Description
In recent years, atomic layer deposition (ALD) on polymer substrates has attracted increasing interest due to potential applications in organic electronics and photovoltaics, as well as for the surface functionalization of packaging and biomaterials. However, the inherent porous structure of polymeric substrates often leads to non-ideal ALD processes that result in precursor diffusion and subsurface growth of the deposited material.The use of plasma-enhanced ALD (PE-ALD) is known to enhance nucleation due to the surface-activating effect of plasma and can be expected to significantly reduce subsurface diffusion, enabling the surface-limited deposition of thin conformal coatings. However, plasma can also have detrimental effects on polymeric substrates causing polymer degradation or etching.
In our work, we have investigated the initial growth of piezoelectric ZnO during PE-ALD on different polymer thin films deposited by initiated chemical vapor deposition (iCVD). iCVD is a prominent method to deposit highly uniform thin films of a wide range of (functional) polymers while fully retaining their rich chemistry. ZnO growth was monitored via in-situ spectroscopic ellipsometry (SE) and the resulting thin films were further characterized in terms of crystallinity, interface and surface morphology and elemental composition. To gain a better understanding of how the chemical structure of the polymer influences ZnO thin film formation, polymers exhibiting varying degrees of reactivity with the ALD precursor were studied. Furthermore, the influence of plasma power on growth behavior was investigated.
Our results show that film formation on the iCVD polymers is a consequence of two competing processes: ZnO PE-ALD growth and plasma etching of the polymer substrate. During the initial ALD cycles, polymer etching dominates, resulting in an overall decrease in thickness. At a certain point, ZnO growth takes over and the regime of normal ALD growth behaviour is entered. The strength of etching is proportional to the applied plasma power and depends strongly on the type of polymer. Despite the initial etching, the resulting thin films exhibit sharp interfaces and a quality, in terms of surface roughness, crystallinity and ZnO density, comparable to those of ZnO deposited on silicon.
This study sheds light on the mechanisms governing initial growth during PE-ALD of ZnO on different polymers and illustrates the potential of the combined use of iCVD and PE-ALD as means to achieve highly uniform and smooth multilayer structures that could be applied in a wide range of functional devices including sensing or actuation.
| Period | 27 Jun 2022 |
|---|---|
| Event title | 22nd International Conference on Atomic Layer Deposition: ALD/ALE 2022 |
| Event type | Conference |
| Location | Ghent, BelgiumShow on map |
| Degree of Recognition | International |