Effects of Substrate Materials on Nanoindentation Tests of AlN Thin Films
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Effects of Substrate Materials on Nanoindentation Tests of AlN Thin Films Shuichi Miyabe, Masami Aono, Nobuaki Kitazawa, and Yoshihisa Watanabe Department of Materials Science and Engineering, National Defense Academy, Yokosuka, Kanagawa 239-8686, Japan ABSTRACT Aluminum nitride (AlN) thin films with different thickness were synthesized by ion-beam assisted deposition on various substrates, Corning 7059 glass, fused silica, Si single crystal, and sapphire, which show the hardness ranging from 7 to 37 GPa. Effects of substrate materials on indentation-hardness of AlN films were studied by using a nanoindentation system equipped with a diamond Berkovich indenter. The maximum force applied to the films was kept at 3 mN. For the films on the Corning 7059 glass substrate, when the normalized penetration depth to the film thickness is 0.98, the film hardness is found to be about 7 GPa, which is close to the hardness of the substrate. While the normalized penetration depth is reduced to 0.11, the film hardness becomes to be about 16 GPa. On the other hand, for the films on the sapphire substrate, when the normalized penetration depth is 0.83, the film hardness is observed to be about 25 GPa, while the normalized penetration depth is reduced to 0.10, the film hardness is found to be about 15 GPa. These results reveal that when the normalized penetration depth to the film thickness is about 0.1, the hardness of the AlN film can be evaluated to be about 15 GPa without being affected by substrate materials.
INTRODUCTION Mechanical properties of thin films have been interesting research topics and a nanoindentation technique has been developed for studying them [1, 2]. Although many researchers have investigated mechanical properties of different kinds of thin films on various substrates [3-5], it is not completely understood how substrate materials affect on film deformation behavior. For example, Tsui et al studied plastic deformation around Knoop indentations for two cases of hard films on soft substrate and soft films on hard substrates [4, 5]. They reported that pileup is formed around the impression in the case of soft films on hard substrates, while indentation sink-in effects are observed for the case of hard films on soft substrates. We have studied indentation-hardness of aluminum nitride (AlN) thin films prepared by ion beam assisted deposition (IBAD). It has been already reported that the film indentation-hardness can be obtained when the normalized penetration depth to the film thickness is less than 0.1 [6]. The indentation-hardness is found to depend on the film microstructure [6]. In the previous work, only soft substrates compared with the AlN films were used and harder materials than the AlN films were not applied as a substrate. Therefore, it is interesting to study the effects of substrate materials on film deformation behavior by using both substrates of harder and softer than AlN films. In this paper, AlN films with different thickness are prepared by the IBAD method on various substrates, which
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