Mechanics of Smart-Cut® technology

Smart-Cut(R) is a recently established, advanced technology for fabricating high-quality silicon-on-insulator (SOI) systems and has found many other successful applications. It meets almost all the high requirements for processing and manufacturing SOI wafers, which provide the basis of ultra-large-scale integration device structures of modern microelectronic industry. In the present paper, we present a fundamental study on the basic mechanisms in the Smart-Cut technology from the viewpoints of mechanics and physics. First, a model for defect nucleation induced by hydrogen ion implantation is established based on the continuum mechanics theory accounting for the crystal structure of silicon. This model is used to provide an upper bound on the implantation dose of hydrogen ions, one of the most important process parameter in the Smart-Cut technology. An analytical formulation is derived to calculate the defect density as a function of the H-implantation dose and the temperature. Then, the splitting of SOI wafers in the Smart-Cut technology is analyzed using the elastic fracture mechanics theory. Accounting for the embrittlement and diffusion effects of hydrogen, a lower bound of the implantation dose of hydrogen ions is derived, which agrees reasonably with experimental observations. Furthermore, the effects of the handle wafer adopted in the Smart-Cut technique are examined on the splitting process. It is found that the handle wafer leads to uniform crack propagation and higher uniformity in the thickness of the final SOI systems, in comparison with conventional techniques to produce SOI substrates, and prohibits the blistering and flaking failure of an H-implanted wafer. This work provides not only a fundamental understanding to the physical mechanisms associated with the Smart-Cut technology but also a useful reference for determining the process parameters of SOI industrial production. (C) 2004 Elsevier Ltd. All rights reserved.