Effects of Charge Build-up of Underlying Layer by High Aspect Ratio Etching

The effects of the “electron shading” charge build-up at the bottom of holes are investigated using fluorocarbon gas plasma. The etch rates of the electrically conductive films such as phosphorus-doped polysilicon at the bottom of the holes change depending on whether the films are patterned or not. This is caused by the decrease of the low-energy ions which reach the bottom of the holes due to positive charging of the underlying layers. Furthermore, the potential at the bottom of the contact holes is investigated using metal-nitride-oxide-silicon (MNOS) capacitors. The positive charging due to the electron shading effect is measured. In order to reduce the electron shading charge build-up, the pulse-modulated plasma is investigated. The selectivity to the underlying layer increases upon using pulse-modulated plasma.