Paper PS-ThM10
The Mechanism of Thin SiO₂ and GeO₂ Film Formation during Low-Temperature Neutral Beam Oxidation Process

Thursday, November 3, 2011, 11:00 am, Room 201

The thermal oxidation process is usually used to form the gate dielectric films of MOSFETs. However, it involves high temperatures (usually > 800°C), which causes problems. For example, after using the high-temperature oxidation process to form SiO₂ films, residual compression stress between the Si substrate and SiO₂ remains due to the difference in the thermal expansion coefficient between Si and SiO₂. This residual stress degrades the sub-threshold characteristics of MOSFETs because it increases interfacial state density. Especially, in case of future 3-dimensional transistors such as FinFETs, stress concentration occurs at corner and edge of 3D structures, which may cause drastic increase of leakage current. There have been recent active investigations on the thermal oxidation of Ge to enable the fabrication of high-mobility Ge MOS transistors. After high-temperature thermal processes, however, Ge oxide has poor thermal stability and a large amount of suboxide.

We developed an alternative oxidation process to solve these problems using a low temperature neutral beam (NB) technique to form the gate dielectric film. In this study, we investigated the mechanism to form thin oxide films using a low-temperature neutral beam oxidation (NBO) process. Arrhenius plot has shown that activation energy of NBO was extremely low, which enabled low-temperature oxidation at 300°C or even at room temperature. This should be because bombardment energy of oxygen beam assisted the oxidation reaction. Also, we investigated that the suboxide in thin oxide film using NBO process. As a result, there was little suboxide at the interface between oxide films and semiconductor using NBO process even at low-temperature. These results demonstrate the outstanding potential of the low-temperature NBO process for fabricating gate dielectric films.