MICROTRENCH FORMATION IN POLYSILICON PLASMA-ETCHING OVER THIN GATE OXIDE

The formation of microtrenches in polysilicon plasma etching over thin gate oxides has been observed and modeled. Microtrenches are small tr enches formed in the bottom of etching features and are caused by the localized breakthrough of the gate oxide and subsequent rapid etching of the underlying silicon. In contrast to previous reports, the microt renches were observed a small distance away from the sidewall. Their f ormation and position were functions of the thickness and angle of the photoresist and polysilicon sidewalls. Simulation of ion scattering f rom the sidewalls of the etching features indicated that the flux of i ons at the bottom of the feature was peaked away from the sidewall und er the process conditions of this study. The position of the peak ion flux predicted by the model and the experimentally observed trench var ied in a similar fashion as a function of the topography of the etched feature.