Plasma-charging damage to gate SiO₂ and SiO₂/Si interfaces in submicron n-channel transistors: Latent defects and passivation/depassivation of defects by hydrogen

New experimental results are presented which provide evidence for hydrogen passivation and depassivation of plasma-charging-induced defects in gate oxides and at oxide/silicon interfaces. The devices used in this study were 0.5 μm n-channel metal-oxide-semiconductor field-effect transistors fabricated on 200 mm boron-doped silicon substrates. The processing included Cl₂/HBr-based chemistries for the polycrystalline silicon gate definition etch, and CHF₃/CF₄-based chemistries for the contact etch. Plasma-charging defects resulting from the processing are shown to have the following properties: (i) plasma-induced charging defects are latent (electrically inactive) directly after our processing and before postmetallization annealing (PMA); (ii) these defects continue to be latent after N₂ and Ar anneals done at temperatures T in the range 200°C≤T≤400°C; (iii) these defects are also latent after our standard PMA done in forming gas at 400°C; (iv) these defects are electrically activated by room-temperature Fowler-Nordheim stress, and (v) equivalently these defects are electrically activated by annealing below 400°C in hydrogen-rich ambients. We show hydrogen passivation/depassivation is responsible for this behavior. This passivation/depassivation has been previously suggested to occur for defects at SiO₂/Si interface; here it is also proposed to describe defect-hydrogen interactions in the bulk gate oxide for defects caused by plasma-charging damage.