| AVS 66th International Symposium & Exhibition | |
| 2D Materials | Monday Sessions |
| Session 2D+AP+EM+MI+NS+PS+TF-MoA |
| Session: | 2D Materials Growth and Fabrication |
| Presenter: | Shashank Balasubramanyam, Eindhoven University of Technology, The Netherlands |
| Authors: | S. Balasubramanyam, Eindhoven University of Technology, The Netherlands M.J.M. Merkx, Eindhoven University of Technology, The Netherlands W.M.M. Kessels, Eindhoven University of Technology, The Netherlands A.J.M. Mackus, Eindhoven University of Technology, The Netherlands A.A. Bol, Eindhoven University of Technology, The Netherlands |
| Correspondent: | Click to Email |
With continued downscaling of device dimensions, ultra-thin two dimensional (2D) semiconductors like WS2 are considered as promising materials for future applications in nanoelectronics. At these nanoscale regimes, device fabrication with precise patterning of critical features is challenging using current top-down processing techniques. In this regard, area-selective atomic layer deposition (AS-ALD) has emerged as a promising candidate for bottom-up processing to address the complexities of nanopatterning. Till date, AS-ALD of metals1 and dielectrics2 have been successfully demonstrated. However, AS-ALD of 2D materials has remained elusive. In this contribution, we demonstrate area-selective deposition of 2D WS2 nanolayers by using a three-step (ABC-type) plasma-enhanced ALD process.
AS-ALD of WS2 was achieved by using acetylacetone (Hacac) inhibitor (A), bis(tertbutylimido)-bis(dimethylamido)-tungsten precursor (B), and H2S plasma (C) pulses. This process resulted in immediate growth on SiO2 while a significant nucleation delay was observed on Al2O3, as determined from in-situ spectroscopic ellipsometry (SE) and ex-situ X-ray photoelectron spectroscopy (XPS) measurements. The surface chemistry of this selective process was analysed by in-situ Fourier transform infrared spectroscopy (FTIR). The analyses revealed that the inhibitor adsorbed on the Al2O3 surface, blocking precursor adsorption, while little or no inhibitor adsorption was detected on the SiO2 surface where WS2 was readily deposited. Furthermore, the area-selective growth was demonstrated on SiO2 samples with patterned Al2O3 on top. On SiO2, WS2 could be deposited with angstrom-level thickness control.
To improve the crystallinity, the AS-ALD WS2 films were annealed at temperatures within the thermal budget of industrial semiconductor processing (≤ 450°C). The annealed films exhibited sharp Raman peaks, which is a fingerprint of highly crystalline WS2. Furthermore, Raman line scans over the patterns showed very sharp peak intensity transitions at the SiO2-Al2O3 interface which confirmed that annealing had no impact on selectivity.
To summarize, this work pioneered the combination of two key avenues in atomic-scale processing: area-selective growth and ALD of 2D materials. It is expected that the results of this work will lay the foundation for area-selective ALD of other 2D materials.
1 R. Chen and S.F. Bent, Adv. Mater. (2006).
2 A. Mameli, M.J.M. Merkx, B. Karasulu, F. Roozeboom, W.M.M. Kessels and A.J.M. Mackus, ACS Nano (2017).