Reduction of charging damage of gate oxide by time modulation bias method

The charging damage of gate oxide films caused during plasma etching is reduced by the time modulation (TM) bias method. The radio frequency (RF) bias applied to the substrate is pulse modulated to control the energy and the quantity of accelerated ions. The charging potential of line patterns caused by the electron shading effect decreases during off periods of RF bias. In addition, the emission intensity signal of the optical endpoint monitor indicates suppression of reactive ion etching (RIE) lag. These factors result in the reduction of charging damage.