Nickel Thin Films Grown by MOCVD Using Ni(dmg)2 as Precursor

The aim of this study was (i) to investigate alternatives to the very toxic Ni(C0)4, (ii) optimization of the parameters for Ni film growth, and (iii) characterization of the film morphology. The thermal behaviour of the precursors bis(dirnethylglyoximato)Ni(II), [Ni(dmg)2], bis(2,2,6,6-tetramethyl-3,5-heptandionato)Ni(II), [Ni(thd)2], N,N'-ethylenebis(2,4-pentandioniminoato)Ni(II), [Ni(enacac)], and bis(2-amino-pent-2-en-4-onato)Ni(II), [Ni(apo)2] were investigated in a model reactor. Furthermore, the evaporation rates of these compounds were determined. Metallic nickel films were obtained using Ni(drng)2 as precursor. The deposition was canied out in a horizontal quartz reactor at reduced pressure in a hydrogen/helium atmosphere. The films were analysed by profilometry, X-ray diffraction, atomic force microscopy (AFM), fourpoint resistivity measurements and electron spectroscopy for chemical analysis (ESCA). Comparison of the AFM and ESCA data with the electrical resistances resulted in a two layer film model. 1.INTRODUCTION Nickel and nickel alloys are currently being investigated in several research fields due to their promising properties. Ni is known to be an excellent catalyst for many processes. The catalytical formation of highly oriented graphite on nickel was recently investigated by TEM[l]. In the fabrication of 111-V semiconductor devices nickel gallides and aluminides could play an important role in the future. These intermetallic compounds are thermodynamically stable with respect to the 111-V semiconductors preventing chemical reactions at the metal/semiconductor interface[2, 31. Lanthanide-Ni systems have been studied for many years for their hydrogen storage capability. They can store and release hydrogen reversibly when cycled electrochemically or under hydrogen pressurization[4-6]. (1) Present address: Superconductivity Research Laboratory (SRL), 10-13 I-chome. Shinonome Koto-ku. Tokyo 135. Japan ( 2 ) Present address: Fedc~-al Insril~rre ol' Technology, DcparLment of Chcrnical Engineerin2 atid Industrial Chemistry, Univcrsitlitsts~~-. 6. 8092 ZLir-ich, Swit-lel-land 13) Prcsent address: Thc Florida Statc I:ni\.crsity, Department of Chemi\tr).. T:illah;l\\ce. Floricla 323063006, U.S.A. Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1995553 (25-466 JOURNAL DE PHYSIQUE IV Thin metallic films of high purity can be prepared by Metal-Organic Chemical Vapor Deposition (MOCVD). The advantages of MOCVD are conformal step coverage, high throughput and low-cost. In the case of Ni only a few reports exist. The deposition of Ni using Ni(C0)4 was first discovered by Mond over a hundred years ago[7]. The high toxicity of Ni(C0)4 is the major disadvantage of this precursor[8]. Alternative precursors are the cyclopentadienides of Ni, Ni(Cp)2 and its methyl derivative Ni(MeCp)2[2,9,10]. In this work, we report growth experiments of nickel films using bis(dimethylglyoximato)Ni(II), Ni(dmg)2, in a horizontal MOCVD reactor. Furthermore, we present the evaporation rates of Ni(dmg)2, bis(2,2,6,6-tetramethyl-3,5-heptandionato)Ni(II), Ni(thd)2, N,Ne-ethylenebis(2,4-pentandion-iminoato) Ni(II), Ni(enacac), and bis(2-amino-pent-2-en-4-onato)Ni(II), Ni(apo)2. These precursors were also used in a model reactor to investigate the influence of the nickel film on the decomposition process[ll]. Srructures of the precursors: 2. EXPERIMENTAL The horizontal hot-wall quartz reactor used was described earlier[l2]. The precursor Ni(dmg)2 was synthesized according to Gnlelir~s Handhuch dcr Anorganischcn Chemic[13]. Ni(thd)2, Ni(enacac), and Ni(apo)2 were prepared following literature procedures[l4, 151. The precursors were investigated in a model reactor shown in Figure 1. The compounds were evaporated (temperatures: Ni(dmg)2 = 240°C, Ni(thd):! = 15O0C, and Ni(enacac) = 170°C) and transported to the reactor (p = 20mbar) by the helium carrier gas (flow = 20mljmin). The temperature in the reactor was increased stepwise and at a certain temperature, T I , signals of the decomposition products could be observed in the mass spectrometer. The temperature was further increased to about 100°C above TI and then decreased. A second temperature, T2, was obtained during cooling where no signals were observed in the MS.