Influence of process parameters on atomic layer deposition of ZrO 2 thin films from CpZr(NMe 2 ) 3 and H 2 O Lauri Aarik a, ⁎, Harry Alles a , Aleks Aidla a , Tauno Kahro a , Kaupo Kukli a,b , Jaakko Niinistö b , Hugo Mändar a , Aile Tamm a , Raul Rammula a , Väino Sammelselg a,c , Jaan Aarik a a University of Tartu, Institute of Physics, Ravila 14C, 50411 Tartu, Estonia b University of Helsinki, Department of Chemistry, P.O. Box 55, FI-00014 Helsinki, Finland c University of Tartu, Institute of Chemistry, Ravila 14A, 50411 Tartu, Estonia abstract article info Article history: Received 13 February 2014 Received in revised form 26 June 2014 Accepted 26 June 2014 Available online 4 July 2014 Keywords: Zirconium oxide Atomic layer deposition Cyclopentadienyl Crystal structure Density Refractive index Atomic layer deposition of ZrO 2 films from tris(dimethylamino)cyclopentadienylzirconium CpZr(NMe 2 ) 3 and H 2 O, was investigated using real-time characterization of the growth process and post-growth measurements of the films. Self-limited nature of the deposition process was observed at substrate temperatures ranging from 120 to 350 °C. In this temperature range growth rate of 0.08–0.1 nm per cycle was obtained on silicon substrates. The films deposited on silicon substrates at 200 °C and higher temperatures contained tetragonal and monoclinic phases of ZrO 2 . The phase composition of the films depended on the deposition temperature as well as on the film thickness. The concentration of carbon residues decreased with increasing deposition tem- perature and did not exceed 0.9 at.% in the films deposited at 250 °C and higher temperatures. The refractive in- dices and densities of films grown from CpZr(NMe 2 ) 3 and H 2 O at 250–350 °C ranged from 2.15 to 2.20 (at a wavelength of 633 nm) and 5.6 to 6.0 g/cm 3 , respectively, being close to the highest values obtained for films de- posited from ZrCl 4 and H 2 O. The former process ensured, however, more uniform nucleation of ZrO 2 on graphene than the latter process did. © 2014 Elsevier B.V. All rights reserved. 1. Introduction Zirconium dioxide (ZrO 2 ) is a dielectric with relatively wide band gap, high refractive index and high dielectric constant. These properties make ZrO 2 very attractive for application in optical [1] and electronic [2–6] devices. For instance, significant efforts have been focussed on characterization of ZrO 2 thin films prepared by various deposition techniques for silicon-based metal-oxide-semiconductor devices [3,4] and capacitor structures with TiN electrodes [5,6]. In addition, inspired by the many potential applications, deposition of ZrO 2 onto graphene [7–9] has been studied. Among the deposition methods, which can be used for these purposes, atomic layer deposition (ALD) is the one that allows precise and simple thickness control and uniform coating of surfaces with complex shapes. One of the earliest and most commonly studied methods for ALD of ZrO 2 is the ZrCl 4 –H 2 O process, which has several disadvantages like rather high evaporation temperature of the precur- sor [10–12], chlorine contamination of the films [11,12] and generation of corrosive HCl as a reaction by-product. For these reasons, it is important to find and/or develop alternative fabrication methods and/ or precursor combinations. In particular, reduction of the concentration of electrically active impurities to very low values is of marked signifi- cance in electronic applications that require low leakage current densi- ties of ZrO 2 dielectrics and/or preventing unintentional trapping of electrons. In earlier studies, Niinistö et al. [13] have demonstrated self-limiting nature of a process based on CpZr(NMe 2 ) 3 (Cp = C 5 H 5 ; Me = CH 3 ) and ozone. In a relatively wide range of growth temperatures (T G ), high growth rate, conformity and low impurity concentrations of the resulting films have obtained. Although alkylamido-cyclopentadienyl- type precursors have problems with thermal stability at higher deposi- tion temperatures, the reaction by-products should not be that corro- sive and therefore CpZr(NMe 2 ) 3 , known also as Zy(ALD), has already found application in electronic industry. At the same time not only the selection of the metal precursor but also the choice of the oxygen precursor is important due to its influence on the growth rate, temperature range of ALD-type growth and/or film properties [14]. In some cases, application of H 2 O instead of ozone is of particular significance due to the detrimental influence of ozone on the substrate material. For instance, deposition of thin films on graphene in ozone-based processes has led to significant degradation of graphene [15]. Moreover, application of ozone sets some additional requirements to the design of ALD reactors. To expand the application range of CpZr(NMe 2 ) 3 we studied the pos- sibility to use water vapor as an alternative oxygen precursor in Thin Solid Films 565 (2014) 37–44 ⁎ Corresponding author. E-mail address: lauri.aarik@ut.ee (L. Aarik). http://dx.doi.org/10.1016/j.tsf.2014.06.052 0040-6090/© 2014 Elsevier B.V. All rights reserved. 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