Low-Temperature Plasma-Enhanced Atomic Layer Deposition of Cu Films Using Liquid Copper Precursor...

Cu atomic layer deposition (ALD) is necessary to deposit thin Cu seed layers with good coverage, high film continuity, and low resistivity onto a high-aspect-ratio substrate. In addition, the Cu metal should be deposited at as low a temperature as possible, ideally ≤100 °C, to minimize the surface roughness, promote facile nucleation, and form continuous films even at thicknesses of a few nanometers. However, Cu ALD requires a temperature greater than 80 °C when conventional Cu ALD precursors are used because they exhibit low volatility and high melting points. In the present study, we investigated Cu aminoalkoxide precursors and found an excellent candidate, bis-(1-ethylmethylamino-2-propoxy)-copper, Cu-(emap)₂, which exhibits both high volatility and a low melting point. We also demonstrated PE-ALD of a thin Cu metal film using Cu-(emap)₂ and H₂ as a coreactant and prepared shiny metallic Cu films at 40 °C. The growth rate of Cu on Ru and SiO₂ substrates was 0.22 and 0.41 Å/cycle, respectively, and the resistivity of the films on the SiO₂ substrate was measured to be 4.1 μΩ·cm. No carbon, nitrogen, or oxygen contaminants were detected by X-ray photoelectron spectroscopic analysis of the resultant Cu metal films. Regarding film morphology, we verified by field-emission scanning electron microscopy that continuous films less than 10 nm thick were deposited on planar Ru and Co substrates. Therefore, we concluded that, compared with conventional Cu ALD precursors, Cu-(emap)₂ is better suited for Cu ALD manufacturing processes. The present results indicate that their application to TH-ALD could, in the future, enable Cu ALD on high-aspect-ratio substrates.