Tungsten metal gate etching in Cl2∕O2 inductively coupled high density plasmas

Abstract

Plasma etching of W in a poly-Si∕TiN∕W∕HfO2 gate stack is investigated in Cl2∕O2 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 Cl2, O2, 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 O2 ratio in Cl2∕O2 and Cl2∕O2∕NF3 plasmas is interpreted. X-ray photoelectron spectroscopy analyses demonstrate that the introduction of O2 in Cl2 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.