Description
Area-selective atomic layer deposition (AS-ALD) has become a hot topic in the field of nanofabrication for combining self-aligned patterning with precise thickness control and high conformality of the resulting thin films. Over the past years, area-selective growth has been successfully demonstrated for a variety of materials. However, to date, most processes have focussed on the selective deposition on inorganic-inorganic or inorganic-organic substrate combinations employing thermal ALD.It is our aim to extend area-selective deposition processes to polymer-polymer patterns, thus accessing new applications fields such as organic electronics or nanodevice fabrication based on 2-photon polymerization. The use of plasma-enhanced ALD (PE-ALD) instead of thermal ALD provides a completely new approach towards area-selective growth by using the etching effect of the plasma on the polymer substrates to achieve different growth delays.
As an essential step towards area-selectivity, nucleation and initial growth of ZnO on two different vapor deposited homopolymer thin films - ethylene glycol dimethacrylate (EGDMA) and hydroxyethylmethacrylate (HEMA) - are investigated using in-situ spectroscopic ellipsometry. This is the first time that an initial growth study is conducted for PE-ALD on polymer thin films.
Our results show that film formation is a consequence of two competing processes: ZnO ALD growth and plasma etching of the polymer substrates. 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. This etching-induced growth delay is found to depend both on the oxygen plasma power and the type of polymer. At 30 W plasma power, ZnO growth starts to dominate after 3 and 5 ALD cycles for EGDMA and HEMA respectively with a total polymer thickness loss of less than 2 nm. At 60 W, stronger etching (3.2 and 3.8 nm/10 s plasma pulse) leads to higher growth delays of 13 and 20 cycles. This material-dependent difference in growth delay is exactly what is needed for area-selective growth.
Raising plasma power further results in higher etching rates (5.7 and 8.3 nm/plasma pulse at 100 W) but does not further increase the growth delays. The resulting ZnO films (20 nm thick) are very smooth with roughness values ranging from 50 pm at 30 W plasma power to 350 pm at 100 W.
Our work provides vital knowledge about the initial growth of ZnO during PE-ALD on polymer thin films and illustrates a novel approach towards area-selective deposition by exploiting material-dependent growth delays induced by plasma etching.
| Period | 21 Oct 2021 → 30 Nov 2021 |
|---|---|
| Event title | AVS 67th Virtual Symposium |
| Event type | Conference |
| Degree of Recognition | International |