Emerging electronic materials and device designs require new capabilities for nanoscale localized material placement and lateral position control that are currently not well developed. While steady-state ALD reactions are well explored for many metal oxides and metals, the specific chemical sequences involved in growth initiation, i.e. the first few ALD cycles, are often less studied. Moreover, while it is well known that many ALD processes show a propensity to nucleation preferentially on some substrates versus others, emerging studies show that these differences can be exploited to achieve well-controlled inherent selective deposition, without the need for integrated blocking layers. To better classify and understand mechanisms for lateral-scale control of thin film growth, our group explores how surface composition affects initial nucleation reactions during metal and metal oxide ALD. We find for example, that tungsten nucleation during ALD using WF6 and SiH4 is strongly affected by the density and local bonding structure of surface OH groups on SiO2. For example, removing clustered OH groups by annealing before ALD tends to promote nucleation, whereas, removing vicinal OH groups tends to delay nucleation, indicating that vicinal OH groups are more reactive with WF6. Other studies of nucleation reactions during TiO<sub>2</sub> ALD on Si-H and SiO<sub>2</sub> surfaces show that nucleation proceeds rapidly on silicon oxide, but the rate of nucleation on Si-H depends strongly on the surface preparation and initial wetting contact angle. Our group also explores novel atomic layer etching and atomic-scale passivation reactions that can be further used to enhance substrate selectivity during ALD. The impact of understanding surface reaction processes will be discussed as it relates to challenges for selective-area ALD and advanced nanoscale material patterning.

Surface reactions for area-selective atomic layer deposition and thermal atomic layer etching of metals and dielectrics

255th National Meeting (2018)

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