A NEW FAILURE MECHANISM BY TUNGSTEN BRIDGING IN A PLUG PROCESS DUE TO INCOMPLETE POST-METAL ETCH RESIDUE CLEAN CAUSING CORROSION AND TUNGSTEN RE-DEPOSITION
IC designers sometimes use zero metal overlap of tungsten plug structures to maximize interconnect density. Zero overlap combined with lithography variations may result in partial exposure of the plug during the metal interconnect etch. A new mechanism of bridging metal with exposed underlying tungsten plugs was observed due to incomplete post-metal etch clean chemistry removal. This new mechanism involves corrosion and re-deposition of the tungsten to form an electrical short. Experimental data show that bridging occurrences worsened with increased time between post-metal etch clean and the next oxide deposition step. In this paper we will discuss the mechanism of tungsten corrosion and re-deposition to form the bridging failures due to incomplete hydroxylamine chemistry removal.
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