Microshells for multi-level vacuum cavities
View Patent ↗Microshells for encapsulation of devices such as MEMS and microelectronics. In an embodiment, 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. 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 as a function of the dimension of the perforation to form cavities having different vacuum levels on the same substrate.
1. A thin film microshell comprising:
a first chamber on a substrate, the first chamber at a first vacuum level;
a second chamber on the substrate, the second chamber at a second vacuum level greater than the first vacuum level;
a pre-sealing layer over the first chamber and second chamber, wherein the pre-sealing layer has a perforation of a first dimension venting the first chamber and a perforation of a second dimension, that is larger than the first dimension, venting the second chamber;
a first occluding layer on the pre-sealing layer to close the perforation venting the first chamber at the first vacuum level; and
a second occluding layer on the first occluding layer to close the perforation venting the second chamber at the second vacuum level.
2. The microshell of claim 1 , wherein the first occluding layer is nonhermetic.
3. The microshell of claim 1 , wherein the first occluding layer is a dielectric.
4. The microshell of claim 1 , wherein the first occluding layer is an oxide layer and the second occluding layer is a metal layer.
5. The microshell of claim 1 , wherein the pre-sealing layer forms at least a portion of the sidewall of the first and second chamber.
6. The microshell of claim 1 , wherein the pre-sealing layer further comprises a getter layer comprising titanium over a gas permeable layer.
7. The microshell of claim 1 , wherein the first and second occluding layers over the pre-sealing layer is nonconformal to physically occlude the perforation.
8. The microshell of claim 1 , further comprising a hermetic layer over the second occluding layer.
9. The microshell of claim 3 , wherein the dielectric is an oxide of silicon.
10. The microshell of claim 8 , wherein the hermetic layer is a metal selected from the group comprising: aluminum, tungsten, copper, titanium, and their alloys.
11. The microshell of claim 8 , wherein the hermetic layer is electrically coupled to a conductive layer adjacent to the microshell.
12. The microshell of claim 11 , wherein the conductive layer is electrically coupled to a ground ring to electrically ground the microshell.
13. A method of forming multi-level vacuum cavities comprising:
forming on a substrate a first chamber partially enclosed by a pre-sealing layer, wherein the pre-sealing layer has a perforation of a first dimension over the first chamber to vent the first chamber;
forming on the substrate a second chamber partially enclosed by the pre-sealing layer, wherein the pre-sealing layer has a perforation of a second dimension that is larger than the first dimension, over the second chamber to vent the second chamber;
forming with a first process condition, a first occluding layer on the pre-sealing layer to close the perforation over the first chamber at a first vacuum level; and
forming with a second deposition condition, a second occluding layer on the first occluding layer to close the perforation over the second chamber at a second vacuum level.
14. The method of claim 13 , further comprising:
allowing the first chamber to leak up to a predetermined pressure level prior to forming the second occluding layer on the first occluding layer.
15. The method of claim 13 , wherein forming a first and second chamber partially enclosed by a pre-sealing layer further comprises:
forming a non-planar sacrificial layer over the 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 to expose the sacrificial layer; and
removing the non-planar sacrificial layer to form the first chamber around a first device under the pre-sealing layer and to form the second chamber around a second device under the pre-sealing layer.
16. The method of claim 15 , wherein forming the non-planar sacrificial layer further comprises:
forming a sacrificial material over the substrate;
etching the sacrificial material with a first mask to define an edge of the chamber;
etching the sacrificial material with a second mask to form an isolated sacrificial layer having a blade of sacrificial material extending upwards from the substrate.
17. The method of claim 15 , wherein the sacrificial material is formed at a temperature below 450° C.
18. The method of claim 15 , wherein forming the sacrificial material further comprises depositing a film comprising germanium.