Short communication Synchrotron X-ray reflectivity study of high dielectric constant alumina thin films prepared by atomic layer deposition Yongtaek Hwang a , Kyuyoung Heo a , Chang Hwan Chang b, * , Man Kil Joo b , Moonhor Ree a, * a Department of Chemistry, National Research Lab for Polymer Synthesis and Physics, School of Environmental Science and Engineering, Center for Integrated Molecular Systems, and Division of Molecular and Life Sciences (BK-21 Program), Pohang University of Science and Technology (Postech), Pohang 790-784, Republic of Korea b Materials Analysis Team, Research Institute of Industrial Science and Technology (RIST), Pohang 790-600, Republic of Korea Received 10 May 2005; received in revised form 18 October 2005; accepted 8 December 2005 Available online 18 January 2006 Abstract High dielectric constant (high-k ) gate dielectric alumina films were prepared with nanoscale thicknesses on p-type silicon substrates by atomic layer deposition (ALD) with alternating pulses of trimethyl aluminum, nitrogen, ozone and nitrogen, and some of them were further thermally annealed. These high-k gate dielectric films were characterized by synchrotron X-ray reflectivity (XR), and the XR data were quantitatively analyzed, providing the following structural parameters of each gate dielectric film: the surface roughness and interfacial roughness, the electron density profile, the number of layers, and the thickness of individual layers. These structural characteristics were then analyzed in detail by considering the ALD processing conditions and post-thermal annealing history. D 2005 Elsevier B.V. All rights reserved. Keywords: Aluminium oxide; Dielectrics; Atomic layer deposition; Synchrotron X-ray reflectivity 1. Introduction The study of high dielectric constant (high-k ) dielectrics with a view to finding replacements for silicon dioxide (SiO 2 ) in complementary metal-oxide-semiconductor devices has become a field of intense interest [1]. The continuous scaling of SiO 2 -based gate dielectrics towards the fundamental limits imposed by large gate leakage and oxide reliability requires the introduction of new high-k materials for sub-100 nm technol- ogy nodes. Most current research into high-k dielectrics focuses on binary metal oxides and silicates. The main motivation for exploring these classes of materials is their thermal stability with silicon and their wide band gaps [2,3]. Alumina (Al 2 O 3 ) is a promising high-k dielectric material. Al 2 O 3 is a very stable and robust material and has been extensively studied. Al 2 O 3 has many favorable properties including a high band gap, thermodynamic stability on silicon up to high temperatures, and is amorphous under the conditions of interest. One drawback is that Al 2 O 3 has a medium k value of 8–10, which means that it only provides a relatively short- term solution for the needs of the semiconductor industry (1st – 2nd generations). Al 2 O 3 n-channel field effect transistor with an 80 nm effective gate length have recently been shown to provide more than two orders of magnitude reduction in the leakage current and a reliability equal to or better than SiO 2 at room temperature [4]. The development of these processes and of future process control requires the optimization of the physical analysis procedures for these materials [5,6]. In addition, such new materials need to be characterized precisely and non-destructively. The X-ray reflectivity (XR) technique meets these requirements. This XR technique with conven- tional X-ray sources generally provides data only in a rather limited range of intensities, typically over three to five orders of magnitude [7,8]. Thus, a well-collimated X-ray beam with a small angular divergence is essential to successfully apply this technique. In particular, synchrotron X-ray radiation source is useful due to its naturally low divergence and very high- intensity. In the present study, for the structural characterization of Al 2 O 3 thin films deposited on p-type Si(100) substrates by 0040-6090/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.tsf.2005.12.162 * Corresponding authors. Ree is to be contacted at Tel.: +82 54 279 2120. Chang, Tel.: +82 54 279 1556; fax: +82 54 279 3399. E-mail addresses: chchang@rist.re.kr (C.H. Chang), ree@postech.edu (M. Ree). Thin Solid Films 510 (2006) 159 – 163 www.elsevier.com/locate/tsf