Tungsten metal gate etching in Cl(2)/O(2) inductively coupled high density plasmas

Plasma etching of W in a poly-Si/TiN/W/HfO(2) 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 NF(3) is required to successfully pattern the W layer without damaging the HfO(2), 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)/NF(3) 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 WOCl(x) deposit on the gate sidewalls. However, the WOCl deposition can be controlled and eliminated by adding fluorine in the plasma during W etching.