Investigation of AlMe3, BEt3, and ZnEt2 as Co-Reagents for Low-Temperature Copper Metal ALD/Pulsed-CVD

The reactions of AlMe3, BEt3, and ZnEt2 with toluene solutions of the copper(II) complexes [CuL2] {L = acetylacetonate (acac; 1), hexafluoroacetylacetonate (hfac; 2), N-isopropyl-β-ketiminate (acnac; 3), N,N-dimethyl-β-diketiminate (nacnac; 4), 2-pyrrolylaldehyde (PyrAld; 5), N-isopropyl-2-pyrrolylaldiminate (PyrIm iPr; 6a), N-ethyl-2-pyrrolylaldiminate (PyrImEt; 6b), and N-isopropyl-2-salicylaldiminate (IPSA; 7)} were investigated, and most combinations were found to deposit metal films or metal powder at 50 °C or less. SEM and XPS of metal films deposited on ruthenium showed a range of morphologies and compositions, including pure copper (excluding oxygen content after atmospheric exposure). These nonaqueous solution screening studies provided a rapid and convenient means to identify the most promising [CuIIL2] precursor/ER n co-reagent combinations for copper metal ALD/pulsed-CVD studies, and subsequent ALD/pulsed-CVD studies were performed using 6b in combination with AlMe3, BEt3 and ZnEt2. As in solution, the reactivity of these reagents (pulsed-CVD) followed the order ZnEt2 ≈ AlMe3 ≫ BEt3. Furthermore, at 120−150 °C, ZnEt2 was used successfully to deposit smooth, conductive films composed of copper with 8−15% Zn. On the basis of CVD studies with ZnEt2, zinc content appears to derive from a parasitic CVD process, which becomes more favorable above 120 °C, detracting from the goal of self-limiting deposition.