Abstract
For quality control in high volume manufacturing of thin layers and for tracking of physical and chemical processes, ellipsometry is a common measurement technology. For such kinds of applications we present a novel approach of fast ellipsometric measurements. Instead of a conventional setup that uses a standard photo-elastic modulator, we use a 92 kHz Single Crystal Photo-Elastic Modulator (SCPEM), which is a LiTaO3 crystal with a size of 28 × 9 × 4 mm. This small, simple, and cost-effective solution also offers the advantage of direct control of the retardation via the current amplitude, which is important for repeatability of the measurements. Instead of a Lock-In Amplifier, an automated digital processing based on a fast analog to digital converter controlled by a highly flexible Field Programmable Gate Array is used. This and the extremely compact and efficient polarization modulation allow fast ellipsometric testing where the upper limit of measurement rates is mainly limited by the desired accuracy and repeatability of the measurements. The standard deviation that is related to the repeatability +/-0.002° for dielectric layers can be easily reached.
Highlights
Ellipsometry plays an important role in many applications like thin coatings, photovoltaic devices, semiconductor devices, flat panel displays, optoelectronic devices, and biological and chemical engineering
To directly measure the retardation amplitude and to calibrate the Single Crystal Photo-Elastic Modulator (SCPEM) one has to check the light intensity I going through parallel polarizers with the SCPEM in between, tilted by 45° around the optical path
The proposed ellipsometer based on a 92 kHz-SCPEM shows a simple, compact, and costeffective design while offering the highest flexibility in operation
Summary
Ellipsometry plays an important role in many applications like thin coatings, photovoltaic devices, semiconductor devices, flat panel displays, optoelectronic devices, and biological and chemical engineering. Ellipsometry measures the polarizing effect of a sample via the ellipsometric angles ψ and Δ in order to deduce basic physical parameters such as the thickness and refractive index of optical layers [1]. For this the polarization of the probe light beam needs to be changed in a defined manner during the measurement. Combinations of different ellipsometric methods are possible [14]
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