| AVS 58th Annual International Symposium and Exhibition | |
| Plasma Science and Technology Division | Tuesday Sessions |
| Session PS1-TuA |
| Session: | Advanced BEOL / Interconnect Etching II |
| Presenter: | Makoto Sekine, Nagoya University, Japan |
| Authors: | Y. Miyawaki, Nagoya University, Japan Y. Kondo, Nagoya University, Japan K. Asano, Nagoya University, Japan M. Sekine, Nagoya University, Japan K. Ishikawa, Nagoya University, Japan T. Hayashi, Nagoya University, Japan K. Takeda, Nagoya University, Japan H. Kondo, Nagoya University, Japan M. Hori, Nagoya University, Japan |
| Correspondent: | Click to Email |
Highly selective etch of dielectric films is one of the key technologies in integrated circuits fabrications. We achieved extreme high SiO2 selectivity against Si3N4, Si and ArF photoresist using hydro-fluorocarbon gas, C5HF7 and O2, Ar gas mixture [1] in a dual frequency (60 MHz / 2 MHz) capacitively coupled plasma (CCP). The selectivity over Si3N4 seemed to be infinite because selective fluorocarbon deposition occurred on Si3N4. The surface roughness that leads to line edge roughness was reduced by the selective deposition. The selective etch mechanism among plasma etch using fluorocarbon gases with and without hydrogen in gas molecule was investigated by the diagnostics of gas phase species and etched surfaces. As comparing CxFy, CxFyO and CHxFy gases, it was found that the hydrogen containing species with larger molecular weight play an important role for forming thick and carbon-rich polymer film especially on Si3N4, as well as on Si, photoresist. For the CHxFy gas plasma, the density of F radical that degrades the selectivity was inclined to be lower. CHxFy species act as an etchant for SiO2 that contains oxygen, similar to the conventional selective etch scheme of SiO2 by fluorocarbon plasma [2]. On the other hand, it could be deposition species to reduce the etch rates after some etch reaction on the surfaces of Si3N4, Si and photoresist that have no or less oxygen content. This means that the CHxFy species are etchants at the very beginning and turn to species for fluorocarbon polymerization just on Si3N4, Si and photoresist. Here, we need some sacrifice layer to initiate that selective deposition. The photoresist surface suffered roughness formation in the beginning, then the roughness was cured by the further deposition with ion bombardment [3]. This protective and roughness curing deposition on photoresist should occur for CxFy gas plasma in some condition (e.g. higher gas-mixing ratio of CxFy/Ar), however it also forms a thick polymer on SiO2 to stop etching. The temperature dependence for the etching and deposition properties [4] suggested that the difference of sticking coefficient for species with and without hydrogen was not so important. It is also speculated that the thick polymer formation on Si3N4, Si and photoresist while less reducing the SiO2 etch rate is due to the relative large flux of specific hydrogen containing species in C5HF7 plasma.
Acknowledgement: Tokyo Electron Ltd., ZEON Corp., JSR Corp.
References: [1] Y. Miyawaki, et al.; Proc. 32nd Int'l. Symp. Dry process, P.181 (The Japan Society of Applied Physics, Tokyo, 2010). [2] M. Sekine; Applied Surface Science 192, (2002) 270. [3] K. Asano, et al.; The 72nd Fall Meeting of JSAP, 31a-M-6 (The Japan Society of Applied Physics, Yamagata, 2011). [4] Y. Miyawaki, et al.; ibid., 31a-M-4