Room temperature plasma oxidation: A new process for preparation of ultrathin layers of silicon oxide, and high dielectric constant materials

In this paper we present basic features and oxidation law of the room temperature plasma oxidation, (RTPO), as a new process for preparation of less than 2 nm thick layers of SiO₂, and high-k layers of TiO₂. We show that oxidation rate follows a potential law dependence on oxidation time. The proportionality constant is function of pressure, plasma power, reagent gas and plasma density, while the exponent depends only on the reactive gas. These parameters are related to the physical phenomena occurring inside the plasma, during oxidation. Metal-Oxide-Semiconductor (MOS) capacitors fabricated with these layers are characterized by capacitance-voltage, current-voltage and current-voltage-temperature measurements. Less than 2.5 nm SiO₂ layers with surface roughness similar to thermal oxide films, surface state density below 3 × 10¹¹ cm^{- 2} and current density in the expected range for each corresponding thickness, were obtained by RTPO in a parallel-plate reactor, at 180 mW/cm² and pressure range between 9.33 and 66.5 Pa (0.07 and 0.5 Torr) using O₂ and N₂O as reactive gases. MOS capacitors with TiO₂ layers formed by RTPO of sputtered Ti layers are also characterized. Finally, MOS capacitors with stacked layers of TiO₂ over SiO₂, both layers obtained by RTPO, were prepared and evaluated to determine the feasibility of the use of TiO ₂ as a candidate for next technology nodes.