SURFACE AND INTERFACE ANALYSIS Surf. Interface Anal. 2004; 36: 1102–1105 Published online in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/sia.1850 Instrument for thin film diagnostics by UV spectroscopic reflectometry M. Urb ´ anek, 1 J. Spousta, 1 K. Navr ´ atil, 2 R. Szotkowski, 1 R. Chmel ´ ık, 1 M. Bu ˇ cek 1 and T. ˇ Sikola 1* 1 Institute of Physical Engineering, Brno University of Technology, Technick ´ a 2, 61669 Brno, Czech Republic 2 Institute of Condensed Matter Physics, Faculty of Science, Masaryk University, Brno, Czech Republic Received 6 August 2003; Revised 28 November 2003; Accepted 1 December 2003 This paper describes the principles, design and testing of an instrument for the UV/Vis-optical-reflectance monitoring of homogeneity of the optical properties of thin films developed in our group. A 200 μm reflection probe, miniature fibre optic spectrometer and a home-built computer controlled x – y mapping stage together with original data fitting software are the principal parts of the instrument. The results achieved show the usability of this instrument for the post-production testing of samples of various optical thin films prepared by different technologies. By this instrument the gradients and other inhomogeneities of thickness and spectral optical constants (n, k) of thin films can be monitored. Copyright  2004 John Wiley & Sons, Ltd. KEYWORDS: UV spectroscopic reflectometry; surface homogeneity INTRODUCTION Reflectometry together with ellipsometry are common meth- ods for measuring optical properties of thin films because they are accurate, non-destructive, and require virtually no special sample preparation. At present, spectroscopic reflectometry and ellipsometry are the two most common optical methods. Spectroscopic reflectometry measures the light intensity within a wavelength interval reflected from a thin film. In this method, the incident light direction is perpendicular to the sample. Spectroscopic ellipsometry is a similar technique, except that it measures reflectance at an oblique light incidence for two different polarizations. In general, reflectometry is much simpler, faster and less expen- sive than ellipsometry, but it is limited to the measurement of less-complex structures. In surface homogeneity measure- ments, the simplicity and speed of reflectometry is a big advantage as thousands of points needs to be measured over the sample area. In our Institute, an instrument working on the principles of spectroscopic reflectometry equipped with a mapping stage allowing surface homogeneity measurements has been developed. This type of instrument is a useful tool for the post-production monitoring of transparent thin-film samples prepared by various deposition techniques—in our case by ion beam assisted deposition (IBAD). L Correspondence to: T. ˇ Sikola, Institute of Physical Engineering, Brno University of Technology, Technick´ a 2, 61669 Brno, Czech Republic. E-mail: sikola@ufi.fme.vutbr.cz Contract/grant sponsor: Czech Grant Agency; Contract/grant number: GA102/02/0506. Contract/grant sponsor: Ministry of Education, Czech Republic; Contract/grant number: ME 334, SEZ:J22/9826200002. MEASUREMENT PRINCIPLES OF SPECTRAL REFLECTANCE The basic principle of reflectometry is very simple—the spectral intensity of a light beam is measured before and after its reflection on the sample under study. 1 The ratio of the intensity of the reflected and incoming beam is termed the absolute reflectance. It is generally very difficult to directly measure the intensity of the light beam before it strikes the sample. Because of that, we use the relative reflectance measurements—the intensity of a light beam reflected from the sample under study is divided by the intensity of the same light beam reflected from a known (standard) sample. The ratio of the reflected intensity from the unknown sample to the reflected intensity from the standard sample is termed the relative reflectance, and represents the reflectance of the unknown sample relative to the standard sample. The absolute reflectance of the unknown sample can always be calculated from its relative reflectance as long as the absolute reflectance of the standard sample is known. We use a single-crystal silicon wafer as the standard sample. DETERMINING FILM PROPERTIES FROM SPECTRAL REFLECTANCE The amplitudes and periodicity of the reflectance spectrum of a thin film are determined by the film thickness, optical constants (index of refraction n, extinction coefficient k), and other properties; for instance, interface roughness. 2 A math- ematical dispersion model describing n and k over a range of wavelengths by using only a few adjustable parameters is generally used—for example, the Cauchy function: n⊲⊳ D A C B  2 C C  4 , k⊲⊳ D D C E  2 C F  4 . Copyright  2004 John Wiley & Sons, Ltd.