Dry Etching of Mo based layers and its interdependence with a poly-Si/MoOxNy/TiN/HfO2 gate stack

Further device scaling below the 65 nm node required the introduction of metal gates/high-k layers. This paper discusses the etching approaches for patterning TiN/Mo, TiN/MoOx and TiN/MoOxNy layers used in poly-silicon metal gate stacks. We found that for these Mo based layers, the dry etching using any Cl2/O2 ratio provoked a severe isotropic etching. HBr gas was used as a key component for controlling side-walls passivation. The MoOx and MoOxNy layers were more prone to lateral attack compared to Mo due to the intrinsic stoichiometric oxygen. A good selectivity towards the substrate was obtained using high O2 flows in Cl2/O2/HBr mixtures. Etching of the TiN layer was carried out with Ar/Cl2. This process was tuned by adding HBr depending on the metal gate stack, which suggests that TiN etching is highly influenced by the Mo layer nature (TiN/Mo, TiN/MoOx and TiN/MoOxNy). We have also compared the complete gate stack pattering characteristic when an oxide or an amorphous carbon hard mask has been used for pattern definition.

In the Figure (a) the Mo side walls suffer an isotropic etching during the metal gate (MG) patterning (Mo/TiN) due to a poor sidewall passivation when the dry etching was carried out with any Cl2/O2 gas mixture. During the MG patterning of MoOx/TiN a more severe isotropic etching of the MoOx was observed using also any ratio of Cl2/O2 gas mixture (b). When the proper amount of HBr gas is added to the Cl2/O2 gas mixture, the side wall passivation of the Mo containing layers is improved suppressing the isotropic etching of Mo or MoOx (c) (the hard-mask has been stripped).Figure optionsDownload as PowerPoint slideHighlights
► We present the dry etching of Si and Mo(OxNy) based layers on TiN/HfO2 gate stacks.
► Mo based layer are etched isotropically when using any ratio of Cl2/O2 gas mixture.
► The Mo(OxNy) isotropic etching was suppressed by adding HBr to the Cl2/O2 mixture.