Plasma etching of W in a poly-Si/TiN/W/HfO2 gate stack is investigated in Cl-2/O-2 based plasmas. Preliminary studies have illustrated the issues induced with the introduction of a metal layer in the gate stack. Based on scanning electron microscopy observations, the authors first show that a mixture of Cl-2, O-2, and NF3 is required to successfully pattern the W layer without damaging the HfO2, poly-Si, and TiN profiles. For a better understanding of etch mechanisms, W etching is studied on blanket wafers and etch rates are presented and discussed with respect to the plasma parameters. The evolution of the etch rates as a function of O-2 ratio in Cl-2/O-2 and Cl-2/O-2/NF3 plasmas is interpreted. X-ray photoelectron spectroscopy analyses demonstrate that the introduction of O-2 in Cl-2 leads to the creation of a thick WOClx deposit on the gate sidewalls. However, the WOCl deposition can be controlled and eliminated by adding fluorine in the plasma during W etching.