Field MOS transistor and semiconductor integrated circuit including the same

A field MOS transistor comprising:

• a semiconductor substrate of first conductivity type;
• an epitaxial layer of second conductivity type formed on the semiconductor substrate;
• a field insulating film formed on the epitaxial layer;
• a heavily-doped isolation layer of first conductivity type formed in a predetermined location on the semiconductor substrate, the heavily-doped isolation layer surrounding an island region of the epitaxial layer;
• a lightly-doped isolation layer of first conductivity type formed on the heavily-doped isolation layer, the lightly-doped isolation layer, along with the heavily-doped isolation layer, surrounding the island region of the epitaxial layer;
• an embedded layer of second conductivity type formed below an island region of the epitaxial layer;
• an embedded layer of first conductivity type formed on the embedded layer of second conductivity type, the embedded layer having substantially the same doping level as that of the heavily-doped isolation layer;
• a channel formation region of first conductivity type formed on the embedded layer of first conductivity type so as to be joined to a lower surface of the field insulating film, the channel formation region having substantially the same doping level as that of the lightly-doped isolation layer;
• a gate electrode formed on the field insulating film above the channel formation region;
• and
• a source region and a drain region of second conductivity type respectively formed within the island region of the epitaxial layer and on the opposite sides of the channel formation region;
• the source region and the drain region of second conductivity type respectively formed on the embedded layer of first conductivity type and on the opposite sides of the channel formation region.