Combine Spectroscopic Ellipsometry and Grazing X-ray Reflectance for Fine Characterization of Complex Epitaxial Structur
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ABSTRACT Spectroscopic Ellipsometry (SE) and Grazing X-ray Reflectance (GXR) techniques are applied on different rn-V epitaxial structures in order to extract accurately their structural information. Thickness information are obtained directly from Fourier transformation of the GXR spectra and confirmed by simulation of the reflectance curve. Compositions are deduced from SE regression using GXR thickness as input values. Examples on monolayer and bilayer structures are first remembered. Then the potentiality of the method is demonstrated to more complex systems (multilayer mirrors and REMT structures).
INTRODUCTION With the development of microelectronics, the epitaxial structures of semiconductors become more and more complex. SiGe system is for example largely studied for optoelectronic applications (1) and high speed hererojunction transistors (2). III-V compound semiconductors are also studied for more than twenty years for high speed components. With the new generation of epitaxy deposition systems it is now possible to deposit hundreds of layers with nanometric thickness, keeping a good control of the layer compositions and thickness (3). The need of a precise characterisation technique capable to determine at the same time the thickness and compositions of such samples is obvious. In fact this task is very difficult to achieve with only one technique. People use generally different experimental methods and compare the different results to obtain at the end a final idea of their sample. In this respect Spectroscopic Ellipsometry (SE) as long been recognised as a powerful technique for non destructive characterisation of thin films and multilayer structures (4). For compound semiconductors, one of the problems is in fact the accuracy of the optical indices database used for the regression of the experimental spectra. This problem has been studied in details in other papers (5,6). In the case of complex multilayer samples the information on the different thickness and compositions are also largely intermixed, so a precise extraction becomes difficult. Grazing X-ray Reflectance (GXR) is known to be a technique of choice to extract precise thickness information on thin films and multilayer systems (7). In this case, direct information on the thickness can be extracted using Fourier transform of the GXR spectra (8), thanks to the complete decorrelation of the thickness and composition information. In this paper we use SE and GXR techniques for non destructive characterisation of complex epitaxial samples. A common physical model is developed and applied to take into account at the same time the two experimental information. The complementary and the limits of the two techniques are developed in view of these experimental results.
399 0 Mat. Res. Soc. Symp. Proc. Vol. 405 1996 Materials Research Society
EXPERIMENTAL SET-UP Spectroscopic Ellipsometry (SE) SE measurements were made with a commercially available SOPRA ES4G rotating polarizer instrument with a high resolution double monochromator and photon counti
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