Thermal Robustness and Improved Electrical Properties of Ultrathin Germanium Oxynitride Gate Dielectric

Abstract

Robustness of ultrathin germanium oxynitrides (GeON) formed by plasma nitridation of thermal oxides (GeO2) on Ge(100) substrates [K. Kutsuki et al.: Appl. Phys. Lett. 95 (2009) 022102] was investigated by means of physical and electrical measurements. The decomposition temperature of a 3.7-nm-thick GeON layer was found to increase up to 550 °C by plasma nitridation, which was about 100 °C higher than that of pure GeO2. While the insulating property of GeON dielectrics begins to degrade just below the decomposition temperature, i.e., at around 540 °C, thermal treatment up to 520 °C effectively improves the electrical properties of the ultrathin GeON dielectrics, such as recovery of bulk defects and quite low interface state density (Dit) even for the ultrathin gate dielectrics. The advantage of GeON dielectrics in designing a fabrication process for Ge-based devices and the physical origins of the improved properties will be discussed.