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

Abstract

Pulse-time-modulated inductively coupled plasma with HBr gas can provide highly selective, high etching rate, charge-free poly-Si metal–oxide–semiconductor field effect transistor etching. We observed that, when the HBr plasma is cycled ON and OFF at a rate of a few tens of microseconds, the etching and deposition on the substrate surface can be controlled precisely. The use of pulsed plasma can also reduce charge buildup because the electron temperature decreases significantly during the pulse-OFF time. As a result, poly-Si can be etched with extremely high selectivity (relative to the resist and gate oxide), and neither trenching of the gate oxide nor topography-dependent charging occurs.