J. MATER. CHEM., 1991, 1(4), 701-702 701 Low-temperature Vapour Deposition of High-purity Copper Coatings from Bis[~(Fluoroalkyl)salicylaldiminato]copper Chelates Jeffrey B. Hoke* and Eric W. Stern Engelhard Corporation, Menlo Park, CN 40, Edison, NJ 08818, USA High-purity copper coatings have been prepared by chemical vapour deposition at low temperature from two novel bis[N-(fluoroalkyl)salicylaldiminato]chelates of copper(I1). When hydrogen is used as the carrier gas at ambient pressure, copper coatings containing < -1 atom.% carbon, oxygen, nitrogen, and fluorine are generated at 290 and 330 "C using Cu(NCH,CF2CF3-SAL), and Cu(NCH,CF,CF2CF3-SAL),, respectively (SAL=salicylaldiminato). When the deposition is carried out in vacuo, ca. 6% carbon, 2% oxygen, and 3% fluorine are incorporated into the films using Cu(NCH,CF,CF,-SAL), as the copper source.Keywords: Metal-organic chemical vapour deposition; copper(I1) complex; coating In recent years there has been growing interest in the develop- ment of volatile organometallic precursors to low-temperature vapour deposited metal and metal oxide coatings.'-6 Of the metals used in the microelectronics industry, copper is of interest, owing to its extensive application in packaging metal- lization.2b Additionally, with the discovery of copper-based high-temperature superconducting oxides, interest in the util- ization of potential copper-containing CVD precursors has grown markedly. Owing to their volatility, air stability, and ready availability, precursors for the chemical vapour deposition of metallic copper traditionally have been confined to the copper(I1) p-diketonates, in particular the fluorinated copper(I1) acetylace- tonato complexes, Cu(hfa), (hfa = hexafluoroacetylacetonato) and Cu(tfa), (tfa = trifluoroacetyla~etonato).~~~Other copper complexes which have been used as precursors for CVD include the related chelates, bis(acetylacetoneimide)copper(II) and (acetylacetoneethylenediimide)copper(II): tert-butoxy-copper(I ), c yclopen t adien yl( t rimet h ylp hosp hine)copper(I ),, a cyclopen tadien y1 (trimet h ylp hosphine)copper(I ),, and tert-butoxy(trimethylphosphine)copper(I).2b These precursors are sufficiently volatile for CVD, but many give rise to coatings that contain carbon, oxygen, or fluorine contamination.Since fluorine-containing copper p-diketonate complexes are known to be more volatile than their non-fluorinated analogues [e-g. Cu(hfacac), us. Cu(acac),], we have attempted to prepare other volatile copper chelates that contain fluorinated substituents and which can be decomposed cleanly to metallic copper. In this communication we describe preliminary findings on the chemical vapour deposition of metallic copper at low temperature (< 330 "C) from two novel, air-stable N-(fluoroalky1)salicylaldi-minatocopper(I1) precursors: Cu(NCH2CF2CF,-SAL), and CU(NCH,CF,CF~CF~-SAL)~. The new chelates were prepared by the Schiff's base conden- sation of bis(salicylaldehydato)copper(Ii) with a three-fold excess of the respective primary fluoroalkylamine in refluxing ethan01.~ Yields > 90% were obtained.Both complexes are volatile and sublime readily at ca. 150 "C and ca. 7 mT0rr.t Characterization data are given below.$ Depositions onto readily available, polished, fused quartz substrates were accomplished using a 2.54 cm (outer diameter) externally thermostatted hot-walled quartz reactor. The cop- per precursor was sublimed into the hot zone of the reactor either in a stream of hydrogen (ca. 1.6 cfhR or under vacuum in the absence of a carrier gas. A typical run lasted ca. 5 h. Hydrogen reduction of CU(NCH,CF,CF~-SAL)~ and Cu(NCH2CF2CF,CF3-SAL), vapours (sublimation tempera- ture ca. 190 "C) at ca. 290 and 330 "C, respectively, resulted in the deposition of reflective, crystalline coatings of copper (Table 1).ESCA depth-profile analyses detected c1 atom% carbon, oxygen, nitrogen, and fluorine within the bulk of the coatings which were obtained up to 2050 A thick. Thin-film (grazing-angle) X-ray analysis (Cu-Ka radiation) confirmed the crystallinity of the coating obtained from Cu(NCH2CF2CF2CF3-SAL),. For coatings derived from either precursor, representative scanning electron microscopy (SEM) photographs (Fig. 1) showed two distinct surface mor- phologies. In Fig. 1 (a), a polycrystalline granular morphology is shown with a roughly uniform crystallite size of 0.5 pm. However, in Fig. l(b) individual crystallites appear to have sintered into a smooth coating retaining wavy microcracks. Although the origin of this variability is not known, it does not appear to result from differences in deposition tempera- ture, film thickness, or CVD precursor.Owing to the gradual decomposition of the source materials under hydrogen during sublimation at 190 "C, the observed deposition rates were slow. (Attempts at using the NCH2CF3- SAL derivative were unsuccessful in producing a continuous copper coating since this precursor decomposed quite readily during sublimation.) In principle this problem can be allevi- ated by a modification to the quartz reactor that allows the organometallic vapours to be directed onto the substrate prior to hydrogen exposure. Id Consequently, the precursor will not see hydrogen until the point of deposition, and a significant improvement in rate should be observed.Nuclear magnetic resonance (NMR) spectroscopy and gas chromatography (GC) were utilized to deduce a possible mechanism for the reduction of Cu(NCH2CF2CF3-SAL), at t 1 Torr z 133.322 Pa. $ (a) Cu(NCH,CF,CF,-SAL),: m.p. 197.5-199.0 "C; Tub 145 "C (ca. 0.007 Torr). (Found: C, 42.46; H, 2.60. Calc. for C,,H14CuFl,N,0,: C, 42.30; H, 2.48%). FAB(-) in NBA: M+ at 567 with the correct isotope pattern for 63Cu and 65Cu. (b) Cu(NCH,CF,CF2CF3-SAL),: m.p. 184-185 "C; Tub 150 "C (ca. 0.007 Torr). (Found: C, 39.72; H, 2.12. Calc. for C22H14C~F14N202: C, 39.56; H, 2.11%). FAB(-) in NBA: M+ at 667 with the correct isotope pattern for 63Cu and 65Cu. (c) Cu(NCH,CF,-SAL),: m.p.225- 226 "c; Tub155 "c(CU. 0.007 Torr). (Found: c,46.58; H, 3.22. Calc. for C1,H,4CuF6N202: C, 46.21; H, 3.02%). FAB(-) in NBA: M+ at 467 with the correct isotope pattern for ',Cu and 65Cu. 9 1 cfhz2.83 XIO-' m3 h-'. J. MATER. CHEM., 1991, VOL. 1 precursor CU(NCH,CF,CF~CF~-SAL), CU(NCH~CF,CF~-SAL)~Cu(NCH,CF,CF,-SAL), Table 1 Data summary for CVD copper coatings ~~ co-reactant Tdecl "C depth/8, composition deposition rate/A h-' H2 330 1190 <1% C, 0, N, F 250 H2 290 2050 <1% C, 0,N, F 400 vacuum 485 2900 6% C, 2% 0,3% F 600 Fig. 1 Representative SEM photographs of deposited copper coatings showing varied coating morphologies (bars = 1 pm) 290 "C. GC analysis of the volatile organic products collected during vapour deposition showed two major species in an approximate 2 :1 ratio.'H, 13C, and I9F NMR spectroscopy identified the major product as free NCH2CF2CF3-salicylaldi- mine ligand and the minor product as o-cresol. These results would indicate that the primary reduction mechanism pro- ceeds via homolysis of the salicylaldimine-copper bonds and subsequent reaction of the transient organic radical with hydrogen to form free NCH,CF,CF3-salicylaldimine. Met-allic copper is thus generated. Apparently, further reduction of the free salicylaldimine ligand with hydrogen at high temperature yields o-cresol as a secondary product. When the decomposition of CU(NCH~CF~CF~-SAL)~was accomplished under vacuum in the absence of hydrogen carrier gas, a coating 2900 A thick incorporating ca.6 atom% carbon, 2 atom% oxygen, and 3 atom% fluorine, as deter- mined by ESCA, was obtained at 485 "C (sublimation tem- perature ca. 180 "C). Presumably, hydrogen is required to react with transient salicylaldiminyl radicals and thus prevent the formation of carbonaceous and fluorine-containing resi- dues. Despite the presence of these impurities, however, the morphology of the coating surface (Fig. 2) displays unusual columnar copper 'whiskers' extending away from rounded crystallites of roughly uniform 1 pm diameter. Further experi- ments aimed at exploring this unusual crystallite growth are in progress. References (a)J. E. Gozum, D. M. Pollina, J. A.Jensen and G. S. Girolami, J. Am. Chem. SOC., 1988, 110, 2688; (b) Z. Xue, M. J. Strouse, D. K. Shuh, C. B. Knobler, H. D. Kaesz, R. F. Hicks and R. S. Williams, J. Am. Chem. SOC., 1989, 111, 8779; (c) H. D. Kaesz, R. S. Williams, R. F. Hicks, Y. A. Chen, Z. Xue, D. Xu, D. Shuh and H. Thridandam, Muter. Res. SOC. Symp. Proc., 1989, 131, 395; (d) E. Feuer, S. Kraus and H. Suhr, J. Vuc. Sci. Technol. A, 1989, 7, 2799; (e) C. Larson, T H. Baum and R. L. Jackson, J. Electrochem. SOC.,1987,134,266; (f) T. H. Baum, J. Electrochem. 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