Controlled ALE-type recess of molybdenum for future logic and memory applications

Molybdenum (Mo) is a promising metal for applications requiring low resistivity interconnects or contact lines in small dimensions. Etching of polycrystalline metals like Mo with conventional etching methods can be challenging because of the increased surface roughness and non-uniform recess. In this paper we describe a novel sequential etching method comprising two steps. The first step is an oxidation step in ozone (O3) at elevated temperatures in the range of 180°C–290°C resulting in a smooth metal/oxide interface. The second step is a selective oxide dissolution. The benefits of this cyclic, ALE-type recess over continuous wet-etching processes are improved etch-rate control and reduced surface roughness. Finally, we also demonstrated lateral recess of Mo word lines in 3D-NAND like structures resulting in uniformly recessed, straight-walled word lines.