Application of a Dual-spectral-range, Divergent-beam Spectroscopic Ellipsometer for High-Speed Mapping of Large-area, La
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Application of a Dual-spectral-range, Divergent-beam Spectroscopic Ellipsometer for High-Speed Mapping of Large-area, Laterally-inhomogeneous, Photovoltaic Multilayers M. Fried1, G. Juhasz1, C. Major1, A. Nemeth2, P. Petrik1, O. Polgar1, C. Salupo2, Lila R. Dahal2, R. W. Collins2 1 Res. Inst. for Technical Physics & Materials Science (MFA) H-1525 Budapest, POB 49, Hungary 2 PVIC, University of Toledo, Toledo, Ohio, USA ABSTRACT We have developed a prototype spectroscopic ellipsometer for imaging/mapping purposes requiring only one measurement cycle (one rotation period of a polarizer or analyzer) for the acquisition of a two-dimensional array of data points. Our new measurement technique serves as a novel form of imaging ellipsometry, using a divergent (uncollimated, diffuse) source system and a detection system consisting of an angle-of-incidence-sensitive pinhole camera. By incorporating broad-band sources and wavelength dispersion optics, the instrument provides continuous high-resolution spectra along a line image of the sample surface. As a result, information on multilayer photovoltaics stacks can be obtained over large areas (several dm2) at high speed. The technique can be expanded to even larger areas by scaling-up the optical geometry. The spatial resolution of the line image is limited by the minimum resolved-angle as determined by the detection system. Small-aperture polarizers (25 mm diameter) are incorporated into the instrument, which reduces its cost. Demonstration mapping measurements have been performed ex situ on a multilayer sample deposited on a polymer substrate, including an intentionally graded 80-350 nm thick hydrogenated amorphous silicon (a-Si:H) layer and an intended uniform 400-500 nm thick transparent conducting ZnO:Al layer, both on opaque silver. Alternative commercial instruments for ex situ SE mapping must translate the sample in two dimensions. Even a 15 x 15 cm2 sample requires > 200 measurements with cm-resolution and at least 15 min. By collecting ex situ data in parallel along one dimension through imaging, the divergent-beam system can measure with similar spatial resolution in < 2 min. In situ measurements on both roll-to-roll polymer and rigid glass will be possible in the future. INTRODUCTION Ellipsometry determines angle-of-incidence dependent relative amplitude ratios and phase difference shifts upon specular reflection of light from a planar surface. Thus, collimated light beams are conventionally used with a well defined angle of incidence at the reflecting surface. Here we present an ellipsometric method fundamentally different from the conventional techniques [1-4]. In our instrument, the sample is illuminated by an almost diffuse, “divergent beam” of light, providing a collection of rays with diverse angles of incidence at every point of the sample. Precise “angle-selection” is performed on the detector side by a pin-hole camera. The pin-hole works as an “angle-of-incidence filter”, selecting only one single light-beam from every direction (or sample position). The a
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