Abstract

The mechanical properties and deformation behaviors of AlN thin films deposited on c‐plane sapphire substrates by helicon sputtering method were determined using the Berkovich nanoindentation and cross‐sectional transmission electron microscopy (XTEM). The load‐displacement curves show the “pop‐ins” phenomena during nanoindentation loading, indicative of the formation of slip bands caused by the propagation of dislocations. No evidence of nanoindentation‐induced phase transformation or cracking patterns was observed up to the maximum load of 80 mN, from either XTEM or atomic force microscopy (AFM) of the mechanically deformed regions. Instead, XTEM revealed that the primary deformation mechanism in AlN thin films is via propagation of dislocations on both basal and pyramidal planes. Furthermore, the hardness and Young’s modulus of AlN thin films estimated using the continuous contact stiffness measurements (CSMs) mode provided with the nanoindenter are 16.2 GPa and 243.5 GPa, respectively.

Highlights

  • AlN is a potential candidate for UV and deep-UV optical and high-power electronic devices because of its unique properties, such as wide bandgap (6.2 eV), high-temperature stability, and excellent thermal conductivity [1, 2]

  • With the continuous contact stiffness measurements, the penetration depth dependence of the hardness and Young’s modulus was obtained from the loaddisplacement data by the analytic method developed by Oliver and Pharr [14], and the results are displayed in Figures 2(b) and 2(c), respectively

  • The Berkovich nanoindentation, FIB, and TEM techniques were used to investigate the mechanical deformation behaviors of AlN thin films deposited on c-sapphire substrates by helicon sputter deposition

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Summary

Introduction

AlN is a potential candidate for UV and deep-UV optical and high-power electronic devices because of its unique properties, such as wide bandgap (6.2 eV), high-temperature stability, and excellent thermal conductivity [1, 2]. In order to successfully implement the fabrication of AlNbased devices, a better understanding of the mechanical properties is of essential importance in addition to its optical and electrical performances. The mechanical responses of a thin film to an applied load might be vastly different from those of the same material in bulk form. For this purpose, the traditional methods such as tensile measurements do not scale well into the micrometer and nanometer regions. In this study the mechanical characteristics of AlN thin films deposited on c-plane sapphire substrates using a helicon sputtering system were systematically investigated by combining the load-displacement data obtained from nanoindentation experiments with the microstructure observations performed in the vicinity of the indents by using atomic force microscopy (AFM) and cross-sectional transmission electron microscopy (XTEM). The results obtained in this study should have technological implications for assessing the robustness against the usual fabrication processes of making AlN-based devices

Experimental Details
80 Pop-ins
Results and Discussion
Conclusion
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