Nanoindentation cracking in gallium arsenide: Part I. In situ SEM nanoindentation

The nanoindentation fracture behavior of gallium arsenide (GaAs) is examined from two perspectives in two parent papers. The first paper (part I) focuses on in situ nanoindentation within a scanning electron microscope (SEM) and on fractographic observations of cleaved cross-sections of indented regions to investigate the crack field under various indenter geometries. In the second parent paper (part II), cathodoluminescence and transmission electron microscopy are used to investigate the relationship between dislocation and crack fields. The combination of instrumented in situ scanning electron microscopy nanoindentations and cleavage cross-sectioning allows us to establish a detailed map of cracking in the indented region and cracking kinetics for conical and wedge indenter shapes. For wedge nanoindentations, the evolution of the half-penny crack size with the indentation load is interpreted using a simple linear elastic fracture model based on weight functions. Fracture toughness estimates obtained by this technique fall within the range of usual values quoted for GaAs.

Nanoindentation cracking in gallium arsenide: Part II. TEM investigation

Jean-Marc Breguet, Jean-Daniel Ganière, Jacques Giovanola, Johann Michler, Cédric Pouvreau

The nanoindentation fracture behavior of gallium arsenide (GaAs) is examined from two perspectives in two parent papers. In the first paper (part I), we address the morphology of the crack field induced by different types of indenters by means of in situ nanoindentation inside a scanning electron microscope (SEM) and of cleavage cross-sectioning techniques. In the present paper (part II), we investigate the early stage of crack nucleation under wedge nanoindentation through cathodoluminescence and transmission electron microscopy. We find that the apex angle of the wedge indenter influences the dislocation microstructure and, as a consequence, the mechanism of crack nucleation under nanoindentation. The formation of microtwins depends on both the orientation of the indenter with respect to the orientation of the GaAs crystal and on the apex angle of the indenter. For dicing applications of GaAs wafers, it is desirable to have an opening angle of the indenter smaller than 70 degrees to facilitate the formation of precursor cracks.

Cambridge University Press2013

Indentation fracture of gallium arsenide

Cédric Pouvreau

The scribe and break technique (or dicing) is a widely employed method in the industry of semiconductors to separate infrared laser diodes made from gallium arsenide (GaAs). The scribing step allows to create a precursor crack which is then propagated during the breaking step, along preferential {110} cleavage planes of GaAs. The main drawback of the scribing process is that it generates a lot of undesirable cracks and particles that degrade the performances of devices. In this dissertation, we have investigated the indentation process as a possible way to replace the scribing operation. For that purpose, we have investigated the morphology of the crack field and the cracking sequence as a function of the indenter geometry (shape, apex angle) and experimental conditions (maximal load, loading rate). Such investigations have been made with the help of a new tool: the in-situ SEM instrumented indentation which allows us to establish the cracking sequence and to correlate direct observations with the load-displacement histories. A new experimental technique has also been developed: cleavage cross-sectioning techniques allow us to determine the morphology of the crack field beneath the surface. The second research axis was focused on the interaction between deformation mechanisms and crack initiation. These investigations have been conducted with the help of Transmission Electron Microscopy (TEM) and cathodoluminescence. In the first part of the dissertation, we have shown that acute wedge indenters with an included angle of 60° promote the formation of a well defined half-penny crack, the nucleation of which is affected by load rate and indenter radius. The relation between the final half-penny crack size and the maximum indentation load was made with the help of a fracture mechanics model. The crack field has been compared for several indenter shape including conical (60° and 120° apex angles), cube corner and Vickers indenters. In the second part of this dissertation we have determined that the indenter apex angle influences the slip systems that are activated and the nature of dislocations that are found under the indenter. In particular, we have shown that below 60° wedge indenters, mainly diverging slip systems are activated whereas under obtuse wedge indenters, mainly converging slip systems are activated. The converging pattern predominant under obtuse indenters is correlated with a delayed half-penny crack formation and is so interpreted as a plastic shielding phenomenon. Some experiments have been performed on commercial devices under production conditions. Although some adjustments are needed to reduce the chipping-out effect that occurs at the indenter extremities, the results are encouraging.

EPFL2007

Indentation fracture of gallium arsenide

Cédric Pouvreau

EPFL2007