J A Woollam VASE Spectroscopic Ellipsometer
Variable angle Spectroscopic Ellipsometer
The VASE® is an accurate and versatile ellipsometer for research on all types of materials: semiconductors, dielectrics, polymers, metals, multi-layers, and more.
It combines high accuracy and precision with a wide spectral range – up to 193 to 3200nm. Variable wavelength and angle of incidence allow flexible measurement capabilities, including:
- Reflection and Transmission Ellipsometry
- Generalised Ellipsometry (Anisotropy, Retardance, Birefringence)
- Reflectance (R) and Transmittance (T) intensity
- Cross-polarised R/T
The VASE features a rotating analyser ellipsometer (RAE) combined with J A Woollam patented AutoRetarder for unparalleled data accuracy.
- Standard Spectral Range: 240-1700 nm
- Vertical sample stage with vacuum mount can accommodate up to 200 mm diameter samples (call for custom sample mounting)
- Automated angle of incidence from 15° to 90°
- Double-chamber monochromator for superior stray-light rejection
Film thickness and optical properties are critical to performance of solar devices. Ellipsometry is used for development and monitoring of all PV materials: a-Si, μc-Si, poly-Si, AR Coatings (SiNx, AlNx), TCO Films (ITO, ZnOx, doped SnO2, AZO), CdS, CdTe, CIGS, organic PV materials, and dye sensitised films.
Thickness measurements are not independent of the optical constants. The film thickness affects the path length of light travelling through the film, but the index determines the light waves’ velocity and refracted angle. Thus, both contribute to the delay between surface reflection and light travelling through the film. Both n and k must be known or determined along with the thickness to get the correct results from an optical measurement.
Accurate wavelength selection using monochromator allows measurements at the operating wavelength for optics, e.g. 1550nm, 1310nm, 980nm, 632.8nm, 589nm.
The film thickness is determined by interference between light reflecting from the surface and light travelling through the film. Depending on the relative phase of the rejoining light to the surface reflection, interference can be defined as constructive or destructive. The interference involves both amplitude and phase information.
The M-2000 can be used for a variety of chemical and biological applications, either as a stand-alone tool or in combination with one of our many accessories. Study materials under liquid ambient, at high or low temperatures, or in conjunction with QCM-D measurements.
Great progress has occurred in the area of organic layers and stacks used for display (OLED) or photovoltaic applications. There are many different materials being studied, from small molecules such as Alq3 to conjugated polymers such as P3HT. Often multiple materials are blended together – which requires the wide spectral range of the M-2000 – to probe different wavelengths where the organics are optically different. Long-chain molecules may also have significant anisotropy, where orientational stacking of the polymer chains produces different optical constants in different directions.
Traditional ellipsometry applications are still going strong. Characterise any semiconductor material: resists, photomasks, SiON, ONO stacks, low-k dielectrics, high-k gates, SOI, SiGe, II-VI and III-V ternary and quaternary compounds.
Lithography thin films were an important motivation for the VUV-VASE® development. It has been successfully used to characterise all types of films in this area, including Photoresists and Bottom and Top AR Coatings.
Metamaterials & the Meta-6 Layer
For ellipsometry, we usually consider only the electric-field component of the electromagnetic (EM) wave interaction with the material. We ignore the interaction of the magnetic-field component because atoms and molecules tend to have a weak magnetic response to EM waves at optical frequencies. Thus we usually consider only dielectric response (permittivity) and ignore magnetic permeability. However, certain kinds of metamaterials change all of that. Metamaterials consist of an artificially-created array of small structures or particles, usually smaller than the measurement wavelength. These structures or particles can be considered “artificial atoms” or “meta-atoms”, with properties tailored to interact with incoming EM waves in ways generally not observed in naturally occurring materials.