Field-effect transistor comprising hollow cavity

1. A field-effect transistor comprising:

a semiconductor substrate having a first cavity, the first cavity being hollow;

a gate electrode buried in said semiconductor substrate;

a second cavity which is continuous with said first cavity, the second cavity being hollow; and

diffusion layers formed in said semiconductor substrate and being in physical contact with said first cavity and said second cavity so as to be separated from said semiconductor substrate; and

a device isolation region formed in said semiconductor substrate and having side surfaces, wherein said gate electrode is formed on one of said side surfaces of said device isolation region, and said diffusion layers are formed on another of said side surfaces of said device isolation region.

2. The field-effect transistor according to claim 1 ,

wherein said first cavity is arranged between said diffusion layers.

3. The field-effect transistor according to claim 1 ,

wherein a bottom of said first cavity is located deeper than a bottom of said gate electrode.

4. The field-effect transistor according to claim 1 ,

wherein said gate electrode projects upward from a surface of said semiconductor substrate, and said projected portion of said gate electrode is surrounded by a sidewall.

5. The field-effect transistor according to claim 1 ,

wherein said first cavity reaches a surface of said substrate.

6. The field-effect transistor according to claim 1 ,

wherein said second cavity extends under said diffusion layers.

7. The field-effect transistor according to claim 6 ,

wherein said device isolation region is exposed to said second cavity under said diffusion regions.

8. The field-effect transistor according to claim 6 ,

wherein the substrate is arranged between a device isolation region and said second cavity under said gate electrode.

9. The field-effect transistor according to claim 7 ,

wherein a side surface of said device isolation region is covered by a thermal oxide film.

10. A semiconductor device comprising:

the field-effect transistor of claim 1 .

11. The semiconductor device according to claim 10 , further comprising a second field-effect transistor formed on said substrate,

wherein said gate electrode or said diffusion layers are shared by said first field-effect transistor and said second field-effect transistor.

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

a channel region disposed between the diffusion layers and arranged laterally relative to the gate electrode, wherein the channel region, diffusion layers, and gate electrode are all arranged in a same plane parallel to a surface of the substrate.

13. A field-effect transistor comprising:

a semiconductor substrate having a first cavity, the first cavity being hollow;

a gate electrode;

a second cavity which is continuous with said first cavity, the second cavity being hollow; and

diffusion layers as a source and a drain, wherein said gate electrode and said diffusion layers surround said first cavity in a plane parallel to a surface of said semiconductor substrate, wherein said first cavity and said second cavity are arranged so as to separate said diffusion layers from said semiconductor substrate;

said second cavity extends under said diffusion layers; and

wherein a device isolation region is exposed to said second cavity.

14. The field-effect transistor according to claim 13 ,

wherein a bottom of said first cavity is located deeper than a bottom of said gate electrode.

15. The field-effect transistor according to claim 13 ,

wherein said gate electrode projects upward from a surface of said semiconductor substrate, and said projected portion of said gate electrode is surrounded by a sidewall.

16. The field-effect transistor according to claim 13 ,

wherein said plane is defined by a first direction and a second direction which are orthogonal to each other,

wherein said first cavity is sandwiched between said source and said drain in said first direction, and

said gate electrode is located away from said first cavity in said second direction.

17. The field-effect transistor according to claim 13 ,

wherein said diffusion layers are adjacent to said first cavity.

18. The field-effect transistor according to claim 13 ,

wherein said device isolation region physically contacts said second cavity.

19. The field-effect transistor according to claim 13 , further comprising:

a channel region disposed between the diffusion layers and arranged laterally relative to the gate electrode, wherein the channel region, diffusion layers, and gate electrode are all arranged in a same plane parallel to a surface of the substrate.

20. The field-effect transistor according to claim 13 ,

wherein said source, said drain and said gate electrode are located in a same direction viewed from said first cavity,

wherein said source and said drain are adjacent to said first cavity and said gate electrode is away from said first cavity.