Synthesis, Structure, and Solution Reduction Reactions of Volatile and Thermally Stable Mid to Late First Row Transition Metal Complexes Containing Hydrazonate Ligands

Abstract

Treatment of MCl2 (M = Ni, Co, Fe, Mn, Cr) with 2 equiv of the hydrazonate salts K(tBuNNCHCtBuO), K(tBuNNCHCiPrO), or K(tBuNNCMeCMeO) afforded the complexes M(tBuNNCHCtBuO)2 (M = Ni, 65%; Co, 80%; Fe, 83%; Mn, 68%; Cr, 64%), M(tBuNNCHCiPrO)2 (M = Ni, 63%; Co, 86%; Fe, 75%), and M(tBuNNCMeCMeO)2 (M = Ni, 34%; Co, 29%; Fe, 27%). Crystal structure determinations of Co(tBuNNCHCtBuO)2, M(tBuNNCHCiPrO)2 (M = Ni, Co), and M(tBuNNCMeCMeO)2 (M = Ni, Co, Fe) revealed monomeric complexes with tetrahedral geometries about the metal centers. To evaluate the potential of these new complexes as film growth precursors, preparative sublimations, thermogravimetric analyses, solid state decomposition studies, and solution reactions with reducing coreagents were carried out. M(tBuNNCHCtBuO)2 sublime between 120 and 135 °C at 0.05 Torr, whereas M(tBuNNCHCiPrO)2 and M(tBuNNCMeCMeO)2 sublime between 100 and 105 °C at the same pressure. All complexes afforded ≥96% recovery of sublimed material, with ≤3% of nonvolatile residues. The solid state decomposition temperatures were highest for M(tBuNNCHCiPrO)2 (273-308 °C), intermediate for M(tBuNNCHCtBuO)2 (241-278 °C), and lowest for M(tBuNNCMeCMeO)2 (235-250 °C). Treatment of Co(tBuNNCHCtBuO)2 in tetrahydrofuran with hydrazine, BH3(L) (L = NHMe2, SMe2, THF), pinacol borane, and LiAlH4 led to rapid formation of cobalt metal, while analogous reductions of Mn(tBuNNCHCtBuO)2 with BH3(THF), pinacol borane, and LiAlH4 appeared to afford manganese metal. The new complexes M(tBuNNCHCtBuO)2, M(tBuNNCHCiPrO)2, and M(tBuNNCMeCMeO)2 have very promising properties for use as precursors for the growth of the respective metals in atomic layer deposition film growth processes.

Editors' Choice—Review—Cobalt Thin Films: Trends in Processing Technologies and Emerging Applications

“…Thermal Co ALD is categorized by: (1) the introduction of the Co source precursor and co-reactant in sequential rather than simultaneous stages, with intervening purge steps to ensure that the co-reactants never cross paths in the reaction zone and that no reactions occur except on the substrate surface; and (2) Co film growth proceeding through self-limiting surface reactions that ensure precise control of film thickness and conformality with atomic level accuracy. 20,[51][52][53] These characteristics suggest the realization of excellent film conformality in extremely aggressive device topographies. The addition of plasma to one of the co-reactants (e.g., H 2 or NH 3 ) has also been shown to enhance the ALD reaction and increase film growth rates by creating a higher concentration of active co-reactant radicals.…”

Low Temperature Thermal Atomic Layer Deposition of Cobalt Metal Films

“…In support of this proposal, we previously observed that growth of cobalt metal only occurred upon pretreatment of the ruthenium substrate with 50 cycles of a pulse sequence comprising Co((Me) (iPr)COCNtBu) 2 (20.0 s)/N 2 purge (5.0 s)/BH 3 (NHMe 2 ) (1.0 s)/N 2 purge (10.0 s). 35 To probe the importance of precursor 1, we carried out depositions at 175, 200, and 225 °C on ruthenium, platinum, silicon(100), and silicon dioxide substrates using the alternative cobalt precursor 3 42 and formic acid with a pulse sequence of 3 (3.0 s)/N 2 purge (10.0 s)/formic acid (0.2 s)/N 2 purge (10.0 s) with 1000 cycles. No film growth was observed.…”

“…The lack of film growth using 3 could arise from its higher thermal stability compared to 1 (dec 1, 235 °C; 37 3, 260 °C42 ) and the fact that thermal decomposition of 3 does not afford cobalt metal. 42 On the basis of the cobalt metal ALD growth, we attempted an analogous nickel metal film growth process employing bis(1,4-di-tert-butyl-1,3-diazabutadienyl)nickel(II) (4) 37 and formic acid at 180 °C using a pulse sequence of 4 (5.0 s)/N 2 purge (10.0 s)/formic acid (0.2 s)/N 2 purge (10.0 s) on ruthenium substrates with 1000 cycles. No films were observed by SEM.…”

New Heteroleptic Cobalt Precursors for Deposition of Cobalt-Based Thin Films

“…In complexes 3 – 7 , as shown in Figures 2–6, the Co–O bond lengths between the central cobalt ion and the oxygen of the β-diketonate ligands were 2.0017(12), 2.015(3), 2.0187(15), 2.0048(11), and 1.996(7) Å, respectively, which were again shorter than that for similar β-diketonate complexes of cobalt (2.064(4) Å for [Co(acac) 2 (TMEDA)], 2.046(3) Å for [Co(acac) 2 (DMAPH)] 2 , 23 2.034(3) Å for [Co(acac) 2 (py) 2 ], and 2.036(12) Å for [Co(tmhd) 2 (py) 2 ]). 24 However, the Co–O bond lengths for complexes 3 – 7 are longer than those in the Co(thd) 3 complex (1.869(2) Å) 25 and in [Co( t BuNNCHCRO) 2 (R = t Bu, i Pr, Me)] 26 (average Co–O bond length is 1.915(1) Å). An increase in the Co1–O1–Co1 i bond angle and relative increase in the Co···Co distances were observed between complex 1 and complexes 3 – 7 (Table 2).…”