FR-Liquid is a table-top optical tool for the real time monitoring of changes in thickness and optical constants of thin/thick (n & k) films during processing in liquids. It is based on FR-Basic platform with the addition of a Teflon cell for hosting the sample under test. In this configuration the reflection probe is placed horizontally outside the Teflon cell at a very short distance from the glass window. A stirrer located underneath the working area provides for mechanical agitation of the solution if necessary. The vertical sample holder is designed to accommodate small samples of arbitrary shape as well as whole Si wafers (3”, 4” diameter). FR-Liquid’s principle of operation is based on White Light Reflectance Spectroscopy (WLRS).

The FR-Liquid tool has been successfully applied for the evaluation of the dissolution process of various smooth, transparent or lightly absorbing films over reflecting substrates (Si wafer). Films studied include: SiO2, SiNX, Photoresist, Polymer layers.

The tool is controlled by FR-Monitor software, performing the data acquisition and film thickness and optical constants calculations. A material database is included and can be easily expanded by the user. The entire system (hardware – software) is shipped ready for measurements and can be easily used by anyone with basic computer skills without any deep knowledge of optics. The only additional part needed is a PC with a free USB port running Windows XP/Vista/7.


Fig. 1: Sample just before enter in to Teflon cell (a), and during the dissolution measurement (b). At left side of the Teflon cell the pipes for the cooling of the liquid under the room temperature are shown.

In FR-Liquid, critical phenomena such as swelling and dissolution also monitored even for films with initial thicknes few tens on nanometers. Depending on the characteristics of the dissolution process, e.g. the dissolution speed, the monitoring is performed either off-line or in real time. In all cases the reflectance data are stored for subsequent processing.

For thickness measurements, all that is required in most cases is a smooth, reflective substrate. The FR-Liquid software can handle layer stacks consisted of numerous layers and two quantities can be calculated simultaneously e.g. the thicknesses of two films or the thickness and n & k of one film etc

Fig. 2: Dissolution measurement of various PMMA films




5nm - 150μm*
Polymer Characterization
Wavelength range
Photoresist Characterization
better than 0.5 %
Materials characterization
Spot size
depends on objective's magnification
Light Source
Microscope's source / External Tungsten - Halogen (>360nm)
Polymer Characterization
Sample size
10 - 100mm, irregular shape
non Metal films
Computer requirements
PC with Windows XP/Vista/7 32/64bit and a USB port available
In-Situ Measurements
Power requirements
110V/230V AC
Dimensions (WxLxH)
36cm x 40cm x 18cm*
* Depends on the configuration, please refer to FR-Basic page.
** Cover top height is not included
*** Specifications are subject to change without any notice
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