Invited Paper PS1+TF-TuM1
Characteristics for HfO₂ Gate Dielectrics Deposited by Remote Plasma ALD Method

Tuesday, October 16, 2007, 8:00 am, Room 606

Many high-k dielectric materials have been studied extensively to replace current gate dielectric materials such as SiO₂ and SiO_xN_y. Among the high-k dielectric materials, Hf-oxide is considered to be one of best choices for 45 nm technology and beyond. However, most of high-k oxides such as HfO₂, ZrO₂, Ta₂O₃, and TiO₂ are transition metal oxides with the ionic nature and have poor interface quality and poor thermal stability with Si substrate. In addition, they exhibits high oxide traps and interface state densities, and large amount of oxygen vacancies, and are easily crystallized compared to SiO₂. To overcome these drawbacks of high-k oxides, the technologies for growing high quality high-k oxides and improving the interface properties between high-k oxide and Si substrate are required. In this study, we chose HfO₂ as high-k gate dielectrics and atomic layer deposition (ALD) as a deposition method. Among many deposition methods, ALD method is studied by many researchers because of its thin film deposition superiority. In our lab we applied both direct plasma ALD (DPALD) and remote plasma ALD (RPALD) methods to grow HfO₂ thin films on Si substrates. These two different plasma methods exhibited the different thicknesses of silicate interlayer. We believe this interlayer is critical for the degradation of high-k dielectric materials. To investigate these interlayers we grew several different buffer layers before HfO₂ growth. These buffer layers were formed by remote plasma oxidation (RPO) and nitridation (RPN) on Si substrates to monitor this interlayer, to suppress the initial formation of Hf silicate or interlayer and to improve the interlayer quality. The buffer layers were thin SiO₂, SiO_xN_y, Al₂O₃, nitrided Al silicate and nitrided Hf silicate layers. The HfO₂ films with buffer layers suppressed silicate formation or growth of an interlayer more effectively than those without buffer layers. The HfO₂ films with buffer layers also showed lower effective oxide thickness (EOT), lower effective fixed oxide charge density (Q_f,eff.), and lower leakage current density compared to those without buffer layers. The physical and electrical properties of HfO₂ with buffer layers will be presented and discussed depending on the various buffer layers.