Atomic layer deposition and selective etching of ruthenium for area-selective deposition: Temperature dependence and supercycle design

Abstract

For future sub-5 nm technology nodes, the fabrication of semiconductor devices will likely involve the use of area-selective atomic layer deposition (ALD). While area-selective ALD processes have been reported for a variety of materials, most approaches yield a limited selectivity, for example, due to growth initiation at defects or impurities on the non-growth area. Recently, we demonstrated that Ru ALD can be combined with selective etching to achieve area-selective ALD of metal-on-metal with high selectivity. Cycles consisting of an O2 plasma and an H2 gas dose were integrated in an ALD-etch supercycle recipe to remove unwanted nuclei on the SiO2 non-growth area, while obtaining deposition on the Pt or Ru growth area. The current work discusses the challenging compromise that needs to be made between selectivity and net deposition, considering that the material is also removed from the growth area. After investigating deposition between 100 and 200 °C on SiO2, Al2O3, Pt, and Ru in terms of selectivity and net deposition, a substrate temperature of 150 °C was selected since the difference in Ru thickness on Pt and SiO2/Al2O3 was maximum at this temperature, even though still some deposition occurred on the SiO2 and Al2O3 non-growth areas. Different ALD-etch supercycles were studied, using varying O2 plasma etch times and etch frequencies. The amount of the (undesired) material deposited on the SiO2 non-growth area was quantified, demonstrating that the selectivity improved for longer O2 plasma times. On the basis of the results, a simple mathematical description of the nucleation, growth, and etching effects during ALD-etch supercycles is discussed, which can assist the design of future area-selective deposition processes. Overall, this work illustrates how ALD and etch processes can be tuned to simultaneously obtain a high selectivity and a high net deposition of the material at the desired locations.