Observation of a new type of plasma etching damage: Damage to N-channel transistors arising from inductive metal loops

We report a new type of damage, referred to here as inductive damage, induced by metal 1 plasma etching. The devices used in this study are lightly doped drain n-channel metal-oxide semiconductor field effect transistors (MOSFETs) fabricated on 200 mm p/p⁺ silicon wafers. The channel lengths of the investigated transistors are 0.5 μm with 90 Å thick thermally grown gate oxides. The metal 1 main etch (duration 30 s) and overetch (50%) employed BCl₃/N₂/Cl₂ chemistry and was done using a standard reactive ion etching tool operated at rf power of 600 W and rf frequency of 13.56 MHz. Specially designed MOSFETs with inductive metal loops connecting the gate and substrate or the gate and drain are used to examine inductive damage. Inductive damage is shown to arise from electrical stress of the gate oxide and oxide/Si interface by the electromotive force generated in the metal loops by the metal plasma etch.