Browsing by Author "Kauppinen, Christoffer, Dr., VTT Technical Research Centre of Finland Ltd., Finland"

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Plasma-enhanced atomic layer deposition of aluminum nitride : characteristics and applications
(2024) Seppänen, Heli
School of Electrical Engineering | Doctoral dissertation (article-based)
Plasma-enhanced atomic layer deposition (PEALD) offers a variety of advantages over other thin film growth techniques, such as conformal coverage of complex surface structures. However, low crystallinity has been a drawback for PEALD aluminum nitride (AlN) thin films, which makes it impossible to use in many applications. In this thesis, a process for reaching a higher quality AlN grown with PEALD was studied. The process included an added plasma step into the PEALD cycle, atomic layer annealing (ALA). The results of this thesis are divided into material characteristics of the improved PEALD ALA AlN and use of PEALD ALA AlN and PEALD AlN thin films in diverse applications. AlN grown with the PEALD ALA process has improved stoichiometry, crystallinity, and c-axis orientation, and contained less carbon and hydrogen impurities. Amount of oxygen impurities has increased. Post deposition annealing at high temperature in vacuum reduced impurities but did not improve the crystallinity further. The substrate also has an impact on the obtained crystal quality of the film and could aid the AlN film to achieve the preferred structure. The ALA AlN was measured to be piezoelectric when deposited on an aluminum substrate. In addition, ALA AlN grows crystalline on vertical sidewalls. The use of PEALD ALA AlN as a transition layer for further metalorganic chemical vapor deposition regrowth was demonstrated successfully. Silicon surface passivation was demonstrated with PEALD AlN. The film provides passivation for the surface and the highest carrier lifetime was obtained with higher deposition temperature and a combination of annealing and firing as a postdeposition heat treatment.