| AVS 60th International Symposium and Exhibition | |
| Plasma Science and Technology | Tuesday Sessions |
| Session PS2-TuA |
| Session: | Deep Etch Processes for Vias, Trenches and MEMS |
| Presenter: | I. Sakai, Toshiba Corporation, Japan |
| Authors: | I. Sakai, Toshiba Corporation, Japan S. Amasaki, Nagoya University, Japan T. Takeuchi, Nagoya University, Japan K. Takeda, Nagoya University, Japan K. Ishikawa, Nagoya University, Japan H. Kondo, Nagoya University, Japan M. Sekine, Nagoya University, Japan N. Sakurai, Toshiba Corporation, Japan H. Hayashi, Toshiba Corporation, Japan T. Ohiwa, Toshiba Corporation, Japan M. Hori, Nagoya University, Japan |
| Correspondent: | Click to Email |
One of the key processes for 3D-LSI is through Si via (TSV) formation. To form large and deep via holes through a wafer, a high etch rate deep etching technology using SF6/O2 plasma has been developed [1]. It is reported that high etch rate is obtained by supplying a large amount of F radicals and the etch profile is controlled by forming an oxidized layer as an etch inhibitor on the TSV sidewall. In the previous study [2] we showed that, as a result of competitive reaction of etching and oxidation by F and O radicals, even at the 75% O2 addition condition Si etching by F radicals is confirmed. In this study, we aimed to suppress sidewall etching further by addition of SiF4 gas to SF6/O2 plasma, and examined its effect by analysis of the Si surface.
Si wafer was placed on a grounded electrode at the remote plasma region of a 500 MHz ultra high frequency plasma reactor. We assumed that the influence of ions was small and radical reaction dominant, so we could simulate the reactions at the sidewall of TSV RIE. The process gas chemistries used were SF6/O2 and SF6/O2/SiF4.
The Si etch depth dependence of SF /O /SiF plasma etching on O2 gas addition was examined. The etch depth of Si after 3 min plasma exposure was measured from SEM images of 8μm square hole patterned Si wafers with 2µm thick SiO2 as mask. Etch depth decreased with SiF4 addition. For example, at 75% O2 addition, the etch depth was about 0.25µm, 1/4 of that without SiF4 addition. Etch depth dependence on O2 flow rate ratio showed a decreasing trend, same as that without SiF4 addition. At 90% O2 gas flow rate ratio, etching stopped and thickness increased, indicating that film was deposited on the Si surface. The thickness of the etch-inhibiting reaction layer including Si, F, O (SiOF film) was calculated from the Si2p spectra of XPS after 1 min plasma exposure. Thickness increased with O2 addition, and especially when the O2 flow rate ratio was more than 75% in the case of SF6/O2/SiF4, it became profoundly thicker, more than 8.7nm. It is speculated that reaction of O radicals and SiF4 occurred on the Si surface and etching was suppressed by Si atoms supplied from the plasma in addition to the inhibiting effect of the SiOF formation. Finally, the F/O ratio of the SiOF layer at the Si surface was calculated from the peaks of F1s and O1s. Under this experimental condition, it was found that the ratio was constant, about 2, regardless of O2 gas flow rate ratio, which is similar to the previous result without SiF4 addition.
[1] I. Sakai, et al: J. Vac. Sci. Technol. A 29, 021009 (2011).
[2] S. Amasaki, et al: Proc. 32nd International Symp. on Dry Process (2010) 97.