Film Nucleation and Substrate Selectivity

Area-selective thin film deposition is important for continuing the historical shrinking of advanced semiconductor devices into the sub-10 nm regime. In particular, reliable Area-Selective ALD  (AS-ALD) may help enable feature patterning and alignment to underlying structures, as well as improve overlay and edge definition accuracy. Several atomic layer deposition (ALD) processes show inherent propensity for substrate-dependent nucleation, including metals such as tungsten and cobalt, as well as dielectrics such as HfO2 and TiO2.  Our work focuses on understanding the basic steps that proceed when ALD metals and dielectrics begin to grow on various substrates.  By understanding growth initiation, we find that we devise schemes to modify and control film nucleation and thereby expand the process “window” available for AS-ALD processes.

The image at left shows AS-ALD of tungsten prepared in our lab on Si and SiO2. The W nucleates readily on Si, but only slowly on SiO2.  In this study, we showed that the rate of W nucleation on SiO2 could be slowed by adding H2 to the ALD reactants, thereby expanding the inherent selectivity “window”.


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