Multiscale Simulation And Experimental Study Of Physical Processes Involved In Magnetron Sputtering Deposition

Magnetron sputtering is a vacuum deposition technology with the advantages of low deposition temperature,high deposition density,and high adhesion strength of deposited films.Furthermore,the unique incident energy and angle distributions of sputtered atoms allow them to reconstruct the growing film surface.Owing to these unique advantages,magnetron sputtering has been extensively applied in the micro-nanofabrication field to prepare the sputtered thin films with well-defined structure and morphology in recent years.This urgently requires for the precise control of the micro-morphology,micro-crystal structure and film uniformity of sputtered films.The key points to the precise control of the sputtered thin film properties are the systematic investigation of the microphysical processes involved in the magnetron sputtering deposition,including the sputtering,transport and deposition of sputtered atoms,and exploration of the influence mechanism of sputtering process parameters on these microphysical processes.However,some shortcomings and technical difficulties still exist in the research of these microphysical processes.In this dissertation,a series of multi-scale simulation approaches were used to study these microphysical processes.It is expected to combine these simulation approaches and experiment method to realize the fast fabrication of high-quality sputtered thin films.The main innovations and research contents of this dissertation are described as follows:1)Sputtering process of single crystal copper target induced by the bombardment of low energy ions: Given the divergence in understanding the formation mechanism of the "Wehner spots" induced by the bombardment of low energy ion onto monocrystal surface,molecular dynamics method was employed to investigate the microscope sputtering process induced by the bombardments of 500 eV argon ions onto Cu(001)surface at different temperatures.The simulation program monitored the trajectories of sputtered atoms and the variation of force exerted onto the sputtered atoms as they left the target surface.The monitoring results suggested that,when low energy ions impinged onto monocrystal surface,the anisotropic ejection of sputtered atom resulted from the regular interaction between the sputtered atom and its three neighbor atoms due to the regular arrangement of surface target atoms,rather than the focused collision emission.The underlying mechanism can be briefly described as "horizontal orientation and ski-jump take-off".With the increase of target temperature,the weakness of the anisotropy of sputtered atom emission was caused by the variation in the distribution of the surface potential energy due to the increase in the thermal vibration amplitude of target atoms.2)A coupled MC-MD method for the simulation of the sputtered atom transport and its application: A coupled MC-MD method to model the sputtered atom transport was proposed in this dissertation.In this coupled method,the MD collision model was established to dynamically reproduce the collision process between the sputtered atom and background gas atom and thus self-consistently calculated the post-collision velocity of sputtered atoms;the MC method was employed to model the free flight process of the sputtered atom during the successive two continuous collisions.The reliability of the MD collision model was confirmed by comparing the results calculated by the MD collision model and an analytical model established to calculate the scattering angle of the sputtered atom in the specific binary collision.The coupled MC-MD method was applied in calculating the incident energy and polar angle distributions of sputtered Cu atoms under the sputtering gas pressure of 0.15,0.5,and 2 Pa during the discharge by the magnetron system with a non-parallel and off-axis target-substrate configuration.3)Molecular dynamics simulation of the deposition of sputtered Cu/Si(100)film based on the calculated results by the MC-MD coupled method and experimental validation: Molecular dynamics method was utilized to perform a realistic simulation of the deposition of Cu film on Si(100)surface.In this simulation,the initial velocities of the deposited Cu atoms were sampled from the calculated results by the coupled MC-MD method.MD simulation results displayed the micro-surface morphology,micro-crystal structure,and Cu/Si interface structure of the sputtered films deposited at different pressures.Meanwhile,experiments under the same sputtering conditions were carried out to prepare sputtered Cu/Si(100)thin films,whose surface morphology,micro-crystal structure,and Cu/Si interface structure were characterized by experimental approaches.The simulation results were consistent well with the experimental results,which verified the reliability of the MD simulation.MD simulation results indicated that,with the increase of sputtering gas pressure from 0.15 Pa to 2 Pa,the surface roughness of sputtered Cu films increased gradually due to the transformation of the growth mode from layered growth to island growth.In addition,the MD simulation results dynamically revealed the mechanisms of the transformation of film growth mode and the formation of Cu/Si interface at micro-scale.4)Numerical investigation of the uniformity of the film deposited by triple-target s magnetron co-sputtering system and experimental validation: Since the existing numerical method,which evaluates the thickness distribution of sputtered films based on analytic theory,calculates the relevant parameters of analytical model according to pure geometric relationship,it can hardly be extended to multi-target magnetron co-sputtering system.In this context,a new approach to calculate the thickness distribution function of films deposited by triple-target magnetron co-sputtering system was proposed based on the traditional analytical theory of calculating the thickness distribution function of sputtered films.In this method,the surfaces of targets and substrate were meshed,and then coordinate transformation and vector operation were adopted in calculating the thickness distribution function of films deposited by triple-target magnetron.This method was used to investigate the effects of the target-substrate angle and target-substrate distance on the thickness distribution functions of thin films deposited by the specific triple-targets magnetron co-sputtering system.Simulation results predicted that the optimum uniformity of deposited films can be obtained when the target-substrate angle and target-substrate distance were set to 35° and 70 mm,respectively.Meanwhile,experiments were carried out under the same sputtering conditions.The experimental results validated the reliability of the numeric simulation.In addition,the simulation results revealed the underlying mechanism of the influence of target-substrate angle and target-substrate distance on film thickness distribution,which is significant in practice.