Synthesis and characterization of hafnium oxide and hafnium aluminate ultra-thin films by a sol–gel spin coating process for microelectronic applications A.R. Phani * , M. Passacantando, S. Santucci CASTI, CNR-INFM Regional Laboratory, Department of Physics, University of L’Aquila Via Vetoio, Coppito, 67010 L’Aquila, Italy Available online 14 February 2007 Abstract Currently there are intense industry-wide efforts in searching for new high dielectric constant (high-k) materials for use in future gen- erations of ultra-large scale integrated circuits (ULSI). There are number of requirements for the new high-k materials, such as high dielectric constant, thermal stability (400 °C or higher), high mechanical strength, and good adhesion to neighboring layers. Oxide spinels comprise a very large group of structurally related compounds many of which are of considerable technological significance. Spinels exhi- bit a wide range of electronic and magnetic properties in particular nickel, hafnium, cobalt, containing spinels. In the present investiga- tion, crack free, dense polycrystalline monoclinic structure of pure HfO 2 , and Al 2 HfO 5 ultra-thin films have been prepared by a simple and cost effective sol–gel spin coating method. The formation of the monoclinic HfO 2 phase at 600 °C and complete formation of the single phase Al 2 HfO 5 at 800 °C has been reported. The composition of the annealed films has been measured and found to be 70 at.% of O, 30 at.% of Hf for HfO 2 and 22 at.% of Al, 12 at.% of Hf and 66 at.% of O for Al 2 HfO 5 films, which are close to the stoi- chiometry of the HfO 2 and Al 2 HfO 5 thin films. Ó 2007 Elsevier B.V. All rights reserved. PACS: 61.10.Nz; 68.60.Bs; 81.20.Fw; 61.20.Ài; 77.55.+f Keywords: Diffraction and scattering measurements; X-ray diffraction; Films and coatings; Spin coating; Measurement techniques; Microscopy; Scanning electron microscopy; Sol–gel, aerogel and solution chemistry; Solution chemistry; X-rays; XPS 1. Introduction In order to reduce direct tunneling in metal–oxide–semi- conductor (MOS) devices with ultra-thin silicon oxide thin films, alternative dielectrics with substantially higher dielectric constant are being considered. Replacing SiO 2 with higher dielectric constant materials [1–3] allows one to use physically thicker films that display lower leakage currents without compromising capacitance and speed of MOS devices. Finding a material to replace silicon oxide is a formidable challenge because SiO 2 is a nearly perfect gate dielectric. Some of the high-k materials being consid- ered for integration into future IC technologies are Al 2 O 3 , HfO 2 , ZrO 2 ,Y 2 O 3 , TiO 2 , and Ta 2 O 5 and/or the sil- icates and aluminates of some of these materials [4–10]. The practical application of these materials have advanta- ges and disadvantages, but none of them are currently at the material quality level of SiO 2 . Still all of these alterna- tive gate dielectrics have a larger dielectric constant than SiO 2 . Therefore, it is necessary to fabricate a gate stack that is physically thicker and thermally stable, yet electronically shows capacitance which is similar to an ultra-thin SiO 2 layer. Oxide spinels comprise a very large group of struc- turally stable compounds many of which are of consider- able technological significance. Spinels exhibit a wide range of electronic and magnetic properties in particular nickel, hafnium, cobalt, containing spinels. Al 2 O 3 , HfO 2 or Al 2 HfO 5 oxides are considered to be good high k-dielec- trics with good thermal stability. They have been deposited 0022-3093/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jnoncrysol.2006.10.041 * Corresponding author. Tel.: +39 0862 315471; fax: +39 0862 433033. E-mail address: phani_ayala@yahoo.com (A.R. Phani). www.elsevier.com/locate/jnoncrysol Journal of Non-Crystalline Solids 353 (2007) 663–669