| AVS 65th International Symposium & Exhibition | |
| Thin Films Division | Tuesday Sessions |
| Session TF-TuM |
| Session: | Emerging Applications for ALD |
| Presenter: | Jasmine Wallas, University of Colorado at Boulder |
| Authors: | J.M. Wallas, University of Colorado at Boulder J.A. Murdzek, University of Colorado at Boulder D.K. Lancaster, University of Colorado at Boulder A.S. Cavanagh, University of Colorado at Boulder S.M. George, University of Colorado at Boulder |
| Correspondent: | Click to Email |
YF3 and YOxFy are materials with excellent chemical and thermal stability. YF3 and YOxFy have both demonstrated exceptional corrosion resistance to highly reactive plasmas. In this work, YF3 atomic layer deposition (ALD) was developed using tris(butylcyclopentadienyl) yttrium and HF-pyridine as the reactants. The ALD of YOxFy alloys was also demonstrated with tunable control of the oxygen and fluorine stoichiometry. This tunable control was difficult because of the rapid exchange of oxygen by fluorine in Y2O3 and YOxFy alloys during HF exposures.
In situ quartz crystal microbalance (QCM) analysis of YF3 ALD revealed linear mass changes and self-limiting behavior using tris(butylcyclopentadienyl) yttrium and HF-pyridine as the reactants. The mass gain per cycle (MGPC) was 21.5 ng cm-2 at 225°C. The growth rate of YF3 ALD was also determined to be 0.3 Å per cycle by ex situ X-ray reflectivity analysis. Energy dispersive spectroscopy (EDS) of a cross-section of the YF3 film yielded a uniform 3:1 ratio of F:Y with low impurities.
YOxFy alloys were deposited using H2O together with the tris(butylcyclopentadienyl) yttrium and HF-pyridine reactants. However, control of the composition of the YOxFy alloys was complicated by the facile exchange of oxygen by fluorine during the HF exposures. The oxygen/fluorine exchange was most obvious during HF exposures on Y2O3 ALD films when a large mass gain was observed during fluorination. The Y2O3 fluorination reaction is believed to be: Y2O3 + 6 HF → 2 YF3 + 3 H2O. In addition to the large mass gain, the presence of fluorine throughout the entire film was revealed by X-ray photoelectron spectroscopy (XPS) measurements with depth-profiling. The XPS depth-profiling results are consistent with rapid fluorine diffusion in the Y2O3 and YOxFy films.
Various super-cycles were employed to obtain YOxFy alloys with particular F:O ratios. The most reliable method for composition control was defined by performing HF exposures between intervals of Y2O3 ALD. The number of Y2O3 ALD cycles and the length of the HF exposure could be varied to produce YOxFy alloy films with tunable and consistent composition as measured with XPS depth-profiling. The growth rate of the YOxFy alloy films was dependent on the number of Y2O3 ALD cycles before the HF exposures. The super-cycles with a larger number of Y2O3 ALD cycles before the HF exposures produced higher growth rates resulting from the higher growth rate of 0.8 Å per cycle for Y2O3 ALD.
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