Power mosfet and forming method thereof

A power MOSFET and a forming method thereof are provided. A device comprises a trench extending to a semiconductor region and having a first conductivity, and a conductive field plate located in the trench. A first dielectric layer separates the bottom and the side wall of the field plate from the semiconductor region. A main grid electrode is located in the trench and overlaps the field plate. A second dielectric layer is arranged between the main grid electrode and the field plate and separates the main grid electrode and the field plate from each other. A doped drain electrode (DD) region with a first conductivity is located under the second dielectric layer and has an edge portion overlapping the DD region. A body region comprises a first portion located on the same layer as one part of the main grid electrode and a second portion contacted with the DD region. The body region has a second conductivity opposite to the first conductivity. An MOS-containing device is located on the surface of the semiconduct