Study On Correction Method Of Depolarization Effect Of Thin Films In Spectroscopic Ellipsometry

As the manufacture process of nano-photoelectric thin films becomes more and more mature,process monitoring requires higher precision for the measurement of optical constants and thickness of thin films.Spectroscopic ellipsometer has the advantages of high accuracy,non-contact,non-destructive,and fast measurement speed for the measurement of thickness and optical constants of thin films.Spectroscopic ellipsometer system model usually assumes that parallel light is incident on a uniform thickness film to achieve measurement,so the incident and reflected light are assumed to be totally polarized light.However,in the actual process of ellipsometry,there are depolarization effects caused by thickness non-uniformity,finite bandwidth,numerical aperture,and scattering.Because the non-depolarization optical property modeling calculation spectrum of the film cannot accurately match the measurement spectrum with depolarization effect,the optical constant and thickness of thin films cannot be accurately extracted.In this thesis,focusing on the optical depolarization of thin films in the process of ellipsometry and in view of the depolarization error factors such as thickness non-uniformity and spectral finite bandwidth,the theory and the rapid calculation method of incompletely polarization optical modeling of thin films in the process of ellipsometry have been proposed,and experimental verification of spectroscopic ellipsometry has been carried out.The specific research contents and innovations of this thesis can be summarized as:(1)A film optical model considering depolarization effect caused by thickness nonuniformity,finite bandwidth,numerical aperture and scattering has been established.Based on the theory of optical film transmission matrix modeling and in view of the depolarization factors such as thickness non-uniformity,bandwidth,standard deviation of incident angle distribution,mean square deviation height and correlation length of rough surfaces,a kind of high-precision,rapid modeling and calculation method of depolarization optical properties of film based on one-dimensional numerical integration method has been proposed.(2)The ellipsometry spectrum of thin films with different depolarization effects have been simulated and analyzed.The difference of ellipsometry spectrum of isotropic films with different depolarization effects have been analyzed.By comparing the depolarization index spectrum of thin films calculated by the rapid modeling method and the modeling method based on the three-dimensional numerical integration method,the calculation accuracy and efficiency of the rapid modeling method have been verified.(3)Based on the Muller matrix ellipsometer,experimental studies on several kinds of isotropic and anisotropic thin films with depolarization effect have been completed.Combining the depolarization effect with thin film optical model,the experimental results show that the calculated optical spectrum of films agrees well with the experimental measurement,and the accuracy of optical constant and thickness of thin films have been improved,and the effectiveness and accuracy of the proposed method to calculate highprecision depolarization optical properties of isotropic and anisotropic films has been verified.