Asymmetric FET for FDSOI devices
The present disclosure relates generally to semiconductor structures, and more particularly to asymmetric field effect transistors (FET) on fully depleted silicon on insulator (FDSOI) semiconductor devices for high frequency and high voltage applications and their method of manufacture. The semiconductor device of the present disclosure includes a semiconductor-on-insulator (SOI) layer disposed above a substrate, the SOI layer having a source region, a channel region, a drift region and a drain region, where the drift region adjoins the drain region and the channel region, a gate structure disposed on the channel region, a multilayer drain spacer disposed on a drain-facing sidewall of the gate structure and covering the drift region, and a source spacer disposed on a source-facing sidewall of the gate structure, where the source and drain spacers are asymmetric with each other.
1. A semiconductor device comprising:
a semiconductor-on-insulator (SOI) layer disposed above a substrate, the SOI layer comprising a source region, a channel region, a drift region and a drain region, wherein the drift region adjoins the drain region and the channel region;
a gate structure disposed on the channel region;
a multilayer drain spacer disposed on a drain-facing sidewall of the gate structure and covering the drift region, wherein the multilayer drain spacer comprises at least three spacer layers overlying the drift region; and
a source spacer disposed on a source-facing sidewall of the gate structure, the source spacer comprising a single layer, wherein the source and drain spacers are shaped asymmetrically when compared with each other.
2. The device of claim 1 , wherein the multilayer drain spacer comprises first, second and third spacer layers.
3. The device of claim 2 , wherein the first spacer layer contacts the drain-facing sidewall of the gate structure and is disposed on the drift region.
4. The device of claim 3 , wherein the second spacer layer is on the first spacer layer, and the third spacer layer is on the second spacer layer.
5. The device of claim 4 , wherein the second spacer layer conforms to the first spacer layer, and the second spacer layer has a L shaped geometry.
6. The device of claim 4 , wherein the multilayer drain spacer has a tapered thickness that increases from a top edge to a bottom edge.
7. The device of claim 1 , wherein the drift region has a dopant concentration in the range of 1e 18 atoms/cm 3 to 5e 19 atoms/cm 3 .
8. The device of claim 1 , wherein the drift region has a length in the range of 20 nm to 60 nm.
9. The device of claim 1 , further comprising an outer spacer layer disposed on the source spacer.
10. The device of claim 1 , wherein the substrate comprises an N-type well flanked by P-type wells.
11. The device of claim 10 , wherein the N-type well is positioned below the drift region.
12. The device of claim 1 , wherein the SOI layer is a fully depleted SOI layer.