RPALD를 이용한 란탄늄 옥사이드의 알루미늄 옥사이드 캡핑효과 연구

Abstract

As conventional gate dielectric films in complementary metal?oxide?semiconductor (CMOS) applications approach their physical and electrical property limits, the leakage current density through the gate dielectric layer rapidly increases and is expected to cause problems such as increased power dissipation or poor circuit reliability. High-k dielectric constant materials such as HfO2, ZrO2, Al2O3, and La2O3 have been widely investigated as possible replacements for current gate dielectric materials, which include silicon oxide (SiO2) and silicon oxynitride (SiOxNy).1-3 Among the high-k gate dielectrics, La2O3 has been extensively studied due to its relatively high permittivity (~27), large band gap (~4.3 eV), high band offset (>2 eV), and thermal stability with Si. 4-7 However, it has been reported that moisture absorption deteriorates the permittivity of La2O3 films on silicon. The main reasons for this are the formation of low permittivity lanthanum hydroxide and La-silicate grown at the interface, which generate charges in the gate dielectric and lead to a large flat-band voltage shift.8-10 This undesirable large flatband voltage is due to the fixed oxide charge located at the interface between the oxide and Si, and the oxide trap charge located in the bulk oxide. Moisture absorption also leads to non-uniform volume expansion due to the density difference between lanthanum hydroxide and lanthanum oxide. Furthermore, non-uniform volume expansion results in changes in surface roughness and film density, causing degradation in La2O3 electrical properties over time when exposed to moisture. In this study, an Al2O3 capping layer was introduced in order to improve the properties of La2O3 gate dielectrics. This Al2O3 layer was impervious to water, thus retarding the possible formation of lanthanum hydroxide. The effects of the Al2O3 capping layer on the electrical properties of La2O3 were investigated in the metal-insulator-silicon capacitor structure after exposure to air.