Současné určení optických konstant, lokální tloušťky a lokální drsnosti tenkých vrstev pomocí zobrazovací spektroskopické reflektometrie

Simultaneous determination of optical constants, local thickness, and local roughness of thin films by imaging spectroscopic reflectometry

conference paper

en

A new optical characterization method based on imaging spectroscopic reflectometry (ISR) is presented and illustrated on the characterization of rough non-uniform epitaxial ZnSe films prepared on GaAs substrates. The method allows the determination of all parameters describing the thin films exhibiting boundary roughness and non-uniformity in thickness, i.e. determination of the spectral dependencies of the optical constants, map of local thickness and map of local rms values of heights of the irregularities for the rough boundaries. The local normal reflectance spectra in ISR correspond to small areas (37×37 µm2 ) on the thin films measured within the spectral range 270–900 nm by pixels of a CCD camera serving as the detector of imaging spectrophotometer constructed in our laboratory. To our experience the small areas corresponding to the pixels are sufficiently small so that the majority of the films can be considered uniform in all parameters within these areas. Boundary roughness is included into the reflectance formulas by means of the scalar diffraction theory (SDT) and the optical constant spectra of the ZnSe films were expressed by the dispersion model based on the parametrization of the joint density of electronic states (PJDOS). In general, there is a correlation between the searched parameters if the individual local reflectance spectra are fitted separately and, therefore, the local reflectance spectra measured for all the pixels are treated simultaneously using so called multi-pixel method in order to remove or reduce this correlation and determine the values of all the parameters with a sufficient accuracy. The results of the optical characterization of the same selected sample of the epitaxial ZnSe thin film obtained using the method presented here and combined method of variable-angle spectroscopic ellipsometry, spectroscopic reflectometry and single-pixel immersion spectroscopic reflectometry are introduced in the contribution as well. spectra of the ZnSe films were expressed by the dispersion model based on the parametrization of the joint density of electronic states (PJDOS). The spectral dependencies of the refractive index and extinction coefficient together with maps of local thickness and local ? of the upper boundary of a selected ZnSe film will be presented.

Nová metoda optické charakterizace umožňující určení všech parametrů popisujících drsnost rozhraní tenké vrstvy a neuniformitu v tloušťce na základě měření zobrazovací spektroskopické reflektometrie (ZSR) jhe prezentována na vcrstvách ZnSe na podložce GaAs. V této metodě se určují lokální spektrální odrazivosti při kolmém dopadu. Lokální odrazivosti odpovídají malým ploškám (37x37 µm2) na tenké vrstvě ve spektrálním rozsahu 270-900 nm měřenými pixely CCD kamery sloužící jako detektor zobrazovacího reflektometru sestaveného v naší laboratoři. Podle našich zkušeností jsou plošky korespondující s pixely kamery tak malé, že většinu vrstev lze považovat za uniformní v rámci těchto plošek. Drsnost rozhraní je obsažena ve vzorcích pro odrazivost pomocí teorie skalární difrakce (SDT) stejně jako v dřívějších publikacích. Spektra optických konstant vrstvy ZnSe byly vyjádřeny pomocí disperzního modelu založeného na parametrizaci spojené hustotě elektronových stavů (PJDOS). Obecně je přítomna korelace mezi hledanými parametry, pokud jsou jednotlivé lokální odrazivosti fitovány jednotlivě. Je nezbytné použít souběžné vyhodnocování lokálních spekter odrazivostí pro všechny pixely (toto je nazýváno multipixelovou metodou). Zjistili jsme, že tato multipixelková metoda umožnila redukovat nebo odstranit tuto korelaci což nám dává možnost určit parametry s dostatečnou přesností. Výsledky optické charakterizace stejného vybraného vzorku tenké vrstvy ZnSe získaných zde prezentovanou metodou a kombinovanými metodami spektroskopické elipsometrie s proměnným úhlem, epktroskopické reflektometrie a jednopixelové imerzní spektroskopické reflektometerie jsou také přítomny v příspěvku.

A new optical characterization method based on imaging spectroscopic reflectometry (ISR) is presented and illustrated on the characterization of rough non-uniform epitaxial ZnSe films prepared on GaAs substrates. The method allows the determination of all parameters describing the thin films exhibiting boundary roughness and non-uniformity in thickness, i.e. determination of the spectral dependencies of the optical constants, map of local thickness and map of local rms values of heights of the irregularities for the rough boundaries. The local normal reflectance spectra in ISR correspond to small areas (37×37 µm2 ) on the thin films measured within the spectral range 270–900 nm by pixels of a CCD camera serving as the detector of imaging spectrophotometer constructed in our laboratory. To our experience the small areas corresponding to the pixels are sufficiently small so that the majority of the films can be considered uniform in all parameters within these areas. Boundary roughness is included into the reflectance formulas by means of the scalar diffraction theory (SDT) and the optical constant spectra of the ZnSe films were expressed by the dispersion model based on the parametrization of the joint density of electronic states (PJDOS). In general, there is a correlation between the searched parameters if the individual local reflectance spectra are fitted separately and, therefore, the local reflectance spectra measured for all the pixels are treated simultaneously using so called multi-pixel method in order to remove or reduce this correlation and determine the values of all the parameters with a sufficient accuracy. The results of the optical characterization of the same selected sample of the epitaxial ZnSe thin film obtained using the method presented here and combined method of variable-angle spectroscopic ellipsometry, spectroscopic reflectometry and single-pixel immersion spectroscopic reflectometry are introduced in the contribution as well. spectra of the ZnSe films were expressed by the dispersion model based on the parametrization of the joint density of electronic states (PJDOS). The spectral dependencies of the refractive index and extinction coefficient together with maps of local thickness and local ? of the upper boundary of a selected ZnSe film will be presented.

thin films, roughness, scalar diffraction theory, Rayleigh–Rice theory, spectrophotometry, ellipsometry, imaging techniques, zinc selenide

2015

24.09.2015

9781628418170

0277-786X

Optical Systems Design 2015: Advances in Optical Thin Films V

9628

0C-1–0C-9

9