Backside contacts for integrated circuit devices

1. An integrated circuit structure comprising:

a first chip comprising:

a semiconductor substrate;

a well region extending from a top surface to a bottom surface of the semiconductor substrate;

a well pickup region in the well region and overlapping a portion of the well region;

a transistor comprising:

a gate stack underlying the semiconductor substrate; and

a source/drain region adjacent to the gate stack;

a through-via penetrating through the semiconductor substrate, wherein the through-via electrically connects the source/drain region to the well pickup region;

an isolation layer encircling and contacting the through-via, wherein the semiconductor substrate encircles, and is in contact with, the isolation layer; and

a dielectric layer, with the gate stack being in the dielectric layer, and the through-via further penetrates through the dielectric layer.

2. The integrated circuit structure of claim 1 , wherein both the well pickup region and the source/drain region are in the well region, and the well pickup region extends to a top surface of the semiconductor substrate.

3. The integrated circuit structure of claim 1 further comprising a second chip bonded to the first chip, wherein the second chip and the gate stack are on a same side of the semiconductor substrate.

4. The integrated circuit structure of claim 1 further comprising an additional dielectric layer encircling the through-via, wherein the dielectric layer and the additional dielectric layer are on opposite sides of the semiconductor substrate.

5. The integrated circuit structure of claim 1 further comprising:

a silicide region at a top surface of, and contacting, the well pickup region; and

a contact plug over and contacting the silicide region, wherein the contact plug is level with a portion of the through-via.

6. The integrated circuit structure of claim 1 , wherein the through-via is tapered, with upper portions of the through-via being wider than respective lower portions of the through-via.

7. The integrated circuit structure of claim 1 , wherein the well region penetrates through the semiconductor substrate.

8. The integrated circuit structure of claim 1 , wherein the well region comprises a top surface and a bottom surface, both being in contact with dielectric materials.

9. An integrated circuit structure comprising:

a first chip comprising a semiconductor substrate;

a well region extending from a top surface of the semiconductor substrate to a bottom surface of the semiconductor substrate;

a first silicide region at a top surface of the semiconductor substrate, wherein the well region has portions on opposite sides of the first silicide region;

a transistor comprising:

a gate stack overlapped by the well region; and

a source/drain region extending from a bottom surface of the semiconductor substrate up into the well region;

a second silicide region contacting a bottom surface of a portion of the source/drain region; and

a through-via penetrating through the semiconductor substrate, wherein the through-via electrically interconnects the first silicide region and the second silicide region, wherein the through-via is tapered, with a first end of the through-via close to the top surface of the semiconductor substrate being wider than a second end of the through-via close to the bottom surface of the semiconductor substrate.

10. The integrated circuit structure of claim 9 further comprising a well pickup region in the well region, wherein the first silicide region is at a top surface of the well pickup region.

11. The integrated circuit structure of claim 9 further comprising a second chip underlying and bonded to the first chip.

12. The integrated circuit structure of claim 9 further comprising:

a first dielectric layer contacting the top surface of the semiconductor substrate; and

a second dielectric layer contacting the bottom surface of the semiconductor substrate, wherein the through-via further penetrates through both the first dielectric layer and the second dielectric layer.

13. The integrated circuit structure of claim 12 , wherein the first dielectric layer is in contact with the well region.

14. The integrated circuit structure of claim 12 , wherein the through-via further extends higher than the first dielectric layer and lower than the second dielectric layer.

15. The integrated circuit structure of claim 9 , wherein the through-via is tapered, with upper portions being wider than respective lower portions.

16. The integrated circuit structure of claim 9 further comprising a dielectric isolation layer encircling the through-via, wherein the dielectric isolation layer has a first end level with the first end of the through-via, and a second end level with the second end of the through-via.

17. The integrated circuit structure of claim 9 , wherein the through-via has a portion at a same level as the gate stack.

18. An integrated circuit structure comprising:

a semiconductor substrate comprising a top surface and a bottom surface;

a Metal-Oxide Semiconductor (MOS) device comprising:

a gate dielectric underlying the semiconductor substrate, wherein the gate dielectric contacts the bottom surface of the semiconductor substrate;

a gate electrode underlying the gate dielectric; and

a source/drain region on a side of the gate electrode;

a well region extending from the top surface to the bottom surface of the semiconductor substrate, with the source/drain region having a part in the well region;

a well pickup region contacting a top surface of the well region, wherein the well pickup region overlaps a part of the MOS device;

a through-via penetrating through the semiconductor substrate, wherein the through-via electrically connects the well pickup region to the source/drain region;

a dielectric layer over and contacting the top surface of the semiconductor substrate, wherein the through-via further penetrates through the dielectric layer; and

a contact plug in the dielectric layer, wherein the contact plug electrically couples the well pickup region to the through-via.

19. The integrated circuit structure of claim 18 further comprising:

an inter-layer dielectric underlying the semiconductor substrate, wherein the gate electrode of the MOS device is in the inter-layer dielectric, and the through-via further penetrates through the inter-layer dielectric.

20. The integrated circuit structure of claim 18 , wherein the through-via has a top width and a bottom width smaller than the top width.