Deep trench capacitor through soi substrate and methods of forming

Abstract

Methods of forming a deep trench capacitor through an SOI substrate, and a capacitor are disclosed. In one embodiment, a method includes forming a trench opening into the SOI substrate to the silicon substrate; depositing a sidewall spacer in the trench opening; etching to form the deep trench into the silicon substrate; forming a first electrode by implanting a dopant into the silicon substrate, whereby the sidewall spacer protects the BOX layer and the silicon layer; removing the sidewall spacer; depositing a node dielectric within the deep trench; and forming a second electrode by depositing a conductor in the deep trench. Implanting creates a substantially uniform depth doped region except at a portion adjacent to a lowermost portion of the deep trench, which may be substantially bulbous. The BOX layer is protected from undercutting by the sidewall spacer, and the implantation removes the need for out-diffusing dopant from silica glass.