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7 July 1997 Precise measurement of ARC optical indices in the deep-UV range by variable-angle spectroscopic ellipsometry
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Antireflective coatings and photoresists are characterized precisely by spectroscopic ellipsometry from near IR to deep UV 190nm. A procedure based on the use of a polynomial dispersion law to take into account the optical indices of the films int he region where they are transparent is used. Thickness values provided by this technique are checked independently by grazing x-ray reflection technique at the cobalt K-(alpha) line. The procedure is valid for a range from very thin ARCs to very thick ones. Knowing the thickness of the film a new method to extract point to point the optical indices of the layer in the entire wavelength range has been developed; at each wavelength, we use different couples of values measured at different incidence angles, and we adjust the optical indices using a Levenberg Marquard algorithm. Compared to the standard point to point procedure, this method has tow main advantage: at the extrema of the interference fringes the better stability of the algorithm leads to more accurate extraction even for very thick film, due to the fact that the position of the extrema is slightly dependent of the angle of incidence; another interest is that the optimum angle of incidence for a given wavelength is generally always included in the interval. A final interest is that standard deviations on the n and k values are also extracted directly using this method giving an evaluation of the accuracy of the procedure at each wavelength. This method is applied first to transparent SiO2 thick film on silicon to demonstrate the better accuracy and then to antireflective coatings of various thickness down to deep UV range. Easy simulations of normal reflectance properties can then be made very easily using these optical indices.
© (1997) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Pierre Boher, Jean-Louis P. Stehle, Jean-Philippe Piel, Christophe Defranoux, and Louis Hennet "Precise measurement of ARC optical indices in the deep-UV range by variable-angle spectroscopic ellipsometry", Proc. SPIE 3050, Metrology, Inspection, and Process Control for Microlithography XI, (7 July 1997);

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