CAREER: Fundamental Reliability Physics of MOS Devices Based on Deuterium Isotope Effects

The proposed CAREER development program is an integrated research and teaching effort in MOS transistor reliability physics. The research component of this CAREER proposal focuses on fundamental study of mechanisms for the MOS device degradation and its isotope effect. The MOS transistor degradation is caused by Si-H (hydrogen) bond breaking at the SiO2-Si interface due to the energetic hot electrons. The current theory and experiments suggest that the Si-H bond breaking is caused by two competing processes: the excitation due to the energetic hot electrons and the de-excitation by energy coupling between the vibrational modes of the Si-H bonds and the phonon modes of the Si lattice. The energy coupling between the Si-D (deuterium) bonds and the Si lattice (TO phonon) is much more efficient than that between the Si-H bonds and the Si lattice. Therefore the Si-D bonds are more robust than Si-H bonds, which is the so-called isotope effect. Based on this principle, the deuterium-treated MOS transistors exhibit much longer hot-carrier lifetime (over 50 times) than the traditional hydrogen treatment. Evidence shows that there is a potential for further improvement of MOS transistor lifetime by over 100 times, if the mechanisms for degradation and its isotope effect are understood. The characterization of the efficient energy coupling between the two vibrational modes is that their frequencies are the same or very close. The study of the energy coupling is vital to understand the mechanisms for degradation and its isotope effect. The proposed research program will focus on two thrusts: 1) Degradation mechanisms for deep-submicron MOS transistors from fundamental point of view and 2) Study of dynamic hot-carrier degradation of MOS devices in CMOS inverters. In the first thrust, I will use Raman and Infrared (IR) spectroscopy to study the vibrational modes of the Si-H and Si-D bonds. The ultimate goal of the research program is to develop predictive principles from which the processing can be designed to achieve the maximum lifetime improvement for MOS transistors. In the second thrust, I will study the deuterium isotope effect for transistors under the dynamic stress or AC stress, because the transistors are operating in AC conditions in the real circuits. The proposed research builds upon and expands the research work that the PI is already undertaking. The educational component of this CAREER program seeks support for development of a new experimental course, integrated circuit device fabrication, and focused educational outreach activities in Appalachian communities (underrepresented groups). With the support from the State of Kentucky through the Research Challenge Trust Fund (RCTF), a Device Fabrication Facility is under construction at UK. A new experimental course focused on fabrication of integrated circuit devices will be developed, which is equivalent to similar courses in other universities in the US. The class is a hands-on lab course where students have the opportunity to build semiconductor devices for integrated circuits. This class will first be taught in the Fall 2001 for senior undergraduate students and graduate students. The multidisciplinary nature of this program will provide students with a unique environment for research and learning. The goal is to build bridges between these traditional disciplines such as physics, materials science, and electrical engineering by conducting research and teaching through an integrated approach. The other component of the educational objectives involves the educational outreach activities targeted for high school students from Eastern and Southern Kentucky including Appalachian communities. One of the objectives is to encourage those high school students to pursue high-tech career by presenting a series of seminars in microelectronics. Another one is to offer an experimental project to teach them to build some useful digital circuits. The high school students will be recruited from the already established program, the Rogers Scholar Program organized by the Center for Rural Development, which the PI already participates.