Low-Temperature Atomic Layer Deposition of High Purity, Smooth, Low Resistivity Copper Films by Using Amidinate Precursor and Hydrogen Plasma

Agglomeration is a critical issue for depositing copper (Cu) thin films, and therefore, the deposition should be preferably performed below 100 degrees C. This work explores an atomic layer deposition (ALD) process for copper thin films deposited at temperature as low as 50 degrees C. The process employs copper(I)-N,N'-diisopropylacetamidinate precursor and H-2 plasma, which are both highly reactive at low temperature. The deposition process below 100 degrees C follows an ideal self-limiting ALD fashion with a saturated growth rate of 0.071 nm/cycle. Benefitting from the low process temperature, the agglomeration of Cu thin films is largely suppressed, and the Cu films deposited at 50 degrees C are pure, continuous, smooth, and highly conformal, with the resistivity comparable to PVD Cu films. In-situ reaction mechanism studies by using quartz crystal microbalance and optical emission spectroscopy are followed, and the results confirm the high reactivity of the Cu amidinate precursor at low temperature. To the best of our knowledge, this is the first successful implementation of metal amidinate precursors for low-temperature (similar to 50 degrees C) ALD process. The strategy of using metal amidinate precursors in combination with highly reactive H-2 plasma is believed to be extendable for the depositions of other pure metals at low temperature.