Nickel amidinates have been proposed and tested as ALD precursor for pure Ni films in the group of R. Gordon
Nickel bis(N,N'-diisopropylacetamidinate) Ni(iPr-MeAMD)2 was synthesized by refluxing overnight the reaction mixture consisting of NiCl2 and Li(N,N'-diisopropylacetamidinate) (obtained in situ from diisopropylcarbodiimide and LiMe). After evaporation of the solvent from the hexanes extract brown solid Ni(iPr-MeAMD)2 was obtained. (yield 70%).).
TGA study at atmospheric pressure revealed a step suggesting decomposition at about 180 °C and higher residual mass (27%). The DSC curve showed an exothermic peak at 180 °C as well.However, at vapour source temperatures lower than 120 °C the precursor is volatile enough for use in ALD of Ni metal fims.
Ni(iPr-MeAMD)2 is volatile – it sublimes at 35°C/ 70 mTorr giving brown crystals of pure Ni(iPr-MeAMD)2 (correspondingly
its vapour pressure is 70mTorr/ 35°C) . Due to its high volatility, Ni(iPr-MeAMD)2 was proposed as potential precursor for MOCVD
and ALD growth of Ni-containing thin films. Lowest deposition temperature on the substrate placed in the heated tube (i.e for thermal MOCVD) was found to be 300° C.[i]
[i] R.G. Gordon, B.S. Lim, US Patent US7737290B2, «Atomic layer deposition using metal amidinates » , https://patents.google.com/patent/US7737290B2/en , https://patentimages.storage.googleapis.com/99/5e/7f/e20606f8f5f3ad/US7737290.pdf
Nickel bis(N,N'-diisopropylacetamidinate) Ni(iPr-MeAMD)2 (combined with H2 as reducing agent) was applied as precursor for the growth of metallic Ni
films by ALD on Si/SiO2/WNx substrates at 280°C. Ni precursor was vaporised at 75°C). The dose of Ni(iPr-MeAMD)2 in each cycle was 4x10-9 moles/cm (exposure of
the substrates to Ni precursor was 3x104 Langmuirs/cycle), the dose of H2 was 8x10-7
moles/cm (the exposure to H2 was 7x106 Langmuirs/cycle). The layers consisted of pure Ni metal, according to RBS. (nickel metal was 5x1016 atoms/cm thick or 8x10-8 moles/cm thick.[i]
[i] R.G. Gordon, B.S. Lim, US Patent US7737290B2, «Atomic layer deposition using metal amidinates » , https://patents.google.com/patent/US7737290B2/en , https://patentimages.storage.googleapis.com/99/5e/7f/e20606f8f5f3ad/US7737290.pdf