Introducing the Revolutionary Open-Air Spatial ALD of Cu, Cu2O, and CuO

Copper is widely used for interconnecting transistors on a chip and as an electrode material due to its low resistivity and high thermal stability against electromigration. Copper oxides are attractive for photovoltaics, catalysis, and sensors.

Industrial copper metallization methods include chemical vapor deposition (CVD), electroless deposition, and electroplating. Copper oxide thin films with varying properties and oxidation states (Cu₂O, CuO) can be obtained through sputtering, pulsed laser deposition (PLD), thermal annealing, and electrodeposition.

ALD can create oxides, nitrides, and metals. It has gained momentum for the deposition of metallic copper in recent years, be it thermal or plasma enhanced ALD. ALD of Cu₂O has been reported through the hydrolysis of precursors containing Cu⁺ ions and that for CuO has been reported using Ozone or Oxygen plasma as co-reactants.

Pure metallic and semiconducting films without the need for a sealed vacuum chamber or the addition of a reducing atmosphere or plasma.

Although ALD has unique advantages (atomic level thickness control, excellent uniformity and conformality based on self-limiting surface reactions, relatively low deposition temp., etc.), is relatively slow (except for batch reactors) and typically performed in vacuum. Atmospheric pressure spatial ALD (AP-SALD) is a promising alternative, allowing fast and scalable deposition of high-quality thin films using inert gas barriers to spatially separate precursor and co-reactant and moving the substrate underneath them.

One step ahead, in a paper by Sekkat et al., the Dr. Muñoz Rojas’ group at Universite Grenoble Alpes, CNRS, Grenoble, France, recently published the use of “open air” AP-SALD as a low-temperature and high-throughput approach to selectively pattern Cu, Cu₂O, and CuO on a substrate in a single process run by using single Cu precursor Cu(I)(hfac)(tmvs) and only changing the co-reactant (H₂O for Cu₂O, O₃ for CuO, and N₂ for Cu). 

The resolution is not as precise as can be obtained with area selective ALD (ASD) or micro head ALD (Atlant 3D), but it’s remarkable that they can create pure metallic and semiconducting films without the need for a sealed vacuum chamber or the addition of a reducing atmosphere or plasma.  The demonstration of these copper based processes demonstrate what is possible under atmospheric conditions, and can expand the number of recipes for  atmospheric spatial ALD and micro head ALD enormously.

The precursor and co-reactants were injected continuously from the manifold head onto the substrate that oscillated at a scanning speed of 8 cm/s for metallic Cu deposition and 10 cm/s for CuO and Cu2O deposition. Films were deposited on borosilicate glass substrates with a surface area of 3 x 5 cm2.

The full research paper by Sekkat et al is available here.