Accuracy and Reproducibility of X-ray Texture Measurements on Thin Films
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Accuracy and Reproducibility of X-ray Texture Measurements on Thin Films 2 1 3 Mark D. Vaudin , Glen R. Fox and Glen R. Kowach 1 National Institute of Standards and Technology, Gaithersburg, MD 20899, USA 2 Ramtron International Corporation, Colorado Springs, CO 80921, USA 3 Agere Systems, Breinigsville, PA, USA
ABSTRACT Rocking curve texture measurements were made on thin films of zinc oxide (ZnO) and platinum (Pt) using a powder x-ray diffractometer, and, in the case of ZnO, an area detector. The intensity corrections for defocussing and other geometric factors were made using a technique and associated software (Texture Plus*) developed at NIST. In both thin film systems, the texture was axisymmetric (fiber) and sharp, with full width at half maximum values of about 2.5°. Care was taken in the Pt case to ensure that the linear range of the x-ray detector was used to measure the intensities; for the ZnO data the degree of detector non-linearity was determined, and corrections were applied where necessary. The suitability of the Pt films for thin film texture standards was studied. *
available at http://www.ceramics.nist.gov/webbook/TexturePlus/texture.htm
INTRODUCTION Preferred crystallographic orientation, or texture, occurs almost universally, both in natural and man-made systems. Many components and devices in electronic and magnetic systems are fabricated from materials that have crystallographic texture. With the rapidly increasing use of thin film technology, where sharp, axisymmetric (fiber) crystallographic texture normal to the film plane is frequently observed, the occurrence and impact of texture are rising. Accurate measurement of texture is not simple and a variety of tools and approaches are being actively employed in texture studies. Techniques based on X-ray, neutron and electron diffraction are practiced around the world at varying levels of complexity with regard to equipment and analysis methods. Despite the well-documented existence of these varied approaches, many reported texture measurements on electronic and magnetic materials are based solely on the relative intensities of conventional θ-2θ x-ray diffraction peaks, which typically yield only semiquantitative results. NIST has developed quantitative texture measurement techniques that employ powder x-ray diffractometers commonly available in most industrial and academic settings. A wide variety of the physical properties of materials, such as ferroelectricity, ferromagnetism, piezoelectricity, conductivity, and dielectric permittivity, are anisotropic, and are therefore strongly affected by texture. Applications such as ferroelectric random access memories (FRAM) rely heavily on strict control of texture, not only for process monitoring but also for achieving high operating efficiency and product reliability.1 Texture is established during the synthesis or post-synthesis heat treatment of a material and thus has a strong dependence upon processing history. For materials and manufacturing development it is necessary to be able to compare
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