Field-effect transistor, method of manufacturing the same, and radio-frequency device

1. A field-effect transistor comprising:

a gate electrode;

a semiconductor layer having a source region and a drain region with the gate electrode in between;

contact plugs comprising a first conductive material, wherein a first contact plug of the contact plugs is provided on the source region, and wherein a second contact plug of the contact plugs is provided on the drain region;

first metals, wherein one of the first metals is stacked on the first contact plug, and wherein a second one of the first metals is stacked on the second contact plug;

one or more insulating films provided in at least one of

a first region below bottom surfaces of the first metals along a stacking direction and between the contact plugs along an in-plane direction of the semiconductor layer,

a second region between top surfaces of the first metals and the bottom surfaces of the first metals along the stacking direction and between the contact plugs along an in-plane direction of the semiconductor layer, and

a third region above the top surfaces of the first metals along the stacking direction and between the contact plugs along an in-plane direction of the semiconductor layer, and

a low-dielectric constant region provided at least in the second region.

2. The field-effect transistor according to claim 1 , wherein the first metals comprising a second conductive material that is different from the first conductive material.

3. The field-effect transistor according to claim 1 , wherein the low-dielectric constant region comprises a cavity.

4. The field-effect transistor according to claim 1 , wherein the one or more insulating films include

a first insulating film at least extending along a side surface of the gate electrode,

a second insulating film, at least a portion of the first insulating film provided between the second insulating film and the gate electrode.

5. The field-effect transistor according to claim 4 , wherein the second insulating film at least extending along the side surface of the gate electrode.

6. The field-effect transistor according to claim 4 , wherein the one or more insulating films further includes a third insulating film provided between the contact plugs along the in-plane direction, wherein the low-dielectric constant region comprises a cavity, and wherein the third insulating film is positioned outside a side section of the cavity.

7. The field-effect transistor according to claim 6 , wherein the third insulating film is provided below the bottom surfaces of the first metals along the stacking direction.

8. The field-effect transistor according to claim 6 , wherein the third insulating film is provided above the top surfaces of the first metals along the stacking direction.

9. The field-effect transistor according to claim 6 , wherein the one or more insulating films further include a fourth insulating film above a top surface of the third insulating film, and wherein the cavity is below the fourth insulating film in the stacking direction.

10. The field-effect transistor according to claim 9 , wherein at least one of the first insulating film, the second insulating film, the third insulating film, and the fourth insulating film is provided between the cavity and the gate electrode.

11. The field-effect transistor according to claim 1 , wherein the low-dielectric constant region comprises a cavity, wherein, as viewed in a cross section including the stacking direction and a direction from the source region to the drain region, the cavity over the gate electrode is a single cavity.

12. The field-effect transistor according to claim 1 , wherein the low-dielectric constant region is provided in the first region.

13. The field-effect transistor according to claim 1 , wherein the low-dielectric constant region is provided in the third region.

14. The field-effect transistor according to claim 1 , further comprising

an active region including

the gate electrode,

the semiconductor layer,

the contact plugs, and

an isolation region provided outside the active region, the isolation region including a gate contact coupled to the gate electrode.

15. The field-effect transistor according to claim 1 , further comprising:

a device region in which the source region and the drain region are provided in the semiconductor layer, the device region including the low-dielectric constant region;

a wiring region including a multilayer wiring section; and

a device isolation layer that partitions the device region and the wiring region.

16. The field-effect transistor according to claim 1 , wherein the low-dielectric constant region includes a first portion and a second portion.

17. The field-effect transistor according to claim 16 , wherein the first portion is positioned in the second region and the second portion is positioned in the third region.

18. The field-effect transistor according to claim 17 , wherein the first portion is positioned in the second region and the first region.

19. The field-effect transistor according to claim 16 , wherein the first portion has a first width in a direction that is traverse to the stacking direction and the second portion has a second width in the direction that is traverse to the stacking direction that is different than the first width.

20. The field-effect transistor according to claim 19 , wherein the gate electrode has a third width in the direction that is traverse to the stacking direction, and wherein the third width is smaller than one of the first width or the second width.

21. The field-effect transistor according to claim 19 , wherein the gate electrode has a third width in the direction that is traverse to the stacking direction, and wherein the third width is larger than one of the first width or the second width.

22. The field-effect transistor according to claim 16 , wherein the first portion is positioned in the first region and the second portion is positioned in the second region.

23. The field-effect transistor according to claim 22 , wherein the first portion is symmetrical with the second portion.

24. The field-effect transistor according to claim 16 , wherein the low-dielectric constant region includes a third portion that is positioned in the third region.

25. The field-effect transistor according to claim 24 , wherein the first portion is symmetrical with the second portion, and wherein the second portion is symmetrical with the third portion.

26. The field-effect transistor according to claim 24 , wherein the first portion is asymmetrical with the second portion, and wherein the second portion is asymmetrical with the third portion.

27. The field-effect transistor according to claim 24 , wherein the first portion has a first width in a direction that is traverse to the stacking direction, wherein the second portion has a second width in the direction that is traverse to the stacking direction that is different than the first width, and the third portion has a third width in the direction that is traverse to the stacking direction that is different than the first width and the second width.

28. The field-effect transistor according to claim 27 , wherein the gate electrode has a fourth width in the direction that is traverse to the stacking direction, and wherein the fourth width is smaller than one of the first width, the second width, or the third width.

29. The field-effect transistor according to claim 27 , wherein the gate electrode has a fourth width in the direction that is traverse to the stacking direction, and wherein the fourth width is larger than one of the first width, the second width, or the third width.