Mobility Model And Surface Passivation Of GeOI MOS Devices With High-k Gate Dielectric

As silicon CMOS device is continuously scaled, it has been increasingly approaching its physical limits, resulting in difficulty in the further scaling and low power consumption. In this case, Ge OI MOSFET with Ge as channel has become one of the most promising candidates due to its advantages of high hole mobility and “on insulator”. So, in this thesis, theoretical and experimental investigations on the effective hole mobility model of Ge OI MOSFET and electrical properties of high-k gate dielectric Ge MOS devices are performed.Theoretically, a hole mobility model of Ge OI p MOSFETs based on the Fermi's Golden Rule has been established by comprehensively analyzing the scattering mechanisms. The simulation results show that the effects of quantum well is very strong, result in a severe degradation of hole mobility for thin Ge film thickness(< 5 nm). Further, this work has also investigated the influence of the remote coulomb scattering for hole mobility, originating in the fixed charge of the interface including stack high-k dielectric and the buried oxide layer in ultra-thin Ge OI p MOSFETs. The simulation results exhibited that the thicker interface layer with smaller dielectric constant is, the higher hole mobility is. On the contrary, the relationship between hole mobility and the high-k gate dielectric is just the opposite with the passivation layer. In addition, for buried oxide layer, the effective hole mobility first increased and then slowly decrease along with the increase of its dielectric constant, however, the influence of its thickness can be ignored.Experimentally, some investigation has been done on the interfacial and electrical properties of Ge MOS devices:(1) Ge MOS capacitors with Zr ON/Ge ON dual passivation layer have been fabricated by nitrogen plasma treatment. The experiment results show that the NH3-plasma treated device exhibits lower interface-state(Dit = 1.64×1011 cm-2 e V-1) and improved interfacial characteristics. XPS analyses reveal that the device treated by NH3-plasma can also form a higher quality interface of high-k/Ge, due to the H atoms and NH radicals from the decomposition of NH3, which can effectively enhance the unstable low-k Ge Ox volatilization, thus resulting in excellent interfacial and electrical properties.(2) Ge MOS capacitors with Zr YON, Zr ON or YON passivation layer have been fabricated and then the influence of yttrium doping has been investigated in detail by comparing the three samples. The experiment results exhibit that compared with Zr ON and YON passivation layer, the Zr YON passivation layer can more effectively inhibit the inter-diffusion of Ti, O and Ge. Besides, yttrium has the minimum of gibbs free energy in the metal oxide, which can effectively suppress the formation of unstable low-k Ge Ox in the annealing process, improving the interfacial and electrical performance of Ge MOS devices.