FTIR ellipsometer IR-VASE
From Woollam Co.
The IR-VASE is the first and only spectroscopic ellipsometer to cover the spectral range from 1.7 to 30 microns (333 to 5900 wavenumbers). The IR-VASE can determine both n and k for materials over the entire width of the spectral range without extrapolating data outside the measured range, as with a Kramers-Kronig analysis. Like other Woollam ellipsometers, the IR-VASE is perfect for thin films or bulk materials including dielectrics, semiconductors, polymers and metals.
|Rotating compensator ellipsometer|
|Widest spectral range|
|Vertical sample mount|
|Combination of ellipsometry and transmittance|
The IR-VASE offers non-contact measurements of many different material properties including thickness, optical constants, material composition, chemical bonding, doping concentration, and more. 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 modulation technique that does not require scans or reference samples to maintain accuracy. Even samples that are 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 remove effects of imperfect optical elements to provide accurate measurements of Ψ and Δ.
- Spectral range: 1.7 µm to 30 µm (further with good reflective samples)
- Verticale sample mount
- Motorized angle of incidence goniometer: 32° to 90°
- Ellipsometry, transmittance and reflectance, Mueller matrix, generalized ellipsometry, depolarisation
Epitaxial layers and 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.
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.
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.