Structural, optical and mechanical properties of aluminium nitride films prepared by reactive DC magnetron sputtering
Introduction
Aluminium nitride (AlN) has many attractive properties including high thermal stability, high electrical resistivity, low dielectric constant, high thermal conductivity, high acoustic wave conduction velocity, wide band gap (6.2 eV) etc. [1], [2] which make AlN a promising material for a variety of applications in electronic, optoelectronic, surface acoustic wave and structural components [3]. Also, AlN is a strong candidate for the fabrication of optical devices for UV–Visible spectral region applications [4]. Many techniques, such as sputtering [5], [6], CVD [7], PLD and MBE [8] have been used to prepare AlN films on different substrates for different kind of applications. In most of the above said methods the preparation temperature is very high which has the potential disadvantage of degradation of the substrate and the AlN thin film during deposition due to thermal damage. Hence, room temperature preparation of AlN is attractive and very important [9]. Reactive sputtering is an important industrial method for the fabrication of thin films at room temperature. Also it can be easily scaled up from small sized laboratory targets to large-scale industrial applications. The attractive properties of AlN have motivated us to investigate the influence of N2 flow variation during sputtering upon the film properties by different methods. Hence, in this study we have prepared AlN films by reactive DC magnetron sputtering and studied the film properties by variety of methods to determine film property correlations.
Section snippets
Experimental procedure
Aluminium nitride films were prepared by reactive DC magnetron sputtering of an Al target (76 mm diameter and 6 mm thickness) in an Ar–N2 atmosphere. The sputtering chamber is equipped with six different cathodes and is capable of sputtering 24 substrates. Initially the chamber was pumped down to 10− 4 Pa by a turbo pump. In the present study, sputtering was performed at room temperature with a target substrate distance of 55 mm, a constant cathode current of 500 mA and a pressure of 0.8 Pa as
Deposition characteristics
Fig. 1(a) shows the mass of aluminium and aluminium nitride deposited per second on a quartz crystal microbalance as a function of nitrogen flow. Nitrogen flow was varied from 0 to 7 sccm. Data have been collected for both increasing and decreasing nitrogen flow. In Fig. 1(b) the variation of Al target potential is plotted as a function of N2 flow for a constant cathode current of 500 mA. It is interesting to note that both mass deposition rate and target potential follow the similar trend for
Conclusion
Aluminium nitride films have been prepared by reactive DC magnetron sputtering on glass, Si(100) and graphite substrates at different nitrogen flow rate but for a fixed total pressure (0.8 Pa). From quartz crystal microbalance studies it has been found that the Al target does not show any pronounced hysteresis as in the case of oxide sputtering. RBS measurements reveal that at low N2 flow the films are non-stoichiometric, while stoichiometrc AlN films can be prepared above 4.75 sccm of N2 flow.
Acknowledgements
One of the authors (S. Venkataraj) would like to thank the Alexander von Humboldt foundation for a fellowship to carry out this work at I. Physikalisches Institut (1A) der RWTH Aachen, Germany. Financial support from the Deutsche Forschungsgemeinschaft within project Wu 243/6 is highly acknowledged.
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