Growth and Properties of Hafnicone and HfO 2 /Hafnicone Nanolaminate and Alloy Films Using Molecular Layer Deposition Techniques Byoung H. Lee, † Virginia R. Anderson, † and Steven M. George* ,†,‡ † Department of Chemistry and Biochemistry, ‡ Department of Mechanical Engineering, University of Colorado, Boulder, Colorado 80309-0215, United States ABSTRACT: Molecular layer deposition (MLD) of the hafnium alkoxide polymer known as “hafnicone” was grown using sequential exposures of tetrakis(dimethylamido) hafnium (TDMAH) and ethylene glycol (EG) as the reactants. In situ quartz crystal microbalance (QCM) experiments demonstrated self-limiting reactions and linear growth versus the number of TDMAH/EG reaction cycles. Ex situ X-ray reflectivity (XRR) analysis confirmed linear growth and measured the density of the hafnicone films. The hafnicone growth rates were temperature-dependent and decreased from 1.2 Å per cycle at 105 °C to 0.4 Å per cycle at 205 °C. The measured density was ∼3.0 g/cm 3 for the hafnicone films at all temperatures. Transmission electron microscopy images revealed very uniform and conformal hafnicone films. The XRR studies also showed that the hafnicone films were very stable with time. Nanoindentation measurements determined that the elastic modulus and hardness of the hafnicone films were 47 ± 2 and 2.6 ± 0.2 GPa, respectively. HfO 2 /hafnicone nanolaminate films also were fabricated using HfO 2 atomic layer deposition (ALD) and hafnicone MLD at 145 °C. The in situ QCM measurements revealed that HfO 2 ALD nucleation on the hafnicone MLD surface required at least 18 TDMAH/H 2 O cycles. Hafnicone alloys were also fabricated by combining HfO 2 ALD and hafnicone MLD at 145 °C. The composition of the hafnicone alloy was varied by adjusting the relative number of TDMAH/H 2 O ALD cycles and TDMAH/ EG MLD cycles in the reaction sequence. The electron density changed continuously from 8.2 × 10 23 e - /cm 3 for pure hafnicone MLD films to 2.4 × 10 24 e - /cm 3 for pure HfO 2 ALD films. These hafnicone films and the HfO 2 /hafnicone nanolaminates and alloys may be useful for flexible thin-film devices. KEYWORDS: molecular layer deposition, atomic layer deposition, hafnicone, HfO 2 , nanolaminates, alloys I. INTRODUCTION Molecular layer deposition (MLD) is a growth technique based on sequential and self-limiting surface reactions that deposits organic or hybrid organic-inorganic films. 1 MLD is very similar to atomic layer deposition (ALD), which has been developed for the deposition of many inorganic films. 2 These techniques allow the film thickness to be controlled at the atom or molecular fragment level. MLD techniques have been developed for depositing organic polymer films. 3-11 The organic precursors can also be combined with the inorganic ALD precursors to produce hybrid organic-inorganic materi- als. 1,12 One class of hybrid organic-inorganic MLD films that can be grown from metal precursors and various organic alcohols produces metal alkoxide polymer films known as the “metalcones.” 12,13 The first metalcone was the aluminum alkoxide polymer known as “alucone” that was grown using sequential exposures of trimethylaluminum (TMA) and ethylene glycol (EG) as the reactants. 14 Other alucone films have also been demonstrated using TMA, ethanolamine (EA), and maleic anhydride (MA) as the reactants to avoid the problem of double reactions that can inhibit film growth. 15 Zinc alkoxide polymers known as “zincones” were another type of metalcone grown using diethylzinc (DEZ) and EG as the reactants. 16,17 In addition, titanium alkoxide polymers known as “titanicones” can be grown using titanium tetrachloride and EG or glycerol as the reactants. 18 Zirconium alkoxide polymers known as “zircones” can also be grown using zirconium tert-butoxide and ethylene glycol as the reactants. 19 Other types of hybrid organic- inorganic MLD films can be also fabricated using various organometallic and organic precursors. 20-23 Hybrid organic-inorganic films can also be deposited by combining ALD with MLD processes. The hybrid films can be grown by interspersing the ALD cycles and MLD cycles. 13 The composition of hybrid films can be tuned precisely by varying the relative number of ALD and MLD cycles. These hybrid films can be designated as “metalcone alloys.” A representative metalcone alloy is an “alucone alloy” grown using Al 2 O 3 ALD and alucone MLD. 24 The alucone alloy films display tunable density, refractive index, elastic modulus, and hardness as the alucone alloy is changed from the pure alucone MLD film to the pure Al 2 O 3 ALD film. 24 Zircone alloy films also showed similar tunable properties by changing the ratio from pure zircone MLD film to pure ZrO 2 ALD film. 19 The ability to mix and match ALD and MLD methods offers a wide variety of Received: July 5, 2014 Accepted: September 9, 2014 Published: September 9, 2014 Research Article www.acsami.org © 2014 American Chemical Society 16880 dx.doi.org/10.1021/am504341r | ACS Appl. Mater. Interfaces 2014, 6, 16880-16887