Differential Phase SPR Detection Method For Film Thickness

Thin films,especially the metal thin films,are becoming more and more important in various application fields due to their excellent electrical,optical and mechanical properties.The characteristics of the film depend on not only the material properties,but also its thickness and surface structure deeply,especially the nanometer metal film.On the basis of analyzing the characteristics of commonly used metal film thickness detection methods,this thesis mainly focuses on thickness detection method of the metal film through the surface plasmon resonance(SPR)effect.Based on the laboratory researches and the preliminary results,the differential-phase SPR measurement method is studied.The SPR effect is excited by injecting laser into the coupler sensing prism with the resonance angle,and the differential angle-phase detection method is adopted to improve the sensitivity and resolution.The coupler is the typical Kretschmann configuration,and the film with different thickness is plated on the coupler to carry out different phase information.The laser beams modulated by the SPR effect form into interference fringes by the Mach-Zehnder interferometer.The thickness of the thin metal film can be derived out by calculating the offset changes of the fringes that reflect the phase changes.The differential phase SPR measurement method used to detect the thickness of metal film is analyzed in the thesis,and several models have been simulated.According to the design requirements and simulation results,the scheme of differential SPR phase detection system is determined.Based on that,the optical path of differential SPR phase detection system is set up and debugged.Through image processing of the phase interference fringe obtained by experiment,the slope of the relationship curve between the phase change and angle of incidence can be calculated to obtain the thickness of metal film.The results are compared with the previous ones obtained before to improve the system.Finally,the error factors in our experiment model and system are analyzed.The simulation and experimental results show that the metal film thickness measurement system based on differential SPR phase effect proposed in this thesis is feasible,and also show that the method can achieve higher measurement accuracy and better sensitivity.