Proper choice of the error function in modeling spectroellipsometric data

Determination of the optical function n(λ) of vitreous silica by spectroscopic ellipsometry with an achromatic compensator

Studies of dielectric materials by rotating-element spectroscopic ellipsometry (SE) are beset with a number of problems such as (1) low reflectance and hence low signal-to-noise ratio and (2) an almost zero (or 1800) change in the ellipsometric parameter A on reflection from the sample, which leads to significant errors in the measured parameters. These difficulties were overcome (1) by developing suitable procedures for correcting nonlinearity in the detection system and the deleterious effects of ambient light and (2) by incorporating an achromatic quarter-wave compensator in the SE system, respectively. A new rapid method of aligning and calibrating the compensator has also been developed. Test measurements with such an SE system on a vitreous silica sample revealed that the accuracy of measurements of Δ and Ψ are 0.03° and 0.015°, respectively, over the spectral range of 300-700 nm. The SE data were then analyzed by standard procedures with linear regression analysis to determine the optical function n(λ) (i.e., refractive index and its dispersion with wavelength) of vitreous silica and at the same time to characterize the microroughness of the surface layer of the sample. The refractive index of vitreous silica determined by this technique is within ±0.0004 of the best reported values in the literature over the spectral range of 300-700 nm. The SE data obtained on the vitreous silica sample revealed the presence of a 1.0-nm-thick microrough layer on the surface of the sample.

Use of the biased estimator in the interpretation of spectroscopic ellipsometry data

The use of the biased estimator in the fitting of spectroscopic ellipsometry data is examined and applied to data from two-channel polarization modulation ellipsometry experiments. It is pointed out that the use of the biased estimator, as opposed to the unbiased estimator that is usually found in the literature, allows the experimentalist to weight properly the more accurate parts of the spectrum, to switch among different representations of the data, and to calculate a goodness of fit. The fit to data taken on a 59-nm SiO(2) film on Si is examined with both the biased and the unbiased estimators.

Ion assisted deposition of thermally evaporated Ag and Al films

Optical, electrical, and microstructural effects of Ar-ion bombardment and Ar incorporation on thermally evaporated Ag and Al thin films are investigated. The results show that as the momentum supplied to the growing films by the bombarding ions per arriving metal atom increases, the refractive index at 632.8 nm increases and the extinction coefficient decreases, lattice spacing expands, grain size decreases, electrical resistivity increases, and trapped Ar increases slightly. In Ag films, stress reverses from tensile to compressive and in Al films compressive stress increases. In the Al films the change in optical constants can be explained by the variation in void volume. The reversal of stress from tensile to compressive in Ag films requires a threshold level of momentum. The increase in electrical resistivity is related to the decrease in grain size and increase in trapped Ar in both types of film. Many of these properties correlate well with the momentum transferred, suggesting that the momentum is an important physical parameter in describing the influence of ion beam on growing thin films and determining the characteristics of thin metal films prepared by ion assisted deposition.

Simultaneous determination of refractive index, its dispersion and depth-profile of magnesium oxide thin film by spectroscopic ellipsometry

A new method of using the spectroscopic ellipsometry technique to determine (a) the true (or bulk) refractive index of the film material, (b) the dispersion of the above refractive index with wavelength, (c) the thickness of the film, and (d) the distribution of the voids in the film is presented.