Characterization of a multilayer highly reflecting mirror by spectroscopic phase-modulated ellipsometry

Area of Science:

• Thin-film optics
• Materials science
• Optical engineering

Background:

• Optical multilayer coatings present complex characterization challenges due to interdependent layer parameters.
• Spectroscopic phase-modulated ellipsometry offers advantages for analyzing these systems by modeling layer structures against measurements.

Purpose of the Study:

• To develop and apply an algorithm for characterizing multilayer optical coatings with numerous layers using spectroscopic ellipsometry.
• To determine the structure and optical constants of a 23-layer highly reflecting mirror.

Main Methods:

• Utilized spectroscopic ellipsometry with a discrete spectral zone fitting approach.
• Analyzed ellipsometric spectra (? and D versus wavelength) in three distinct wavelength regimes (700-1000 nm, 280-340 nm, 340-700 nm).

Main Results:

• Successfully determined the sample structure of a 23-layer highly reflecting mirror in the 700-1000 nm range.
• Obtained the dispersion relation for the optical constants of TiO(2) near its absorption edge (280-340 nm).
• Derived the true dispersion of the refractive index for TiO(2) and refined the sample structure in the 340-700 nm range.

Conclusions:

• The discrete spectral zone fitting algorithm effectively characterizes complex multilayer optical coatings.
• Spectroscopic ellipsometry is a powerful technique for determining both the structure and optical properties of thin films.