Thomas E. Tiwald

Application of IR variable angle spectroscopic ellipsometry to the determination of free carrier concentration depth profiles

Abstract Free carrier concentration profiles were determined by Fourier Transform Infrared (FTIR) variable angle spectroscopic ellipsometry. The technique exploits carrier absorption in the mid-infrared spectral range and combines the sensitivity of ellipsometry with a simple Drude free carrier absorption model to determine the carrier profile. In this study, the carrier profiles were modeled as graded multilayers that were constrained to a specific functional form (e.g. Gaussian, complementary error function) when appropriate. Carrier profiles from boron and arsenic ion-implanted that had been subjected to furnace or Rapid Thermal Annealing (RTA) annealed silicon wafers were compared to Spreading Resistance Probe and Secondary Ion Mass Spectrometry profiles. p−p+doped epitaxial silicon samples (before and after annealing) were also measured and the results were compared to theory.

EXPLICIT SOLUTIONS FOR THE OPTICAL PROPERTIES OF ARBITRARY MAGNETO-OPTIC MATERIALS IN GENERALIZED ELLIPSOMETRY

Analytic expressions for the eigenvalues for the four-wave components at an oblique angle of light incidence inside a randomly oriented anisotropic magneto-optic dielectric medium are reported explicitly. In particular, these solutions are valid as long as the dielectric function tensor consists of a symmetric and an antisymmetric part. The normalized Jones reflection and transmission coefficients, i.e., the generalized ellipsometric parameters of homogeneously layered systems having nonsymmetric dielectric properties, are obtained immediately from a recently reviewed 4 x 4 matrix approach. Our explicit solutions allow a future analysis of the generalized ellipsometric data of multilayered magneto-optic media regardless of the orientation of the material magnetization and crystalline axes and the angle of light incidence. Possible experimental thin-film situations are discussed in terms of generalized ellipsometric parameters and illustrated for birefringent free-carrier effects in heavily doped semiconductor thin films and for oblique magnetization directions in magneto-optic multilayer systems.

Progress in spectroscopic ellipsometry: Applications from vacuum ultraviolet to infrared

Spectroscopicellipsometry (SE) is a noncontact and nondestructive optical technique for thin film characterization. In the past 10 yr, it has migrated from the research laboratory into the semiconductor, data storage, display, communication, and optical coating industries. The wide acceptance of SE is a result of its flexibility to measure most material types: dielectrics, semiconductors, metals, superconductors, polymers, biological coatings, and even multilayers of these materials. Measurement of anisotropic materials has also made huge strides in recent years. Traditional SE measurements cover the ultraviolet, visible, and near infrared wavelengths. This spectral range is now acquired within seconds with high accuracy due to innovative optical configurations and charge coupled device detection. In addition, commercial SE has expanded into both the vacuum ultraviolet (VUV) and midinfrared (IR). This wide spectral coverage was achieved by utilizing new optical elements and detection systems, along with UV or Fourier transform IR light sources. Modern instrumentation is now available with unprecedented flexibility promoting a new range of possible applications. For example, the VUVspectral region is capable of characterizing lithographic materials for 157 nm photolithography. The VUV also provides increased sensitivity for thin layers (e.g., gate oxides or self-assembled monolayers) and allows investigation of high-energy electronic transitions. The infrared spectral region contains information about semiconductor doping concentration, phonon absorption, and molecular bond vibrational absorptions. In this work, we review the latest progress in SE wavelength coverage. Areas of significant application in both research and industrial fields will be surveyed, with emphasis on wavelength-specific information content.

Recent developments in spectroscopic ellipsometry for in situ applications

The in situ measurement capabilities and advantages of recently developed spectroscopic ellipsometry (SE) instrumentation, which covers wide spectral ranges (190-1700 nm, or 0.73-6.5 eV) and is based on rotating-compensator technology, are described. A technique which can quantitatively correct for window birefringence is presented. Current in situ SE deposition monitoring and control applications in the compound semiconductor, display, and optical coatings industries are also presented.

Measurement of rutile TiO 2 dielectric tensor from 0.148 to 33 μm using generalized ellipsometry

We have determined the complex uniaxial dielectric tensor of bulk rutile titanium dioxide (110), (100) and (111) samples using reflection generalized ellipsometry, which measures both the diagonal and off- diagonal elements of the reflection Jones matrix. Data were acquired using three commercially available ellipsometers, each covering the following spectral ranges: 0.148 to 0.292, 0.200 to 1.7 (mu) m; and 1.7 to 33 (mu) m. Generalized ellipsometry measures three complex ratios involving all four Jones matrix elements. In principle, this means that the complex dielectric tensor of a uniaxial crystal can be determined in a single measurement, provided that the sample is oriented such that the off-diagonal components of the Jones matrix are non-zero. To improve our results, we measure the samples at several rotational orientations around the surface normal. This insures that the probing electric fields vibrate along substantially different directions with respect to the optic axis. In some cases, we also varied the angle of incidence. The dielectric tensor was determined at every wavelength directly from a simultaneous fit to data from all rotational orientations and incident angles. A similar methodology should be applicable to a wide range of anisotropic optical materials.

Determination of the mid-IR optical constants of water and lubricants using IR ellipsometry combined with an ATR cell

Abstract The mid-IR bulk optical constants for the lubricants Fomblin, Demnum S200, 2001A and Krytox 16256N, as well as water, are determined by infrared ellipsometric analysis using an Attenuated Total Reflection (ATR) cell. The water optical constants closely match those found in other studies. In addition, the real and imaginary parts of the dielectric functions for all the fluids are self-consistent under Kramers–Kronig transformation.

Determination of optical anisotropy in calcite from ultraviolet to mid-infrared by generalized ellipsometry

Abstract Generalized (Jones matrix) ellipsometry is gaining considerable interest because of its ability to determine properties of anisotropic samples. Here, the strong uniaxial anisotropy of calcite (calcium carbonate) was investigated using generalized ellipsometry. The wavelength range from 0.73 to 6.5 eV (190 nm to 1.7 μm) was covered using a standard variable angle spectroscopic ellipsometer; from 0.089 to 0.68 eV (1.8–14 μm), using a similar instrument based on a Fourier transform spectrometer. Measurements were made on a single air–calcite interface for which the optic axis lay nominally in the plane of the surface. To determine the optical constants and orientation of cut, both the angle of incidence and rotation of the sample about its surface normal were varied. Properties of the sample were arrived at by optimizing the parameters of a material model such that the calculated normalized Jones matrix elements best matched the measured ones. Localized spectral regions of absorption due to the internal vibrational modes of the carbonate ions were observed in the infrared at energies which differed for the ordinary and extraordinary optical constants. The certainty to which sample properties could be determined was maximized by judicious choice of measurement configurations.

Optical determination of shallow carrier profiles using Fourier transform infrared ellipsometry

Dopant profiles were determined by ex situ Fourier transform infrared variable-angle spectroscopic ellipsometry. The technique exploits carrier absorption in the mid-infrared spectral range and combines the sensitivity of ellipsometry with a simple Drude free carrier absorption model to determine the carrier profile. The noncontact, nondestructive nature of the measurement suggests both ex situ and in situ monitoring and control applications. In this study, the carrier profiles were modeled as graded multilayers that can be constrained to a given functional form (Gaussian, erfc, etc.) when desired. Boron and arsenic implanted silicon wafers that were rapid thermal anneal and furnace annealed were measured and compared to spreading resistance probe data.

Infrared emittance modulation devices using electrochromic crystalline tungsten oxide, polymer conductor, and nickel oxide

Abstract A prototypical small area electrochromic device was fabricated, and emissivity was measured from 1 to 30 microns. The devices show change in emissivity from about 0.60 to about 0.68, that is a total modulation of 13%. The emittance performance was calculated, based on the reflectivity modulation. One difference between these devices and the more frequently explored visible light transmission devices is the utilization of crystalline tungsten oxide instead of highly disordered amorphous tungsten oxide. The crystalline tungsten oxide and nickel oxide charge storage films are characterized by IR transmission/reflection, and spectroscopic ellipsometry. A theoretical model has been developed which describes the device performance to within 10% of experimental results.

Optical constants of crystalline WO3 deposited by magnetron sputtering

Crystalline WO3−x is an infrared (IR) electrochromic material having possible applications in satellite thermal control and IR switches. Optical constants of electrochromic materials change upon ion intercalation, usually with H+ or Li+. Of primary concern for device design are the optical constants in both the intercalated and deintercalated states. In situ and ex situ ellipsometric data are used to characterize both the deposition process and the optical constants of the films. Ex situ data from a UV-Vis-NIR ellipsometer are combined with data from a mid-infrared Fourier-transform-infrared-based ellipsometer to provide optical constants over a spectral range of 0.031–6.1 eV.