Technology
Cubo productizes dynamic spectroscopic ellipsometry research carried out at the Optical Metrology Lab of Jeonbuk National University since 2014. At its core is a monolithic polarizing interferometer that obtains the polarization phase difference without any rotating part.
What a spectroscopic ellipsometer measures
When light reflects off a surface, its polarization state changes. A spectroscopic ellipsometer measures that change as two quantities: Ψ, the amplitude ratio between p- and s-polarization, and Δ, the phase difference between them.
Those values are not thickness. You build an optical model and iterate (fit) until the calculated values match the measurement, which yields thickness and optical constants. Δ is especially sensitive to thickness changes in thin transparent films — a 1 nm difference shows up as a clear signal.
Monolithic Polarizing Interferometer
Extracting the phase term requires a carrier frequency, and precise Δ requires that frequency to stay put. When the optical components are mounted separately, vibration and temperature drift move it.
The MPI puts an interferometer with two polarizers at 0° and 90° into a single body. The carrier frequency is fixed mechanically, so Δ can be pulled from one spectrum acquisition. Nothing needs to rotate — which is what makes real-time measurement possible.
Measuring in real time
Because the interferometer is monolithic, Δ comes out of a single spectrum acquisition with nothing rotating. Below is Cubo Ver.3 measuring.
How it differs
| Aspect | Conventional ellipsometer | Cubo |
|---|---|---|
| Polarization modulation | Mechanical rotation of polarizer or compensator | Monolithic interferometer, no moving parts |
| Measurement time | Seconds per point | More than 20 per second |
| Sample | Must be static | Static or changing |
| Size | Benchtop | 141 × 50 × 105 mm |
| Wavelength range | Broadband, UV to IR | 493.8 – 679.6 nm |
| Angle of incidence | Variable | Fixed at 45° |
What Cubo does not do
Compensating temperature drift
Interferometer phase drifts with temperature. The usual fix is a separate compensation channel, which makes the system larger. Because the initial phase drift is common across all wavelengths, adding an offset term to the fit parameters was enough: measurement held stable for 20 minutes with no compensation channel at all.
Patents
US 10,890,487 B2United States · 2021
Integrated polarization interferometer and snapshot spectro-polarimeter applying same
EP 3413022 B1Europe (DE, NL)
Integrated polarization interferometer
KR 10-1812608Republic of Korea · 2017
Snapshot spectro-polarimetry based on one-piece interferometric module
KR 10-2017-0092803Republic of Korea
Snapshot spectro-polarimetry based on one-piece interferometric module
Roadmap
The items below are not product specifications yet. Each is labelled by whether it is planned for launch or still at the research stage.
Expanded material library
Validated today on SiO₂ over Si. At launch the software is planned to ship with n and k libraries for Si₃N₄, Al₂O₃ and PR.
Ψ estimation model
Δ was implemented first because it is the more thickness-sensitive parameter for transparent films such as SiO₂. A model that estimates Ψ alongside it is in development.
AI-assisted fitting
Commercial fitting software converges to a local minimum when the initial thickness guess is off by more than about 100 nm. We are researching a hybrid approach that infers the initial value with a deep-learning model and then converges it with Levenberg–Marquardt fitting. The goal is a measurement that needs no initial guess at all.
Embedded system
Operation has been demonstrated on a Linux edge device as well as a Windows laptop. We are researching an embedded configuration that separates the sensor from the compute board.
DSE 4.0 / 4.5
The next optical scheme, adding a beam splitter and a compensator for higher accuracy. We are evaluating a move from the current upside-down layout to a bottom-plate layout for structural stability.
DSIE — imaging
An imaging ellipsometer that extends point sampling to a line scan. On the lab system, a full 12-inch wafer has been mapped in under an hour at 50 × 50 µm spatial resolution.
Research history
Snapshot spectroscopic ellipsometry (2014) → monolithic polarizing interference module and patents (2019) → dynamic spectroscopic imaging ellipsometry (2022) → Cubo (2026).