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ith iN ra tivi we pro 35# ved oc 0 © Dow~ICP!. The etch rate and etch selectivity were explored as a function of etch parameters including coil radio frequency ~rf! power, gas pressure, dc bias voltage, and the concentration of an etch gas. The etch profiles were also observed at different etch conditions and correlated with the etch selectivities. Finally, the optimum concen-tration of the etch gas for iridium etching with a hard mask was proposed for fast etch rate, high selectivity, and high degree of an-isotropy. Experimental In order to examine the iridium etch rate, the TiN mask etch rate, and the sidewall profile of the etched iridium film, three types of etch samples were prepared. For the samples of the iridium sidewall profile, iridium films 120 nm thick representing the top electrode were deposited by dc magnetron sputtering onto TiO2 /SiO2 /Si wa-fers. A 30 nm thick TiN thin film was then deposited on top of the iridium by reactive sputtering. The TiN films were patterned with a The etch rates of the iridium film and the TiN mask were mea-sured as a function of O2 and Cl2 concentrations in a Cl2 /O2 /Ar gas mix. The TiN mask was suitable as an etching mask in Cl2 /O2 /Ar because the etch rate was quite low at most of the etch conditions. At present, the iridium thickness for FeRAM application is in the range 100-150 nm. Therefore, a very thin TiN layer was enough to be applied as a hard mask in this study. Figure 1 shows the effect of O2 concentration on the etch rates of the iridium film and the TiN mask at a constant Cl2 concentration of 30%. As the O2 concentration increases, the etch rate of the TiN mask declines rapidly, while the iridium etch rate decreases gradu-ally. Therefore, the iridium/TiN etch selectivity increases with in-creasing O2 concentration, exhibiting a maximum selectivity of 8 at 50 % O2 concentration. It is believed that the addition of O2 gas promotes the transformation of TiN film to TiOx and TiOxNy, thus making the formation of titanium chloride difficult.3 For the case of iridium films, the decrease in etch rate is thought to be caused by the reduced sputtering of iridium by the incident ions due to the in-High-Density Plasma Etch