Planar microshells for vacuum encapsulated devices and damascene method of manufacture
View Patent ↗Low temperature, multi-layered, planar microshells for encapsulation of devices such as MEMS and microelectronics. The microshells include a planar perforated pre-sealing layer, below which a non-planar sacrificial layer is accessed, and a sealing layer to close the perforation in the pre-sealing layer after the sacrificial material is removed. In an embodiment, the pre-sealing layer has perforations formed with a damascene process to be self-aligned to the chamber below the microshell. The sealing layer may include a nonhermetic layer to physically occlude the perforation and a hermetic layer over the nonhermetic occluding layer to seal the perforation. In a particular embodiment, the hermetic layer is a metal which is electrically coupled to a conductive layer adjacent to the microshell to electrically ground the microshell.
1. A method of forming a microshell comprising:
forming a non-planar sacrificial layer over a substrate;
forming a pre-sealing layer over the non-planar sacrificial layer;
planarizing the pre-sealing layer to perforate the pre-sealing layer with a topographic feature of the non-planar sacrificial layer with a plurality of perforations, with adjacent perforations in the plurality offset to form a staggered perforation pattern;
removing the non-planar sacrificial layer through the perforations to form a chamber around a device under the pre-sealing layer; and
sealing the pre-sealing layer.
2. The method of claim 1 , where the staggered perforation pattern of the formed microshell is configured to distribute stress placed on the microshell in a substantially uniform manner such that the microshell deflects substantially isotropically in response to the stress.
3. A method of lowering the magnitude of residual stress in a microshell comprising:
depositing a pre-sealing layer with a first stress over a sacrificial layer;
perforating the pre-sealing layer;
removing the sacrificial layer; and
sealing the perforation with a sealing layer having a stress opposite the first stress to lower the magnitude of the residual stress of the microshell below the magnitude of stress in either the pre-sealing layer or the sealing layer.
4. The method of claim 3 , wherein the forming the pre-sealing layer further comprises depositing a compressively stressed film over the sacrificial layer.
5. The method of claim 3 , wherein the pre-sealing layer further comprises depositing a tensilely stressed film.
6. The method of claim 3 , wherein sealing the pre-sealing layer further comprises first depositing a compressively stressed film and then depositing a tensilely stressed film.
7. The method of claim 3 , where the first stress is a compressive stress; and where sealing the pre-sealing layer further comprises first depositing a compressively stressed film and then depositing a tensilely stressed film.
8. The method of claim 3 , further comprising:
forming the pre-sealing layer to include a microshell support pillar extending downwardly into the sacrificial layer; and
removing the sacrificial layer to form a common chamber under the pre-sealing layer with the microshell support pillar supporting the span of the microshell above the substrate and across the common chamber of the microshell.
9. The method of claim 8 , further comprising forming the sealing layer to comprise:
a non-hermetic layer to occlude the perforation; and
a metal hermetic layer to seal the perforation.
10. The method of claim 8 , further comprising forming a sacrificial material of the sacrificial layer over a structural component of a MEMS; removing the non-planar sacrificial layer through a perforation to form a common chamber containing the MEMS.
11. The method of claim 8 , further comprising forming a sacrificial material of the sacrificial layer over a structural component of a MEMS and a drive/sense electrode; removing the non-planar sacrificial layer through a perforation to form a common chamber containing the MEMS and the drive/sense electrode, the microshell support pillar drive/sense electrode being coupled to the drive/sense electrode, and the drive/sense electrode forming a base for the microshell support pillar.
12. The method of claim 11 , where the resonator comprises a ring resonator that circumscribes the drive/sense electrode.
13. The method of claim 8 , further comprising forming a sacrificial material of the sacrificial layer over a plurality of MEMS devices; and removing the non-planar sacrificial layer through a perforation to form a common chamber containing the plurality of MEMS devices encapsulated within the common chamber.
14. The method of claim 13 , where the plurality of MEMS devices each comprises a resonator; and where at least one of the plurality of MEMS devices comprises a resonator having a different frequency than one other of the MEMS devices.
15. A microshell, comprising:
a perforated pre-sealing layer over a chamber around a device on a substrate, the perforated pre-sealing layer having a first stress; and
a sealing layer that seals the pre-sealing layer, the sealing layer comprising a material having a stress opposite in sign to the pre-sealing layer to tune the residual stress of the microshell to be tensile.
16. The microshell of claim 15 , where the pre-sealing layer is formed by depositing a compressively stressed film.
17. The micro shell of claim 15 , where the sealing layer is formed by depositing a tensilely stressed film.
18. The micro shell of claim 15 , where the sealing layer is formed by first depositing a compressively stress film and then depositing a tensilely stressed film.
19. The microshell of claim 15 , where the device is a structural component of a MEMS.
20. The microshell of claim 15 , where the sealing layer is formed by imparting a magnitude of stress to the sealing material that is higher than the magnitude of the residual tensile stress in the microshell.
21. The microshell of claim 15 , where the perforated pre-sealing layer comprises a plurality of perforations in adjacent rows, the plurality of perforations of each row having a spacing between individual perforations staggered from a spacing between individual perforations in an adjacent row.
22. The micro shell of claim 15 , where the perforated pre-sealing layer comprises a perforation having an aspect ratio greater than 8:1.
23. The microshell of claim 15 , where the sealing layer is formed by imparting a magnitude of tensile stress to the sealing layer that is greater than the magnitude of compressive stress in the pre-sealing layer.
24. A microshell comprising:
a perforated pre-sealing layer to partially enclose a chamber on a substrate; and
a sealing layer over the pre-sealing layer to close a perforation, wherein the pre-sealing layer is compressively stressed and at least a portion of the sealing layer is tensilely stressed to tune the residual stress of the microshell.
25. The microshell of claim 24 , wherein the pre-sealing layer comprises a compressively stressed oxide of silicon and the sealing layer comprises a tensilely stressed aluminum.
26. The microshell of claim 25 , wherein the sealing layer further comprises a compressively stressed oxide of silicon between the pre-sealing layer and the tensilely stressed aluminum.
27. The microshell of claim 24 , wherein the tensilely stressed layer imparts a tensile residual stress on the microshell.
28. The microshell of claim 24 , wherein the residual stress of the microshell has a magnitude less than that of either the pre-sealing layer or the sealing layer.
29. A microshell comprising:
a perforated pre-sealing layer to partially enclose a chamber on a substrate: and
a sealing layer over the pre-sealing layer to close a perforation, wherein the pre-sealing layer has a stress opposite a stress of the sealing layer to lower the magnitude of the residual stress of the microshell below the magnitude of stress in either the pre-sealing layer or sealing layer.
30. The microshell of claim 29 ,
wherein the pre-sealing layer extends downwardly into the common chamber to form a microshell support pillar that is configured to support the span of the microshell above the substrate and across the common chamber of the microshell.
31. The apparatus of claim 30 , wherein the wherein the sealing layer further comprises:
a non-hermetic layer to occlude the perforation; and
a metal hermetic layer to seal the perforation.
32. The apparatus of claim 30 , further comprising a structural component of a MEMS encapsulated within the common chamber.
33. The apparatus of claim 30 , further comprising a resonator and a drive/sense electrode encapsulated within the common chamber, the microshell support pillar drive/sense electrode being coupled to the drive/sense electrode, and the drive/sense electrode forming a base for the microshell support pillar.
34. The apparatus of claim 33 , where the resonator comprises a ring resonator that circumscribes the drive/sense electrode.
35. The apparatus of claim 30 , further comprising a plurality of MEMS devices encapsulated within the common chamber.
36. The apparatus of claim 35 , where the plurality of MEMS devices each comprises a resonator; and where at least one of the plurality of MEMS devices comprises a resonator having a different frequency than one other of the MEMS devices.