Shedding light on the initial growth of ZnO during plasma-enhanced atomic layer deposition on vapor-deposited polymer thin films

Abstract

Interest in atomic layer deposition (ALD) processes on polymer substrates is fueled by the increasing rise of organic electronics and polymer-based nanodevices. This study provides new insights into the initial growth and interface formation during plasma-enhanced ALD (PE-ALD) of ZnO on poly ethylene glycol dimethylacrylate (pEGDMA) and poly 2-hydroxyethyl methacrylate (pHEMA) thin films, both deposited by initiated chemical vapor deposition (iCVD). In-situ spectroscopic ellipsometry showed that PE-ALD growth on the investigated polymers is a result of two competing processes: plasma etching of the polymer substrate and ZnO nucleation and growth. During the first 10–15 ALD cycles, polymer etching was found to prevail until at a certain point (depending on plasma power and type of polymer) ZnO growth takes over and the regime of linear ALD growth is entered. On pHEMA, though more sensitive to etching, ZnO film formation starts early on, whereas on pEGDMA, subsurface nucleation and island growth appear to dominate the initial stage of deposition. Despite the initial etching, resulting ZnO films are smooth and of comparable structural quality to those grown on silicon. These findings contribute to a deeper understanding of PE-ALD growth on polymers providing knowledge essential for the successful development of new processes and applications.