| AVS 64th International Symposium & Exhibition | |
| Plasma Science and Technology Division | Thursday Sessions |
| Session PS+TF-ThA |
| Session: | Plasma Enhanced ALD |
| Presenter: | Alberto Perrotta, Graz University of Technology, Austria |
| Authors: | A. Perrotta, Graz University of Technology, Austria J. Pilz, Graz University of Technology, Austria A.M. Coclite, Graz University of Technology, Austria |
| Correspondent: | Click to Email |
Wurtzite-structured ZnO thin films have been extensively investigated because of their unique optical, electrical, and piezoelectric properties, making it the material of choice in various applications such as transparent conducting electrodes, surface acoustic wave devices, and as sensors. In engineering ZnO-based devices, the material characteristics have to meet specific requirements in terms of opto-chemical and electrical properties and crystalline structure, together with very high conformality and thickness control. Plasma-assisted atomic layer deposition (PA-ALD) has been shown able to deposit very high quality ZnO thin films, combining the low process temperature with the exceptional atomic-thickness control. Furthermore, the properties of the material can be tuned by varying the plasma characteristics, making it suitable to adapt the material to specific applications.
In this contribution, high quality ZnO thin films have been deposited by PA-ALD optimized at room temperature, adopting diethyl zinc (DEZ) and oxygen plasma. The properties of the material have been investigated as a function of the radio frequency plasma power and plasma exposure time, and characterized by X-ray diffraction (XRD), gracing incidence XRD with synchrotron radiation, spectroscopic ellipsometry (SE), and X-ray photoelectron spectroscopy (XPS). The X-ray diffraction patterns of polycrystalline ZnO thin films showed rather preferred (100) orientation and XPS analysis showed the complete removal of the DEZ carbon ligands, confirming the possibility to obtain high quality crystalline ZnO at room temperature. Furthermore, the effect of the plasma power on the opto-chemical properties, growth, and crystalline structure has been investigated. Finely tuning of the optical properties of the PA-ALD ZnO layers has been achieved, with refractive index ranging between 1.82 and 1.89 at 633 nm. Moreover, the absorption has been found to increase and shift in the visible range at low plasma power. In addition, XRD showed a distortion of the (100) peak at low and high plasma power, indicating the possibility to vary the crystallite size as a function of the plasma parameters.
As an outlook, the optimized PA-ALD process at room temperature allows the deposition of ZnO on thermo-sensitive nanostructured templates, inferring the possibility to adopt it in engineering (flexible) structured devices.