Low-load indentation behavior of HfN thin films deposited by reactive rf sputtering
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Low-load indentation behavior of HfN thin films deposited by reactive rf sputtering R. Nowak, C. L. Li, and S. Maruno Department of Electrical and Computer Engineering, Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya 466, Japan (Received 13 October 1995; accepted 7 May 1996)
Deformation of HfN thin films deposited by the reactive sputtering method on silicon and alumina substrates has been investigated using depth-sensing indentation. The experiments performed in a low load range (2–50 mN) revealed that even extremely shallow indentations were affected by the elastic/plastic response of the substrate. The analysis of the shape of the indentation load-depth hysteresis loops and of conventional hardness data was supplemented by considerations based on the recently proposed energy principle of indentation.
I. INTRODUCTION
The recently developed depth sensing indentation test designed for thin films7 enables us to perform high accuracy measurements; however, further effort is required to clarify and model novel phenomena which come into light due to the application of this sophisticated method. The main advantage of the above test is that it provides the kind of results for the investigated thin film which are not affected by the substrate properties. The assumption is that significantly shallower penetration depth of the indenter loaded in the mN range ensures that a deformation of the substrate under the indenter will not occur. However, the observations of indentation impressions by Hainsworth et al.8 and independently by Shiwa et al.9 raised some doubt as to the correctness of the above thesis, particularly after studying very hard films deposited on softer substrates, a conclusion which might also apply to HfN films on silicon or alumina, as in the present paper. Thus, the present work is devoted to the surface deformation of HfN thin films deposited on silicon and alumina substrates investigated in the nanoindentation range. The indentation hysteresis loops have been analyzed and discussed in terms of the Energy Principle of
Interest in HfN films started about two decades ago, when their high degree of hardness and excellent wear resistance came to be widely recognized. This resulted in the immediate application of hafnium nitride coatings to the manufacture of cemented carbide cutting tools.1 Since HfN films have also been found useful in the electronic industry, their physical properties have been studied in terms of deposition conditions (see, e.g., Refs. 2 and 3) and subsequently in terms of their particular structure.4,5 However, the hardness data reported for HfN films appeared to be inconsistent (see Table I) despite the fact that the layers investigated by the different authors seemed quite similar with regard to their composition and morphology. The large discrepancies in experimental results raised a doubt as to whether the hardness test in its conventional form is good enough to estimate the properties of the HfN films. Radical steps have al
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