Study On The Application Of Micro-nano Fabrication And Characterization Of FIB-SEM Dual Beam System

With the rapid development of nanoscience and integrated circuit technology,more and more requirements are put forward for nano-scale fine machining technology.The FIB-SEM dual-beam system combines the ultra-high precision micro-nano processing capability of the focused ion beam with the high spatial resolution imaging and analysis capability of the scanning electron microscope.It can be used for precise ion beam milling,metal/insulator layer deposition,and 3D characterization of microstructure and composition.Moreover,it is widely used in microelectronics and materials science.With the development and wide applications of spherical aberration-corrected transmission electron microscopy(TEM)and in-situ TEM,the FIB-SEM dual-beam system has become very useful in preparing high-quality TEM samples and in-situ TEM samples.Due to the diversity of samples and the complexity of sample preparation process,it needs higher skill level of users.Especially,many difficulties including process flow,cutting geometry,high precision positioning,reliable conducting connection,and 3D information extraction,have not been well solved.It leads to poor reproducibility and low success rate in the experiment.Therefore,it is of great significance to establish new techniques and methods to improve the level of ultra-fine machining and characterization of the FIB-SEM dual-beam system by further optimizing the process flow and parameters of the sample preparation.Therefore,it is of great significance to improve the ultra-fine processing and role shaping level of the FIB-SEM dual-beam system by further optimizing the process flow and process parameters in the sample preparation process.In this thesis,the difficulties in ultra-fine processing and characterization of FIB-SEM dual-beam system,such as accurate positioning in the thickness direction,microstructure-electrical properties relationship of FIB deposited Pt nanowires,information extraction of three-dimension(3D) energy dispersive spectroscopy(EDS) reconstruction,are investigated.Furthermore,the results are applied to study the microstructure of hafnium-based ferroelectric thin films.(1)A real-time monitoring and positioning method of sample slice thickness based on EDS quantitative analyses.Compared with the conventional cross-section TEM samples,the plan-view sample can provide the in-plane microstructure information of the thin film.It is expected to realize that the in-plane micro-nano-scale characterization.One of the most challenging problems in preparing plan-view sample using the dual beam system is the precise positioning and monitoring of the middle layer in the thickness direction.Based on the principle that the characteristic X-ray intensity of each layer is proportional to its relative thickness,an online positioning method in thickness direction is developed based on the EDS signal in this chapter.The BiFeO₃ cubic nanodot arrays with a thickness of 25nm and size of 100nm were fabricated on SrTiO₃ (001) substrate and SrRuO₃ electrode with a thickness of 20nm.The characteristic X-ray intensities of Pt-M,Sr-L,Ti-K,Ru-L,Fe-K,and Bi-M peaks were monitored by EDS in the milling process.The relative thickness of the Pt protective layer,BiFeO₃,SrRuO_3,and SrTiO_3,was obtained.Thus,the precise position of BiFeO₃ nanodot array in the thickness direction was determined,which provides a basis for optimizing cutting parameters and determining the cut-off time.Finally,high-quality planar samples of BiFeO₃ nanodot array were prepared,which provides a successful example for plan-view TEM sample preparation with similar buried structures.In addition,the 38° pre-tilt stage helps simplify the plan-view FIB lift-out operations by reducing tilt operation and eliminating rotation operation of the sample and nano manipulators.Furthermore,the success rate of in-situ transfer of plan-view samples was significantly improved.(2)The relationship between microstructure evolution and resistivity of electron-beam deposited Pt nanowire in FIB-SEM.The combination of the ion beam or the electron beam with a gas injection system can achieve high-precision controllable deposition of Pt,C,W,and SiO₂,which was an essential ultra-fine machining process in the dual-beam system.It is widely used in IC chip circuit modification.The Pt nanowires are usually used as connecting wires to prepare in-situ electrical TEM samples,so the microstructure and electrical properties of the deposited Pt nanowires significantly influence the experimental results.In this chapter,the microstructure evolution and electrical properties of Pt nanowires prepared by electron beam deposition(EBD) were analyzed through Cs-TEM and thermal/electric in-situ holder.During the heating process,the Pt nanowires underwent crystallization,organic matter decomposition,Pt nanocrystal growth,grain connection,and conductive path formation,companied with several orders of resistance reduction.Based on the above results,the Pt deposition process can be further optimized,and more detailed primary data can be contributed to the design of in-situ microcircuits.(3)Three-dimensional EDS tomography and extraction of characteristic microstructure information based on the FIB-SEM system.The microstructure of magnesium-doped calcium silicate bioceramic was studied through a FIB-SEM system.The region of 36.7×27.1×15.5?m³ in 10%Mg-doped calcium silicate bioceramic was selected for series sectioning.156 slices were obtained by EDS maps instead of conventional SE and BSE images.High-precision 3D reconstruction of Mg-rich and Na-rich second phases was achieved;a high-quality 3D model was obtained with a voxel size of 48×48×100nm³.Furthermore,the volume fraction,chemical composition,equivalent diameter,and interface area of the secondary phases were quantitatively analyzed,which provided solid evidence for explaining the optimal comprehensive mechanical properties of the sample.The image data of 156 slices were analyzed further by stereology methods,and the results were similar to the 3D reconstruction analyses.It demonstrates that the stereological method can obtain three-dimensional structure information reliably from two-dimensional images.(4)The preparation of plan-view and In-situ TEM samples of hafnium-based ferroelectric thin films by FIB-SEM system.Hafnium-based ferroelectric thin films are difficult to image because of their thickness(less than 20 nm),grain size(up to tens of nanometers),and sandwich structure formed between the two electrodes.A high-quality plan-view TEM sample of 15nm hafnium-based ferroelectric thin films was prepared using the method proposed previously.Clear polycrystalline diffraction ring patterns were obtained by the selected area electron diffraction(SAED) technique.The existence of a non-ferroelectric monoclinic phase in hafnium zirconia thin film is confirmed by eliminating the effect of Ti N electrode.Furthermore,the in-plane morphology of hafnium zirconia crystal was revealed.A cross-section in-situ TEM sample of hafnium-based ferroelectric thin films was designed and prepared.It is the first time to observe the transition from the non-ferroelectric tetragonal phase to the ferroelectric orthogonal phase of hafnium zirconium oxide(HZO)under an electric field.It provides basic knowledge to understand the micromechanism of orthogonal phase formation and the various electrical properties.