| AVS 62nd International Symposium & Exhibition | |
| Plasma Science and Technology | Tuesday Sessions |
| Session PS1-TuA |
| Session: | Novel Materials and Etch Chemistry |
| Presenter: | Tomohiro Kubota, Tohoku University, Japan |
| Authors: | T. Kubota, Tohoku University, Japan Y. Kikuchi, Tohoku University, Japan S. Samukawa, Tohoku University, Japan |
| Correspondent: | Click to Email |
Anisotropic and damage-free etching of transition metals (especially magnetic materials) is important for realization of MRAM. However, it is generally difficult to etch such materials with conventional plasma etching and Ar ion milling has been widely used which causes problems such as damage, re-deposition, and etc. Recently Gu et al. reported [1] that anisotropic and damage-free etching of transition metal (Ta, Ru, and Pt) is possible based on complex reaction of transition metal by introduction of ethanol gas and irradiation of argon/oxygen neutral beam [2]. It is expected the process proceeds as following: (1) metal surface is oxidized by bombardment of oxygen neutral beam, (2) ethanol molecules adsorb at the surface, and (3) metal complex like Ta(OC2H5)5 is formed by argon neutral beam bombardment. However, detail of the mechanism (especially, why oxidation is needed) was not clear. To understand the etching mechanism, computational investigation was performed using first principle calculation.
Calculations based on density functional theory and cluster model were performed using a SGI UV1000/2000 system in Institute of Fluid Science, Tohoku University.
First, adsorption of ethanol on tantalum oxide and metallic tantalum was investigated. As a result, it was found that ethanol adsorbs spontaneously on both surfaces. It means that adsorption step is not a reason why oxidation is needed for the etching.
Then, we investigated possible reaction which may occur after the adsorption of ethanol. It was found that O–H bond in the adsorbed ethanol can be dissociated, the H can be moved, and a new O–H bond can be formed between an oxygen atom in the metal oxide and the dissociated hydrogen (hydrogen movement). This should cause dissociation of Ta-O bonds in the oxide to proceed etching. Note that this process should not occur at metallic tantalum surface because it does not have oxygen atom to accept the moving hydrogen, and this should be the reason why oxidation is needed for etching.
Furthermore, it was found that collision of argon caused the hydrogen movement reaction mentioned above. It means that the hydrogen movement reaction and possibly tantalum etching can occur in the experimental condition under argon neutral beam irradiation.
Acknowledgement: We thank Dr. Nozawa from Tokyo Electron Ltd. for valuable discussions.
[1] X. Gu, Y. Kikuchi, T. Nozawa and S. Samukawa: J. Phys. D: Appl. Phys. 47 (2004), p. 322002.
[2] S. Samukawa, K. Sakamoto and K. Ichiki: Jpn. J. Appl. Phys. 40 (2001), p. L779.
[3] M. Yonemoto, K. Sano, K. Endo, T. Matsukawa, M. Masahara and S. Samukawa: Jpn. J. Appl. Phys. 48 (2009), p. 04C007.