Dry Etching of TaN/HfO2 Gate Stack Structure by Cl2/SF6/Ar Inductively Coupled Plasma

The dry etching characteristics of the TaN/HfO2 gate stack structure using Cl2/Ar, Cl2/SF6/Ar and Cl2/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.