AVS 57th International Symposium & Exhibition
    Plasma Science and Technology Tuesday Sessions
       Session PS1-TuA

Paper PS1-TuA8
Mechanism of Highly Selective SiO2 Etching over Photoresist Using New Alternative Gas, C5HF7

Tuesday, October 19, 2010, 4:20 pm, Room Aztec

Session: Advanced BEOL/Interconnect Etching II
Presenter: Y. Miyawaki, Nagoya University, Japan
Authors: Y. Miyawaki, Nagoya University, Japan
Y. Kondo, Nagoya University, Japan
K. Takeda, Nagoya University, Japan
K. Ishikawa, Nagoya University, Japan
M. Sekine, Nagoya University, Japan
H. Kondo, Nagoya University, Japan
A. Ito, Zeon Corporation, Japan
M. Nakamura, Zeon Corporation, Japan
M. Hori, Nagoya University, Japan
Correspondent: Click to Email
With the continuous demand for increasing the storage capacity of semiconductor memory devices, a much precise etching process for high aspect ratio contact holes in SiO2 film is indispensable. The aspect ratio of more than 20 will be required for 45-nm node in 2010. Furthermore, deterioration of the SiO2 selectivity over a fragile, thin photoresist would cause the sidewall roughness and poor pattern-width definition. In this study, we utilized a newly designed environmentally-friendly (low global warming potential) gas, C5HF7, and compared the etch performances with conventional C5F8 gas. A very-high-frequency (VHF) capacitively coupled plasma (CCP) etcher was used with 1800 W VHF power and 2 MHz bias of 1200 W. C5F8 or C5HF7 gas was introduced with O2 and Ar (C5F8 or C5HF7 /O2/Ar = 15 / 10-35 / 300 sccm). We evaluated the dependence of O2 flow rate on the etching rates of SiO2 and KrF photoresist and SiO2 selectivity to the resist. The gas phase species, O radical (O*) and CF3+, were measured using Vacuum Ultraviolet Laser absorption spectroscopy (VUVLAS) and a quadruple mass spectroscopy (QMS). The C5F8 gas chemistry showed the maximum selectivity of 3.7 with the etching rate of 416 nm/min at 20 sccm O2 flow rate. In contrast, C5HF7 chemistry realized much higher selectivity (more than 13.5) with the etching rate of 356 nm/min at 25 sccm O2 flow rate. It was confirmed that almost four times higher selectivity than that of the conventional C5F8 gas was obtained by using the new C5HF7 gas. In the both gas chemistry, the density of CF3+ ion, that could be one of the dominant etch species for SiO2, showed the maximum value at the maximum etch rate conditions. The variation trends for O* densities were similar to the resist etch rate in C5HF7/O2/Ar plasma. It was also speculated that the H atoms from C5HF7 reduced the density of F radical that would enhance the resist etch rate. The reason for the high selectivity would be examined by measuring the surface chemical compositions and the gas phase species, such as CFX and F.