Analysis of injection current through thin gate oxide during metal etch

A charging damage mode due to "latent antenna" formation for high aspect ra tio structures in a metal etch process was investigated by a new surface ch arging simulation technique. The latent antenna is formed at the end of the metal etch process because of the microloading effect, and is connected to a transistor gate with 35 Angstrom thickness. By using a new simulation al gorithm, the plasma stress current current-voltage (I - V) characteristic c aused by topography dependent charging was calculated for different ranges of the injection current to the antenna structure. Subsequent gate injectio n current through the thin gate oxide was estimated by the plasma I - V wit h a measured holding current I - V characteristic especially optimized for high current injection. The plasma I - V was calculated for the latent ante nna and a mask-defined structure (overetch structure), which are formed dur ing an overetch period. The steady state gate injection current is largest during the latent antenna formation. Because of a device degradation charac teristic that is mostly controlled by an initial gate injection charge, the high injection current for the latent antenna defines the degree of damage , and the observed degradation independence of the overetch time is well ex plained by the results. Since the initial gate injection charge depends on the period of latent antenna formation, damage increases as the etching rat e decreases at the narrow space region. The injection current gets smaller with a smaller antenna ratio, and antenna structures without high aspect fr om the gate injection current. For the analysis of thin gate oxide degradat ion, the injection current is more important than the charging voltage. (C) 2001 American Vacuum Society.