Semiconductor structure having NFET and PFET formed in SOI substrate with underlapped extensions
A semiconductor structure which includes a semiconductor on insulator (SOI) substrate. The SOI substrate includes a base semiconductor layer; a buried oxide (BOX) layer in contact with the base semiconductor layer; and an SOI layer in contact with the BOX layer. The semiconductor structure further includes a circuit formed with respect to the SOI layer, the circuit including an N type field effect transistor (NFET) having source and drain extensions in the SOI layer and a gate; and a P type field effect transistor (PFET) having source and drain extensions in the SOI layer and a gate. There may also be a well under each of the NFET and PFET. There is a nonzero electrical bias being applied to the SOI substrate. One of the NFET extensions and PFET extensions may be underlapped with respect to the NFET gate or PFET gate, respectively.
1. A semiconductor structure comprising:
a semiconductor on insulator (SOI) substrate comprising:
a base semiconductor layer;
a buried oxide (BOX) layer in contact with the base semiconductor layer; and
an SOI layer in contact with the BOX layer;
a circuit formed with respect to the SOI layer, the circuit comprising:
an N type field effect transistor (NFET) having source and drain extensions in the SOI layer and an NFET gate;
a P type field effect transistor (PFET) having source and drain extensions in the SOI layer and a PFET gate;
a first well in the base semiconductor layer under the NFET; and
a second well in the base semiconductor layer under the PFET; and
the SOI substrate having a nonzero electrical bias;
wherein (i) the NFET source and drain extensions are overlapped with respect to the NFET gate and the PFET source and drain extensions are underlapped with respect to the PFET gate, or (ii) the NFET source and drain extensions are underlapped with respect to the NFET gate and the PFET source and drain extensions are overlapped with respect to the PFET; and
wherein for the NFET and PFET each having source and drain extensions and a gate channel underneath a gate, overlapped is defined as the source and drain extensions extending into the gate channel and underlapped is defined as the source and drain extensions spaced away from the gate channel.
2. The semiconductor structure of claim 1 wherein the NFET source and drain extensions are overlapped with respect to the NFET gate, the PFET source and drain extensions are underlapped with respect to the PFET gate and the SOI substrate has a negative SOI substrate bias.
3. The semiconductor structure of claim 2 wherein the NFET gate has a spacer directly contacting the NFET gate and the PFET gate has a spacer directly contacting the PFET gate such that the PFET gate spacer is thicker than the NFET gate spacer.
4. The semiconductor structure of claim 2 wherein the underlap is 2 to 6 nanometers.
5. The semiconductor structure of claim 1 wherein the PFET source and drain extensions are overlapped with respect to the PFET gate, the NFET source and drain extensions are underlapped with respect to the NFET gate and the SOI substrate has a positive SOI substrate bias.
6. The semiconductor structure of claim 5 wherein the NFET gate has a spacer directly contacting the NFET gate and the PFET gate has a spacer directly contacting the PFET gate such that the NFET gate spacer is thicker than the PFET gate spacer.
7. The semiconductor structure of claim 5 wherein the underlap is 3 to 8 nanometers.
8. The semiconductor structure of claim 1 wherein the SOI layer is an extremely thin SOI layer.
9. The semiconductor structure of claim 1 wherein the SOI layer is an extremely thin SOI layer having a thickness of 3 to 15 nanometers.
10. The semiconductor structure of claim 1 wherein the first well has a polarity opposite to a polarity of the second well.
11. A semiconductor structure comprising:
a semiconductor on insulator (SOI) substrate having a nonzero electrical bias being applied to the SOI substrate, the SOI substrate comprising:
a base semiconductor layer;
a buried oxide (BOX) layer in contact with the base semiconductor layer; and
an SOI layer in contact with the BOX layer; and
a circuit formed with respect to the SOI layer, the circuit comprising:
an N type field effect transistor (NFET) having source and drain extensions in the SOI layer and an NFET gate; and
a P type field effect transistor (PFET) having source and drain extensions in the SOI layer and a PFET gate;
wherein the NFET drain and source extensions are underlapped with respect to the NFET gate or the PFET drain and source extensions are underlapped with respect to the PFET gate; and
wherein for the NFET and PFET each having source and drain extensions and a gate channel underneath a gate, underlapped is defined as the source and drain extensions spaced away from the gate channel.
12. The semiconductor structure of claim 11 , wherein the PFET source and drain extensions are underlapped with respect to the PFET gate and the SOI substrate has a negative SOI substrate bias.
13. The semiconductor structure of claim 12 wherein the NFET source and drain extensions are not underlapped or overlapped with respect to the NFET gate.
14. The semiconductor structure of claim 12 wherein the NFET source and drain extensions are overlapped with respect to the NFET gate.
15. The semiconductor structure of claim 12 wherein the NFET gate has a spacer and the PFET gate has a spacer such that the PFET gate spacer is thicker than the NFET gate spacer.
16. The semiconductor structure of claim 12 wherein the PFET source and drain extensions are underlapped in an amount of 2 to 6 nanometers with respect to an edge of the gate.
17. The semiconductor structure of claim 11 wherein the NFET source and drain extensions are underlapped with respect to the NFET gate and the SOI substrate has a positive SOI substrate bias.
18. The semiconductor structure of claim 17 wherein the PFET source and drain extensions are not underlapped or overlapped with respect to the PFET gate.
19. The semiconductor structure of claim 17 wherein the PFET source and drain extensions are overlapped with respect to the PFET gate.
20. The semiconductor structure of claim 17 wherein the NFET gate has a spacer directly contacting the NFET gate and the PFET gate has a spacer directly contacting the PFET gate such that the NFET gate spacer is thicker than the PFET gate spacer.
21. The semiconductor structure of claim 17 wherein the NFET extensions are underlapped in an amount of 3 to 8 nanometers with respect to an edge of the gate.
22. The semiconductor structure of claim 11 wherein the SOI layer is an extremely thin SOI layer having a thickness of 3 to 15 nanometers.
23. The semiconductor structure of claim 11 further comprising a first well in the base semiconductor layer under the NFET and a second well in the base semiconductor layer under the PFET wherein the first well has a polarity opposite to a polarity of the second well.