Tungsten Silicide Gate Etching with Very High WSix to Poly-Si Selectivity and Low WSix Etch Rate Micro-Loading in the High Density Plasma

Tungsten Silicide Gate Etching with Very High WSix to Poly-Si Selectivity and Low WSix Etch Rate Micro-Loading in the High Density Plasma

As the design rule of DRAM device decreases to less than 100 nm and the aspect ratio between gate electrode and space increases dramatically (3.5~ 4), it is coming difficult to fill the spaces with insulating materials. It is also becoming more preferable to reduce the thickness of poly-Si rather than to reduce WSix film because of reducing electrical resistivity. To meet these requirements, highly selective and anisotropic etching for WSix/poly-Si has been developed by fully utilizing a high density plasma source. In this study, O₂ and N₂ gases were added to achieve high selectivity in NF₃/Cl₂ gas process. The addition of O₂ increases WSix etch rate by forming W-oxyhalides and passivates poly-Si by forming Si-O layer. On the other hand, the addition of N₂ gas decreases both poly-Si and WSix, but it forms a sidewall protection layer (WN) on WSix, achieving an isotropic etching. The role of cathode temperature was found to not only increase WSix etch rate and the WSix /poly-Si selectivity but also provides a wider process margin for the production environment.

As the design rule of DRAM device decreases to less than 100 nm and the aspect ratio between gate electrode and space increases dramatically (3.5~ 4), it is coming difficult to fill the spaces with insulating materials. It is also becoming more preferable to reduce the thickness of poly-Si rather than to reduce WSix film because of reducing electrical resistivity. To meet these requirements, highly selective and anisotropic etching for WSix/poly-Si has been developed by fully utilizing a high density plasma source. In this study, O₂ and N₂ gases were added to achieve high selectivity in NF₃/Cl₂ gas process. The addition of O₂ increases WSix etch rate by forming W-oxyhalides and passivates poly-Si by forming Si-O layer. On the other hand, the addition of N₂ gas decreases both poly-Si and WSix, but it forms a sidewall protection layer (WN) on WSix, achieving an isotropic etching. The role of cathode temperature was found to not only increase WSix etch rate and the WSix /poly-Si selectivity but also provides a wider process margin for the production environment.