Control of nitrogen depth profile in ultrathin oxynitride films formed by pulse-time-modulated nitrogen beams

Abstract

Ultrathin Si oxynitride (SiOxNy) films have been identified as leading candidates to replace conventional SiO2 gate dielectrics in current and future ultralarge-scale integrated circuits. Remote plasma processes to nitridate the top surface of thermally grown oxides have been developed and employed in complementary metal–oxide–silicon device applications. However, it is very difficult to control the nitrogen depth profile in ultrathin Si oxynitride film using plasma processing and there are many serious problems, such as plasma radiation damage and increases in interface state density due to the N penetrating into the SiO2–Si interface. To overcome these problems, we propose the use of pulse-time-modulated N2 neutral beams. We first found that the nitrogen depth profile in ultrathin Si oxynitride film could be controlled by changing the pulse-on time and source power in the pulse-time-modulated N2 neutral beams. We speculated that injected N2 was diffused due to the surface activation with the energetic neutral beam at a time constant of a few tens of microseconds in the thermal SiO2 film. Additionally, by increasing the substrate temperature to 300 °C, SiO–N bonds were effectively formed and a shallower, sharper, and higher density N concentration profile in a thin 2 nm SiO2 film was produced using a pulsed N2 neutral beam.