US Patent 7223653 Process for forming a buried plate

A method is provided for making a buried plate region in a semiconductor substrate. According to such method, a trench is formed in a semiconductor substrate, the trench having a trench sidewall, the sidewall including an upper portion, and a lower portion disposed below the upper portion. A dopant source layer is formed along the lower portion of the trench sidewall, the dopant source layer not being disposed along the upper portion of the trench sidewall. A layer is formed to cover the upper portion of the trench sidewall. Annealing is then performed to drive a dopant from the dopant source layer into the semiconductor substrate adjacent to the lower portion of the trench sidewall.