Effect of deposition angle on the structure and properties of pulsed-DC magnetron sputtered TiAlN thin films

This article reports the comparison of structure and properties of titanium aluminum nitride (TiAlN) films deposited onto Si(100) substrates under normal and oblique angle depositions using pulsed-DC magnetron sputtering. The substrate temperature was set at room temperature, 400 degrees C and 650 degrees C, and the bias was kept at 0, -25, -50, and -80 V for both deposition angles. The surface and cross-section of the films were observed by scanning electron microscopy. It was found that as the deposition temperature increases, films deposited under normal incidence exhibit distinct faceted crystallites, whereas oblique angle deposited (OAD) films develop a kind of "tiles of a roof" or "stepwise structure", with no facetted crystallites. The OAD films showed an inclined columnar structure, with columns tilting in the direction of the incident flux. As the substrate temperature was increased, the tilting of columns nearly approached the substrate normal. Both hardness and Young's modulus decreases when the flux angle was changed from alpha = 0 degrees to 45 degrees as measured by nanoindentation. This was attributed to the voids formed due to the shadowing effect. The crystallographic properties of these coatings were studied by theta-2 theta scan and pole figure X-ray diffraction. Films deposited at = 0 showed a mixed (111) and (200) out-of-plane orientation with random in-plane alignment. On the other hand, films deposited at alpha = 45 degrees revealed an inclined texture with (111) orientation moving towards the incident flux direction and the (200) orientation approaching the substrate normal, showing substantial in-plane alignment. (C) 2011 Elsevier B.V. All rights reserved.