Study On The Preparation Of Nano-layer Oxide Films On Graphene Surface And In-situ Monitoring Of RHEED

With the development of science and technology,the device size is getting smaller and smaller,therefore,traditional silicon-based semiconductor devices have become inapplicable.Graphene materials have been extensively studied due to their high carrier mobility,low resistivity and excellent optical,mechanical and thermal properties.In graphene-based semiconductor devices,it is necessary to deposit a high-K gate dielectric on graphene surface.However,since the surface of graphene is relatively smooth,it becomes difficult to deposit a thin film on the surface.Among the currently widely used thin film preparation methods,the thin films deposited by Atomic Layer Deposition（ALD）are at the forefront level in terms of uniformity,shape retention and quality.Therefore,this paper selects ALD technology on the surface of graphene.Deposit high quality Al₂O₃film.In this thesis,we study the influence of different pretreatment methods,different growth temperatures,and different purging methods on the growth of thin Al₂O₃films during the film deposition on the surface of graphene using ALD technology.And in this process,a Reflection High Energy Electron Diffraction（RHEED）was used to monitor the deposition process in situ and in real time.First,H₂O molecules were refilled with different times to attach them to the surface of graphene as the seed layer for subsequent film deposition.For comparation,filling 30times,50 times and soaking for two hours were chosen as variables.The Atomic Force Microscope（AFM）,Raman,X-ray Photoelectron Spectroscopy（XPS）and Transmission Electron Microscopy（TEM）characterization data show that this method is an effective pretreatment method,and will not bring new impurities and defects to graphene.The quality of the Al₂O₃ film deposited after 50 times of H₂O filling and immersion in water for two hours is higher.Secondly,the influence of different growth temperatures on film deposition is studied.Between 100-140℃,every 10℃was selected as a node for testing.It is found that 110-130℃is the best film growth temperature range.Subsequently,the purge time after trimethylaluminum（Al（CH₃）₃,TMA）and H₂O was extended to explore the effect of different purge methods on the film deposition.It can be seen from the 2D and 3D images measured by AFM that when the film growth is basically controlled by the physical adsorption of H₂O molecules,the deposited film is more continuous and of higher quality.Finally,RHEED was used to monitor the ALD film deposition process in real time and in situ.In the initial stage of the reaction,by lifting and rotating the sample stage,a clear and bright diffraction pattern of different crystals orientations can be obtained.During the deposition process,several cycle nodes were selected to observe the diffraction pattern,and it was found that as the number of cycles increased,the diffraction pattern gradually darkened and eventually became blurred,which was in line with the expectation that the ALD low-temperature growth of Al₂O₃ would be amorphous.The intensity of the diffraction fringes was recorded,and it was found that the intensity showed obvious periodic changes,but it was irregular in each cycle,presumably due to the short purging time.After prolonging the purge time,it was found that this phenomenon has been significantly improved.The use of AFM to monitor the growing samples confirmed this conclusion.