| AVS 57th International Symposium & Exhibition | |
| Plasma Science and Technology | Monday Sessions |
| Session PS-MoM |
| Session: | Advanced BEOL / Interconnect Etching I |
| Presenter: | T. Yamaguchi, Nagoya University, Japan |
| Authors: | T. Yamaguchi, Nagoya University, Japan K. Takeda, Nagoya University, Japan C. Koshimizu, Tokyo Electron AT Limited, Japan H. Kondo, Nagoya University, Japan K. Ishikawa, Nagoya University, Japan M. Sekine, Nagoya University, Japan M. Hori, Nagoya University, Japan |
| Correspondent: | Click to Email |
The dual frequency capacitively coupled plasma (CCP) with negative DC bias superimposed to the upper electrode has been proposed to realize high performance etching technologies. Denpoh et al. have discussed a mechanism under the DC bias superimposition that secondary electrons generated at the upper electrode transport through a bulk Ar plasma to the counter electrode. Kawamura et al. have also discussed about effects of the secondary electrons and a characteristic of the superimposed DC/RF sheath. Since the fluorocarbon (CF) etching plasma with the DC bias has not ever analyzed, we have measured various parameters and discuss the effect of the DC bias on the selective etching of SiOCH over SiC.
We used a CCP reactor for 300 mm wafer. VHF (60 MHz) power and DC bias were simultaneously applied to the upper electrode. RF (13.56 MHz) power was applied to the lower electrode where the samples were placed for etching experiments. A mixture gas of Ar, N2 and C4F8 introduced with flow rates of 800, 100, and 10 sccm, respectively. Pressure was kept at 5.3 Pa.
Bulk plasma parameters such as electron density and CFx densities were measured when the DC bias changed. The electron density was 1.3×1011 cm-3 without the DC bias. In contrast, with the bias of -1200V, that gained up to 2.1×1011 cm-3. This increase can be interpreted that positive ions accelerated by the DC bias bombarded the upper electrode with higher energy and then generated and supply more secondary electrons to the bulk plasma.
Notably, CF2 radical density was decreased from 2.5 to 1.5×1013 cm-3 with the DC bias. It is well known that the bulk density depends on the surface loss probability, α, of the CF2 radical. The α gained by dangling bonds creation by the ion bombardments. As the result, we believed that more fluorine-rich compounds in bulk plasma were lost by the adsorption and reaction on the reactive surfaces. In fact, with the DC bias of -1200V, SiOCH/SiC selectivity was improved significantly to 68 from 5.5without the DC biasing. This improvement was mainly brought by the etch rate decreasing SiC from 18.5 to 1.3 nm/min while the etch rate of the SiOCH film was maintained almost constant.
Surface analysis results showed that CF polymerized layer was not grew thicker on the SiOCH by such chemical reactions as C + O → CO, C + N + H → HCN. However, in the SiC case, a polymerized layer was relatively thicker because removal reactions were suppressed by lack of F-rich compound. Consequently, the highly selective etching for SiOCH/SiC films was achieved by differentiating the polymerized layer formation.