Sidewall-Fence-Free Pt Etching with an Ar/O 2 Mixed Gas Plasma
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appearance of the fence residue is caused by redeposition of the etch product onto the sidewall of the photoresist and Pt structure being etched. The residue may deteriorate the sidewall slope of the etched pattern and result in a loss of control over critical feature size. A high etch selectivity and a thin hard mask may alleviate this problem. In this work, a thin TiN mask was used to obtain a fence-free etched Pt pattern with an Ar/0 2 helicon wave plasma. The etch rate, etch selectivity of Pt/TiN, and etch profiles as a function of the oxygen concentration were studied. Experimental Platinum films covered with photoresist or hard mask patterns were etched in a helicon wave plasma reactor, and Ar/O2 or Ar/Cl2 gas mixtures were used as the plasma gas source. The plasma source was constructed from a fused quartz source chamber of 100mm in diameter, and an anodized aluminum diffusion chamber of 350mm in diameter. The antenna was connected to a 13.56 MHz rf generator via a matching network and supplied rf power up to 3 kW. A bias power of 1.6 MHz was imposed to the wafer stage
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Mat. Res. Soc. Symp. Proc. Vol. 564 © 1999 Materials Research Society
to control the incident ion energy. The wafer to be etched was clamped on an electrostatic chuck (ESC). Helium was flown to the backside of the wafer to improve the thermal conductivity. The temperature of the stage holder and chamber were 70' C and 60' C, respectively. Samples were prepared as follows: a 50-nm-thick TiN film was deposited on the thermally oxidized silicon wafer using dc reactive magnetron sputtering. A platinum film with a thickness of 2400A was then deposited by dc magnetron sputtering. Then, a 500--600A thick TiN film was sputtered to act as a mask for Pt patterning. Photoresist was used for patterning the TiN mask with a C12/BC13 plasma. After platinum etching, the TiN mask was removed using a CF 4/CHF 3 plasma. The etch rate and etch profile of the Pt and TiN films were evaluated using field emission scanning electron microscope (FESEM). The etch residues on the sidewall of the etched pattern were analyzed by Auger electron spectroscopy (AES), and the surface composition of the etched Pt and TiN films was investigated by x-ray photoelectron spectroscopy (XPS).
Results and Discussion Formation of fence residues standing on the Pt pattern etched with a photoresist mask in an Ar/Cl 2 mixed gas plasma has been widely reported. Under the helicon wave plasma condition adopted in this study, we observed a thick sidewall residue left on the Pt structure etched in the Ar/Cl 2 plasma. As shown in Fig. 1, a thick sidewall residue surrounds the etched Pt structure after the removal of the photoresist by oxygen plasma ashing. Etch byproducts may redeposit onto the sidewall of the photoresist pattern and the Pt structure during the etching process due to the difficulty to form volatile etch products. According to Auger analysis, the fence residue is composed of Cl, Pt, C, and oxygen. Milkove et al.4 1 reported that chlorine could enhance the etch rate o
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