Thermal and humidity stability of Ge3N4 thin layers fabricated by high-density plasma nitridation

Germanium has recently drawn tremendous attention due to its higher hole and electron mobility than those of Si. Nitride-based dielectrics are important and promising not only as a buffer layer to grow high-k gate dielectrics on Ge, but also as a gate insulator itself for Ge-based FETs, in spite of GeO_x being unstable. While it has been reported that fabricating oxygen-free, pure Ge₃N₄ layers is hard to deposit, the fact that pure Ge nitride is available by using atomic nitrogen radicals has been reported by Maeda et al. Accordingly, first of all, we focused our attention on the direct nitridation of Ge substrates by using our custom-built high-density plasma source. Furthermore, in order to apply this Ge nitride to integrate high-k gate dielectrics with Ge and its alloy for FET-based devices, some issues related to the stabilities should be well understood first to optimize the device fabrication process. For these reasons, in this paper, we investigated thermal stability of Ge₃N₄ layers. In addition, since it is reported that Ge surface is very sensitive to moisture, we have also characterized stability of the Ge nitride layers against moisture in the air.