K. Vedam

Spectroscopic ellipsometry: A new tool for nondestructive depth profiling and characterization of interfaces

The ability of spectroscopic ellipsometry to analyze the multilayer surface structure of an implanted semiconductor with 1–2 A resolution has been demonstrated. Spectroscopic ellipsometric data from 1.5 to 4.5 eV on a number of self‐ion‐implanted silicon samples have been analyzed using the regression analysis technique. It is shown that such a procedure can yield information nondestructively and in a nonperturbing manner: (i) on the depth profile of multilayer structures; (ii) quantitative information on the thicknesses of each layer (within 90% confidence limits); (iii) the structure (whether crystalline or amorphous) as well as the degree of crystallinity in the region; (iv) characterize the oxide layer if present on specimen; and (v) microroughness of the surface, if present. Furthermore, it is shown that these results are in excellent quantitative agreement with the completely independent results obtained on the same specimens using cross‐section transmission electron microscopy.

Fast scanning spectroelectrochemical ellipsometry : in-situ characterization of gold oxide

Abstract A study of the solid/liquid interface using a fast scanning spectroscopic ellipsometer with an optical multichannel analyzer (SE-OMA) is described. Here, we discuss the basic operating principles of the SE-OMA and, as an example of its application, report the optical properties and growth of monolayer gold oxide films formed on polycrystalline Au surfaces. These studies were performed using a specially-designed spectroelectrochemical cell operated with 0.5M H2SO4 under anodic potential. For the first time, spectroscopic ellipsometry measurements reveal the oxide dielectric function in real time from 1.5 to 3.3 eV. The thickness of the gold oxide was deduced to be approximately 4 A at 1.3 V versus a saturated calomel reference electrode (SCE).

Effect of preparation conditions on the morphology and electrochromic properties of amorphous tungsten oxide films

Electrochromic tungsten oxide thin films have been prepared by reactive dc‐magnetron sputtering under different deposition conditions. Through the use of electrochromic coloration and spectroscopic ellipsometry experiments, the effect of preparation conditions on film morphology and electrochromic properties has been studied. The results of this study are consistent with previous reports finding that amorphous tungsten oxide thin films are dominated by a columnar morphology and an intercolumnar void network that strongly influence the electrochromic properties. In addition real‐time spectroscopic ellipsometry (SE) experiments on the tungsten oxide electrochromic coloration process have been performed for the first time. In studies of very thin (∼15 nm) films by real‐time SE, the formation of tungsten bronze exhibits reaction‐limited kinetic behavior, and thus we are able to extract accurate dielectric function spectra for the film in different stages of the coloration process. These spectra can be underst...

Optical characterization of a four-medium thin film structure by real time spectroscopic ellipsometry: amorphous carbon on tantalum

A real time spectroscopic ellipsometry (RTSE) investigation is reported for comprehensive optical characterization of a thin film/substrate system, vacuum-deposited hydrogenated amorphous (diamondlike) carbon on tantalum. Precision RTSE measurements were carried out from 1.6 to 4.0 eV with a time resolution of 3 s and a repetition period of 15 s. Spectra collected during substrate exposure to an Ar(+) beam identify processing conditions for optimum precleaning and provide the bulk dielectric function of the Ta. Spectra collected during alpha-C:H growth to approximately 1700 A by ion beam deposition are best interpreted with a four-medium model (Ta/interface/alpha-C:H/ambient). From the analysis, we deduce the bulk dielectric function for alpha-C:H and an approximate dielectric function for the interface layer, interpreted as a carbide. The time evolution of the bulk and interface layer thicknesses is also determined. The dielectric functions of alpha-C:H deduced assuming a four-medium model and a three-medium model which neglects the interface layer differ by as much as 5%. The capabilities of measurement and analysis reported here represent a major new advance in the optical characterization of thin films.

Elastic Constants of Selenium in the Hexagonal and Glassy Phases

The elastic constants c33 and c44 of hexagonal selenium have been determined and are compared with the elastic constants of glassy selenium. It is shown that the bonding forces in glassy selenium are mainly of van der Waals type. The temperature variation of these elastic constants in the region of glass transition temperature has also been studied.

Formation and nondestructive characterization of ion implanted silicon‐on‐insulator layers

High‐temperature oxygen ion implantation has been used to form buried oxide layers in silicon single crystals. The ion implantation and substrate variables, particularly the substrate temperature, were optimized to obtain silicon layers with controlled microstructures near the surface. The as‐implanted specimens were subsequently annealed at high temperatures to form a buried SiO2 layer with sharp interfaces and to minimize dislocation densities in the top silicon layers. The specimens were characterized by cross‐section transmission electron microscopy and these results were compared with those obtained using spectroscopic ellipsometry. We discuss the application of the nondestructive scanning ellipsometry technique in the characterization of silicon‐on‐insulator materials.

Proper choice of the error function in modeling spectroellipsometric data

The modeling procedure for analyzing the rotating analyzer spectroellipsometric data using the linear regression analysis technique is examined. The best set of optical parameters which should be employed in the modeling procedure is searched out with the help of variance–covariance matrices and the correlation properties of optical parameters. It was found that α and β, which are the Fourier coefficients of sinusoidal components of the intensity, constitute the best set for such an analysis for the case of single-crystal silicon and gold film evaporated on glass substrate. Also suitable expressions of α and β in terms of the ellipsometric parameters Δ and ψ have been derived to enable a linear regression analysis using α and β.

Roughness measurements by spectroscopic ellipsometry.

The surface roughnesses of fifteen well-characterized aluminum roughness standards were studied using spectroscopic ellipsometry in the spectral range from 300 to 650 nm at 70° angle of incidence. It was found that the measured ellipsometric parameters ψ and Δ qualitatively discriminated between the rms roughnesses of the specimens. The rms local surface slopes (tanβ) were also calculated from the measured ellipsometric parameters Δ and ψ using the theory of Ohlidal and Lukes. All the ellipsometric results were compared with those obtained from total integrated scattering measurements. Good qualitative agreement was found.

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.

The Laser as a Light Source for Ultramicroscopy and Light Scattering by Imperfections in Crystals. Investigation of Imperfections in LiF, MgO, and Ruby

A cw 1‐mW He–Ne laser was used for the study of 90° light scattering in crystals in the arrangement of an ultramicroscope. Motorized translation of the illuminating objective allowed us to take photographs of extended sections through the crystal. When the laser was compared with light‐scattering performance of an unfiltered unpolarized 100‐W mercury arc lamp it appeared to be appreciably more intense. On calibration, 880‐A latex particles suspended in water were easily visible by eye, and 3570‐A particles were photographed at 132‐sec exposure. It is estimated that 1‐h exposures would make visible particles of some 300 A e.l.d. (equivalent latex diameter) and with more powerful lasers, particles of about 100 A e.l.d. could be theoretically reached. Lithium fluoride crystals of high purity show scattering defects concentrated at small‐angle boundaries. Magnesium oxide crystals of lesser purity show many imperfections. Ruby laser crystals show imperfections at small‐angle boundaries and also along lines per...