The Modeling And Application Research On The Focused Ion Beam Sputtering Process

The focused ion beam sputtering etching is an important process in MEMS applications.It can perform high-precision device structure processing,surface treatment,device inspection,device repair and adjustment,etc.at sub-micron/nano scale.However,in practical applications,its complex physical processes and the dynamic changes in equipment environment have an important impact on the actual processing results.In this study,the focused ion beam sputtering process was researched through the experimental exploration,theoretical analysis,process modeling,and practical application.And a focused ion beam sputtering etching process model was established and applied in the process design and parameter design optimization.The study firstly carried out the experimental design for the research of process problems and effects.Single pixel processing,represented by single-pixel line scanning,was used to analyze the actual size of ion beam spots compared with the theoretical beam full diameter.In this way,the effect of beam spot size,ion beam current density distribution,processing time on the depth and opening of single-pixel etching is studied.The problem of the difference between the actual and the theoretical beam size,was verified and discussed by negative overlap rate scanning experiments.The depth and opening control of microstructure processing was studied by rectangular multi-scan experiments.The principle and influencing factors of the redeposition effect were analyzed by a group of single rectangular scan and dwell time change scan experiments.By controlling the size and parameters of the scanned pattern,the formation of the redeposition layer and its attenuation effect during the scanning process are studied.And a simplified contour calculation model is established to verify the theory.Series of experiments are designed for the asymmetric effects of overlay processing.Through studying of the performance variation of the effect,the sputtering yield-incident angle distribution model and the scanning strategy were combined to make the explanation.A preliminary study on focused ion beam processing methods and effects on single crystal quartz was also proposed.Based on the combination of experimental results analysis and process effect research,this paper established a FIB sputtering etching process model.The study first analyzed the process and the series of physical processes involved.Then,according to the logical sequence of these physical processes in the processing,the physical models are performed separately.Firstly,the current density distribution of the incident ion beam is analyzed.Combined with the theoretical study of the theoretical beam spot size and the actual opening width,a multi-Gaussian distribution is established.The study combines the incident ion dose distribution,the incident angle calculation,and the sputtering yield model to establish a flux model.A redeposition flux model was also established based on the sputtering distribution model and the particle movement model.The deposition flux model is combined with the sputtering flux model to establish a particle growth and reduction flux model on the surface of the substrate.Finally,the corresponding scanning strategy planning model is proposed by taking rectangle and ring scan as examples.These models together constitute the physical model of the focused ion beam sputter etching process.It describes the scanning trajectory of the ion beam during the scanning process,the ion incident process,the particle sputtering and deposition on the surface of the material.The surface material increase and decrease are described through the particle flux calculation,which realizes the modeling of sputtering etching and redeposition effects.The particle swarm optimization-continuous cellular automaton method is proposed and introduced into the computational model modeling and model parameter transformation and optimization of FIB sputtering process.In the model,the study abstracts the substrate and the reaction space into a three-dimensional cell space.Each node in the space,also called the cell,represents the spatial state within the cell size range in this space.The concept of cell occupation was introduced to allow the cell state calculations to become continuous.When the occupation value increases or decreases to reach the threshold of the current cell state,the state of the cell in the space is changed.The physical significance of the occupation rate lies in the ratio of the occupancy of different materials in the cell range in the space.Therefore,the particle flux calculation in the cell range space in the physical model can be converted into the cell occupation rate calculation,and the material state change in the space can be controlled to realize the process simulation.In the calculation,the study found that a series of model parameters and process environment related parameters could not be directly obtained from the key parameters in the process design.The study established a collection of these parameters as independent particles.The particle swarm optimization algorithm is introduced and combined with the basic structure experiment to obtain the optimal solution of these parameters for the current processing environment.And it provides the possibility for the model to realize the application in the actual process.The research further implements the computational model,develops a simulation calculation tool based on the model,and an observation tool for calculating the three-dimensional rendering of the result.This provides the basis and convenience for the practical application of the model and tools as well as the subsequent process research.The research carried out model calculation verification through the existing experimental design and results.The accuracy of the model in the calculation of the basic structure processing is proved by single pixel scanning and rectangular multiple scanning.In the model calculation,the study successfully reproduced the redeposition effect and the overlapping asymmetry effect.The potential of the model and tools in different materials applications was verified by quartz deposition calculation.These series calculation results of the model are in good agreement with the experimental results and the effect process analysis,which demonstrates the effectiveness and accuracy of the model as well as the simulation tool proposed in this study.The success in the simulation provides a basis for the subsequent process design and application.Finally,the research explores the application of this model and the simulation calculation tools in the design of complex microstructures in focused ion beam sputtering process in several cases.The cylindrical structure processing application verifies the applicability of the scanning strategy planning model to more complex scanning planning problems.The consistency between the calculated results and the experimental results demonstrates the potential of the model to predict the results of complex microstructure processing.The design of dense cylindrical array structure processing is proposed,and the parameter design,optimization and processing result prediction are carried out with the aid of model tools.In order to verify the ability of the model in complex processes,the study further introduced the slice-by-slice method to process complex curved structures.With the help of the model tool for image size planning of batch overlay scanning and 3D model prediction of machining results,the final machining results are consistent with the theoretical design.Thsese series of application cases demonstrate the ability of this model and model-based simulation tools to face complex microstructure processing.Accurate models and excellent 3D result display show great potential for the widespread application in focused ion beam sputtering process design and optimization.