A nanoindentation study of SiN/GaAs film/substrate structures for analysis of the deformation mechanisms and interfacial properties

Lu, Mingyuan (2013). A nanoindentation study of SiN/GaAs film/substrate structures for analysis of the deformation mechanisms and interfacial properties PhD Thesis, School of Mechanical and Mining Engineering, The University of Queensland.

       
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Author Lu, Mingyuan
Thesis Title A nanoindentation study of SiN/GaAs film/substrate structures for analysis of the deformation mechanisms and interfacial properties
School, Centre or Institute School of Mechanical and Mining Engineering
Institution The University of Queensland
Publication date 2013
Thesis type PhD Thesis
Total pages 125
Language eng
Subjects 0912 Materials Engineering
1007 Nanotechnology
0913 Mechanical Engineering
Formatted abstract
In silicon nitride/gallium arsenide bilayer systems, the delamination of the silicon nitride (SiNx) passivation layer from a gallium arsenide (GaAs) substrate has been a critical issue that affects the performance and reliability of GaAs based devices for some decades. Understanding the interfacial failure behaviour and quantifying the interfacial adhesion property are thus essential for improving the performance of the SiN/GaAs based systems. The major pursuits of this thesis were to investigate the interfacial deformation mechanics of SiNx/GaAs bilayer structures, and to develop simple and reliable testing methods for assessing the SiNx/GaAs interface adhesion.

Nanoindentation was used to investigate the mechanical properties and interfacial adhesion of SiN/GaAs film/substrate structures. To comprehensively understand the deformation behaviour involved in interfacial delamination, nanoindentation was performed on single crystal GaAs (001) wafers and SiNx/GaAs bilayers. The onset of plastic deformation in GaAs was marked by a pop-in event from the load-displacement (P-h) curve during loading, corresponding to sudden plane slip occurring on the {111} plane in the GaAs crystal. The critical mean pressure and shear stress that trigger the pop-in event were found to be 8.2±1.9 GPa and 3.9±0.8 GPa, respectively.

Pop-out events were observed during unloading when the indentation load exceeded a critical value. Pop-out was induced by the interfacial delamination between SiNx film and GaAs substrate. Finite element modelling (FEM) was used to analyse the stress evolution during unloading. The FEM result revealed that the stress at the interface evolved from compression to tension during the withdrawal of indentation load, and interfacial debonding was induced at a critical tensile stress, leading to the occurrence of pop-out.

To determine the adhesion properties of the interface, sequential dual-indentation and cyclic indentation methods were developed. The indentation tests were carefully designed to induce interfacial delamination, but avoid the occurrence of through-thickness fracture or buckling of the film. A clamped circular plate model was used to approximate the elastic deflection of the detached film and hence the delamination area. The Griffith energy balance was then used to compute the energy release associated with the delamination. The energy release rate Gin calculated by these methods was found to be independent on the testing conditions, which agrees with the fundamental assumption of Griffith energy balance concept. 
Keyword Interfacial adhesion
Delamination
SiN
GaAs
Bilayer
Nanoindentation
Energy release rate

 
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Created: Mon, 07 Apr 2014, 15:01:23 EST by Mingyuan Lu on behalf of Scholarly Communication and Digitisation Service