Fabrication And Characterization Of Strained Germanium Material

High mobility materials are attracting more and more attention for their ability of alleviating carrier mobility reduction during the scaling down. Germanium (Ge) film stands out as one of the most potential materials because of its high hole mobility. In this work, preparation and characteristic of strained Ge materials were extensively studied, and challenges during Ge channel devices fabrication process were also discussed. A new method of growing strained Ge film was first developed.The high-temperature oxidation characteristic of strained Silicon-Germanium (SiGe) layer was firstly studied in this paper. A relaxed Ge-rich SiGe virtual substrate was then achieved by oxidizing strained SiGe layer. An almost fully relaxed Ge-rich SiGe virtual substrate was achieved by combination of ion injection with high-temperature annealing. The surface roughness of the layer after oxidation is less than 1 nm, which is good to be a virtual substrate. The thickness of Ge-rich SiGe layer in this paper is about 50nm, which is much thinner than that of other techniques published in literatures.The influence of different growth temperatures on the Ge layer characteristic was studied by ultra-high vacuum chemical vapor deposition (UHV/CVD) system. Strained Ge films were then achieved and analyzed. For growth temperature at 325℃, the surface roughness of strained Ge epitaxial layer is less than 1 nm, the thickness can be controlled below 7nm and 1.5% strain was achieved.Method of growing strained Si on strained Ge film by UHV/CVD system was studied. An ultra-thin strained Si film was achieved. The characteristics of strained Si films were discussed. According to the results of research, the growth rate of Si is acceptable at 550℃,the thickness of strained Si film can be controlled accuracy at this condition. For growth temperature at 550℃, the surface roughness of strained Si epitaxial layer is less than 1 nm, the thickness is 2.5nm and 1.6% strain was achieved.The temperature window during Ge channel devices fabrication process was studied. The temperature of the devices fabrication processes must be below 600℃to avoid performance degradation of strained Ge channel device. In order to achieve high performance strained Ge channel MOS device, the key issue is to develop a set of steady low temperature process bellow 600℃. A method of optimizing Ge-rich SiGe virtual substrates was shown. The selections of gate dielectrics on different channel materials were analyzed at last.This research supplies the materials for fabricing strained Ge channel devices, and provides the experimental data and base for developing strained Ge technique.