Low-temperature ALD/MLD growth of alucone and zincone thin films from non-pyrophoric precursors

Abstract

The combined atomic/molecular layer deposition (ALD/MLD) technique is emerging as a state-of-the-art synthesis route for new metal–organic thin-film materials with a multitude of properties by combining those of the inorganic and the organic material. A major part of the studies so far reported have focused on aluminum or zinc alkyls, so-called alucone and zincone films, typically grown from trimethyl aluminum (TMA) or diethyl zinc (DEZ) as the metal-bearing precursor, and a simple aliphatic bi-functional alcohol molecule such as ethylene glycol (EG) as the organic precursor. However, these common precursors possess certain disadvantages: both TMA and DEZ are pyrophoric, DEZ being additionally thermally unstable, while EG has a strong tendency for various unideal reaction modes. Here we report novel ALD/MLD processes for alucone and zincone films based on non-pyrophoric bis-diisopropylamido-[3-(N,N-dimethylamino)propyl] aluminum(III) [Al(NiPr₂)₂(DMP)] and bis-3-(N,N-dimethylamino)propyl zinc(II) [Zn(DMP)₂] precursors in combination with hydroquinone (HQ) as the organic precursor. We demonstrate that the [Al(NiPr₂)₂(DMP)] + HQ and [Zn(DMP)₂] + HQ ALD/MLD processes work even at record low deposition temperatures (140 °C and 60 °C, respectively) yielding high-quality and relatively stable Al-HQ and Zn-HQ thin films with appreciably high growth rates (2.8 Å / cycle and 3.2 Å / cycle, respectively). Moreover, these ALD/MLD processes are compatible with the corresponding ALD processes, i.e. [Al(NiPr₂)₂(DMP)] + H₂O and [Zn(DMP)₂] + H₂O, for the Al₂O₃ and ZnO films, thus opening up new horizons for the fabrication of novel metal–oxide : organic superlattice structures for e.g. flexible gas-barrier coatings or wearable thermoelectrics.