Reduction of Si residues for trench etching

To reduce gate leak current failure,it is required to reduce Si residues on trench isolation for high voltage devices. In this issue,process improvement of the trench etching is evaluated. The continuous plasma of Breakthrough step and Si etching step on the trench etching is effective to achieve reduction of Si residues without the profile variation of trench isolation. Gate leak failure on high voltage device is successfully reduced by continuous plasma condition.