In this study, we evaluate the effect of water vapor on the plasma processing of materials using a model system consisting of a well-characterized radio-frequency (RF) plasma jet, controlled gaseous environment, and polystyrene (PS) as target material. We find that the effluent of Ar/H2O plasma jet is capable of (1) etching polymers with relatively high etch rate and (2) weakly oxidizing the etched polymer surface by forming O containing moieties. When increasing the treatment distance between the polymer and the Ar/H2O plasma, we find that the polymer etch rate drops exponentially whereas the O elemental composition of the etched surface shows a maximum at intermediate treatment distance. The OH density in the Ar/H2O jet was measured near the substrate surface by laser induced fluorescence (LIF), and the density change of the OH radicals with treatment distance is found to be consistent with the exponential decrease of polymer etch rate, which indicates that OH may play a dominant role in the polymer etching process. A control experiment of Ar/H2 plasma shows that the observed fast polymer etching by Ar/H2O plasma cannot be attributed to H atoms. By correlating the OH flux with the polymer etch rate, we estimated the etching reaction coefficient (number of C atoms removed per OH radical from the gas phase) of OH radicals as ~10-2. The polymer etch rate of Ar/H2O plasma is enhanced as the substrate temperature is lowered, which can be explained by the enhanced surface adsorption of gas phase species. For the same molecular admixture concentration and plasma power, we find that Ar/H2O/O2 plasma has much reduced etching efficiency compared to either Ar/H2O or Ar/O2 plasma.
Luan, Pingshan, et al. "Effect of water vapor on plasma processing at atmospheric pressure: polymer etching and surface modification by an Ar/H<sub>2</sub>O plasma jet." Journal of Vacuum Science and Technology A, vol. 37, no. 3, Apr. 2019. https://doi.org/10.1116/1.5092272
Luan, Pingshan, Kondeti, V. S. Santosh K., Knoll, Andrew J., Bruggeman, Peter J., & Oehrlein, Gottlieb S. (2019). Effect of water vapor on plasma processing at atmospheric pressure: polymer etching and surface modification by an Ar/H<sub>2</sub>O plasma jet. Journal of Vacuum Science and Technology A, 37(3). https://doi.org/10.1116/1.5092272
Luan, Pingshan, Kondeti, V. S. Santosh K., Knoll, Andrew J., et al., "Effect of water vapor on plasma processing at atmospheric pressure: polymer etching and surface modification by an Ar/H<sub>2</sub>O plasma jet," Journal of Vacuum Science and Technology A 37, no. 3 (2019), https://doi.org/10.1116/1.5092272
@article{osti_1505040,
author = {Luan, Pingshan and Kondeti, V. S. Santosh K. and Knoll, Andrew J. and Bruggeman, Peter J. and Oehrlein, Gottlieb S.},
title = {Effect of water vapor on plasma processing at atmospheric pressure: polymer etching and surface modification by an Ar/H<sub>2</sub>O plasma jet},
annote = {In this study, we evaluate the effect of water vapor on the plasma processing of materials using a model system consisting of a well-characterized radio-frequency (RF) plasma jet, controlled gaseous environment, and polystyrene (PS) as target material. We find that the effluent of Ar/H2O plasma jet is capable of (1) etching polymers with relatively high etch rate and (2) weakly oxidizing the etched polymer surface by forming O containing moieties. When increasing the treatment distance between the polymer and the Ar/H2O plasma, we find that the polymer etch rate drops exponentially whereas the O elemental composition of the etched surface shows a maximum at intermediate treatment distance. The OH density in the Ar/H2O jet was measured near the substrate surface by laser induced fluorescence (LIF), and the density change of the OH radicals with treatment distance is found to be consistent with the exponential decrease of polymer etch rate, which indicates that OH may play a dominant role in the polymer etching process. A control experiment of Ar/H2 plasma shows that the observed fast polymer etching by Ar/H2O plasma cannot be attributed to H atoms. By correlating the OH flux with the polymer etch rate, we estimated the etching reaction coefficient (number of C atoms removed per OH radical from the gas phase) of OH radicals as ~10-2. The polymer etch rate of Ar/H2O plasma is enhanced as the substrate temperature is lowered, which can be explained by the enhanced surface adsorption of gas phase species. For the same molecular admixture concentration and plasma power, we find that Ar/H2O/O2 plasma has much reduced etching efficiency compared to either Ar/H2O or Ar/O2 plasma.},
doi = {10.1116/1.5092272},
url = {https://www.osti.gov/biblio/1505040},
journal = {Journal of Vacuum Science and Technology A},
issn = {ISSN 0734-2101},
number = {3},
volume = {37},
place = {United States},
publisher = {American Vacuum Society},
year = {2019},
month = {04}}