Simulation Of Terahertz Single-wavelength Ellipsomety And Thickness Measurement By Ellipsometric Data Inversion

Over the past 30 years,terahertz time-domain spectroscopy(THz-TDS)has attracted more and more attention.As a complementary measurement technology,terahertz ellipsometry can be divided into two branches.On the one hand,imported directly from THz-TDS,terahertz time-domain ellipsometry(THz-TDE)is developed earlier and based on terahertz pulse,using the fundamental theory of THz-TDS.On the other hand,Terahertz frequency-domain ellipsometry(THz-FDE)is based on high intensity terahertz continuous wave source.It’s a pleasing thing that THz-TDE and THz-FDE has a certain effect on applicatory.In this dissertation,we combine two technologies: terahertz technology and ellipsometry.Based on the theory of vectorial angular spectrum transform and that of ellipsometry data inversion,and considering the high penetration of terahertz wave,we study terahertz single-wavelength ellipsometry based on the scheme of polarizer-rotaing-compesator-sample-analyzer(PCSA).We also demonstrate the analytic method and numerical method of ellipsometry data inversion.To prove the validity of the methods of ellipsometry data inversion,without any experimental data in hand,we use COMSOL software as alternative to simulate the ellipsometry,providing simulation ellipsometry data.Then we obtain refractive index and thickness of thin films by ellipsometry data inversion and compare them to setting values.Therefore,we summarize the main results as follows:(1)The ellipsometric parameters of thin films can be obtained by terahertz single-wavelength ellipsometer based on PCSA scheme using intensity of terahertz wave under four distinct angles of compensator.Then the structure parameters can be obtained by ellipsometry data inversion.Thanks to this fact,terahertz single-wavelength ellipsometry can be applied in thickness measurement of thin films.(2)The methods of ellipsometry data inversion can be divided into two branches: the analytic method and the numerical method.On the one hand,the analytic method is suitable to ellipsometric data of transparent thin films when error or bias of ellipsometric data is small enough.On the other,the numerical method is suitable to ellipsometric data of transparent or aborbing thin films when error or bias of ellipsometric data is large enough.Without any prior knowledge,the method combining ellipsometric data under different incident angles should be adopted to uniquely determine the refractive index and thickness of thin films.(3)When terahertz single-wavelength ellipsometer of collimated-type based on PCSA scheme is applied to measure the thin films,we find that the reflection wave can be described as Guassian beam and the center of the wave may shift left or right from propagation axis.However,when terahertz single-wavelength ellipsometer of focused-type based on PCSA scheme is applied to measure the thin films,we find that the reflection wave can not be described as Guassian beam.We also find several peaks in the cross section of reflection wave.We find that simulation error exist in simulated ellipsometric parameters.Due to this fact,the analytic method do not always works.As a result,the refractive index obtained by the analytic method is not always in accordance with setting values.However,the numerical method still works.We perform numerical ellipsometric inversion by combining ellipsometric data under different incident angles.After that,we find the relative errors refractive index and thickness of thin films are not greater than 1%,which prove the validty of ellipsometric inversion method.