| AVS 63rd International Symposium & Exhibition | |
| Thin Film | Tuesday Sessions |
| Session TF-TuM |
| Session: | Advanced CVD and ALD Processing, ALD Manufacturing and Spatial-ALD |
| Presenter: | Michael Reinke, Empa, Swiss Federal Laboratories for Materials Science and Technology, Switzerland |
| Authors: | M. Reinke, Empa, Swiss Federal Laboratories for Materials Science and Technology, Switzerland Y. Kuzminykh, Empa, Swiss Federal Laboratories for Materials Science and Technology, Switzerland P. Hoffmann, Empa, Swiss Federal Laboratories for Materials Science and Technology, Switzerland |
| Correspondent: | Click to Email |
All chemical vapor deposition (CVD) processes rely on the decomposition of precursors on the substrate to deposit the desired material. While in thermal CVD, high substrate temperatures are employed to induce pyrolytic decomposition of the adsorbed precursor molecules, lower temperatures are applied in atomic layer deposition (ALD) to deliberately avoid pyrolysis of the precursor and favor self-saturating surface reactions between two or more reactive partners.
A crucial aspect in ALD processes is the proper separation of reactive partners in order to prevent spontaneous gas phase condensation; this is most commonly achieved in a vacuum process where the reaction volume is sequentially filled with one of the different reactive partners and their exposure is separated by a purge time. Contrary, in spatial ALD the substrate is moved through different reaction volumes that are continuously filled with one reactive partner allowing decreased cycle times and, consequently, increased growth rates.
An alternative way of separating reactive precursor molecules is realized in a high vacuum chemical vapor deposition (HV-CVD) process. If the background pressure during the deposition is sufficiently low, the free mean path of precursor molecules exceeds their trajectory length between effusion source and substrate – in this way gas phase reactions are avoided and the substrate can be simultaneously exposed even to reactive ALD chemistries.
Exemplary, we will review in detail the thin film deposition process of titanium dioxide utilizing titanium tetraisopropoxide (TTIP) and water. We demonstrate the continuous CVD growth of titanium dioxide thin films within the ALD window and show that even selective growth methods applicable in ALD are suitable for HV-CVD processes.
We will discuss a comprehensive surface kinetic model of the TTIP surface reactions, including hydrolysis and pyrolysis. The model was fitted to the large number of experimental results and can describe the experimental observations ranging from thermal CVD depositions to co-depositions with water in the ALD window. The model’s good agreement with the experimental data in a wide parameter range suggests its high relevance.
The proposed model and the derived process parameters can be used for quantitative predictions of the precursor behavior in CVD processes, such as prediction of growth rates, deposition efficiencies and pyrolytic decomposition threshold. It reveals furthermore insight in the ALD process itself and allows modelling of the ALD growth rates - including the position of the ALD window.