This invention discloses an improved trenched metal oxide semiconductor
field effect transistor (MOSFET) device that includes a trenched gate
surrounded by a source region encompassed in a body region above a drain
region disposed on a bottom surface of a substrate. The MOSFET cell
further includes a shielded gate trench (SGT) structure below and
insulated from the trenched gate. The SGT structure is formed
substantially as a round hole having a lateral expansion extended beyond
the trench gate and covered by a dielectric linen layer filled with a
trenched gate material. The round hole is formed by an isotropic etch at
the bottom of the trenched gate and is insulated from the trenched gate
by an oxide insulation layer. The round hole has a lateral expansion
beyond the trench walls and the lateral expansion serves as a vertical
alignment landmark for controlling the depth of the trenched gate. The
MOSFET device has a reduced gate to drain capacitance Cgd depending on
the controllable depth of the trenched gate disposed above the SGT
structure formed as a round hole below the trenched gate.