Method of forming a buried plate by ion implantation

A method of forming a semiconductor structure comprising:

• forming a mask layer over a semiconductor substrate, wherein the semiconductor substrate is a semiconductor-on-insulator (SOI) substrate including a bottom semiconductor substrate, a buried insulator layer, and a top semiconductor substrate;
• forming an opening in said mask layer by patterning said mask layer;
• extending the opening through the top semiconductor substrate stopping on the buried insulator layer of the SOI substrate;
• implanting first dopant ions of a first polarity through said opening and said buried insulator layer into a first portion of the bottom semiconductor substrate of said semiconductor substrate, whereby a first doped region is formed underneath said opening;
• forming a trench through a portion of said first doped region by an anisotropic etch, wherein said trench extends downward from said opening through the buried insulator layer into the bottom semiconductor substrate;
• and
• implanting second dopant ions of a same polarity as the first polarity through a bottom surface and sidewall surfaces of said trench into a second portion of the bottom semiconductor substrate of said semiconductor substrate, wherein a second doped region is formed underneath said first doped region such that said second doped region and said first doped region are contiguous with each other.