Efficient Process for Direct Atomic Layer Deposition of Metallic Cu Thin Films Based on an Organic Reductant

We report a promising approach to use an organic reductant for in situ atomic layer deposition (ALD) of metallic copper films. The process is based on sequentially pulsed precursors copper acetyl acetonate (acac), water, and hydroquinone (HQ) and yields crystalline copper films at temperatures as low as <200 °C with an appreciably high deposition rate of ∼2 Å/cycle. Deposition parameters are explored for the process m × [ n × (Cu(acac) 2 –H 2 O)–HQ] with several values of m and n, keeping m × n fixed to 500. The films are found crystalline with metallic copper as the main phase, but different trace amounts of Cu 2 O are observed when the HQ pulse frequency decreases below 1 / 5 . The as-deposited copper films are shiny and specularly reflecting and show metallic-type electrical conductivity. The absolute resistivity of the films estimated at room temperature is in the order of 2–5 μΩ cm, having a sizable contribution, with 0.5 μΩ cm from residual resistivity as a result of impurities and/or imperfections. We believe that the new process could yield benefits in interconnect applications.