Preparation And Instability Of AZO Films Using Reactive Magnetron Sputtering Method

Al-doped ZnO?AZO?films with high transparency and good conductivity have broad application prospects in transparent thin film transistors and transparent conductive electrodes,and are expected to replace the commonly used indium tin oxide?ITO?transparent conductive materials.Reactive magnetron sputtering is a highly efficient film deposition method,but the process instability of reactive magnetron sputtering deposition of AZO films limits its wide application in industrial production.In this thesis,the effect of reactive RF magnetron sputtering deposition on the optical and electrical properties of AZO thin films was studied by using 5wt%Zn-Al alloy target.We explored the relationship between plasma and deposition processes in reactive magnetron sputtering and the process instability of reactive magnetron sputtering.The main conclusions are summaried below.?1?The effect of oxygen partial pressure on the deposition of AZO films by reactive RF magnetron sputtering was studied with fixed working pressure of 0.7 Pa and natural heating of quartz substrate.When the oxygen atom density in the plasma near the sputtering target is less than 3?10⁸ cm^-3,the reactive magnetron sputtering works in the metal mode,and a transparent AZO film with high conductivity can be prepared with a minimum resistivity close to 0.5 m?·cm;When the oxygen atom density is greater than 4?10⁸ cm^-3,the reactive magnetron sputtering works in the oxidation mode,and the transparency of the AZO film is improved,but the conductivity is drastically decreased.The conductivity of AZO film mainly depends on the content of Al in the grain,and the oxygen atom density is the key factor determining the precipitation of Al atoms.The main reason for the increase of resistivity of AZO thin films is that low Al content in grains,which leads to the decrease of carrier density and mobility.?2?The growth behavior of AZO thin films on sapphire and quartz substrates and their effects on photoelectric properties were studied by controlling the substrate temperature between 200 to 600?C at a fixed working pressure of 0.7 Pa.AZO films grown on sapphire and quartz substrates have single c-axis or c-axis preferred orientation,but the crystal quality of AZO films grown on sapphire substrates is better.AZO films grown on quartz and sapphire substrates at different temperatures have very high transparency,and the near-band edge defects decrease with the increase of substrate temperature.The resistivity of AZO films increases with the increase of substrate temperature,but the conductivity of AZO films grown on sapphire and quartz substrates is obviously different.On sapphire substrates,the resistivity of AZO films ranges from 0.5¹.5 m?·cm,while on quartz substrates,it ranges from 0.5¹5m?·cm.Hall measurements show that AZO films grown on sapphire and quartz substrates have similar carrier densities,but their mobility varies with substrate temperature.On quartz substrates,the main reason for the increase of resistivity is that the carrier mobility decreases obviously with the increase of substrate temperature.The effective mass of the electron in the conduction band is about 0.6 m₀,which is fitted by the optical bandgap and carrier density.?3?The oxygen atom density and electron excitation temperature near the surface of the sputtering target during the deposition of AZO thin films by RF magnetron sputtering were analyzed by plasma emission spectroscopy.The process instability of AZO film was discussed.In the case of fixed Ar/O₂ ratio,the electron excitation temperature of the plasma gradually decreases with the increases of working pressure,which is inversely proportional to the logarithm of the working pressure,and the oxygen atom density increases gradually.Under the fixed working pressure,with the increase of O₂ partial pressure,the electron excitation temperature gradually increases,which is related to the degree of surface oxidation of the sputtering target,and the oxygen atom density gradually increases.In addition,substrate temperature is also an important factor affecting plasma discharge.Under given working pressure and oxygen partial pressure,when the substrate temperature is less than 400?C,the substrate temperature has little effect on reactive RF magnetron sputtering plasma;When the substrate temperature is higher than 400?C,the electron excitation temperature of the plasma and oxygen atom density increase sharply with the increase of substrate temperature,which leads to the increase of the dissociation rate of the oxygen molecule.When the sputtering target is etched to a certain thickness,an abnormal metal-oxidation periodic oscillation mode is observed in the transition zone between metal and oxidation mode.The electron excitation temperature and Ar atomic emission spectra remain basically constant,while the oxygen atomic spectral intensity shows obvious periodic oscillation,which corresponds to the alternate transformation of metal and oxidation mode.AZO/Zn multilayer films with good visible-near-infrared reflectivity were successfully fabricated using a metal-oxidation periodic oscillation mode.