Improved Interfacial And Electrical Properties Of Ge MOS Devices With LaON-based Interfacial Passivation Layer

As the development of integrated circuit,the performance of MOSFET should be further improved.Therefore,novel substrates with higher mobility,e.g.Ge and ?-? compound semiconductors,are proposed to replace traditional Si.Among them,Ge is one of the most promising candidates,due to its highest hole mobility(1900 cm2/V·s),which is also symmetrical with its electron mobility.However,compared with traditional Si substrate,the oxide of Ge substrate,i.e.GeO2,is unstable at high temperature,which will react with Ge substrate to form volatile GeO and degrade the interface quality and performance of Ge MOS device.The interface quality has become the most critical obstacle to realize high-performance Ge MOSFET.For the purpose of improving the interface quality of Ge MOS,in this thesis,a series of meaningful investigations has been carried out based on the popular rare-earth oxides,including the forming mechanism of interface between rare-earth oxides and Ge substrate,the degrading principle of interface quality by HfO2 high-k layer,the application and further improvement of rare-erath oxides as interfacial passivation layer(IPL),the modification of rare-erath oxides and so on.Firstly,two different kinds of rare-earth oxides(La2O3 and Y2O3)are used to investigate the forming mechanism of interface between rare-earth oxide and Ge substrate.The results show that compared with Y2O3,La2O3 is more likely to react with Ge substrate and form thicker germanate interlayer,thus resulting in a better interface quality.Furthermore,the effects of N incorporation in La2O3 or Y2O3 on the formation of germanate and interface quality are studied,and finding that N incorporation could suppress the diffusion of Ge and O to suppress the formation of LaGeOx and GeOx at the interface.Therefore,LaON could form an excellent interface with Ge substrate(Dit=4.96×1011 cm-2eV-1)and is believed to be a promising material to passivate the interface of Ge MOS device.Based on the results above,LaON is used as IPL,capped by HfO2 high-k layer to form HfO2/LaON/Ge MOS capacitor,and results show that the LaON IPL significantly improve the quality of HfO2/Ge interface.However,compared with the LaON/Ge interface without HfO2 high-k layer,the interface quality of HfO2/LaON/Ge still degrades(Dit = 8.02 × 1011 eV-1cm-2).Two different kinds of IPLs(LaON and YON)are used to investigate the degrading principle of interface quality by HfO2 high-k layer,and two kinds of dual IPLs(YON/LaON and TaON/LaON)are designed to further improve the interface quality.Compared with YON,TaON could reduce the effect of HfO2 on LaON/Ge interface more effectively and obtain a nearly ideal LaON/Ge interface(Dit= 5.32×1011 cm-2eV-1).In addition,other schemes are studied to further improve the interface quality of HfO2/LaON/Ge stack by optimizing the HfO2 high-k layer.N and Ta incorporations and F plasma treatment to HfO2 are used to reduce the effect of Hf-based high-k layer on the interface quality.Results show that N and Ta incorporations could improve the density and uniformity of HfO2 film,and meanwhile effectively suppress the diffusion of Hf and thus the formation of LaHfOx and HfGeOx.Therefore,N and Ta incorporations could effectively reduce the effect of Hf-based high-k layer on the LaON IPL,and obtain an excellent interface(Dit = 5.77×1011 cm-2eV-1).Meanwhile,F plasma treatment could form stable Hf-F bonds in HfO2,thus suppress the diffusion of Hf and reduce the effect of HfO2 on the LaON IPL,resulting in the further improvement of the interface quality.Finally,by incorporating Ta in LaON to improve its hygroscopic property,LaTaON are studied as a novel high-k dielectric,which could be used directly as gate dielectric for Ge MOS device.Results show that Ta incorporation could greatly improve the hygroscopic property of LaON while maintaining the excellent interface quality with Ge substrate.The Ge MOS device with LaTaON as gate dielectric could obtain excellent interfacial and electrical properties,and therefore,the LaTaON is believed to be a promising gate dielectric for Ge MOS device.