Ellipsometry
Thin film analysis using a spectroscopic imaging ellipsometer.
Ellipsometry at a glance
Ellipsometry is a non-destructive technique that can be used to measure the properties of thin films. It can be used to determine film thickness as well as optical properties such as refractive index or extinction coefficients. This can be done with a lateral accuracy as small as 5 microns.
Applications of Ellipsometry
- Thickness measurements of thin films
- Measurements of optical constants
- Multilayer measurements
- Measurements or anisotropic materials
- Mapping of substrates
How does Ellipsometry work?
Ellipsometry works by measuring how the polarisation of light changes as it is reflected off a sample. The change in polarisation is measured using two valves, delta, and psi which are taken over a range of wavelengths and angles to improve accuracy. To convert these values to physical properties modelling needs to take place. Modelling involves fitting a number of oscillators to the data, the choice of oscillators depends on the material, e.g. transparent films often use a Cauchy model whilst semiconductors would use a Tauc-Lorentz oscillator. Whilst this modelling means we are unable to directly measure properties it does allow us to calculate a range of values such as thickness, band gaps, absorption peaks and even conductivity with high precision allowing for sub nm accuracy.
Our Ellipsometry Facilities
Accurion Nanofilm_EP4 Imaging Ellipsometer
- Hosted within the Nanoscale and Microscale Research Centre's Nanofabrication Nottingham (NaNo) Suite
- Imaging ellipsometer for visualisation of samples with ellipsometic contrast e.g. thickness mapping
- Spectral Range of between 190nm-1000nm
- Can measure at a range of angles
- Lateral resolution of down to 1 micron for high resolution mapping
- 5x, 10x, 20x, 50x and Nanochromat (UV/IR) objective lenses for a range of field of views and light sources
- Fully automated measurements for autonomous data collection
- Full data processing and modelling software
- Located within a class 4 cleanroom to prevent sample contamination
Alpha-SE Ellipsometer (J. A. Woolan)
- Non-imaging ellipsometer
- Spectral Range: 380nm to 900nm, 180 wavelengths
- Angle of Incidence: 65°, 70°, 75° or 90° (transmission)
- Data Acquisition Rate: 3 sec. (Fast mode) 10 sec. (Standard mode) 30 sec. (High-precision mode)
- Rotating compensator technology with CCD detection
Publications of Interest
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, Amin, S. S., Cameron, J. M., Cousins, R. B., Wrigley, J., Liirò-Peluso, L., Sans, V., Walsh, D. A. & Newton, G. N., Inorganic Chemistry Frontiers (2022). doi:10.1039/D2QI00174H