Substrate Selectivity in the Low Temperature Atomic Layer Deposition of Cobalt Metal Films from Bis(1,4-Di- Tert -Butyl-1,3-Diazadienyl)Cobalt and Formic Acid


The initial stages of cobalt metal growth by atomic layer deposition are described using the precursors bis(1,4-di-tert-butyl-1,3-diazadienyl)cobalt and formic acid. Ruthenium, platinum, copper, Si(100), Si-H, SiO₂, and carbon-doped oxide substrates were used with a growth temperature of 180 °C. On platinum and copper, plots of thickness versus number of growth cycles were linear between 25 and 250 cycles, with growth rates of 0.98 Å/cycle. By contrast, growth on ruthenium showed a delay of up to 250 cycles before a normal growth rate was obtained. No films were observed after 25 and 50 cycles. Between 100 and 150 cycles, a rapid growth rate of ∼1.6 Å/cycle was observed, which suggests that a chemical vapor deposition-like growth occurs until the ruthenium surface is covered with ∼10 nm of cobalt metal. Atomic force microscopy showed smooth, continuous cobalt metal films on platinum after 150 cycles, with an rms surface roughness of 0.6 nm. Films grown on copper gave rms surface roughnesses of 1.1-2.4 nm after 150 cycles. Films grown on ruthenium, platinum, and copper showed resistivities of < 20 μΩ cm after 250 cycles and had values close to those of the uncoated substrates at ≤150 cycles. X-ray photoelectron spectroscopy of films grown with 150 cycles on a platinum substrate showed surface oxidation of the cobalt, with cobalt metal underneath. Analogous analysis of a film grown with 150 cycles on a copper substrate showed cobalt oxide throughout the film. No film growth was observed after 1000 cycles on Si(100), Si-H, and carbon-doped oxide substrates. Growth on thermal SiO₂ substrates gave ∼35 nm thick layers of cobalt(II) formate after ≥500 cycles. Inherently selective deposition of cobalt on metallic substrates over Si(100), Si-H, and carbon-doped oxide was observed from 160 °C to 200 °C. Particle deposition occurred on carbon-doped oxide substrates at 220 °C.


Includes supplementary material


Atomic force microscopy, Atomic layer deposition, Chemical vapor deposition, Cobalt, Copper, Formic acid, Metallic films, Metals, Platinum, Ruthenium, Silicon, Surface roughness, Temperature, Vapor-plating, X ray photoelectron spectroscopy, Film growth

U.S. National Science Foundation (Grant Nos. CHE-1212574, CHE-1607973, CHE-1300180, CHE-1427926 and DMR-0922912


CC BY 4.0 (Attribution), ©2016 The Authors.