A MOS transistor having a recessed gate electrode and a fabrication method thereof
are provided. The MOS transistor includes an isolation layer formed at a predetermined
region of a semiconductor substrate to define an active region and double trench
regions formed in the active region. The double trench region is composed of an
upper trench region crossing the active region and a lower trench region located
under the upper trench region. Thus, the active region is divided into two sub-active
regions. Sidewalls of the upper trench region are covered with a spacer, which
is used as an etching mask to form the lower trench region in the semiconductor
substrate of the upper trench region. The upper and lower trench regions are then
filled with a gate electrode. Also, high concentration source/drain regions are
formed at the top surfaces of the sub-active regions respectively. Therefore, an
effective channel length of the MOS transistor is determined according to the dimension
of the lower trench region.
