Combined studies of gratings by X-ray reflectivity, GISAXS, and AFM M. Yan, a J.F. Bardeau, a G. Brotons, a T. Metzger b and A. Gibaud a* a- Laboratoire de Physique de l'Etat Condensé, UMR 6087 CNRS, Université du Maine, Faculté des Sciences, 72085 le Mans Cedex 09, France b- European Synchrotron Radiation Facility (ESRF), BP 220, 38043 Grenoble Cedex, France Abstract. The study of gratings has been carried out by different techniques such as specular and off-specular x-ray reflectivity, Grazing Incidence Small Angle X-ray Scattering (GISAXS) in coplanar and non coplanar geometries and atomic force microscopy (AFM). The comparison of the results is presented . The advantage of each technique is discussed. The new information obtained in GISAXS geometry concerning the very high sensitivity to the orientation of the gratings is commented. INTRODUCTION Surface gratings are beautiful synthetic objects exhibiting periodic arrays of grooves, lines and even dots. Their fabrication is nowadays perfectly mastered at the submicronic level but for technological applications, the trend is to go beyond this limit by targeting the nanometer scale. For instance, they remain of fundamental interest for applications in magnetic storage with the aim to achieve a density of dots allowing a storage capacity of one terabit or even more. Gratings have been also used in the past decade to study the coherence of x-ray beams at home laboratory and synchrotron facilities [1,2,3,4]. In this work, we have carried out the study of a series of gratings by means of X-ray techniques (such as X-ray reflectivity, Grazing Incidence Small Angle X-ray Scattering (GISAXS) in coplanar and non coplanar geometries) and atomic force microscopy (AFM). Our aim is to present the advantage of each technique in the analysis of these periodic objects. The samples have been realized on the LETI Silicon platform (LETI-DPTS), within the framework of national RTB program. Starting from an SOI wafer (55nm Si / 145nm SiO 2 / Silicon bulk), features were defined by 193nm photolithography, followed by Silicon Reactive Ion etching. Using this process, gratings of different periods (400, 450 and 650nm)have been realized collectively, the height of the gratings being defined by the thickness of the SOI film.. Each motif was 1.5cm long and 1.4mm wide and altogether 9 motifs separated by a distance of 1.4mm were covering the surface of a given grating. The technology used for making the gratings is the Silicon On Insulator (SOI) technology for which a silicon layer of 55nm (nominal value) is deposited on a 145nm thick thermally grown silicon oxide. The silicon is then covered with a photosensitive resin that is insolated by UV light (λ=195nm) through the mask. The opaque zones of the mask prevent the exposition of the resin to UV radiation and correspond to the motifs that are replicated on the surface of the substrate. The typical periodic profile of a grating in which the relevant parameters describing the profile is shown in Fig. 1 METHODS OF INVESTIGATION The easiest way to investigate the morphology of such gratings is to carry out direct imaging of the surface of these materials by Atomic Force Microscopy (AFM) or alternatively by Scanning Electron Microscopy (SEM). * To whom correspondence should be addressed, gibaud@univ-lemans.fr