Method and structure for CMOS-MEMS thin film encapsulation

1. A method of manufacturing a micro-electromechanical system (MEMS) device, the method comprising:

depositing an insulating layer over a substrate;

forming a plurality of conductive vias in a plurality of first layers of the insulating layer;

forming a plurality of metal structures in a plurality of second layers of the insulating layer, wherein the plurality of first layers are interleaved with the plurality of second layers;

etching a first set of the plurality of conductive vias and a first set of the plurality of metal structures to form a void region in the insulating layer, wherein the etching removes the first set of the plurality of conductive vias and the first set of the plurality of metal structures;

forming a conductive pad on and within a top surface of the insulating layer; and

sealing the void region with an encapsulating structure, wherein at least a portion of the encapsulating structure is above a top surface of the conductive pad.

2. The method of claim 1 , further comprising forming a transistor below the plurality of first layers and the plurality of second layers.

3. The method of claim 2 , further comprising forming a conductive interconnect structure between a top surface of a gate of the transistor and a bottom surface of the conductive pad, the conductive interconnect structure comprising a second set of the plurality of metal structures and a second set of the plurality of conductive vias.

4. The method of claim 1 , further comprising forming a passivation layer over at least one of the plurality of metal structures.

5. A method of manufacturing a complementary metal oxide semiconductor (CMOS) micro-electromechanical system (MEMS) device, the method comprising:

depositing a dielectric layer over a substrate;

forming a plurality of via layers in the dielectric layer, the plurality of via layers comprising a plurality of via structures;

forming a plurality of metal layers in the dielectric layer, the plurality of metal layers comprising a plurality of metal structures, the plurality of metal layers alternating with the plurality of via layers;

etching to remove at least a portion of via structure material and at least a portion of metal structure material to form a void region;

depositing a sealant material on an upper-most via layer of the plurality of via layers, the sealant material sealing the void region, the upper-most via layer comprising a dummy dielectric layer;

depositing a photoresist over the sealant material;

patterning the photoresist to expose a portion of the sealant material;

first etching to remove exposed portions of the sealant material; and

second etching to remove at least a portion of the dummy dielectric layer.

6. The method of claim 5 , further comprising removing photoresist.

7. The method of claim 5 , further comprising forming a passivation layer over an upper-most metal layer of the plurality of metal layers.

8. The method of claim 5 , further comprising forming a conductive pad on and within a top surface of the dielectric layer.

9. The method of claim 8 , further comprising forming a transistor device in at least one of the substrate and the dielectric layer.

10. The method of claim 9 , further comprising forming an interconnect structure between a top surface of a gate of the transistor device and a bottom surface of the conductive pad, the interconnect structure comprising a first set of the plurality of metal structures interleaved with a second set of the plurality of via structures.

11. The method of claim 5 , wherein the first etching and the second etching comprise a same etching.

12. A method of manufacturing a micro-electromechanical system (MEMS) device, the method comprising:

forming a dielectric layer over a substrate;

forming a plurality of via layers and a plurality of metal layers in the dielectric layer by alternately forming a via layer and a metal layers over the substrate, the plurality of via layers having a plurality of vias, and the plurality of metal layers having a plurality of metal features;

forming a metal cap in a top-most metal layer;

forming a passivation layer over the metal cap;

removing a set of vias and a set of metal features to form a void region;

depositing a sealing material over the void region and the metal cap, the sealing material sealing the void region;

depositing a photoresist over the sealing material;

patterning the photoresist to expose a portion of the sealing material;

removing the exposed portion of the sealing material, wherein a dummy insulation structure in a top-most via layer is exposed as a result of removing the exposed portion of the sealing material; and

removing the exposed dummy insulation structure in the top-most via layer.

13. The method of claim 12 , wherein a top-most metal layer is disposed over a top-most via layer after forming the plurality of via layers and the plurality of metal layers.

14. The method of claim 12 , wherein removing the set of vias and the set of metal features is performed using a maskless wet etching.

15. The method of claim 12 , wherein before depositing the sealing material, the void region is purged with an inert gas.

16. The method of claim 12 , further comprising removing at least partially an ambient gas from the void region using a vacuum before depositing the sealing material.

17. The method of claim 12 , wherein the metal cap is formed to have a thickness between about 20 kilo-angstrom and about 40 kilo-angstrom.

18. The method of claim 12 , wherein patterning the photoresist exposes a portion of the sealing material over the passivation layer, wherein the passivation layer remains after removing the exposed portion of the sealing material.

19. The method of claim 12 , wherein after removing the exposed dummy insulation structure, a remaining metal feature in the void region forms an active membrane of the MEMS device, and a metal feature under the void region forms a reference membrane of the MEMS device, wherein the active membrane and the reference membrane are separated by the void region.

20. The method of claim 1 , further comprising:

forming a patterned mask layer over the encapsulating structure;

removing portions of the encapsulating structure exposed by the patterned mask layer, wherein removing portions of the encapsulating structure exposes a dummy dielectric structure in a top-most layer of the plurality of first layers; and

removing the exposed dummy dielectric structure.