Dry etching of TaN/HfO₂ gate stack structure by Cl ₂/SF₆/Ar inductively coupled plasma

The dry etching characteristics of the TaN/HfO₂ gate stack structure using Cl₂/Ar, Cl₂/SF₆/Ar and Cl ₂/SF₆/O₂/Ar inductively coupled plasmas (ICPs) were investigated and the etch rates of the TaN and HfO₂ layers and TaN/HfO₂ etch rate selectivities were compared. The results obtained for the TaN/HfO₂ etching by varying the Cl₂/Ar gas mixing ratio, the top ICP electrode power, and the dc self-bias voltage (V _dc) in the Cl₂/Ar plasmas showed that low etch selectivities were obtained, due to the high HfO₂ etch rate. The effects of adding SF₆, to the Cl₂/Ar plasmas and adding O₂ flow to the SF₆/Cl₂/ Ar chemistry were investigated for the purpose of improving the etch selectivity. Etch experiments performed by varying the Cl₂/SF₆/Ar gas mixing ratio and V_dc value in SF₆/Cl₂/Ar plasmas, combined with X-ray photoelectron spectroscopy measurements, showed that the etch rates were reduced compared to those in Cl₂/Ar chemistry, due to the heavy fluorination of the surface, however the etch selectivity was increased, due to a disproportionate decrease in the TaN and HfO₂ etch rates. The addition of O₂ flow to the SF₆/Cl₂/Ar plasma also increased the etch selectivity at an O₂ flow rate of 5 sccm, due to the TaN etch rate being increased, while the HfO₂ etch rate remained almost constant.