Divergent Illumination Optical Testing Device M. Fried 1, Z. Horváth 2, G. Juhász 1, T. Mosoni 1, P. Petrik 1 1 Research Institute for Technical Physics and Materials Science 2 Research Institute for Solid State Physics and Optics, H-1525 Budapest, POB 49, Hungary A new technique* and device for fast testing of polarization state changes after reflection from large surfaces is presented. Conventional ellipsometers and other optical methods measure at one oblique angle and a single point of the sample making these methods relatively slow for mapping purposes. The new technique uses divergent illumination from a point-like light-source and after reflection from the target the image is acquired on a CCD-camera giving multiple-angle-of- incidence and mapping information. *Patent pending Presentation made by StarImpress 5.0 of Sun StarOffice 5.2 and converted to PowerPoint

The prototype is built in the form of a wide-angle single- wavelength ellipsometer using film polarizers. The point-like source is an optical fiber coupled with a diode-laser and the elements are moved by simple stepping motors. (1) point-like source (2) light-conus (3) polarizer (4) sample on a moving stage (5) analyzer (6) CCD-camera

The axis of the light-cone is at 65 o relative to the normal of the sample surface and the opening angle of the beam is more then 14 degrees, determining the range of incidence angles that can be used for measurement

With this arrangement, the angle of incidence is different for different positions of the light spot on the sample surface. Using a motorised X-Y moving stage, the sample surface can be scanned relative to the light- spot, yielding a huge amount of measured ellipsometric data (amplitude ratio – tan  and phase shift – cos  ) corresponding to the different angles. Because of the linear translation one can measure the polarisation state at all the points and at every angle inside the cone. The collected data are processed by an additional computer that provides real-time polarisation state parameter maps (and thicknesses and/or refractive indices maps ) over a large area of the sample surface. The speed of the measuring system makes it suitable for use even on production lines. The amount of data and the dynamics of the CCD-detector can be optimized by grouping of the pixels.

As a demonstration, electrochemically etched porous silicon layers were made with different porosity (refractive index) and different thicknesses. Etched areas were limited by teflon O-ring causing significant edge-effects.

We see now two possible enhancements to the prototype: - A spectroscopic version where the light source (13) is a continuos spectra white lamp (or LED) and the cone is reduced to a line by a slit. In this case a grating (16) (or prism) deflects the light into the perpendicular direction after the analyser (5) according to the spectral content. In this case multiple-angle and spectral information can be obtained simultaneously from the surface of the sample if needed to test the complexity of the film structure. - The other possibility is a multiwavelength version using more than one discrete wavelength (for instance different laser-diodes) at the entrance of the single optical fiber. After the analyser the different colours can be split into different images detected by discrete CCD-matrixes.

Prototype of a wide-angle multi-wavelength ellipsometer: (1) point-like source (2) light-conus (3) polarizer (4) sample on a moving stage (5) analyzer (6) CCD-camera (11) optical fiber (12) exit aperture (13) multi-wavelength (white) light source (14) slit (15) optical axis (16) grating (17) screen (18) forming optics