used in write-once read many optical storage instead of tellurium.Until now, Cu₃N films have been prepared with different methods, including ion-assisted vapor deposition, reactive rf magnetron sputtering, and direct current sputtering. The method of reactive rf magnetron sputtering with the character of highly active and convenient is used most. In our work, Cu₃N films were prepared on glass substrates via this method. We focus on the influence of nitrogen partial pressure on the structure, the grain size, the surface morphology and the electrical resistivity of the as-deposited films. Moreover, the sputtering pressure and the temperature of substrate were also studied to find the optimal deposition conditions.The structure of the films was analyzed by X-ray diffractometer (XRD) using Cu Kα radiation (D/Max-2400X, Rigaku Co., Japan). The fracture section and surface morphology of the films were studied using the scanning electron microscope (SEM, NanoScope-â…¢a, America) and the atomic force microscope (AFM). The UV-VIS spectroscopy (Specord-50, Germany) was employed to investigate the optical properties of the films. And the chemical composition of the films was identified by X-ray Photoelectron Spectroscopy (XPS, PhI5702, US) using A1 Kα radiation. The electrical resistivity of the films was measured using the four point resistivity test system.The major conclusions of this work were summarized as followings:Nano-structure Cu₃N films with excellent crystallization were deposited on glass substrate when the sputtering pressure was 1Pa, the temperature was 150℃, and the working gas was nitrogen. Nitrogen partial pressure greatly affects the preferential orientation of the crystalline films. By increasing nitrogen partial pressure, the densityof N atoms increase and N atoms reaching the substrate with high kinetic energy can possess appropriate kinetic energy to react with Cu atoms for constructing N-rich planes like (100), which leads to high density of Cu-N bonds for the preferential growth along the [100] direction. The as-deposited samples present brown color whereas present reddish purple after annealed about 300℃, which suggests that Cu3N has decomposed into Cu and N2 completely when the temperature is approaching about 300℃. The sectional SEM and plane-view AFM observations reveal that the films with clean and smooth surface morphology consist of tightly packed columnar grains and each of the columnar grain has a dome top with diameter size of about 25nm. The RMS roughness is very small. XRD and XPS confirm that the films only contain crystalline CU3N phase. The Cu/N ratio in the films is far larger than 3:1 according to EDS analysis. The as-deposited films were insulator when the distance between substrate and target was 60mm, but they were semiconductor when the distance was 40mm. The electrical resistivity increases from 1.51xlO2ï¿¡>cm to 1.13xl03ï¿¡>cm with increasing nitrogen partial pressure, and the optical energy of films increase accordingly. The films show low optical transmission in visible light, yet show high optical transmission in near-infrared regions. The difference in transmittance at about 900nm between the as-prepared CU3N film and the Cu film obtained by thermal decomposition of CU3N film is large enough (approximately 50%). The microscope hardness and reduced modulus of films was 6.0GPa and 108.3GPa, respectively. The mechanical property of films must be improved further.