Pulse-time-modulated plasma etching for high performance polysilicon patterning on thin gate oxides

This paper reports a high performance gate electrode patterning technology which uses a HBr-Cl₂-O₂ gas mixture in a pulse-time-modulated inductively-coupled plasma (ICP) etcher. We observed that when the plasma is cycled on and off at a rate of a few tens of microseconds, the deposition and charging on the substrate surface can be precisely controlled. As a result, plasma etching can be performed with no topography-dependent charging, no gate oxide trenching, and with extremely high resist and gate oxide selectivities. These results are also obtainable with modifications to conventional etch systems