Pinacolborane as a Reducing Agent in the Atomic Layer Deposition of Copper and Bismuth

In this work, we developed a new atomic layer deposition (ALD) process for copper and bismuth metal thin films using pinacolborane (HBpin) to reduce the metals from their respective alkoxide precursors bis-(1-dimethylamino-2-propoxy)-copper-(II) (Cu-(dmap)₂) and tris-(2,3-dimethyl-2-butoxy)-bismuth-(III) (Bi-(OCMe₂ ⁱPr)₃). A comprehensive ALD process study was conducted with copper at deposition temperatures of 65-130 °C, and self-limiting reactions were confirmed. At 80 °C, the copper process had a growth rate of 0.25 Å/cycle, and fully continuous films had a resistivity of 4 μΩ cm. The growth of Cu was unexpectedly found to be inherently selective, with negligible growth on Pt and Co surfaces, as opposed to growth on surfaces of nonmetals such as Si, TiN, and soda lime glass. Metallic bismuth was also successfully deposited at 90 °C, but this process was not studied in further detail.