| AVS 55th International Symposium & Exhibition | |
| Plasma Science and Technology | Wednesday Sessions |
| Session PS1-WeA |
| Session: | Fundamentals of Plasma-Surface Interactions II |
| Presenter: | K. Miwa, Nagoya University, Japan |
| Authors: | K. Miwa, Nagoya University, Japan N. Takada, Nagoya University, Japan K. Sasaki, Nagoya University, Japan |
| Correspondent: | Click to Email |
Al2O3 is a typical wall material for plasma processing chambers. Interactions between the surface and fluorine-based plasmas would result in process drifts and/or particle generations.1,2,3 Recently, replacing Al2O3 by Y2O3 was tried in an etching tool.3 However, the interaction mechanisms have not been examined in detail. We studied the mechanisms and compared the robustness of Al2O3 and Y2O3 against the irradiation of high density fluorine-based plasmas excited by a helicon wave.4 In the experiment, an rf power at 13.56MHz (2kW, 10Hz pulse) was supplied to a helical antenna around a quartz tube of 1.6 cm inner diameter. A uniform magnetic field was applied, so that the plasma was confined radially. A sample piece (25 mm squared Al2O3 or Y2O3) was placed on the end plate of the experiment chamber. The total pressure of CF4 (or SF6) and O2 was 7 mTorr. The duration of the irradiation was 2 hours. The sample surfaces were analyzed by XPS. On the Al2O3 surface irradiated by the CF4/O2 plasma column, fluorinated (AlOxFy and/or AlFx) and metallic Al were detected at relative concentrations of 11 % and 1.6 %, respectively. In the outside area of the irradiation, concentrations of those were 5.7 % and 1.1 %. On the contrary, lower concentrations of those were observed by the SF6/O2 plasma. These results suggest that CFx (x=1-3) radicals react with Al-O with the ion bombardment in the plasma column. The fluorination would be induced by the reaction between carbon and oxygen. In contrast, reaction probabilities between SFx (x=1-5) radicals and Al-O would be lower than that of CFx, since the bonding energy of S-O (549 kJ/mol) is much lower than that of C-O (1077 kJ/mol). In addition, the metallic Al might be induced from the fluoride by high-flux bombardment of low-energy ions.5 On the other hand, in both irradiations of CF4/O2 and SF6/O2 plasmas onto the Y2O3 samples, the relative concentrations of fluoride (YOxFy and/or YFx) and metallic Y were much lower than the concentrations of aluminum fluoride and metallic Al on the Al2O3 samples. The results can be attributed to the fact that Y-O bonding energy is larger than that of Al-O (512 kJ/mol). In other words, Y2O3 is more robust than Al2O3.
1G. Cunge, et. al., Plasma Sources Sci. Technol. 14, 599 (2005)
2K. Miwa and T. Mukai, J. Vac. Sci. Technol. B 20, 2120 (2002)
3K. Miwa, et, al., Proceedings of the IEEE. ISSM 2007, PO-O-210, 479 (2007)
4M. Aramaki, et. al., Jpn. J. Appl. Phys. 43, No.3, 1164 (2004)
5J. Roth, et. al., Nucl. Fusion, 36, No. 12, 1647 (1996)