SURFACE AND INTERFACE ANALYSIS Surf. Interface Anal. 30, 612–615 (2000) Silicate formation at the interface of a calcium-modified lead titanate thin film deposited on Si(100) D. Leinen, 1 * E. Rodr´ ıguez-Castell´ on, 2 R. Sirera 3 and L. Calzada 4 1 Departamento de F´ ısica Aplicada I, Facultad de Ciencias, Universidad de M´ alaga, 29071 M´ alaga, Spain 2 Departamento de Qu´ ımica Inorg´ anica, Facultad de Ciencias, Universidad de M´ alaga, 29071 M´ alaga, Spain 3 Departamento de Qu´ ımica y Edafolog´ ıa, Universidad de Navarra, 31080 Pamplona, Spain 4 Instituto de Ciencia de Materiales de Madrid (CSIC), Cantoblanco, 28049 Madrid, Spain A calcium-modified lead titanate (Pb 0.76 Ca 0.24 TiO 3 ) thin film has been prepared by spin-on sol–gel on an Si(100) substrate. The film deposited from a stoichiometric solution was subjected to thermal treatment at 650 ° C for 720 s with a heating rate of 8 ° Cs -1 . The film presents a perovskite-type structure, as indicated from x-ray diffraction powder pattern data, giving it ferroelectrical properties. The chemical composition at the film surface and at increasing depth into the substrate was studied by XPS combined with 4 keV Ar Y depth profiling. Ion bombardment gives rise to compositional and chemical changes in the sample surface, in which case lead and oxygen are sputtered preferentially. After 50 min of 4 keV Ar Y bombardment, a steady-state composition is reached. At further depth (>200 min) an increase of the Pb 4f signal indicates a non-homogeneous Pb distribution in the film. At the interface between the ferroelectric film and the Si(100) substrate, silicon is found as Si(IV), as well as chemical shifts of the O 1s and Ca 2p 3=2 peaks to higher binding energies are observed. Both facts support the formation of calcium silicate. At the same time, titanium is reduced from Ti(IV), Ti(III) and Ti(II) to Ti(0). Copyright  2000 John Wiley & Sons, Ltd. KEYWORDS: thin films; XPS; depth profiling; interface; calcium lead titanate; Si(100) INTRODUCTION Ferroelectric thin films are materials of interest because of their possible integration into multifunctional micro- electronic devices. 1 For instance, properties such as spon- taneous polarization, pyroelectricity and piezoelectric- ity have been exploited for non-volatile ferroelectric random-access memories (NVFRAMs), infrared sensors and microelectromechanical systems (MEMS), respec- tively. But one of the main problems of these devices appears during the deposition of the ferroelectric film on the silicon substrate. In this interfacial region, chemical reactions between the substrate and ferroelectric layer, as well as the diffusion of some elements, can cause a negative effect on the electric response of the device. X-ray photoelectron spectroscopy (XPS) combined with low-energy ion bombardment (used for depth profiling) is a technique that gives information about the interfa- cial regions by providing atomic concentration profiles with chemical information related to the characteristics of the interface with a depth resolution within the nanome- tre scale. This information is not only useful for a better understanding of these materials but also for the pos- sible improvement of their properties by changing the processing parameters that alter the interface. 2 Many of the main properties of a thin-film-based device depend on * Correspondence to: D. Leinen, Departamento de F´ ısica Aplicada I, Facultad de Ciencias, Universidad de M´ alaga, 29071 M´ alaga, Spain. E-mail: dietmar@uma.es Contract/grant sponsor: Junta de Andaluc´ ıa, Spain; Contract/grant number: FQM192. the substrate and the deposition method. 3 The available substrates on which the ferroelectric film is deposited are those used in the microelectronic industry. Thus, most research work has been carried out with regard to ferro- electric thin films on silicon as a substrate. Among the different deposition techniques, spin-on sol–gel is a method that provides several advantages, such as stoichiometric control of mixed oxides, the uniform incorporation of dopants, etc. 4,5 However, thin films deposited from sol–gel solutions are amorphous and require thermal treatment for crystallization into the desired phase. In the case of calcium-modified lead per- ovskite thin films, volatilization of lead occurs during annealing, which can give rise to lead-deficient phases. Also during annealing, interdiffusion between the ferro- electric film and the underlaying substrate may occur. These phenomena damage the electrical properties of the material. 2,6 In this paper, using XPS combined with Ar C depth profiling, we study the characteristics of the interface between the ferroelectric thin film and the Si(100) sub- strate. Calcium-modified lead perovskite thin films of for- mula Pb 0.76 Ca 0.24 TiO 3 were selected because they present much lower coercive fields, E c , and similar or better piezo- electric anisotropy and spontaneous polarization values 7–9 than PbTiO 3 . EXPERIMENTAL The preparation of the calcium-modified lead titanate precursor solution with a nominal composition of Copyright  2000 John Wiley & Sons, Ltd. Received 15 July 1999 Revised 30 November 1999; Accepted 17 December 1999