Spectroscopic ellipsometry data analysis: Measured vs. calculated quantities

Spectroscopic ellipsometry is a very powerful technique for optical characterization of thin-film and bulk materials, but the technique measures functions of complex reflection coefficients, which are usually not of interest per se. The interesting characteristics such as film thickness, surface roughness thickness, and optical functions can be determined only by modeling the near-surface region of the sample. However, the measured quantities are not equivalent to those determined from the modeling. Ellipsometry measurements determine elements of the sample Mueller matrix, but the usual result of modeling calculations are elements of the sample. Often this difference is academic, but if the sample depolarizes the light, it is not. Ellipsometry calculations also include methods for determining the optical functions of materials. Data for bulk materials are usually accurate for substrates, but are not appropriate for most thin films. Therefore, reasonable parameterizations are quite useful in performing spectroscopic ellipsometry data analysis. Recently, there has been an increased interest in anisotropic materials, both in thin-film and bulk form. A generalized procedure will be presented for calculating the elements of the Jones matrix for any number of layers, any one of which may or may not be uniaxial

Development of the Two-Modulator Generalized Ellipsometer (2-MGE) for Commercial Application

The two-modulator generalized ellipsometer (2-MGE) is an instrument that measures the change of light polarization upon interacting with a sample. The 2-MGE can operate in either reflection or transmission. In reflection, it acts as a generalized ellipsometer, measuring the standard ellipsometry parameters, as well as the cross-polarization parameters. In transmission, it measures all parameters associated with a general diattenuation and retarder. In this CRADA, Hinds and ORNL have explored the commercial possibilities of the 2-MGE. This exploration has taken two primary paths. First, prototypes were built at both ORNL and Hinds. Second, various scientific applications were explored, including characterization of Polaroid-like materials and various materials under electric field. The main purpose of this CRADA was to develop the two-modulator generalized ellipsometer (2-MGE) into a commercial product. The 2-MGE is an ORNL patented technology (U. S. Patent No. 5956147 (1999)). Associated with the 2-MGE is the computer program EllipsCalc, which is used to simulate spectroscopic ellipsometry data in order to determine useful parameters, such as film thickness, surface roughness, interface thickness, and spectroscopic refractive indices, from the 2-MGE data. To this end, the CRADA had several objectives contained in two phases

Spectroscopic ellipsometry characterization of thin-film silicon nitride

We have measured and analyzed the optical characteristics of a series of silicon nitride thin films prepared by plasma-enhanced chemical vapor deposition on silicon substrates for photovoltaic applications. Spectroscopic ellipsometry measurements were made by using a two-channel spectroscopic polarization modulator ellipsometer that measures N, S, and C data simultaneously. The data were fit to a model consisting of air / roughness / SiN / crystalline silicon. The roughness was modeled using the Bruggeman effective medium approximation, assuming 50% SiN, 50% voids. The optical functions of the SiN film were parameterized using a model by Jellison and Modine. All the {Chi}{sup 2} are near 1, demonstrating that this model works extremely well for all SiN films. The measured dielectric functions were used to make optimized SiN antireflection coatings for crystalline silicon solar cells

Optical properties of MgH2 measured in situ in a novel gas cell for ellipsometry/spectrophotometry

The dielectric properties of alpha-MgH2 are investigated in the photon energy range between 1 and 6.5 eV. For this purpose, a novel sample configuration and experimental setup are developed that allow both optical transmission and ellipsometric measurements of a transparent thin film in equilibrium with hydrogen. We show that alpha-MgH2 is a transparent, colour neutral insulator with a band gap of 5.6 +/- 0.1 eV. It has an intrinsic transparency of about 80% over the whole visible spectrum. The dielectric function found in this work confirms very recent band structure calculations using the GW approximation by Alford and Chou [J.A. Alford and M.Y. Chou (unpublished)]. As Pd is used as a cap layer we report also the optical properties of PdHx thin films.Comment: REVTeX4, 15 pages, 12 figures, 5 table

Interdiffusion at Sb/Ge interfaces induced in thin multilayer films by nanosecond laser irradiation

Thin films consisting of 3 or 4 Sb and Ge alternating layers are irradiated with single nanosecond laser pulses (12 ns, 193 nm). Real time reflectivity (RTR) measurements are performed during irradiation, and Rutherford backscattering spectrometry (RBS) is used to obtain the concentration depth profiles before and after irradiation. Interdiffusion of the elements takes place at the layer interfaces within the liquid phase. The reflectivity transients allow to determine the laser energy thresholds both to induce and to saturate the process being both thresholds dependent on the multilayer configuration. It is found that the energy threshold to initiate the process is lower when Sb is at the surface while the saturation is reached at lower energy densities in those configurations with thinner layers

Calibration Procedures for a Two-Modulator Generalized Ellipsometer

A Two-Modulator Generalized Ellipsometer (2-MGE) has been extremely useful in characterizing optical properties of uniaxial bulk materials, thin films and diffraction gratings. The instrument consists of two polarizer-photoelastic modulator pairs, one operating as the polarization state generator and the other as the polarization state detector. Each photoelastic modulator operates at a different remnant frequency (such as 50 kHz and 60 kHz), making it possible to measure eight elements of the reduced sample Mueller matrix simultaneously. In certain configurations, light reflection from non-depolarizing anisotropic samples can be completely characterized by a single measurement, and the entire reduced Jones matrix can be determined, including the cross polarization coefficients. The calibration of the instrument involves the measurement of the azimuthal angle of the polarizer with respect to the modulator, the modulation amplitude, and the modulator strain for each polarizer photoelastic modulator pair, where the last two are functions of wavelengths. In addition, it is essential to calibrate the azimuthal angles of the polarization state generator and the polarization state detector with respect to the plane of incidence in the ellipsometry configuration that is used in the measurements. Because two modulators operating at different frequencies are used, these calibrations are actually easier and more accurate than for one modulator ellipsometers. In this paper, we will discuss these calibrations and the resultant accuracy limitations of the 2-MGE

Amorphous diamond-like carbon film growth by KrF- and ArF- excimer laser PLD: Correlation with plume properties

A comparative study of ArF- and KrF-laser deposition of amorphous diamond-like carbon (DLC) films and relevant carbon plasmas has been performed. Spectroscopic ellipsometry and EELS analysis of the DLC films deposited on Si and NaCl substrates were utilized to characterize the high quality ArF- and KrF-laser deposited films (up to 84% of sp{sup 3} bonded carbon in 7 J/cm{sup 2} -ArF-laser DLC film). Gated ICCD imaging, luminescence and ion current probe diagnostics of the carbon plume have revealed quite different properties of carbon plasmas generated by ArF- and KrF- lasers. KrF-laser (6.7 J/cm{sup 2}) irradiation produces a less energetic carbon plasma containing larger amounts of C{sub 2} and probably larger clusters compared with ArF-laser irradiation at the same energy fluence. We conclude that the more energetic and highly-atomized ArF-laser carbon plasma results in the better diamond-like properties

Fundamental aspects of pulsed-laser irradiation of semiconductors

Fundamental aspects of pulsed laser melting and solidification of crystalline silicon and germanium are reviewed. The discussion concentrates on time-resolved experiments performed with nanosecond pulsed lasers, although some picosecond and femtosecond experiments are also considered. The creation of amorphous material from crystalline material induced by ultrarapid melting and resolidification using either nanosecond or picosecond lasers is surveyed and the inverse process of recrystallization of a-Si by explosive crystallization is described. Finally, melting model calculations, which have proven to give a very accurate description of the pulsed laser irradiation process, are discussed

Comparative diagnostics of ArF- and KrF-laser generated carbon plumes used for amorphous diamond-like carbon film deposition

A comparative study of ArF- and KrF-laser generated carbon plasmas has been performed under pulsed laser deposition conditions of amorphous diamond-like carbon (DLC) films. Gated-ICCD species-resolved imaging, luminescence spectroscopy and ion probe diagnostics have revealed distinct differences between the carbon plumes generated by ArF- and KrF-lasers. KrF-laser (6.7 J/cm{sup 2}) irradiation produces a less energetic carbon plasma containing larger amounts of luminescent C{sub 2} compared with ArF-laser ablation at the same energy fluence. Spectroscopic ellipsometry and EELS analysis of the DLC films deposited on Si and NaCl substrates were utilized to characterize the high quality ArF- and KrF-laser deposited films (up to 84% of sp{sup 3} bonded carbon for 7 J/cm{sup 2}-ArF-laser DLC film). The more energetic and highly-atomized ArF-laser carbon plasma appears to be responsible for the better diamond-like properties