Poly-Si/TiN/Mo/HfO2 gate stack etching in high-density plasmas

Plasma etching of thin Mo layer integrated in a poly-Si/TiN/Mo/HfO2 gate stack is investigated using various halogen based plasma chemistries. Preliminary studies of Mo film etching show that SF6/Ar, HBr/O2, and Cl2/O2 plasmas lead to spontaneous chemical etching of the molybdenum layer through the formation of volatile MoFX, MoOXClY, or MoOXBrY by-products, while Mo etching in Cl2 and SF6/CH2F2 plasmas requires the assistance of the ion bombardment. High Mo:HfO2 selectivity can be tuned in HBr/O2 and Cl2/O2 plasmas as a function of O2 concentration in the gas mixture and bias power, while SF6/CH2F2/Ar plasma leads to the formation of HfF residues. Subsequent patterning studies of the poly-Si/TiN/Mo/HfO2 gate stack show that HBr/O2 plasmas are the most promising to achieve anisotropic Mo etching without impacting the poly-Si/TiN sidewalls while keeping identical dense and isolated gate profiles. All results indicate that the gate etch anisotropy is driven by the redeposition and subsequent oxidation of MoOBrX etch by-products on the pattern sidewalls. The O2 concentration in the plasma gas phase controls the passivation layer thickness.