Semiconductor element and manufacturing method thereof

The invention discloses a semiconductor element. The semiconductor element comprises a semiconductor substrate comprising a plurality of active regions, a first groove formed in the active regions andextending into shallow trench isolations on two sides, and a second groove formed in the semiconductor substrate and extending into the shallow trench isolations, wherein each bit line comprises a superposed structure formed by a bottom conductive material layer and a top conductive material layer; a first contact plug composed of a bottom conductive material layer is formed in the first groove,and the two side faces of the first contact plug are formed by extending downwards from the two side faces of the bit line; a first sub-groove is formed in the first groove on the first side of the first contact plug, a third sub-groove is formed in the active region at the bottom of the first sub-groove, and the bottom surface of the third sub-groove is lower than the top surface of the active region. The invention disclo