IR-VASE® Mark II
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Mark II Features The J.A. Woollam IR-VASE was first introduced in 1998, with incremental changes through the years. It is recognized world-wide as the premiere thin film characterization tool in the infrared. After more than 15 years, the IR-VASE has been given a complete update. The new Mark II design is half the size of its predecessor, requiring less benchtop space and using less purge gas. The globar light source and scanning laser inside the FTIR are designed for a much longer lifespan, reducing the need for maintenance. The Mark II design is also easier to construct and service....

Capabilities The IR-VASE is the first spectroscopic ellipsometer to combine the chemical sensitivity of FTIR spectroscopy with thin film sensitivity of spectroscopic ellipsometry. Covering a wide spectral range from 1.7 to 30 microns (333 to 5900 wavenumbers), it is used to characterize both thin films and bulk materials in research and industry. This rapidly growing technology is finding applications in the optical coatings, semiconductor, biological and chemical industries, as well as material research labs. The IR-VASE is often used to characterize: • Bulk materials • Optical constants...

Technology: How It Works Optics The IR-VASE Mark II integrates a Fourier Transform Infrared (FTIR) interferometer source with a rotating compensator ellipsometer to provide accurate ellipsometric measurements. Wide-band polarizers and patented compensator design are combined with an optimized beam splitter, collimators, and a DTGS detector to provide the widest available spectral range in a commercial infrared ellipsometer. During measurement, the compensator is rotated 360° in a series of steps, and an intensity spectrum is recorded at each step as shown below. The intensity spectrum is...

Accessories Sample Translation Standard Heat Stage Option Cryostat Option • Temperature range: • Temperature range: Room Temp to 300°C • Sample size: up to 50 mm diameter and 7.6 mm thick. • Includes programmable temperature controller and thermocouple built into the sample chuck to the monitor sample temperature. • Enclosed cover allows measurements at 70° angle of incidence, and full variable angle capability without cover. • No active cooling needed. • Enclosed cover with optical windows allows sample purge. Standard window material is ZnSe, which limits upper wavelength range to about...

Basic IR Ellipsometry: Thickness & Index Determining the thickness and index of a transparent film is one of the easiest measurements to make with an IRVASE. The thickness and refractive index of the film can be determined by simply matching the amplitudes and periods of the oscillations seen in the Ψ and Δ vs. wavenumber spectra, assuming that index of the substrate is already known. During measurement, the incident light separates into multiple rays that reflect from the top and bottom interfaces of the film. Each of the rays travels with different path lengths, causing them to have...

Information in the Infrared Many of the features observed by Infrared Spectroscopic Ellipsometry are related to the following absorption mechanisms: Vibrational Absorption Vibrational absorption occurs when molecules and lattices resonate at infrared frequencies. These absorptions act as fingerprints of the materials, as the frequencies of resonance depend on the types of bonds and weight of resonating atoms or molecules. Organic materials exhibit well-known molecular vibrations, but vibrational absorptions also occur in dielectrics and semiconductors. Acrylic Optical Constants Most...

Free Carrier Absorption Gold Indium Tin Oxide Doped Silicon Absorption occurs when free charge carriers (electrons and “holes”) are accelerated by the electric fields of a light beam. At infrared wavelengths, free carrier absorption can be detected in metals, heavily doped semiconductors, and conductive oxides such as Indium Tin Oxide (ITO). This absorption is readily modeled with a Drude-oscillator, which provides details of the material conductivity. Wave Number (cm-1) Comparison of the Free-carrier absorption for different conductive materials. Electronic Transitions There are a few...

IR-VASE Applications Optical Coatings The IR-VASE allows you to characterize thickness and IR refractive index of single and multilayer films; bulk uncoated substrates; infrared optical systems; AR, HR, and singlelayer and multilayer coatings of both high and low index films. Multilayer films can be extensively studied with the wide spectral range and variable angle capability of the IR-VASE. Measurements at multiple angles provide additional information by varying the path length through each layer. The ellipsometric spectra on the right are sensitive to all 4 layers. The difference in...

Epitaxial Layers, Doping Concentration and Doping Profiles At infrared wavelengths, differences in free carrier density produce optical contrast between epitaxial or implanted layers and underlying substrate. This results in great sensitivity to epitaxial layer thickness and substrate doping concentration, which are not seen using UV-VIS wavelengths. The IR-VASE also provides good sensitivity to carrier gradients at interfaces. Carrier profiles versus depth are generated from non-destructive IR-VASE analysis compare well with those generated by destructive SIMS and Spreading Resistance...

Advanced Applications Depolarization Beyond the standard ellipsometric Psi and Delta values, the IR-VASE rotating compensator technology allows users to measure other quantities, including depolarization. The ellipsometer illuminates the sample with light that is completely polarized. An ideal sample will simply change that polarization from one state into another (for example, linear becomes left-circular). Non-ideal samples will partially depolarize the reflected light. The causes of depolarization include variations in film thickness, incomplete film coverage, bandwidth effects, and other...