IR-VASE Mark II Ellipsometer

The IR-VASE® is the first and only spectroscopic ellipsometer to combine the chemical sensitivity of FTIR spectroscopy with thin fi lm sensitivity of spectroscopic ellipsometry. The IR-VASE covers the wide spectral range from 1.7 to 30 microns (333 to 5900 wavenumbers). It is used to characterize both thin fi lms and bulk materials in research and industry. This rapidly growing technology is finding uses in the optical coatings, semiconductor, biological and chemical industries, as well as research labs.

OVERVIEW

Why an IR-VASE Mark II?

Wide Spectral Range

Covers near to far infrared.
1.7 to 30 microns
(333 to 5900 wavenumbers)
Resolution from 1cm-1 to 64cm-1

High Sensitivity to Ultra-thin Films

Spectroscopic ellipsometry data contain both “phase” and “amplitude” information from reflected or transmitted light. The phase information from IR ellipsometry offers higher sensitivity to ultrathin films than FTIR reflection/absorbance, while retaining the sensitivity to chemical composition.

Non-destructive Characterization

The IR-VASE offers non-contact, non-destructive measurements of many different material properties. Measurements do not require vacuum, and can be used to study liquid/solid interfaces common in biology and chemistry applications.

No Baseline or Reference Sample Required

Ellipsometry is a self-referencing technique that does not require reference samples to maintain accuracy. Samples smaller than the beam diameter can be measured because the entire beam does not need to be collected.

Highly Accurate Measurement

Patented calibration and data acquisition procedures, provide accurate measurements of Ψ and Δ over the full range of the instrument. The IR-VASE can determine both n and k for materials over the entire spectral range from 1.7 to 30 microns without extrapolating data outside the measured range, as with a Kramers-Kronig analysis. Perfect for thin films or bulk materials including dielectrics, semiconductors, polymers, and metals.

APPLICATIONS

OPTICAL COATINGS

Characterize thickness and IR index of single and multilayer films. Bulk uncoated substrates. Infrared optical systems. AR, HR, single-layer and multilayer coatings. High-index and low-index.

MOLECULAR BOND VIBRATIONS

Like standard FTIR spectroscopy, IR ellipsometry relies on the information about molecular bond vibrations. Infrared absorption caused by these vibrations can be studied in bulk or thin film materials. IR ellipsometry offers increased sensitivity over FTIR spectroscopy. It also presents the advantage of obtaining both n and k rather than just absorbance values. Figures below show measured optical constants of a silicone thin film with vibrational absorptions labeled.

MULTILAYER CHARACTERIZATION

Multilayer films can be extensively studied using the wide spectral range and variable angle capability of the IR-VASE®. Multiple angles provide additional information by changing the light’s path length through each layer. The following results show sensitivity to 3 layers. Infrared optical contrast between similar materials allows measurement of each layer’s thickness.

multilayer-characterization-layers

CHEMICAL COMPOSITION VIA MOLECULAR BOND VIBRATIONAL ABSORPTIONS

Like standard FTIR spectroscopy, IR ellipsometry contains information about molecular bond via vibrational absorptions. Infrared absorption caused by these vibrations can be studied in bulk or thin film materials. IR ellipsometry offers increased sensitivity over FTIR spectroscopy. It also obtains both n and k rather than just absorbance. Figures below show measured optical constants of a silicone thin film with vibrational absorptions labeled.

molecular-bond-graph

EPITAXIAL LAYERS, DOPING CONCENTRATION AND DOPING PROFILES

At infrared wavelengths, the difference in free-carrier levels can cause optical contrast between epitaxial or implanted layers. This gives IR-VASE® excellent sensitivity to epitaxial layer thickness and substrate doping concentration. The ellipsometer also has good sensitivity to carrier gradients at interfaces. Carrier profiles show near-perfect in agreement when nondestructive IR-VASE® and destructive SIMS measurements are compared.

T.E. Tiwald et al., Phys. Rev. B, 60 (1999) 11 464.

T.E. Tiwald et al., Phys. Rev. B, 60 (1999) 11 464.

PHONON STRUCTURE (COMPOUND SEMICONDUCTORS)

The Wide spectral range IR-VASE® is important for phonon absorption studies. Data on the left show phonon modes of a GaN / AlGaN laser structure, modeled to determine alloy ratios, doping concentrations, and film quality.

M. Schubert et al., SPIE Vol. 4449-8 (2001)

M. Schubert et al., SPIE Vol. 4449-8 (2001)

SPECIFICATIONS

Specifications

Ellipsometer Configuration RCE
Wavelength Range 1.7μm to 30μm
333cm-1 to 5900cm-1
Resolution 1cm-1 to 64cm-1 (user defined)
Detector DTGS
Angles of Incidence 26° to 90°
Data Acquisition Rate
(Complete Spectrum)
1 to 30 minutes, typical
(1 angle of incidence at 16cm-1 resolution)
*Finer resolution will require longer time.
Max substrate thickness 20mm

Facility Requirements

Please contact J.A. Woollam Co. for complete list of facility requirements.

Dimensions

ir-vase-mark-ii-ellipsometer-dimensions

ACCESSORIES

Cryostat

ir-vase-mark-ii-with-cryostat Temperature range: 4.2 to 500 Kelvin OR 4.2 to 800 Kelvin

Angle: 70°

Includes UHV chamber/cryostat, turbo pump,and temperature controller.

Cryostat can be installed and removed, which allows the user to switch between the standard sample stage and the cryostat.

Wide-Range Temperature Stage

linkam-ellipsometer-heatcell-horizontal Temperature range: -70°C to 600°C

Angle: 70°

Active Cooling with Liquid Nitrogen

Sample area 22mm in diameter

Standard Heat Stage (HTC-100)

htc-100-heatcell-vertical-stage

Temperature range: Room Temp to 300°C

Angle: 70°

Passive Cooling

Sample area up to 50mm diameter

Rotation Stage

vertical-ellipsometer-rotation-stage

Automated high precision sample rotation (360° Theta-only) stage.

Useful when studying anisotropy. Through-hole behind sample allows transmitted beam measurements from normal incidence (0°) to ±19°.

Standard stage and rotation stage are swappable.

Manual Sample Translation

50-50mm-manual-vertical-translation-stage

Translator Size: 50×50 mm XY

Standard stage and Manual Sample Translation stage are swappable.

RESEARCH

Publications

“Application of IR variable angle spectroscopic ellipsometry to the determination of free carrier
concentration depth profiles” Authors: H. Arwin, A. Askendahl, P. Tengvall, D.W. Thompson,
J.A. Woollam Thin Solid Films, 313-314, (1998) 661-666.

“Determination of the Mid-IR Optical Constants of Water and Lubricants Using IR Ellipsometry
Combined with an ATR Cell” Authors: T. Tiwald, D. Thompson, J. A. Woollam, and S. V.
Pepper Thin Solid Films, 313-314, (1998) 718-721.

“Carrier concentration and lattice absorption in bulk and epitaxial silicon carbide determined
using infrared ellipsometry” Authors: T.E. Tiwald, J.A. Woollam, S. Zollner, J. Christiansen,
R.B. Gregory, T. Wetteroth, S.R. Wilson, A.R. Powell Phys. Rev. B, 60, 16, (1999) 11464-
11474.

“Infrared dielectric anisotropy and phonon modes of sapphire” Authors: M. Schubert, T.E. Tiwald,
C.M. Herzinger. Phys. Rev. B, 61, 12, (2000) 8187-8201.

“Free-carrier and phonon properties of n- and p-type hexagonal GaN films measured by infrared
ellipsometry” Authors: A. Kasic, M. Schubert, S. Einfeldt, D. Hommel, T.E. Tiwald Phys. Rev.
B, 62, 11, (2000) 7365-7377.

“Infrared ellipsometry studies of thermal stability of protein monolayers and multilayers”
Authors: H. Arwin, A. Askendahl, P. Tengvall, D.W. Thompson, J.A. Woollam physica status
solidi (c), 5, 5, (2000) 1438-1441.

“Use of Molecular Vibrations to Analyze Very Thin Films with Infrared Ellipsometry” Authors:
H. G. Tompkins, T. Tiwald, C. Bungay, and A. E. Hooper J. Phys. Chem. B, 108, 12, (2004)
3777-3780.

“Toward Perfect Antireflection Coatings. 3. Experimental Results Obtained with the Use of
Reststrahlen Materials” Authors: J. A. Dobrowolski, Y. Guo, T. Tiwald, P. Ma, and D. Poitras
Applied Optics, 45, 7, (2005) 1555-1562.