MEMS structure with bilayer stopper and method for forming the same

1. A microelectromechanical systems (MEMS) package, comprising:

a semiconductor substrate having a metallization layer over the semiconductor substrate;

a first planarization layer over the metallization layer and a second planarization layer over the first planarization layer, wherein the first and second planarization layers have an inner sidewall defining a first cavity therein exposing the metallization layer;

a MEMS device structure bonded to the second planarization layer, wherein the MEMS device structure comprises a moveable element over the first cavity; and

a first stopper placed on the exposed metallization layer and in the first cavity, comprising a patterned conductive layer and an underlying patterned insulating layer, wherein the inner sidewall of the first and second planarization layers is entirely spaced apart from the first stopper.

2. The MEMS package as claimed in claim 1 , wherein the metallization layer comprises a first metal feature below a bottom of the first cavity, and the first stopper further comprises a conductive connector in the patterned insulating layer, such that the patterned conductive layer is electrically connected to the first metal feature through the conductive connector.

3. The MEMS package as claimed in claim 2 , wherein the first metal feature is electrically connected to ground.

4. The MEMS package as claimed in claim 2 , wherein the metallization layer further comprises a second metal feature that is coupled to an electric potential and is electrically connected between the first metal feature and the moveable element.

5. The MEMS package as claimed in claim 1 , further comprising a second stopper placed on the exposed metallization layer in the first cavity, wherein the second stopper is made of the same material as the patterned insulating layer of the first stopper and the first planarization layer, and the second stopper has a height substantially equal to that of the patterned insulating layer of the first stopper.

6. The MEMS package as claimed in claim 1 , further comprising a second stopper placed on the exposed metallization layer in the first cavity, wherein the second stopper is made of material layers that are the same as the first planarization layer and the second planarization layer, and the second stopper has a height greater than that of the patterned insulating layer of the first stopper.

7. The MEMS package as claimed in claim 1 , wherein the patterned conductive layer comprises metal or conductive polymer, and the patterned insulating layer comprises silicon oxide, silicon nitride, silicon carbide, or silicon oxynitride.

8. A microelectromechanical systems (MEMS) package, comprising:

a semiconductor substrate having a metallization layer over the semiconductor substrate;

a planarization structure over the metallization layer, having an inner sidewall defining a first cavity exposing the metallization layer;

a MEMS device structure bonded to the planarization structure, wherein the MEMS device structure comprises a moveable element over the first cavity; and

a first stopper and a second stopper placed on the exposed metallization layer and in the first cavity,

wherein the inner sidewall of the planarization structure is entirely spaced apart from the first stopper and the second stopper, wherein the first stopper has a height greater than that of the second stopper, and wherein the first stopper comprises a patterned conductive layer and an underlying patterned insulating layer.

9. The MEMS package as claimed in claim 8 , wherein the metallization layer comprises a first metal feature below a bottom of the first cavity and electrically connected to ground, and the first stopper further comprises a conductive connector in the patterned insulating layer, such that the patterned conductive layer is electrically connected to the first metal feature through the conductive connector.

10. The MEMS package as claimed in claim 8 , wherein the metallization layer comprises a first metal feature below a bottom of the first cavity and a second metal feature coupled to an electric potential and electrically connected between the first metal feature and the moveable element, and the first stopper further comprises a conductive connector in the patterned insulating layer, such that the patterned conductive layer is electrically connected to the first metal feature through the conductive connector.

11. The MEMS package as claimed in claim 8 , wherein the second stopper is made of the same material layer as the patterned insulating layer of the first stopper, and the second stopper has a height substantially equal to that of the patterned insulating layer of the first stopper.

12. The MEMS package as claimed in claim 8 , wherein the second stopper is made of the same material as that of the planarization structure, and the second stopper has a height greater than that of the patterned insulating layer of the first stopper.

13. The MEMS package as claimed in claim 8 , wherein the patterned conductive layer comprises metal or conductive polymer, and the patterned insulating layer comprises silicon oxide, silicon nitride, silicon carbide, or silicon oxynitride.

14. A microelectromechanical systems (MEMS) package, comprising:

a semiconductor substrate having a metallization layer;

a planarization structure over the metallization layer, having an inner sidewall defining a first cavity exposing the metallization layer;

a MEMS device structure bonded to the planarization structure, wherein the MEMS device structure comprises a moveable element over the first cavity;

a cap layer bonded to the MEMS device structure, having a second cavity over the moveable element; and

a first stopper placed on the exposed metallization layer and in the first cavity, comprising a patterned conductive layer and an underlying patterned insulating layer, wherein the inner sidewall of the planarization structure is entirely spaced apart from the first stopper.

15. The MEMS package as claimed in claim 14 , further comprising a second stopper placed on the exposed metallization layer in the first cavity, wherein the second stopper is made of the same material as the patterned insulating layer of the first stopper and the planarization structure, and wherein the first stopper has a height greater than that of the second stopper.

16. The MEMS package as claimed in claim 15 , wherein the cap layer comprises a third stopper facing the moveable element.

17. The MEMS package as claimed in claim 16 , wherein the third stopper is aligned with the first stopper.

18. The MEMS package as claimed in claim 14 , wherein the metallization layer comprises a first metal feature below a bottom of the first cavity, and the first stopper further comprises a conductive connector in the patterned insulating layer, such that the patterned conductive layer is electrically connected to the first metal feature through the conductive connector.

19. The MEMS package as claimed in claim 18 , wherein the metallization layer further comprises a second metal feature that is electrically connected between the first metal feature and the moveable element.

20. The MEMS package as claimed in claim 14 , wherein the patterned conductive layer comprises metal or conductive polymer, and the patterned insulating layer comprises silicon oxide, silicon nitride, silicon carbide, or silicon oxynitride.