Research On Interfacial Properties Of Ge-Based MOS Devices With High ? Gate Dielectrics

As scaling down over the past several decades has pushed integrated circuits to its technical and fundamental scaling limit,traditional Si-based CMOS devices begin to appear aseries of problems,such as leakage-induced barrier lowering effect,drain-source punch-through effect,short-channel effect,reduced mobility and subthreshold leakage,which is restricting the device performance and the development of Moore's law.In order to extend the advantages of low cost and high performance brought by CMOS technology,Gemaniun and HfO₂ high-?gate dielectrics have gradually become one of the promising candidate channel materials for next generation of high-performance IC.Unfortunately,it is not ideal like SiO₂ directly contacted with high?gate dielectric.There are many problems in direct contact between Ge and high?gate dielectric.The main reason is that the GeO_x has a series of problems,such as poor thermal stability,easy hydrolysis and poor interface quality.Consequently,this thesis focuses on the research of the insertion one of passivation layers between HfO₂ and Ge substrate.Specifically including:Utilize the method of Si passivation to fabricate and analyze Ge pMOSFET,explore the method of O₃ passivation technique.The main works are summarized as follows:Firstly,GeO_x,the natural oxides of Ge,has the problem of poor thermal stability,easy hydrolysis and poor interface state quality after contacting with high-?medium of HfO₂,when it is used as a gate dielectric material.Therefore,the Si passivated of Ge pMOSFET fabrication is presented in this paper.The main purpose of this method is to introduce mature Si based CMOS technology into Ge devices.With the help of HfO₂/SiO₂/Si/Ge system,high performance Ge MOSFET devices can be achieved in the experiment.Consequently,suptter technology is used to explore the influence of Si passivation layer with different thickness on Ge pMOSFET fabrication.Meanwhile,in order to further enhance the device characteristics,Si passivation of Ge substrates with different orientations is also studied.The experimental results show that:in 50s passivation time,the devices can achieve better performance relatively.Under this condition,the highest effective mobility of Ge devices can achieve 278.6cm²/V·s,which is twice higher than that of Si devices.At the same time,Ge?100?crystal direction maximum open state current increases nearly 21%,when it compares to Ge?111?crystal direction;The effective mobility of Ge?100?is nearly 32.7%higher than that of Ge?110?crystal.Secondly,because GeO_x is the fundamental reason for the high concentration of Ge interface state,one of O₃ post oxidation technology based on the PEALD growth of Al₂O₃as an oxidation barrier is proposed in this paper.The advantage of this method is that Al₂O₃barrier layer can achieve low temperature and long time Ge interface processing,which can avoid high temperature causing GeO_x thermal decomposition.Moreover,the thickness of different Al₂O₃ barrier layers is chosen as the contrast condition in the experiment.By analysising of MOS capacitors by C-V and XPS,the growth of Al₂O₃ barrier layer in 10 to15 cycles can show better passivation effect,when the passivation time is under the 20min.Finally,based on high quality interface features acquired by MOS capacitors,the O₃passivation of pMOSFET devices is investigated.The results of the fabricated pMOSFET device show that the maximum effective mobility of 15 cycles Al₂O₃ barrier is252.7cm²/V·s?with increase 107%compared to Si?.At the same time,this condition pMOSFET can obtain I_on=28.5?A/?m,I_off=2.9×10^-3?A/?m and the I_on/I_offff is 10⁴.In conclusion the results of the above research have some guiding significance for high mobility Ge MOSFET fabrication.