Ultrathin oxynitride films formed by using pulse-time-modulated nitrogen beams

Ultra thin Si oxynitride (SiO_xN_y) films have been identified as leading candidates to replace conventional SiO₂ gate dielectrics for present and future ultra large-scale integrated circuits. Remote plasma processes for top surface nitridation of thermally grown oxides have been developed and applied in complementary metal-oxide-silicon (MOS) device applications. However, it is much difficult to control the concentration and position of nitrogen in ultrathin Si oxynitride film by using plasma processing and there are many serious problems, such as plasma radiation damage and increases in interface state density due to N penetrating the SiO₂-Si interface. To overcome these problems, we propose using pulse-time-modulated N₂ neutral beams. We first found that the concentration and position of nitrogen in ultrathin Si oxynitride film could be controlled by changing the pulse-on time in the pulse-time-modulated N₂ neutral beams without any radiation damage. It is speculated that the injected N₂ was diffused at a time constant of a few tens of μseconds in the thermal SiO₂ film.