Device and method for improving RF performance

1. A semiconductor device comprising:

a first silicon-on-insulator (SOI) substrate having a first surface and a second surface opposite the first surface, the first substrate comprising a front-end device disposed on the first surface, the front-end device comprising a transistor, a radio frequency (RF) device and a first interconnect structure; and

a second substrate comprising a cavity disposed at a location corresponding to a location of the RF device;

wherein:

the first SOI substrate and the second substrate are bonded together such that the first surface of the first SOI substrate is facing the cavity in the second substrate, and the cavity is over the RF device,

the second surface of the first SOI substrate comprises a buried insulating layer, and

a passivation layer on the buried insulating layer of the second surface of the first SOI substrate.

2. The semiconductor device of claim 1 , wherein the RF device has a top surface disposed in the cavity.

3. The semiconductor device of claim 1 , wherein the cavity is a vacuum chamber or a cavity filled with a gas.

4. The semiconductor device of claim 1 , wherein the RF device comprises an inductor.

5. The semiconductor device of claim 1 , further comprising:

a second interconnect structure extending through the first SOI substrate and connected to the first interconnect structure; and

a pad disposed on the second surface opposite the first surface of the first SOI substrate, the pad connected to the second interconnect structure.

6. The semiconductor device of claim 5 ,

wherein the passivation layer covers the second surface of the first SOI substrate and exposes a bonding region of the pad.

7. The semiconductor device of claim 5 , wherein the second interconnect structure comprises a through-silicon via.

8. A method for manufacturing a semiconductor device, the method comprising:

providing a first silicon-on-insulator (SOI) substrate having a first surface and a second surface opposite the first surface, the first substrate comprising a front-end device disposed on the first surface, the front-end device comprising a transistor, a radio frequency (RF) device and a first interconnect structure;

providing a second substrate;

forming a cavity in the second substrate at a location corresponding to a location of the RF device;

bonding the first substrate and the second substrate together such that the first surface of the first substrate is facing the cavity in the second substrate, and the cavity is over the RF device;

performing a thinning process on the second surface of the first SOI substrate until a buried insulating layer is exposed.

9. The method of claim 8 , wherein forming the cavity comprises:

forming a patterned mask layer having an opening at a location corresponding to a location of the RF device; and

etching the second substrate using the patterned mask layer as a mask.

10. The method of claim 8 , wherein the RF device comprises an inductor.

11. The method of claim 8 , wherein performing the thinning process comprises a chemical mechanical polishing process.

12. The method of claim 8 , further comprising:

forming a second interconnect structure extending through the first SOI substrate, the second interconnect structure connected to the first interconnect structure;

forming a pad on the second surface of the first SOI substrate, the pad connected to the second interconnect structure.

13. The method of claim 12 , further comprising:

forming a passivation layer covering the buried insulating layer of the first SOI substrate and exposing a portion of a surface of the pad.

14. The method of claim 12 , wherein the second interconnect structure comprises a through-silicon via.

15. An electronic device comprising an electronic component and a semiconductor device connected to the electronic component, wherein the semiconductor device comprises:

a first silicon-on-insulator (SOI) substrate having a first surface and a second surface opposite the first surface, the first substrate comprising a front-end device disposed on the first surface, the front-end device comprising a transistor, a radio frequency (RF) device and a first interconnect structure; and

a second substrate comprising a cavity disposed at a location corresponding to a location of the RF device;

wherein:

the first SOI substrate and the second substrate are bonded together such that the first surface of the first substrate is facing the cavity in the second substrate, and the cavity is over the RF device,

the second surface of the first SOI substrate comprises a buried insulating layer, and

a passivation layer on the buried insulating layer of the second surface of the first SOI substrate.

16. The electronic device of claim 15 , wherein the semiconductor device further comprises:

a second interconnect structure extending through the first SOI substrate and connected to the first interconnect structure; and

a pad disposed on the second surface opposite the first surface of the first SOI substrate, the pad connected to the second interconnect structure and having a bonding surface exposed by the passivation layer.

17. The electronic device of claim 15 , wherein the cavity is a vacuum chamber or a chamber filled with a gas.

18. The electronic device of claim 15 , wherein the RF device comprises an inductor.