Study On Low Temperature Deposition Of Thin Films By Pulsed Bias Arc Ion Plating

It is well known that the temperature of substrate has important pole on the microstructures and properties of thin films during arc ion plating (AIP) process, and therefore a recent trend of its development is applying pulsed biases to the substrate in order to decrease the temperature. It is necessary and significant to study the basic relationship between the temperature of the substrate and microstructures and properties of the films.The present work investigates the temperature of substrate through thermocouple during depositing TiN thin films by AIP, when d.c biases and pulsed biases are used in AIP-1 and Bulat6 deposition systems, respectively. The results show that the temperature of substrate is influenced by the distance between the substrate and the cathodes, the power of evaporating arcs and in particular the substrate biases, of which pulsed ones may effectively decrease the temperatures. It can also been seen that the temperatures are different in different systems even though the process parameters are the same. After discussing the effecting factors and their weights, a formula is derived to calculate the temperatures of the substrates on the basis of the Law of Conservation of Energy, and the reliability of this formula has been verified by the experimental results.The temperatures of substrates are basically and mainly determined by bombardments of ions, thermal radiation of the substrates and thermal conductivity through the axis of substrate holder. While other processes related thermal exchange are too insignificant and are neglected. The calculated results are consistent well with the experimental temperatures tested at d.c. biases, but the temperatures calculated at pulsed biases are not consistent well with the experimental ones. This can be attribute to the fact that the waveforms of voltage and current oscillate irregularly under pulsed biases, therefore the actual time average power is lower than the one used in calculation. Calculated and experimental results also show that the temperatures of substrates are effected by the shapes of substrates, physical properties of substrate materials, structure of apparatuses as well as other process parameters. These calculations can be used as references to design process of AIP in terms of the temperatures of substrates.The microstructures and properties of TiN thin films obtained by AIP are characterized. The general properties of TiN keep the same level or even are improved when d.c biases are replaced by pulsed ones even though the temperatures of substrates decrease distinctly. This can be verified by transitional electron microscopy (SEM)analysis. The grains of TiN obtained at pulsed biases are fine and uniform within the whole area while those obtained at d.c. biases are not uniform?fine in some areas but coarse in other areas. It is argued that the bombardment of an ion with the surface of the film accelerated by the biases may result in a very short time process of high temperature and high pressure within a very small volume, which is useful to synthesis TiN. The continuous bombardments at d.c. biases increase the whole temperature of the substrate and so a part of originally fine grains grows up and become coarse while others keep fine. When pulsed biases are used, the high temperature and high pressure process only occurs in the very small volume while the whole temperatures are lower, thus all of the grains don't grow and keep fine. At the premise of excellent properties, higher pulsed voltage and larger duty cycle (defined as the ratio of the time of a pulse to one period) cause better thin films. According to present work, the optimum results can be obtained at pulsed bias of 1000V with duty cycle of 20%.The experimental results show that the macroparticles (MPs) on the surface of TiN films can be eliminated by d.c. biases to some extent but too high voltages may decrease the deposition rate of TiN thin films because of the sputtering effects of strong bombardments of ions. Pulsed biases can be used to improve t...