First principles studies of point defects in HfO2 and Si-HfO2 interfaces

Date of Completion

January 2009


Engineering, Materials Science




In the last four decades the semiconductor industry has seen the success of continuously improving the performance of integrated circuits. Behind this success is the miniaturization of the Si-based transistors through down scaling the thickness of the SiO2 gate dielectric layer. As the SiO 2 layer is approaching the atomic scale limit (∼ 1 nm), it needs to be replaced by some higher dielectric constant material, such as HfO 2, to keep the miniaturization continuing. ^ Although HfO2 appears to be a promising replacement candidate, there are several issues that need to be addressed prior to widespread application. Among them are the formation of interfacial phases between the Si substrate and the HfO2 film and the crystallization of the amorphous HfO 2 film during annealing. ^ In this project, the above problems have been addressed using first principles density functional theory modeling. Firstly, the behaviors of point defect chemistries in Si-HfO2 heterostructures and their implications for the formation of interfacial phases have been investigated. Specifically, depending on the processing conditions, oxygen vacancies, oxygen interstitials and hafnium vacancies can occur in HfO2 and segregate to the interface, allowing for the formation of silicides, silica and silicates, respectively. These point defect studies have included both crystalline (monoclinic) and amorphous HfO2. Secondly, the relative stabilities of various crystalline phases during the crystallization of Zr-, Si-, and Y-doped HfO 2 have been studied, and the mechanisms of the stabilization of high temperature phases by Si and Y dopants have been considered. The influences of dopants on the behavior of point defects have also been investigated. The findings in this project provide important insights concerning point defect chemistries in high dielectric constant materials such as HfO2, and may aid in the rational design of heterostructures for next generation microelectronic devices. ^