Formation of metal oxide particles in atomic layer deposition during the chemisorption of metal chlorides: A review

As has been known for a decade, metal oxide particles can form in a single reaction of gaseous metal chlorides with solid oxides. This is an undesirable effect in the fabrication of thin films by atomic layer deposition (ALD). This work reviews the experimental results related to the metal oxide particle formation and the mechanisms suggested to account for it. The suggested mechanisms cannot explain the observations, but systematic analysis of the possible reaction paths delivers one reaction mechanism candidate, based on a reaction between surface chlorine groups and the hydroxyl groups of gaseous metal hydroxychloride intermediates. The consequences of the proposed mechanism are discussed.