Determination of properties of wedged, nonuniformly
thick, and absorbing thin films by using a new
numerical method

Jonghoon Baek, Desiderio Kovar, John W. Keto, and Michael F. Becker

Nonuniformity in the thickness of thin films can severely distort their transmission spectra as compared
with those of flat, smooth films. Methods that extract properties such as refractive index, thickness, and
extinction coefficient of such films can suffer inaccuracies when they are applied to wedged or nonuniformly
thick films. To accurately extract optical properties of nonuniform films, we have developed a novel
numerical method and efficient constitutive relations that can determine film properties from just the
transmission spectrum for films that are locally smooth with negligible scattering loss. This optimum
parameter extraction (OPE) method can accommodate films with two-dimensional thickness variation
that would result in significant errors in the values of refractive index and film thickness if not considered.
We show that for carefully chosen test cases and for actual pulsed-laser-deposition AlN thin films,
properties such as refractive index, extinction coefficient, and film thickness were very accurately determined
by using our OPE method. These results are compared with previous techniques to determine the
properties of thin films, and the accuracy of and applicable conditions for all these methods are
discussed. © 2006 Optical Society of America
OCIS codes: 310.6860, 310.3840, 240.0310.