Methods for forming MEMS devices

1. A method comprising:

forming a Micro-Electro-Mechanical System (MEMS) device on a front surface of a substrate, wherein the MEMS device comprises a capacitor;

after the step of forming the MEMS device, etching a through-opening from a backside of the substrate to separate the substrate into a first portion and a second portion;

etching an additional through-opening from the backside of the substrate to separate the substrate into the second portion and a third portion;

filling the through-opening and the additional through-opening with a dielectric material, wherein the dielectric material insulates the first portion from the second portion, and the second portion from the third portion; and

forming a first electrical connection and a second electrical connection on the backside of the substrate, wherein the first electrical connection and the second electrical connection are electrically coupled to a first capacitor plate and a second capacitor plate, respectively, of the capacitor through the first portion and the third portion, respectively, of the substrate.

2. The method of claim 1 , wherein the step of forming the MEMS device comprises a high-temperature process performed at a high temperature, and wherein the dielectric material comprises a low-temperature material damageable at the high temperature.

3. The method of claim 1 , wherein an entirety of the through-opening is filled with a homogenous dielectric material.

4. The method of claim 1 , wherein the dielectric material comprises a photosensitive material.

5. The method of claim 1 , wherein the through-opening forms a ring encircling the first portion of the substrate, wherein after the step of filling the through-opening with the dielectric material, a portion of the dielectric material covers a back surface of the first portion of the substrate, and wherein the method further comprises removing the portion of the dielectric material to expose the back surface of the first portion of the substrate.

6. The method of claim 1 further comprising bonding a cap over the MEMS device, wherein the step of filling the through-opening and the step of forming the electrical connection are performed after the step of bonding the cap.

7. A method comprising:

forming a Micro-Electro-Mechanical System (MEMS) device on a front surface of a substrate;

bonding a cap on the front surface of the substrate to cover the MEMS device;

forming a through-opening from a backside of the substrate after bonding the cap, wherein the through-opening forms a ring encircling a first portion of the substrate;

filling the through-opening with a dielectric material, wherein the dielectric material electrically insulates the first portion of the substrate from a second portion of the substrate, and wherein after the step of filling the through-opening with the dielectric material a portion of the dielectric material covers a back surface of the substrate;

removing a first part of the portion of the dielectric material to expose the back surface of the first portion of the substrate, wherein a second part of the portion of the dielectric material is not removed, and remains to cover the back surface of the substrate; and

forming an electrical connection on the backside of the substrate, wherein the electrical connection is electrically coupled to the MEMS device through the first portion of the substrate.

8. The method of claim 7 , wherein the step of forming the through-opening is performed after the step of forming the MEMS device.

9. The method of claim 7 , wherein the dielectric material is damageable at a temperature higher than about 150° C.

10. The method of claim 7 , wherein an entirety of the through-opening is filled with the dielectric material, and wherein the dielectric material is homogenous.

11. The method of claim 7 , wherein the dielectric material comprises a photosensitive material.

12. The method of claim 7 , wherein the MEMS device comprises a capacitor comprising two capacitor plates, and wherein the electrical connection is electrically coupled to one of the two capacitor plates.

13. A method comprising:

forming a Micro-Electro-Mechanical System (MEMS) capacitor on a front surface of a semiconductor substrate comprising:

depositing a conductive layer over the semiconductor substrate;

patterning the conductive layer to form a first capacitor plate of the MEMS capacitor;

depositing a polysilicon layer over the semiconductor substrate;

patterning the polysilicon layer to form a second capacitor plate of the MEMS capacitor, wherein the second capacitor plate overlaps the first capacitor plate;

forming a first and a second contact plug electrically connecting the first and the second capacitor plate to a first portion and a second portion, respectively, of the semiconductor substrate;

etching the semiconductor substrate to electrically decouple the first portion and the second portion of the semiconductor substrate from each other; and

forming a first and a second electrical connection electrically coupled to the first portion and the second portion, respectively, of the semiconductor substrate.

14. The method of claim 13 further comprising, after the step of etching the semiconductor substrate, filling recesses in the semiconductor substrate with a dielectric material, wherein the recesses are formed during the step of etching the semiconductor substrate.

15. The method of claim 14 , wherein the dielectric material comprises a photosensitive material.

16. The method of claim 13 further comprising bonding a cap on the front surface of the substrate.

17. The method of claim 13 , wherein the first and the second contact plugs penetrate through, and are in physical contact with, a first portion and a second portion of the conductive layer, wherein the first portion of the conductive layer and the first capacitor plate form a continuous portion of the conductive layer.

18. The method of claim 13 further comprising, before forming the conductive layer and the polysilicon layer, forming a dielectric layer, wherein the dielectric layer electrically insulates the conductive layer from the semiconductor substrate.