MEMS devices and methods for forming same

1. A method for forming a microelectromechanical system (MEMS) device, the method comprising:

forming a MEMS wafer having a first cavity;

bonding a carrier wafer to a first side of the MEMS wafer, the bonding forming a second cavity, the second cavity having a second pressure, the second pressure being an ambient pressure;

sealing the first cavity, wherein after the sealing the first cavity, the first cavity has a first pressure, the first pressure being less than the second pressure; and

bonding a cap wafer to a second side of the MEMS wafer, the second side being opposite the first side, the bonding forming a third cavity, the third cavity having a third pressure, the third pressure being greater than the first pressure and less than the second pressure.

2. The method of claim 1 , wherein the second pressure is about 1 atmosphere and the third pressure is from about 0.1 mbar to about 500 mbar.

3. The method of claim 1 , wherein the forming the MEMS wafer further comprises forming a fourth cavity having a fourth pressure, the fourth cavity laterally spaced from the first cavity.

4. The method of claim 3 , wherein the first pressure and the fourth pressure are a same pressure.

5. The method of claim 3 , wherein the first cavity and the second cavity comprise a pressure sensor, the third cavity comprises a motion sensor, and the fourth cavity comprises a gyroscope.

6. The method of claim 1 , wherein the sealing the first cavity further comprises forming a conductive bond to seal the first cavity, the first pressure of the first cavity being defined by the process used to form the conductive bond.

7. A method for forming a microelectromechanical system (MEMS) device, the method comprising:

forming a MEMS wafer comprising:

forming a first dielectric layer on a first side of a first substrate;

forming a first polysilicon layer over the first dielectric layer;

forming a bonding layer over the first polysilicon layer; and

exposing a first portion of the first polysilicon layer by removing a portion of the bonding layer;

bonding a carrier wafer to the MEMS wafer using the bonding layer, the carrier wafer having an opening aligned with the first portion of the first polysilicon layer, the opening and the removed portion of the bonding layer forming a first cavity;

patterning the first substrate, the patterning exposing portion of the first dielectric layer;

forming a second dielectric layer on a second side of the first substrate, the second side being opposite the first side;

forming a second polysilicon layer over the second dielectric layer;

patterning the second polysilicon layer to expose portions of the second dielectric layer;

removing portions of the first and second dielectric layers to form a second cavity;

forming a first plurality of conductive bonds on the second polysilicon layer, at least one of the first plurality of conductive bonds sealing the second cavity;

forming a second plurality of conductive bonds to a cap wafer;

bonding the cap wafer to the MEMS wafer by bonding the second plurality of conductive bonds to the first plurality of conductive bonds, the bonding forming a third cavity; and

thinning a backside of the carrier wafer, the thinning exposing a portion of the opening in the carrier wafer.

8. The method of claim 7 , wherein the first cavity has a first pressure, the second cavity has a second pressure, the second pressure being less than the first pressure, the third cavity having a third pressure, the third pressure being greater than the second pressure and less than the first pressure.

9. The method of claim 7 , wherein the removing portions of the first and second dielectric layers forms a fourth cavity laterally adjacent the second cavity, and wherein at least one of the first plurality of conductive bonds seals the fourth cavity.

10. The method of claim 9 , wherein the second cavity and the fourth cavity have a same pressure.

11. The method of claim 9 , wherein the third cavity is laterally between the second cavity and the fourth cavity.

12. The method of claim 9 , wherein the first cavity and the second cavity comprises a pressure sensor, the third cavity comprises a motion sensor, and the fourth cavity comprises a gyroscope.

13. The method of claim 7 , wherein forming the first plurality of conductive bonds on the second polysilicon layer comprises a sputtering process, the pressure level of the second cavity being defined by the sputtering process.

14. A method comprising:

forming a microelectromechanical system (MEMS) wafer having a first cavity and a second cavity, the first cavity having a first pressure and the second cavity having a second pressure;

bonding a carrier wafer to a first side of the MEMS wafer, the bonding forming a third cavity, the third cavity having a third pressure, the third pressure being greater than the first pressure and the second pressure; and

bonding a cap wafer to a second side of the MEMS wafer, the second side being opposite the first side, the bonding forming a fourth cavity, the fourth cavity having a fourth pressure, the fourth pressure being greater than the first pressure and the second pressure and less than the third pressure.

15. The method of claim 14 , wherein the third pressure is about 1 atmosphere and the fourth pressure is from about 0.1 mbar to about 500 mbar.

16. The method claim 14 , wherein the first pressure and the second pressure are a same pressure.

17. The method of claim 14 , wherein the first cavity and the third cavity comprise a pressure sensor, the second cavity comprises a gyroscope, and the fourth cavity comprises a motion sensor.

18. The method of claim 14 , wherein the fourth cavity is between the first cavity and the second cavity.

19. The method of claim 14 , wherein the third cavity comprises an opening extending through the carrier wafer.

20. The method of claim 14 , wherein the fourth cavity comprises a recess in the cap wafer.

21. The method of claim 14 further comprising:

sealing the first cavity and the second cavity, wherein after the sealing the first cavity and the second cavity, the first cavity has the first pressure and the second cavity has the second pressure.