JASCO’s ellipsometer employs a proprietary polarization modulation technique (a PEM dual lock-in system) utilizing a photoelastic modulator, instead of the rotational drive mechanism of conventional ellipsometers.
Ellipsometry is a method for determining the refractive index and extinction coefficients of a sample by measuring the change in polarization state of surface reflected light. Film thickness and optical constants of an adsorption layer or oxide film on a substrate surface can be determined with exceptional sensitivity.
Conventional interference spectroscopy utilizes light passed through separate optical paths, while ellipsometry is a form of interferometry that uses two vibrational components with the same optical path, providing measurements with excellent accuracy and sensitivity.
The PEM dual lock-in system of JASCO's ellipsometer provides a stable measurement with additional capabilities including high-speed data sampling and wavelength scanning.
Automated wavelength scanning
The PEM dual lock-in system (JP Pat. # 2064627) automatically controls the PEM drive voltage for the current wavelength with an optical servo (JP Pat. #2081599) to increase ordinate accuracy during high speed scanning.
High-speed data sampling
Using high-speed electrical modulation, the PEM dual lock-in system enables high-speed data sampling in as little as 1 millisecond (optional 20 microseconds), far faster than systems that mechanically rotate a polarizer/analyzer combination.
High stability and reliability
The PEM dual lock-in system offers a static measurement free from mechanical error with high stability by using the optical servo and an optical reference.
Highly sensitive thin film analysis
The PEM dual lock-in system employs a proprietary polarizing configuration offering maximum sensitivity for extremely thin dielectric and semiconductor films.
|Measurement System||PEM dual lock-in|
|Wavelength||650 nm utilizing LD light source
Xe light source with a single monochromator to provide a range of 350 - 800 nm
|Spectral Bandwidth||1 nm|
|Incidence Angle||Continuous automated settings from 45° to 90°|
|Film Thickness||1 - 99,999 Å|
|Measurement Time||1 msec or greater (20 µsec optional)|
|Beam Diameter||Refractive index: ±0.01
Film thickness: ±1 Å (±0.1 nm)
Extinction coefficient: ±0.01
Values are for measurements of 100 msec or more and vary according to surface state and film quality
|Sample Stage||Standard sample size: 15 to 150 mm square or circular samples|
|Optical System||Optical path switching mechanism
Polarizer (Rochon prism), photo-elastic modulator (PEM), and optical servo and reference optics
(Glan-Taylor prism, plane mirror, and photomultiplier)
|Sample Chamber||Standard stage allows custom incidence angles and variable sample sizes.|
|Detector System||Analyzer (Glan-Taylor prism) and photomultiplier (R928)|
PEM dual lock-in system
The PEM dual lock-in system exposes a sample to light that has undergone high-speed modulation (50 kHz) by a photo-elastic modulator (PEM) and then measures the change in polarization by simultaneously detecting the primary (50 kHz) signal and second harmonic (100kHz) signals with a dual lock-in amplifier.
Innovative optical servo and optical reference control
The PEM is sensitive to environmental changes such as temperature because it modulates the refractive index of the transmissive material. JASCO’s spectroscopic ellipsometer employs a proprietary optical servo and optical reference in addition to a temperature control system, markedly improving instrument stability.
Multilayer Film Analysis
JASCO developed a special program for calculating the film thickness and optical constants for each layer of a multilayer film based on the ellipsometric dispersion parameters (?, ψ)λ for the material. A multilayer film model is developed for the sample, the film thickness and optical constants optimized to minimize the error for the measured values.
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