Silicon Nitride Thin Films Deposited By Reactive Gas-timing Magnetron Sputtering For Protective Coating Applications

¹College of Nanotechnology, King Mongkut’s Institute of Technology Ladkrabang, Bangkok 10520, Thailand 

²NECTEC, National Science and Technology Development Agency (NSTDA),  Thailand Science Park, Pathumthani 12120, Thailand 

³Rajanagarindra Rajabhat University, Chachoengsao 24000, Thailand 

Adv. Mater. Lett., 2015, 6 (6), pp 554-559

DOI: 10.5185/amlett.2015.SMS5

Publication Date (Web): May 28, 2015

Copyright © IAAM-VBRI Press

E-mail: kpsirapa@live.kmitl.ac.th

Abstract

Silicon nitride is a promising alternative to carbon based materials for protective coatings, owing to its compatibility with existing silicon-based microfabrication. The complexity of the fabrication processes and contaminations hamper fine-tuning to obtain desirable coating properties. We have explored the reactive gas-timing rf plasma sputtering technique for silicon nitride thin film deposition as an alternative method to fine-tune the film properties. The gas-timing technique controls the on-off sequence of the sputtering gas (Ar) and the reactive gas (N₂) during deposition. We focus this investigation to the effect of the Ar:N₂  gas timing ratio (10:0,  10:1,  10:3,  10:5,  10:7 and 10:10) on the composition, the morphology, the corrosion resistance, and the hardness properties of the films, in comparison to the films deposited by conventional reactive sputtering with Ar-N₂ gas mixture. These deposited silicon nitride films were characterized by Auger electron spectroscopy, Raman spectroscopy, and atomic force microscopy. The chemical resistance was measured by the electrochemical corrosion test in sulfuric acid, while the hardness properties were obtained by nanoindentation. The results reveal that although the nitrogen content in the films increases only slightly when the N₂ timing is prolonged, the corrosive current of the films decreases abruptly. A thin passivating oxidized layer is found to play a major role in the corrosion resistance. In contrast, the hardness properties exhibit a uniform variation with the N₂ timing. The gas-timing sequence may induce morphological changes the underlying silicon nitride films. The highest hardness obtained by the gas-timing technique almost doubles that produced by the conventional mixed gas sputtering. Thus the reactive gas-timing technique suggests a new route to selectively control the properties of silicon nitride films with minor modification to existing microfabrication processes.

Keywords

Hard coatings, silicon nitride, corrosion, plasma sputtering.