Daniel Franta

Ellipsometric parameters and reflectances of thin films with slightly rough boundaries

Abstract In this theoretical paper, formulae for important optical quantities of single layers with slightly randomly rough boundaries are derived by means of a generalized Rayleigh–Rice theory. Thus the formulae for the specular reflectances and ellipsometric parameters of the layers mentioned are presented. The theoretical results are illustrated by a numerical analysis. Practical features implied by this analysis to be relevant from the experimental point of view are introduced as well. Moreover, relations expressing the flux of scattered light are presented.

3 – Ellipsometry of Thin Film Systems

In this paper, a review of both the important theoretical and experimental results concerning ellipsometry is presented.

Models of dielectric response in disordered solids

Two dispersion models of disordered solids, one parameterizing density of states (PDOS) and the other parameterizing joint density of states (PJDOS), are presented. Using these models, not only the complex dielectric function of the materials, but also some information about their electronic structure can be obtained. The numerical integration is necessary in the PDOS model. If analytical expressions are required the presented PJDOS model is, for some materials, a suitable option still providing information about the electronic structure of the material. It is demonstrated that the PDOS model can be successfully applied to a wide variety of materials. In this paper, its application to diamond-like carbon (DLC), a-Si and SiO2-like materials are discussed in detail. Unlike the PDOS model, the presented PJDOS model represents a special case of parameterization that can be applied to limited types of materials, for example DLC, ultrananocrystalline diamond (UNCD) and SiO2-like.

Deposition of protective coatings in rf organosilicon discharges

The paper discusses the deposition of protective coatings ranging from organosilicon plasma polymers to SiO2-like films and hard diamond-like carbon/silicon oxide (DLC?:?SiOx) coatings in radio frequency capacitively coupled discharges using hexamethyldisiloxane (HMDSO). As a result of the optimization of the deposition conditions it was possible to obtain high performance protective coatings. In the HMDSO/O2 mixture, it was shown that rather than the SiO2-like film a hard cross-linked SiOxCyHz polymer film can be used as a protective coating for polycarbonate. The optimum conditions for the deposition of an almost stress-free film were 17% of HMDSO and dc bias voltage of ?240?V. The film hardness and elastic modulus were 10?GPa and 75?GPa, respectively. The refractive index at 600?nm was 1.5 and the extinction coefficient decreased from 0.02 at 240?nm down to zero at 600?nm.The films deposited from HMDSO/CH4 and HMDSO/CH4/H2 mixtures exhibited the attractive properties of DLC films with the partial elimination of some of their drawbacks, such as absorption in the visible and a high intrinsic stress. The optimum concentration of the HMDSO was approximately 21%. Under these conditions the concentration of SiOx in the films was approximately 9?at.%. The film hardness and elastic modulus were above 22?GPa and 120?GPa, respectively.

Influence of overlayers on determination of the optical constants of ZnSe thin films

In this article a multisample modification of variable angle spectroscopic ellipsometry is used to characterize ZnSe thin films prepared by molecular beam epitaxy on substrates formed by GaAs single crystals. Atomic force microscopy (AFM) is employed to characterize the morphology of the upper boundaries of these films. To interpret the ellipsometric data a relatively complicated physical model that contains a rough overlayer between the ambient and the ZnSe film and a transition layer between the GaAs substrate and the ZnSe film is employed. Several models of dispersion of the optical constants of the overlayers are examined to interpret the ellipsometric data. It is shown that the choice of overlayer dispersion model has a strong influence on determining the optical constants and dielectric function of the ZnSe films in the near-UV region. Within the visible region there are no differences between the overlayer dispersion models regarding determination of the ZnSe optical constants. The spectral depende...

Deposition of hard thin films from HMDSO in atmospheric pressure dielectric barrier discharge

An atmospheric pressure dielectric barrier discharge burning in nitrogen with a small admixture of hexamethyldisiloxane (HMDSO) was used for the deposition of thin organosilicon films. The thin films were deposited on glass, silicon and polycarbonate substrates, and the substrate temperature during the deposition process was increased up to values within the range 25 - 150 C in order to obtain hard SiOx-like thin films.

Analysis of Slightly Rough Thin Films by Optical Methods and AFM

Abstract. In this paper the analysis of a family of rough silicon single crystal surfaces covered with native oxide layers is performed using a combined optical method based on a multisample treatment of the experimental data obtained using variable angle of spectroscopic ellipsometry and near normal spectroscopic reflectometry. Within this analysis the values of the thicknesses of the native oxide layers are determined together with the values of statistical parameters of roughness, i.e. with the rms values of the heights and the values of the autocorrelation lengths, for all the samples studied. For interpreting experimental data the perturbation Rayleigh–Rice theory and scalar diffraction theory are employed. By means of the results of the analysis achieved using both the theories limitations of the validity of these theories is discussed. The correctness of the values of the statistical parameters determined using the optical method is verified using AFM measurements.

Variable-angle spectroscopic ellipsometry of considerably non-uniform thin films

A theoretical approach for including considerable thickness non-uniformity of thin films into the formulae employed within variable-angle spectroscopic ellipsometry is presented. It is based on a combination of the efficient formulae derived for the thickness distribution density corresponding to a wedge-shaped non-uniformity with dependences of the mean thickness and root mean square (rms) of thickness differences on the angle of incidence that take into account the real non-uniformity of the shape. These dependences are derived using momentum expansion of the thickness distribution density. The derived formulae are tested by means of numerical analysis. An application of this approach is illustrated using the optical characterization of a selected sample of non-uniform SiOxCyHz thin films using phase-modulated ellipsometry.

Influence of lateral dimensions of the irregularities on the optical quantities of rough surfaces

In this paper the influence of lateral dimensions of the irregularities on the optical quantities, i.e. on reflectance, transmittance, scattering losses and ellipsometric ratio of randomly rough surfaces, is discussed in detail. This discussion is based on theoretical (simulated) data calculated using the Rayleigh–Rice theory (RRT). It is shown that the optical quantities mentioned are strongly dependent on the quantities characterizing the lateral dimensions of the irregularities, e.g. on the autocorrelation length. The simulated data are also used to investigate the possibilities and limitations of the scalar diffraction theory (SDT) and effective medium approximation (EMA) in treating the experimental data in practice. On the basis of these theoretical studies it is, moreover, shown that a combination of the SDT and EMA can be employed as a reasonable approximation for describing the interaction of light with randomly rough surfaces. Thus, from the results presented in this paper, it is evident that this combination could be a promising treatment for experimental data corresponding to the optical quantities of randomly rough surfaces.

Optical properties of diamond-like carbon films containing SiOx

In this paper the optical properties of amorphous DLC films containing SiOx (DLC:SiOx) prepared by plasma enhanced chemical vapour deposition are studied. For this study a combined optical method based on simultaneous interpretation of experimental data obtained within variable angle spectroscopic ellipsometry and near-normal spectroscopic reflectometry is used. The interpretation of these combined experimental data is performed using a new empirical dispersion model of the optical constants characterizing the films under investigation. This dispersion model is based on parameterizing the density of the electronic states belonging to both the valence and conduction bands. It is shown that there are the strong differences between spectral dependences of the optical constants of the DLC films on the one hand and DLC:SiOx films on the other hand. Further, it is shown that the absorption of the DLC:SiOx films is smaller than the absorption of the pure DLC films in the visible. This is explained by the fact that the density of the pi electrons inside the DLC:SiOx films is lower than the density of these electrons in the pure DLC films. It is also found that the existence of small amounts of the silicon and oxygen impurities contained in the DLC films strongly influence their optical properties.