Trapped sacrificial structures and methods of manufacturing same using thin-film encapsulation

1. A method of forming a trapped sacrificial structure, comprising:

providing a MEMS region over a substrate, the MEMS region including a MEMS structural layer;

forming a first sacrificial layer over the MEMS structural layer;

removing a part of the first sacrificial layer to leave at least a remaining portion of the first sacrificial layer disposed over the MEMS structural layer;

forming a second sacrificial layer over the remaining portion of the first sacrificial layer, the second sacrificial layer being thicker than the first sacrificial layer;

removing a part of the second sacrificial layer to leave a portion of the second sacrificial layer;

forming an upper microshell layer over the remaining portions of the first and second sacrificial layers;

creating one or more upper release holes in the upper microshell layer; and

removing at least a part of the remaining portions of the first and/or second sacrificial layers through the upper release holes without removing a first sacrificial layer portion and/or a second sacrificial layer portion under the upper microshell layer to form at least one trapped sacrificial structure under the upper microshell layer.

2. The method of claim 1 , further comprising:

forming the first sacrificial layer over and in contact with the MEMS structural layer;

forming the second sacrificial layer over and in contact with the remaining portion of the first sacrificial layer;

removing a part of the second sacrificial layer to leave a portion of the second sacrificial layer over and contacting the remaining portion of the first sacrificial layer;

forming the upper microshell layer over the remaining portions of the first and second sacrificial layers, the upper microshell layer being formed to trap the first and second sacrificial layer portions within a cavity filled with first and second sacrificial material under the upper microshell layer to form the at least one trapped sacrificial structure under the upper microshell layer;

removing at least a part of the remaining portions of the first and/or second sacrificial layers through the upper release holes to form one or more open cavities or open areas under the upper microshell layer and over the MEMS structural layer and not removing the trapped first and second sacrificial layer portions of the trapped sacrificial structure under the upper microshell layer; and

forming a sealing layer to seal the upper release holes in the upper microshell layer.

3. The method of claim 2 , further comprising forming multiple trapped sacrificial structures as multiple individual spacer structures disposed in spaced relationship with each other as part of a semiconductor device die that includes the substrate, a top of each of the spacer structures being formed to extend to a height above the substrate that is greater than a height of tops of one or more other structures above the substrate that are disposed over the substrate in an area defined between the multiple spacer structures.

4. The method of claim 3 , further comprising bringing a molding tool together with the semiconductor device die and contacting the tops of the multiple spacer structures with the molding tool such that the spacer structures act to prevent the molding tool from contacting the tops of the other structures disposed over the substrate in the area defined between the multiple spacer structures.

5. The method of claim 4 , where the other structures disposed over the substrate in the area defined between the multiple spacer structures comprise a membrane transducer structure.

6. The method of claim 2 , further comprising forming the trapped sacrificial structure as a humidity-sensitive capacitor structure by performing steps that comprise:

providing the MEMS region over the substrate to include the MEMS structural layer configured as a first sensor electrode, the MEMS structural layer being disposed on a MEMS sacrificial release layer of the MEMS region;

forming one or more sensor electrode openings to extend through the first sensor electrode of the MEMS structural layer;

forming the first sacrificial layer over and in contact with the MEMS structural layer and within the sensor electrode openings;

removing a part of the first sacrificial layer to leave a portion of the first

sacrificial layer disposed over and within the sensor electrode openings of the MEMS structural layer;

removing a part of the second sacrificial layer to leave a portion of the second sacrificial layer over and contacting the remaining portion of the first sacrificial layer to form a humidity-sensitive capacitor dielectric structure disposed over the sensor electrode openings defined in the MEMS structural layer;

forming an upper microshell layer as a second sensor electrode over and in contact with the humidity-sensitive capacitor dielectric structure, the upper microshell layer being formed to trap the first and second sacrificial layer portions within a cavity filled with the first and second sacrificial material of the humidity-sensitive capacitor dielectric structure disposed under the upper microshell layer;

removing at least a part of the remaining portions of the first and/or second sacrificial layers through the upper release holes to form one or more open cavities or open areas under the upper microshell layer and over the MEMS structural layer and not removing the trapped first and second sacrificial layer portions of the humidity-sensitive capacitor dielectric structure;

removing the MEMS sacrificial release layer and removing the first sacrificial layer portions disposed within the sensor electrode openings of the MEMS structural layer through the upper release holes to form an open fluid communication path under the MEMS structural layer and through the sensor electrode openings to the underside of the humidity-sensitive capacitor dielectric structure following the step of removing at least a part of the remaining portions of the first and/or second sacrificial layers through the upper release holes; and

creating one or more inlet openings in the sealing layer and upper microshell layer that are in fluid communication with the open fluid communication path under the MEMS structural layer and through the sensor electrode openings to the underside of the humidity-sensitive capacitor dielectric structure.

7. The method of claim 6 , where the first sacrificial layer portion trapped within the cavity under the upper microshell layer comprises polyimide.

8. The method of claim 6 , where each of the first and second sacrificial layer portions trapped within the cavity under the upper microshell layer comprises polyimide.

9. The method of claim 6 , where the humidity-sensitive capacitor dielectric structure has an outer periphery; and where the method further comprises creating the inlet openings in the sealing layer and upper microshell layer outside the outer periphery of the humidity-sensitive capacitor dielectric structure.

10. The method of claim 6 , further comprising forming a trapped sacrificial structure as a non-humidity sensitive matched capacitor structure over the same substrate as the humidity-sensitive capacitor structure by steps that comprise:

providing the MEMS region over the substrate to include a MEMS structural layer configured as a first sensor electrode, the MEMS structural layer being disposed on a MEMS sacrificial release layer;

forming the first sacrificial layer over and in contact with a portion of the MEMS structural layer having no sensor electrode openings;

removing a part of the first sacrificial layer to leave a portion of the first sacrificial layer disposed over and the MEMS structural layer having no sensor electrode openings;

removing a part of the second sacrificial layer to leave a portion of the second sacrificial layer over and contacting the remaining portion of the first sacrificial layer to form a matching capacitor dielectric structure disposed over the portion of the MEMS structural layer having no sensor electrode openings;

forming an upper microshell layer as a second sensor electrode over and in contact with the matching capacitor dielectric structure, the upper microshell layer being formed to trap the first and second sacrificial layer portions within a cavity filled with the first and second sacrificial material of the matching capacitor dielectric structure disposed under the upper microshell layer; and

removing at least a part of the remaining portions of the first and/or second sacrificial layers through the upper release holes to form one or more open cavities or open areas under the upper microshell layer and over the MEMS structural layer and not removing the trapped first and second sacrificial layer portions of the matched capacitor dielectric structure.