| AVS 65th International Symposium & Exhibition | |
| Thin Films Division | Tuesday Sessions |
| Session TF+PS-TuA |
| Session: | Atomic Layer Processing: Chemistry & Surface Reactions for Atomic Layer Processing |
| Presenter: | Tyler Myers, University of Colorado at Boulder |
| Authors: | T.J. Myers, University of Colorado at Boulder A.M. Cano, University of Colorado at Boulder J.W. Clancey, University of Colorado at Boulder D.K. Lancaster, University of Colorado at Boulder S.M. George, University of Colorado at Boulder |
| Correspondent: | Click to Email |
Atomic layer deposition (ALD) is typically described by the self-limiting reaction of precursors with surface species that leads to controlled thin film growth. Missing from this picture is the possibility that the precursors can also undergo exchange reactions and convert the surface of the initial substrate to a new material. These exchange reactions are expected if the conversion produces a more thermodynamically favorable reaction product. These exchange reactions may be common during ALD nucleation.
In this study, the exchange between Zn and Al is explored during the initial reaction of trimethylaluminum (TMA) on ZnO films during Al2O3 ALD at temperatures from 150-250°C. The exchange is evident from a variety of experimental measurements. Fourier transform infrared (FTIR) investigations detect absorbance changes consistent with ZnO loss and Al2O3 gain after the TMA reaction on ZnO ALD films. Quadrupole mass spectrometry (QMS) measurements also observe Zn(CH3)2 reaction products as expected from the conversion reaction: 3ZnO + 2Al(CH3)3 → Al2O3 + 3Zn(CH3)2. In addition, studies of the effect of TMA exposures on ZnO nanoparticles with a diameter of ~10 nm measured the conversion of ZnO to Al2O3. The conversion produces a large mass loss that is consistent with the formation of an Al2O3 surface layer. The ZnO to Al2O3 conversion is also self-limiting as a function of TMA exposure.
X-ray photoelectron spectroscopy (XPS) and X-ray reflectivity (XRR) investigations are also consistent with the conversion of the surface of ZnO ALD films to Al2O3 after the initial TMA exposure. The XPS and XRR measurements both yield an Al2O3 surface layer with a thickness of ~1.0 nm on the ZnO ALD film. In addition, quartz crystal microbalance (QCM) measurements detect a substantial conversion of ZnO to Al2O3 after the initial TMA exposure during Al2O3 ALD. The QCM studies reveal that the mass losses are much more pronounced for thin ZnO films compared with thick ZnO films. In addition, the mass losses are more for ZnO surfaces terminated with Zn-CH3CH3 species compared with Zn-OH species.
These studies of the exchange between Zn and Al during the initial reaction of TMA on ZnO illustrate that ALD precursors can convert the surface of the initial substrate to a new material. These exchange reactions must be considered when analyzing ALD nucleation.