Description
The trend towards ever smaller feature sizes in microelectronic device architectures fuels the interest in vapor-based deposition techniques that allow for the fabrication of highly uniform and conformal thin films. Initiated chemical vapor deposition (iCVD) and plasma-enhanced atomic layer deposition (PE-ALD) are two important candidates able to meet these requirements. While PE-ALD is a powerful tool to deposit thin films of various inorganic compounds with precise control of film thickness at low temperatures, iCVD allows for the thin film deposition of a wide range of (functional) polymers while fully retaining their rich chemistry.By combining iCVD with PE-ALD, highly conformal and smooth organic-inorganic multilayers can be obtained that represent the basic building block of a whole range of applications from thin film encapsulations to (bio-)sensors and other functional devices. A prerequisite for the successful integration of these techniques into novel device architectures is a thorough understanding of the growth processes and interface formation. While the mechanisms determining growth during thermal ALD on polymers are quite well-understood, little is known on PE-ALD growth on organic substrates.
Our work aims to fill this gap by providing fundamental insights into the growth process and interface formation during PE-ALD of ZnO on selected iCVD polymer thin films. Initial growth of ZnO on the iCVD polymers was monitored via in-situ spectroscopic ellipsometry 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 precursor-substrate and plasma-substrate interactions, three polymers with varying reactivity with the ALD precursor were studied: hydroxyl-rich poly hydroxyethylmethacrylate (pHEMA), carbonyl-rich poly ethylene glycol dimethylacrylate (pEGDMA), and the weakly reactive poly(2,4,6,8-tetravinyl-2,4,6,8-tetramethyl cyclotetrasiloxane) (pV4D4).
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 with almost negligible thickness losses for pV4D4 and strongest etching for pHEMA. 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.
| Period | 31 May 2022 |
|---|---|
| Event title | European Materials Research Society Spring Meeting 2022: EMRS spring meeting 2022 |
| Event type | Conference |
| Location | Virtuell, TransnationallyShow on map |
| Degree of Recognition | International |