Since ellipsometry uses polarized light, an ellipsometer system is typically a complex and expensive optical instrument. However, the FS‑1 Multi-Wavelength Ellipsometer hides the complexity from the user, packaging powerful multi-wavelength ellipsometer technology into a compact, robust and affordable sensor, and enabling quick and accurate ellipsometric measurements. With the FS‑1, you do not need to understand the details of how the ellipsometric measurement is made, and operating the sensor is simple. Some of the innovative features which are incorporated into the FS-1 are described below.
The FS‑1 Light Source Unit provides the Polarization State Generator for the ellipsometer system. 4 visible Light Emitting Diodes LED’s (blue, green, yellow, and red) are used as light sources. LED’s are an ideal light source for an ellipsometer system. The only down side to using LED’s as a light source is their wide spectral bandwidth, but this is accurately and automatically corrected for in the FS-1 data analysis procedure*. Since they have long lifetimes (>50,000 hours), the FS‑1 LED’s never need to be replaced or realigned over the lifetime of the instrument. In operation, the 4 LED’s are sequentially scanned in less than 10 ms to provide ellipsometric data at 4 wavelengths essentially simultaneously. The internal optics of the FS‑1 Light Source Unit* combine the light from the 4 LED’s into a common beam, which is bright and uniform. The FS‑1 Light Source Unit also includes a Polarizer mounted on a manual rotation mechanism. In normal operation, the Polarizer is left at a fixed position. To calibrate the orientation of the Source and Detector units to the sample, the Polarizer is manually rotated to 4 positions. This simple calibration procedure takes only a few seconds, and only needs to be done when the Source and Detector units are mounted on a process chamber for in situ measurements, or when the Source and Detector units are remounted to the ex situ measurement Frame.
The FS‑1 Detector Unit provides the Polarization State Detector for the ellipsometer system. The FS‑1 Detector design has no moving parts, and is based on the Division of Amplitudes Polarimeter (DOAP) concept first proposed by Azzam (‘‘Division-of-amplitude photopolarimeter (DOAP) for the simultaneous measurement of all four Stokes parameters of light’’, R. M. A. Azzam, Opt. Acta Vol. 29, page 685, 1982). One disadvantage of the traditional DOAP design is that the polarization measurement accuracy can be affected by the alignment and uniformity of the incoming beam. To overcome this disadvantage, the FS‑1 Detector implements a novel optical configuration* to cancel measurement errors caused by mis-alignment or uniformity of the measurement beam. Since there are no moving parts, the ellipsometric data can be acquired very quickly (10 ms minimum acquisition time for 4 wavelengths of data), and long term measurement stability and robustness is also improved. The computer which controls the data acquisition and performs the data analysis is also integrated into the FS‑1 Detector Unit, resulting in a compact sensor that requires no additional control electronics.
For typical measurements, the FS‑1 Light Source and Detector units are mounted on the standard frame. This frame can accommodate samples up to 200 mm in diameter, up to 23 mm in thickness, and it provides manual height adjustment for the sensor units with respect to the sample surface. Custom attachments can be added to the frame, and the Light Source and Detector units can be attached to a custom frame (contact us for CAD drawings for custom interfacing or OEM applications). Standard options for in situ mounting, focusing, and more, are also available (see Products page).
* US Patent #9,354,118