Possibilities and limitations of imaging spectroscopic reflectometry in optical characterization of thin films

conference paper

English

Imaging spectroscopic reflectometry (ISR) provides methods enabling us to perform an optical characterization of thin films non-uniform in optical parameters (e.g. in thickness). It measures spectral dependencies of a local reflectance at normal incidence of light belonging to small areas on these films (37x37 µm^2 in our case) imaged onto individual pixels of a CCD camera serving as a detector of a spectrophotometer. The local reflectance can mostly be expressed using formulas corresponding to a uniform thin film. There are three methods for treating ISR experimental data in the special case of thickness non-uniformity, i.e. in the case of the same optical constants along the whole area of the film: i) If optical constants of the non-uniform film are known, spectral dependencies of the local reflectance are used to determine a map of the local film thickness (one pixel method). ii) If optical constants are unknown, spectral dependencies of these constants are determined using standard spectroscopic ellipsometry and reflectometry under taking into account postulated non-uniformity in thickness (e.g. wedge-shaped non-uniformity) and a suitable dispersion model for optical constants. Then local reflectances are again utilized for determining the local thickness map (the combined method of the onepixel ISR method and the standard methods). Note that the spectra of the local reflectance can also be used for the determination of the map of roughness rms values together with the map of the local thickness if the rough non-uniform thin film is characterized by this combined method. iii) If the situation concerning the optical constants is the same as in ii) one can utilize a simultaneous treatment of the experimental data measured by all the individual CCD pixels without using auxiliary methods. This multi-pixel method enables us to determine simultaneously the spectral dependencies of optical constants and the map of local thickness if a suitable dispersion model of the film is employed. In this contribution examples of the optical characterization of thin films non-uniform in thickness corresponding to all cases i)-iii) will be presented.

Reflectometry ; Spectroscopy ; Thin films ; Reflectivity ; Optical constants ; CCD cameras ; Sensors ; Spectrophotometry ; Spectroscopic ellipsometry

OHLÍDAL, M.; OHLÍDAL, I.; NEČAS, D.; VODÁK, J.; FRANTA, D.; NÁDASKÝ, P.; VIŽĎA, F.

2015

24. 9. 2015

9781628418170

Optical Systems Design 2015: Optical Fabrication, Testing, and Metrology V

0277-786X

Proceedings of SPIE

9628

United States of America

0R-1

0R-13

13