MODELING OF OXIDE BREAKDOWN FROM GATE CHARGING DURING RESIST ASHING

Plasma damage was observed after exposing antenna capacitor structure to an O2 plasma in a single wafer resist asher. The observed early bre akdown is well modeled by surface charging caused by plasma nonuniform ity. Here, the plasma nonuniformity was induced by gas flow and electr ode configuration. The present results agree well with our previous re sults where magnetic field leads to a nonuniform plasma. In this model , nonuniformity leads to a local imbalance of ion and electron current s which charge up the gate surface and degrade the gate oxide. Using S PICE, a circuit model for the test structure and plasma measurements, the Fowler-Nordheim current through the thin oxide regions at differen t points on the wafer was calculated and found to agree well with the observed damage. The important implication of this work on oxide relia bility is that the modeling gives a clear picture to this breakdown me chanism. The charging model can also be applied to any ashing process in any nonuniform plasma. Moreover, this model provides a physical bas is for design rules of device structures for the fabrication of reliab le gate oxides in submicron MOS technology.