Corey L. Bungay

Overview of variable-angle spectroscopic ellipsometry (VASE): I. Basic theory and typical applications

Variable angle spectroscopic ellipsometry (VASE) is important for metrology in several industries, and is a powerful technique for research on new materials and processes. Sophisticated instrumentation and software for VASE data acquisition and analysis is available for the most demanding research applications, while simple to use software enables the use of VASE for routine measurements as well. This article gives a basic introduction to the theory of ellipsometry, references “classic” papers, and shows typical VASE applications. In the following companion paper, more advanced applications are discussed.

Overview of variable-angle spectroscopic ellipsometry (VASE): II. Advanced applications

A preceding companion paper provides a general introduction to Variable Angle Spectroscopic Ellipsometry (VASE), and also describes many typical applications of the technique. In this paper, more advanced VASE applications are discussed. These applications rely on recent advances in ellipsometric hardware, which allow extremely accurate ellipsometric data to be acquired over a broad spectral range, from the IR to VUV. This instrumentation can also quantitatively measure the optical response of nonisotropic samples. Advanced data analysis techniques are also presented.

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.

IR ellipsometry studies of polymers and oxygen plasma-treated polymers

Abstract An infrared variable angle spectroscopic ellipsometer (IR-VASE) was used to study organic polymers in the infrared (2.5–14 μm wavelength) spectral region. For the analysis of thin film polymers IR spectroscopic ellipsometry has greater sensitivity over traditional FTIR spectroscopy providing an exciting way to characterize these materials optically. The IR-VASE used in this study is of high accuracy, rotating polarizer, rotating compensator ellipsometer that uses an FTIR spectrometer as a light source. The IR-VASE was used to measure the infrared optical constants of various polymers in both solid and liquid form. These optical constants were then used to model the percentage of water in a thin film of gelatin and the percentage of residual solvent in a thin film of silicone. In addition, the IR-VASE provided a sensitive measurement of silicone chemistry and chemical changes caused by exposure to an oxygen plasma.

Optical characterization in the vacuum ultraviolet with variable angle spectroscopic ellipsometry: 157 nm and below

As device feature sizes shrink below 0.18 micrometer, shorter wavelength exposure tools are being investigated to meet the requirements for higher resolution. Understanding the optical properties of thin films and substrate materials at short wavelengths (193 nm, 157 nm, and shorter) will be necessary to develop the lithographic process. Variable Angle Spectroscopic Ellipsometry (VASE) offers nondestructive and precise measurement of thin film thickness and refractive index in the wavelength range from 146 nm to 1700 nm. VASE measurements provide a complete description of the thin film optical properties, which can be used to track process changes or variations in sample structure. Recent hardware innovations have extended VASE into the vacuum ultraviolet to meet lithography requirements at 157 nm.

Study of surface chemical changes and erosion rates for CV-1144-O silicone under electron cyclotron resonance oxygen plasma exposure

CV-1144-O silicone thin films were irradiated in an electron cyclotron resonance oxygen plasma, which is a simulation of the low earth orbital environment. A crude equivalence between this plasma system and the low earth orbital environment was determined by measuring Kapton weight loss in the plasma and comparing to Kapton weight loss in space experiments. Changes in optical properties and erosion rates under ultraviolet light and atomic oxygen radiation were studied using in situ spectroscopic ellipsometry (SE). The erosion rate at the beginning of the plasma exposure was significantly faster than that at later stages. Approximately one third of the total silicone thickness was etched away within 1 h, which according to the equivalence experiment, corresponds to about two months in low earth orbit. The refractive index of silicone in the visible range increased during the exposure, indicating that the film was being densified. Optical constants (both before and after plasma exposure) were determined by ...

Variable angle spectroscopic ellipsometry in the vacuum ultraviolet

Optical properties of thin films and bulk materials at short wavelengths, including 157 nm and shorter, are needed for development of new lithographic processes, new fundamental science, and new metrology in the semiconductor, optical and data storage industries. Variable angle spectroscopic ellipsometry offers non-destructive and precise measurement of thin film thickness and refractive index in the wavelength range from 140 nm to 1700 nm (0.73 eV to 8.9 eV). The addition of short wavelengths allows analysis of multilayer dielectric stacks, often difficult to do using visible spectroscopy alone. Another major application is in study of wide bandgap materials such as SiC and GaN related compound semiconductors for blue lasers and detectors. This paper reviews the present status of spectroscopic ellipsometry applications in the vacuum ultraviolet.

VUV and IR spectroellipsometric studies of polymer surfaces

Abstract This article reviews applications of spectroscopic ellipsometry (SE) in polymers and irradiated polymers. SE has long been used to determine optical constants, layer thicknesses in multi-layer stacks and microstructure (voids, alloy fraction, or mixed phase composition). Modern spectroscopic ellipsometers now cover a range from 140 nm (≈9 eV) in the vacuum ultraviolet to 100 μm (100 cm −1 ) in the far infrared. Examples of ellipsometric measurements for irradiated and un-irradiated thin film and bulk polymers, and biological materials are presented. Analysis yields index of refraction and dispersion, optical absorption and optical anisotropy as studied by “generalized ellipsometry”. Both ex situ and in situ ellipsometry are discussed, as are future trends and opportunities.

Application of spectroscopic ellipsometry to characterization of optical thin films

Spectroscopic ellipsometry is used to determine optical constants, layer thicknesses in multilayer stacks, and microstructure (voids, alloy fraction, or mixed phase composition), and is a well-developed technique for analysis of optical thin films. Ellipsometers now cover from 140 nm (≈ 9 eV) in the vacuum-ultraviolet to 200 microns (50cm-1) in the far infrared. Generalized anisotropy and depolarization are measurable using rotating compensator ellipsometers or controlled retarders for partial Mueller Matrix analysis. Rotating compensator ellipsometers allow accurate and rapid in situ diagnostics, including window birefringence calibration. Steady progress has been made in both ex situ and in situ ellipsometry hardware, software, and applications. These advances are reviewed and examples given.

Measuring the thickness of organic/polymer/biological films on glass substrates using spectroscopic ellipsometry

In this work we discuss a method of determining film thickness for film/substrate combination where the index of refraction of the film and substrate in the transparent spectral regions is almost identical. Common examples of this situation are organic/polymer/biological films on glass substrates. Infrared ellipsometry is used and we use weight gain to provide some necessary additional information for determining the optical functions for the film material. The spectral regions of strong molecular vibrations are then used for determining film thickness.