The mechanical properties of semiconductors

While the electronic and optical properties of semiconductors have been and still are the subject of extensive investigation, the mechanical properties of semiconductors often dictate fundamental limits on the fabrication and packaging of modern semiconductor devices. The goal of this volume is to describe the mechanical properties of semiconductors and the role they play in modern semiconductor technology. To that end, we have chosen to emphasize mechanical properties per se and refer the reader elsewhere for the influence of mechanical properties on electrical and optical properties. Mechanical properties define the regions of dislocation-free boule growth and epitaxial layer growth. They define processing limitations and often dominate issues related to packaging and failure of semiconductor devices. We have chosen to emphasize the fundamental mechanical phenomena instead of merely detailing examples of these phenomena. The volume begins with a discussion of elastic properties of semiconductors, including elemental, compound, and the pseudobinary alloy semiconductors. It is the elastic constant that dictates the first response of the material under mechanical or thermal loading. Experimental measurements of these constants are examined in Chapter 1 and are compared to three theoretical methods for estimating the elastic constants: ab initio calculations, valence force field methods, and tight binding theory. The emphasis of the chapter is on the comparison of these theoretical predictions of elastic constants with experimental measurements and a discussion of the accuracy of the approximations needed for timely theoretical calculations. Chapter 2 describes the conditions for failure when elastic limit of brittle semiconductors is reached. Both the mechanics and mechanisms by which failure occurs are discussed along with ample examples of measured fracture energies and microscopic evidence for fracture mechanisms. Perhaps most revealing is recent in situ transmission electron microscopic evidence for the brittle-to-ductile transition that occurs at high temperature. Three chapters (Chapters 3, 4, and 5) are devoted to deformation of semiconductor materials. Chapter 3 provides the necessary background for understanding plasticity in semiconductor materials and demonstrates how these phenomena are applied to both elemental and compound semiconductors. The stages of dynamical recovery during creep and constant strain-rate experiments are reviewed in this chapter. The role of dopants in deformation processes in elemental semiconductors is also explored. Chapter 4 is devoted to deformation of compound semiconductors and the influence of both isovalent and non-isovalent dopants. The implication of solid solution strengthening by dopants as it affects crystal growth is reviewed. In the final part of the sequence (Chapter 5), the deformation of ternary and quaternary semiconductor alloys is included. Photoplastic effects, whereby electron-hole recombinations occur near a dislocation and the released energy facilitates glide, are also discussed. As a further treatise on deformation behavior, Chapter 6 examine conditions for the stability of strained layer superlattices. In order to avoid the nucleation of misfit dislocations at interfaces between the strained layers, the equilibrium argument is used to establish a critical layer thickness. These results have significant practical import for the growth of devices based on strained multilayers. A further practical aspect of device fabrication involves the micromachining of semiconducting materials to provide three-dimensional structures. Wet chemical etching as well as dry etching techniques are reviewed in Chapter 7. The physics of bonding and its relevance to micromachining is also considered. Finally, thermoelastic behavior of semiconductors as it related to annealing and growth of oxide films on semiconductors is described in Chapter 8. A model of dislocation generation is proposed by considering the temperature profile of the wafer during growth of the oxide film and the conditions whereby the temperature distribution is altered and the thermal stresses reduced. The model has been applied successfully to the fabrication of VLSIs. It is intended that this volume be useful for both the physical or materials scientist interested in the science of fracture and deformation, as well as for the crystal growers who desire a more fundamental understanding of the parameters that influence the growth process. It is further anticipated that electrical engineers or device manufacturers would be interested in this volume to provide models in which an understanding of the fundamental science can directly aid in the production of more reliable devices. We are indebted to the contributors and editors for making this volume possible