Mobility Model And Processing Of High-k Gate Dielectric Ge MOS Devices

With the aggressive scaling of devices and the continuous improvement of integrated circuits, the polysilicon is no longer a perfect gate electrode because of the Fermi pinning in high k / polysilicon structure. According to some research, there are many virtues of the high k / metal gate structure, e.g. the low thin gate resistance, no gate depletion, and so on. Further more, the coupling between channel carrier and optical phonons is also reduced and the mobility is increased while metal is used as the gate electrode. At present, the high k / metal gate has already become the research focus. At the same time, the preparation and electrical characteristics research of Ge MOS capacitor with the high k gate dielectric are still hot.The mobility of Ge MOSFET with high k gate dielectric and metal gate is studied in this paper. A physical model on the device is proposed and the effects of metal gate electrode on improvement of mobility are investigated. Firstly, the influence of some factors on the optical phonon mobility is analyzed of a MOSFET with non-ideal metal gate electrode. Secondly, the difference between high k / metal gate and high k / polysilicon gate on the optical phonon mobility and the total effective mobility are compared. By this model, the screening effect of metal gate is analyzed and discussed in theory, and the result is metal gate can screen the optical phonon from high k dielectric indeed and enhance the total effective mobility.In this paper, Ge MOS capacitors with high k gate dielectric passivated by the oxynitrides of AlON or TaON are fabricated and tested. At first, the appropriate annealing atmosphere and temperature are chose through the comparison between the electrical properties of Ge MOS capacitor. Then, the electrical properties and reliabilities of HfTa-based oxide and oxynitride with AlON and TaON or without interlayer on Ge substrate are investigated. The experimental results exhibit that the MOS capacitors with interlayer show better characteristics. These should be attributed to ultrathin AlON and TaON interlayer, which effectively suppresses formation of unstable low k GeOx and gives a superior interface between high k and germanium substrate. At last, according to the comparison among the Ge MOS samples with interface, the one with TaON interface has better characteristics.