CMOSデバイスに向けたゲルマニウム基板上高誘電率絶縁膜ゲートスタック技術

Ge沟道是后硅时代CMOS器件最有前途的解决方案之一。迁移率的提高是限制Ge-Ce-ETS应用的最关键的问题。近年来，虽然高迁移率Ge MOSFET取得了很大的进展，但高正常场区的迁移率退化仍然很严重，极大地降低了Ge MOSFET的导通电流。这种现象的机制尚不清楚，尽管重要。因此，在我们的研究中，导致高正常场迁移率退化的物理根源进行了系统的研究。通过对Ge MOSFET的霍尔迁移率的研究，发现Ge的价带和导带内存在大量的表面态，导致沟道内移动的载流子浓度显著降低，Ge MOSFET的有效迁移率迅速降低，同时证实了Ge nMOSFET在原子氘气氛中退火可以钝化Ge导带内的表面态。除表面态外，还证实了表面态粗糙度散射对Ge MOSFET的高垂直场迁移率起主导作用，这与Si MOSFET的情况类似。随着后氧化温度的降低，GeOx/Ge界面的表面粗糙度可以充分降低，而不会失去很大的上级电钝化。结果表明，通过将后氧化温度从300℃降低到室温，在N_s=10 μ cm ~ 2的高法向场区，Ge pMOSFET和nMOSFET的迁移率分别提高了20%和25%<13><-2>。

Ge channel is one of the most promising solution for CMOS devices in post-Si age. Mobility enhancement is the most critical issue limiting the application of Ge MOSFETS. Recently, although many progresses have been achieved for high mobility Ge MOSFETs, mobility degradation in high normal field region is still severe which strongly reduces the ON state current in Ge MOSFETs. The mechanism of this phenomenon is not clear yet, in spite of importance. Therefore, in our research the physical origins causing high normal field mobility degradation were systematically investigated. Through the evaluation of Hall mobility in Ge MOSFETs, it is found that large amount of surface states exist inside valence and conduction band of Ge, which results in significant decrease of mobile carrier concentration in the channel and rapid reduction of effective mobility of Ge MOSFETs.Additionally, it is confirmed that the surface states inside conduction band of Ge can be passivated by annealing the Ge nMOSFETs in atomic deuterium ambient. Besides of surface states, it is also confirmed that the surface state roughness scattering dominates the mobility in high normal field for Ge MOSFETs, similar with the situation in Si MOSFETs. With decreasing the post oxidation temperature, the surface roughness at GeOx/Ge interfaces can be sufficiently reduced without losing the superior electrical passivation much. As a result, around 20% and 25% mobility enhancement can be realized for Ge pMOSFETs and nMOSFETs, respectively, in a high normal field region of N_s=10^<13> cm^<-2> by reducing the post oxidation temperature from 300℃ down to room temperature.