Method for forming a capacitor in a mixed mode circuit device by ion implantation

摘要

The invention provides a method for forming a capacitor in a mixed mode circuit device through ion implantation. The method includes forming a polysilicon layer over a substrate, which substrate has isolation region formed thereon. An ion implantation process is performed to implant oxygen ions into the polysilicon layer. An annealing process is performed to trigger an reaction between the oxygen ions and the silicon ions. As a result, a silicon oxide layer is formed within the polysilicon layer. The silicon layer and the polysilicon layer are patterned, where the top portion of the polysilicon layer above the silicon oxide layer serves as an upper electrode of a capacitor. The polysilicon layer below the silicon oxide layer serves as the lower electrode.