Methods of fabricating high voltage mosfet having doped buried layer

Abstract

A MOSFET includes an insulated gate electrode on a surface of a semiconductor substrate having an impurity region of first conductivity type therein that extends to the surface. Source and drain regions of second conductivity type are provided in the impurity region. The source region includes a highly doped source contract region that extends to the surface and a lightly doped source extension. The lightly doped source extension extends laterally underneath a first end of the insulated gate electrode and defines a source-side P-N junction with the well region. The drain region includes a highly doped drain contact region that extends to the surface and a lightly doped drain extension. The lightly doped drain extension extends laterally underneath a second end of the insulated gate electrode and defines a drain-side P-N junction with the well region. This well region, which extends within the impurity region and defines a non-rectifying junction therewith, is more highly doped than the impurity region. The well region extends opposite the insulated gate electrode and has a sufficient width that dopants therein partially compensate innermost portions of the lightly doped source and drain extensions that extend underneath the insulated gate electrode. However, the well region is not so wide as to provide compensation to remaining portions of the lightly doped source and drain extensions or the source and drain contact regions.