Double gate depletion mode MOSFET
View Patent ↗A metal-oxide-semiconductor field effect transistor (MOSFET) has a body layer that follows the contour of exposed surfaces of a semiconductor substrate and contains a bottom surface of a shallow trench and adjoined sidewalls. A bottom electrode layer vertically abuts the body layer and provides an electrical bias to the body layer. A top electrode and source and drain regions are formed on the body layer. The thickness of the body layer is selected to allow full depletion of the body layer by the top electrode and a bottom electrode layer. The portion of the body layer underneath the shallow trench extends the length of a channel to enable a high voltage operation. Further, the MOSFET provides a double gate configuration and a tight control of the channel to enable a complete pinch-off of the channel and a low off-current in a compact volume.
1. A semiconductor structure comprising:
a first shallow trench isolation (STI) portion and a second STI portion embedded in a semiconductor substrate comprising a semiconductor material and separated from each other;
a gate dielectric contacting a top surface of said semiconductor substrate, wherein a portion of a top surface of said semiconductor substrate is located between said first STI portion and said second STI portion;
a body layer comprising a first portion of said semiconductor material and contacting said gate dielectric and a bottom surface of said second STI portion and a pair of sidewalls of said second STI portion directly adjoined to opposite ends of said bottom surface of said second STI portion, wherein said body layer contiguously extends between said first STI portion and said second STI portion;
a bottom electrode layer comprising a second portion of said semiconductor material, vertically contacting said body layer, located in said semiconductor substrate, and having a doping of a first conductivity type, wherein said body layer has a doping of a second conductivity type that is the opposite of said first conductivity type;
a source region comprising a third portion of said semiconductor material, having a doping of said second conductivity type, contacting said first STI portion;
a drain region comprising a fourth portion of said semiconductor material, having a doping of said second conductivity type, and contacting said second STI portion and a surface of said semiconductor substrate; and
a top gate electrode contacting said gate dielectric.
2. The semiconductor structure of claim 1 , wherein a resistivity of a body layer sidewall region of said body region is from about 2 to 20 times greater than a resistivity of body layer top regions of said body region.
3. The semiconductor structure of claim 1 , further comprising:
a bottom electrode contact well laterally abutting said bottom electrode layer and having a doping of said first conductivity type; and
a bottom electrode contact region vertically abutting said bottom electrode contact well and yet another surface region of said substrate top surface and having a doping of said first conductivity type.
4. The semiconductor structure of claim 3 , wherein said bottom electrode contact well laterally abuts said body layer directly underneath a shallow trench isolation portion.
5. The semiconductor structure of claim 3 , further comprising:
a primary isolation well layer located directly beneath said bottom electrode layer and having a doping of said second conductivity type;
a secondary isolation well layer located directly beneath said bottom electrode contact region, laterally abutting said primary isolation well layer, and having a doping of said second conductivity type; and
an isolation layer contact well laterally abutting said secondary isolation well layer and having a doping of said second conductivity type.
6. The semiconductor structure of claim 5 , wherein said isolation layer contact well laterally abuts said bottom electrode contact region.
7. The semiconductor structure of claim 5 , further comprising an isolation layer contact region abutting said isolation layer contact well and still another surface region of said substrate top surface and having a doping of said second conductivity type.
8. The semiconductor structure of claim 5 , further comprising a substrate layer abutting said primary isolation well layer, said secondary isolation well layer, said isolation layer contact well, and having a doping of said first conductivity type.
9. The semiconductor structure of claim 8 , wherein said substrate layer, said primary isolation well layer, said secondary isolation well layer, said isolation layer contact well, said bottom electrode contact well, said bottom electrode layer, and said body layer are single crystalline and epitaxially aligned.
10. The semiconductor structure of claim 1 , wherein said gate dielectric abuts said surface region of said substrate top surface and a top surface of said second dielectric portion.
11. The semiconductor structure of claim 1 , wherein a first portion of said body layer vertically abutting said gate electrode and a second portion of said body layer vertically abutting said bottom surface of said second STI portion have a same first thickness.
12. The semiconductor structure of claim 11 , further comprising a bottom electrode contact well laterally abutting said bottom electrode layer, wherein a first portion of said bottom electrode layer vertically abutting said first portion of said body layer and a second portion of said bottom electrode layer vertically abutting said second portion of said body layer have a same second thickness.