| AVS 63rd International Symposium & Exhibition | |
| Thin Film | Monday Sessions |
| Session TF+PS+SE-MoA |
| Session: | Plasma-based Deposition Techniques and Film Characterization |
| Presenter: | Agnes Granier, IMN, University of Nantes CNRS, France |
| Authors: | A. Granier, IMN, University of Nantes CNRS, France S. Elisabeth, IMN, University of Nantes CNRS, France R. Michaud, IMN, University of Nantes CNRS, France N. Gautier, IMN, University of Nantes CNRS, France M. Richard Plouet, IMN, University of Nantes CNRS, France M. Carette, IEMN CNRS/Université Lille 1, France A. Goullet, IMN, University of Nantes CNRS, France |
| Correspondent: | Click to Email |
TiO2 thin films are good candidates for the development of passive optical components due to high optical refractive index (1.8 < n < 2.7 at 633 nm) combined with high transparency in the visible range. They are compatible with semiconductor technologies and can be synthesized at low temperature by plasma enhanced chemical vapor deposition (PECVD). PECVD is known for its ability to prepare amorphous or partially crystallized films at low temperature and to tune the film composition and optical properties. In the case of TiO2, columnar polycrystalline anatase films can be prepared by PECVD at substrate temperature less than 150°C. Whereas these TiO2 films are very attractive for photocatalysis, their columnar structure and low optical gap (3.2 eV) appear to be drawbacks for optical applications. Adding a small amount of silicon to TiO2 allows both obtaining amorphous films and increasing the optical gap, which is highly suitable for optical applications.
In this study, TiO2 and Ti-Si-O films were deposited in a low pressure rf inductively coupled plasma (ICP) from titanium tetraisopropoxide (TTIP - Ti(OC3H7)4) and hexamethyldisiloxane (HMDSO - SiO2(CH3)6) vapors mixed with oxygen. The structure and chemical composition of the films were investigated by X-ray diffraction, photoelectron spectroscopy, Fourier transform infrared spectroscopy and Raman spectroscopy. The morphology of the thin films was characterized by scanning and transmission electron microscopies. The optical properties were investigated by UV -Visible spectroscopic ellipsometry and absorption spectroscopy. When deposited at the floating potential, the TiO2 films deposited in the continuous mode in oxygen rich O2/TTIP ICP plasmas were previously shown to be columnar and highly crystallized in the anatase form. As silicon is added to titanium, the films become amorphous. Their refractive index decreases and their optical gap increases [1].
Here, we investigate the effects of pulsing both the rf power and the precursor injection on the film structure and optical properties.
On the one hand, in the case of TiO2 and Ti-O-Si films, the pulse frequency was fixed at 1 kHz and the duty cycle was varied from 100 to 10%. Pulsing the power allows to decrease the deposition temperature (down to about 50°C) while conserving the anatase structure in the case of TiO2 films, so that anatase and amorphous high refractive index Ti-Si-O films can be deposited on polymer substrates.
On the other hand, TTIP and HMDSO flow rates have been pulsed, either to get benefit from oxygen plasma treatment following oxide deposition or to deposit TiO2/SiO2 stacks.
[1] D. Li et al, Plasma Processes and Polymers, 2016