Demonstration And Reliability Study On Si-Based InGaAs/Ge CMOS

With the conventional scaling down of Si MOSFETs,it is becoming difficult to go further more due to many problems like gate leakage current increase,short channel effect and so on.As promising alternative channel materials,Ge and InGaAs have attracted lots of interest as Ge and InGaAs have higher hole and electron mobility than that of Si.This thesis focuses on the development of high performance and low power MOSFETs.First,high performance ultra-thin-body InGaAs-OI nMOSFETs have been fabricated based on the direct wafer bonding InGaAs-OI substrates.Due to its superior crystal quality and flat surface,the peak electron mobilities of 8-nm-thick and 15-nm-thick InGaAs-OI MOSFETs reach 643 and 1167 cm2/Vs,respectively.A compatible fabrication process of integrating InGaAs nMOSFET and Ge pMOSFET is developed by using dual gate oxide structure.A dual gate oxide fabrication method that can optimize the InGaAs interface and Ge interface separately was employed to construct the InGaAs gate stack and Ge gate stack together.High on current of 8.26 uA/um for InGaAs nMOSFET and 3.91 uA/um for Ge pMOSFET are realized simultaneously by using this dual gate oxide process.Moreover,with the fabricated InGaAs-OI nMOSFETs,the influence of back gate(Vbg)modulation on the UTB InGaAs-OI nMOSFETs has been explored.It is find that,before the formation of the back channel,the mobility decreases by the more severe coulomb and surface roughness scattering with a larger negative Vbg applied.On the other hand,with the back channel formed by applying a positive Vbg,the back channel/BOX interface has a more prominent influence on the carrier distribution and mobility,especially in low electric field.In the high field,the deeper migration of the wave function towards the InGaAs channel leads to a mobility increase,which can be used as a performance booster for the InGaAs-OI CMOS transistors.At last,the reliability issue of high mobility materials is studied.Positive bias temperature instability(PBTI)and hot carrier injection(HCI)characterizations are performed on the InGaAs-OI nMOSFETs.The threshold voltage and saturation current of InGaAs-OI nMOSFETs are significantly affected by the PBTI and HCI stresses.It is confirmed that InGaAs-OI nMOSFETs with a thinner body thickness suffer from more severe degradations under both PBTI and HCI stresses.The superimposed effect of the recoverable acceptor traps and the permanent donor traps dominates the performance of InGaAs-OI nMOSFETs under stress.The reliability of high pressure oxygen oxidized(HPO)-GeO2 and Yttrium-doped GeO2(YGO)germanium gate stacks was also investigated.It is found that HPO-GeO2 degrades severely under electrical stress.Superior initial characteristics of Ge gate stacks cannot ensure good reliability as trap generation happens under electrical field stress.The films quality has a tremendous effect on the reliability of Ge gate stacks and both good initial property and excellent reliability performance can be achieved by applying cation-doping to optimize the quality of GeO2.