Low temperature area-selective atomic layer deposition of NiO, Ni and Pd for next-generation nanomanufacturing
Nickel, nickel oxide and palladium are used within various device heterostructures for chemical sensing, solar cells, batteries, etc. There is increasing interest in realizing flexible, low-cost, wearable electronics to enable ubiquitous sensors, next-generation displays, and improved human-machine interfaces. A major hurdle for flexible technology is the development of low temperature fabrication processes for the integration of inorganic devices with polymeric substrates. Here we investigate area-selective atomic layer deposition of NiO performed at 100 °C using bis(N,N'-di-tert-butylacetamidinato)nickel(II) and water on SiO₂ and polystyrene. NiO grows two dimensionally and without nucleation delay on oxide substrates but not on SiN [subscript x] or polystyrene, which require surface treatments such as an Al₂O₃ buffer layer or O₂ plasma treatment to promote NiO nucleation. Additionally, pre-patterned sp² carbon-rich resists inhibit the nucleation of NiO. This way, carbon-free NiO may be patterned. A NiO grid pattern is fabricated as a demonstration. Additionally, thermal reduction of NiO to Ni was explored using H₂ (50-300 mTorr) and thermally generated H-atoms (3×10⁻⁵ Torr chamber pressure). Due to the relatively high free surface energy of metals, Ni films undergo dewetting at elevated temperatures when solid-state transport is enabled. Reduction of NiO to Ni is demonstrated at 100 °C and below using atomic hydrogen, a temperature low enough to be compatible with organic substrate temperature constraints as well as to avoid significant dewetting. Finally, the area-selective atomic layer deposition of Pd by area-activation is studied. Thermal atomic layer deposition of Pd can only proceed at low temperatures on surfaces that can dissociate the coreactant, H₂. Prepatterned Ni functions to catalyze the nucleation of Pd at 100 °C. H-atom reduction of NiO grown by atomic layer deposition can generate an atomically smooth Ni surface, which allows the growth of void-free Pd films. Finally, the area-selective atomic layer deposition of Pd on patterned Ni grid lines is explored.