Thin Solid Films Volumes 453–454, 1 April 2004, Pages 203–207 Proceedings of Symposium H on Photonic Processing of Surfaces, Thin Films and Devices, of the E-MRS 2003 Spring Conference Interface of ultrathin HfO 2 films deposited by UV-photo-CVD Q. Fang a, , , J.-Y. Zhang b , Z. Wang b , M. Modreanu c , B.J. O'Sullivan c , P.K. Hurley c , T.L. Leedham d , D. Hywel d , M.A. Audier e , C. Jimenez e , J.-P. Senateur e , Ian W Boyd a http://dx.doi.org/10.1016/j.tsf.2003.11.186 Abstract We report in this article the deposition of ultra-thin HfO 2 films on silicon substrate at 300–450 °C by photo- induced CVD using 222 nm excimer lamps. As-deposited films from 2.5 to 10 nm in thickness with refractive indices from 1.60 to 1.85 were grown. The deposition rate measured by ellipsometry was found to be 3 nm/min at a temperature of 400 °C. XRD showed that as-deposited HfO 2 films were basically amorphous. Investigation of the interfacial layer by XPS and TEM reveals that thickness of the interfacial SiO 2 layer slightly increases with the UV-annealing time and UV annealing can convert suboxide at interface into stoichiometric SiO 2 , leading to improved interfacial quality. Fourier transform infrared spectroscopy (FTIR), revealed that Hf–O absorption in the photo-CVD deposited HfO 2 films is quite different at various deposition parameters. When compared to similar studies performed previously in zirconium, titanium and tantalum oxides, the interface layer of HfO 2 is generally thinner than that of other materials. UV annealing can convert a suboxide at interface between the HfO 2 and Si into stoichiometric SiO 2 , leading to improved interfacial quality. The thickness of the interface layer (silicon oxide or hafnium silicate) decreases with increasing thickness of the top HfO 2 layers. Keywords UV-photo-CVD; Excimer lamp; HfO 2 films; High-k dielectrics 1. Introduction Hafnia (HfO 2 ) is an attractive candidate material for High-k dielectrics due to its high melting point, thermal and chemical stability and relatively high refractive index (dielectric constant k≈25) [1] and [2]. However, the interface properties of these films are not well understood such as interface layer thickness and composition can vary according to the deposition method and post-deposition processing. It is critical important that a thermodynamic stability of the high permittivity dielectric material with silicon substrate. Relatively, little thermodynamic data exist for HfO 2 . However, ZrO 2 has been found to be stable when is in contact with Si [3]. Because the Gibbs energy of formation for HfO 2 is more negative than ZrO 2 (−1088 kJ/mol vs. −1040 kJ/mol) [4], and hafnia and zirconia are similar compounds [5], HfO 2 is predicted to be stable when in contact with Si. As is well known, a thin native SiO 2 layer always exists on Si substrate after a routine cleaning. The thickness of the SiO 2 layer depends on the surface cleaning processes. Accurately, HfO 2 thin film is deposited onto Si covered by an intermediate SiO 2 layer. Therefore, how to control the HfO 2 /SiO 2 interface is a key issue to improve the physical and electrical properties of HfO 2 dielectric thin films. The aim of this work is to deposit and characterise ultra-thin HfO 2 films by photo-induced CVD using 222 nm excimer lamps. In order to keep the equivalent oxide thickness of the HfO 2 /SiO 2 stack low the intermediate SiO 2 layer should be minimised. Furthermore, the interface chemistry of HfO 2 /SiO 2 /Si stack should be assessed through an accurate determination of the bonding states. Fourier transformation infrared spectroscopy (FTIR), AFM, XPS depth profile technique and TEM were used to identify the structure and composition of the deposited layers and their interface with the Si substrate. The thickness of the intermediate SiO 2 layer was precisely measured by TEM. Capacitance–voltage and current–voltage methods were also used to obtain the electrical properties of the films when incorporated into simple capacitor structures. The effect of UV-annealing on the microstructure, interfacial and electrical properties of these films will also be investigated. 2. Experimental details A photo-CVD reactor combined with an injection liquid source and a shower-head was used for the deposition of HfO 2 films. More details of such an excimer UV source and the complete photo-CVD apparatus used have been described in previous articles [6], [7], [8], [9], [10] and [11]. A new precursor, Hafnium (IV) bis-t- Learn more about our redesign on our blog. Click here for details. 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