High voltage field effect transistors with superjunctions and method of making the same
A field effect transistor includes a semiconductor channel having a doping of a first conductivity type, a gate structure overlying the semiconductor channel, a source region and a drain region, a source-side extension region including a source-side-extension plate portion and source-side-extension rail portions that overlie the source-side-extension plate portion, source-side counter-doped rails having a doping of the first conductivity type, a drain-side extension region including a drain-side-extension plate portion and drain-side-extension rail portions that overlie the drain-side-extension plate portion, and drain-side counter-doped rails interlaced with the drain-side-extension rail portions. A first superjunction structure is provided between the source-side counter-doped rails and the source-side extension region. A second superjunction structure is provided between the drain-side counter-doped rails and the drain-side extension region.
1 . A field effect transistor, comprising:
a semiconductor channel having a doping of a first conductivity type;
a gate structure overlying the semiconductor channel and comprising a stack of a gate dielectric and a gate electrode;
a source region and a drain region having a doping of a second conductivity type and laterally spaced from the gate structure and from each other along a first horizontal direction, the second conductivity type being an opposite of the first conductivity type;
a source-side extension region laterally extending between the source region and a first bottom surface segment of the gate dielectric, having a doping of the second conductivity type, and including a source-side-extension plate portion and source-side-extension rail portions that overlie the source-side-extension plate portion;
source-side counter-doped rails having a doping of the first conductivity type, embedded in the source-side extension region, and interlaced with the source-side-extension rail portions along a second horizontal direction to provide a first superjunction structure;
a drain-side extension region laterally extending between the drain region and a second bottom surface segment of the gate dielectric, having a doping of the second conductivity type, and including a drain-side-extension plate portion and drain-side-extension rail portions that overlie the drain-side-extension plate portion; and
drain-side counter-doped rails having a doping of the first conductivity type, embedded in the drain-side extension region, and interlaced with the drain-side-extension rail portions along the second horizontal direction to provide a second superjunction structure.
2 . The field effect transistor of claim 1 , wherein:
the source-side-extension rail portions laterally extend along the first horizontal direction and have a respective uniform width along the second horizontal direction; and
the drain-side-extension rail portions laterally extend along the first horizontal direction and have a respective uniform width along the second horizontal direction.
3 . The field effect transistor of claim 2 , wherein the source-side counter-doped rails and the source-side-extension rail portions with a uniform periodicity along the second horizontal direction.
4 . The field effect transistor of claim 1 , wherein:
the source-side counter-doped rails are in contact with a sidewall of the source region; and
the drain-side counter-doped rails are in contact with a sidewall of the drain region.
5 . The field effect transistor of claim 1 , wherein:
the source-side counter-doped rails are not in direct contact with the semiconductor channel; and
the drain-side counter-doped rails are not in direct contact with the semiconductor channel.
6 . The field effect transistor of claim 1 , wherein:
top surfaces of the source-side counter-doped rails are located within a same horizontal plane as a top surface of the source-side extension region;
the source-side extension region has a first thickness; and
the source-side counter-doped rails have a second thickness that is less than the first thickness.
7 . The field effect transistor of claim 6 , wherein the source region has a third thickness that is less than the first thickness and is greater than the second thickness.
8 . The field effect transistor of claim 1 , further comprising a dielectric gate spacer that laterally surrounds the gate electrode, wherein each of the source-side counter-doped rails and the drain-side counter-doped rails has an areal overlap with a respective portion of the dielectric gate spacer in a plan view that is perpendicular to an interface between the semiconductor channel and the gate dielectric.
9 . The field effect transistor of claim 8 , wherein each of the source-side-extension rail portions and the source-side counter-doped rails are in contact with a respective segment of a bottom surface of the gate dielectric.
10 . The field effect transistor of claim 1 , wherein each of the source-side counter-doped rails and the drain-side counter-doped rails has an areal overlap with a respective portion of the gate electrode in a plan view that is perpendicular to an interface between the semiconductor channel and the gate dielectric.
11 . The field effect transistor of claim 1 , wherein each of the source-side counter-doped rails and the drain-side counter-doped rails does not have any areal overlap with the gate electrode in a plan view that is perpendicular to an interface between the semiconductor channel and the gate dielectric.
12 . The field effect transistor of claim 1 , wherein:
the semiconductor channel comprises dopants of the first conductivity type at a first average atomic concentration;
the source-side-extension plate portion comprises dopants of the second conductivity type at a second average atomic concentration that is higher than the first average atomic concentration; and
the source-side counter-doped rails comprise dopants of the first conductivity type at a third average atomic concentration that is higher than the second average atomic concentration.
13 . The field effect transistor of claim 12 , wherein the source-side-extension rail portions comprises dopants of the first conductivity type at the third average atomic concentration and comprises dopants of the second conductivity type at a fourth average atomic concentration that is higher than the third average atomic concentration.
14 . The field effect transistor of claim 12 , wherein the source region and the drain region comprises dopants of the second conductivity type at a higher average atomic concentration than the source-side-extension rail portions and the drain-side-extension rail portions.