Wednesday, September 12, 2018

Thermal Atomic Layer Etching of copper by University of Illinois at Urbana-Champaign

Copper is a wonder metal used in moth integrated circuits but is very difficult to etch by a dry process. That is why copper is typically removed by wet chemistry or rather brutal CMP processes. So now quite fantastic news for all BEOL people who have had all kinds of problem etching copper or for those FEOL people who absolutely do not like copper - now there is a way to thermally etch copper as presented in the publication below by scientists form University of Illinois at Urbana-Champaign in the United States.

Thank you Prof. Pedersen for sharing this article on Twitter using the hashtag #ALEtch (#ALDep for ALD).

According to the abstract, the published ALE method of copper relies on:
  • a cyclic exposure to an oxidant and hexafluoroacetylacetone (Hhfac) at 275°C
  • exposure of a copper surface to molecular oxygen, O2, a weak oxidant, forms a ∼0.3 nm thick layer of Cu2O, which is removed in a subsequent step by exposure to Hhfac. 
  • the process has high selectivity and does not attack dielectrics such as SiO2 or SiNx 
  • the surface reactions are self-limiting
  • the roughness of the copper surface increases slowly over successive etch cycles 
Promising is also that rhermochemical and bulk etching data indicate that the approach should also work for other metals.

Thermal Atomic Layer Etching of Copper by Sequential Steps Involving Oxidation and Exposure to Hexafluoroacetylacetone

doi: 10.1149/2.0211809jss ECS J. Solid State Sci. Technol. 2018 volume 7, issue 9, P491-P495

Screendump from ECS Journal of Solid State Science and Technology (http://jss.ecsdl.org/content/7/9/P491.abstract?etoc 2018.12.09)