Thin film microshells incorporating a getter layer
View Patent ↗Low temperature, multi-layered microshells for encapsulation of devices such as MEMS and microelectronics. The microshells may include a perforated pre-sealing layer, below which a sacrificial layer is accessed, and a sealing layer to close the perforation in the pre-sealing layer after the sacrificial material is removed. The pre-sealing layer includes a large surface area getter layer to remove contaminants from the space ultimately enclosed by the microshell to improve the pressure control and cleanliness of the microshell.
1. A method of forming a microshell over a substrate, comprising:
depositing a sacrificial material over the substrate;
etching a first partial thickness of the sacrificial material with a first mask to define a perimeter trench in the sacrificial material;
etching a second partial thickness of the sacrificial material with a second mask to form a protrusion of sacrificial material extending upwards from a top surface of the sacrificial material confined within the perimeter trench and to transfer the perimeter trench through the sacrificial material;
forming a pre-sealing layer on the sacrificial layer to cover the protrusion and the perimeter trench, wherein the pre-sealing layer further comprises a getter layer on a permeable layer;
perforating the pre-sealing layer to expose the sacrificial layer;
removing the sacrificial layer to form a chamber under the pre-sealing layer; and
sealing the perforated pre-sealing layer.
2. The method of claim 1 , wherein forming the getter layer on the permeable layer further comprises depositing a getter material adjacent to the sidewalls of the protrusion of sacrificial material to increase the surface area of the getter layer.
3. The method of claim 1 , wherein the second mask defines staggered rows of protrusions to form within the perimeter trench a crenulated sacrificial layer which distributes stresses in the subsequently deposited pre-sealing and sealing layers.
4. The method of claim 1 , wherein the sacrificial material is etched to form the protrusion with a sloped profile.
5. The method of claim 1 , wherein the getter layer is titanium.
6. The method of claim 1 , wherein the permeable layer is a silicon oxide.
7. The method of claim 1 , wherein perforating the pre-sealing layer further comprises planarizing the pre-sealing layer to perforate the pre-sealing layer with the protrusion of the sacrificial layer.
8. The method of claim 7 , wherein the getter layer remains non-planar after the planarizing of the pre-sealing layer.
9. The method of claim 1 , wherein sealing the pre-sealing layer further comprises:
nonconformally depositing a dielectric to occlude the perforation; and
depositing a metal to hermetically seal the perforated pre-sealing layer.
10. The method of claim 9 , wherein the chamber is heated for at least 30 seconds to a temperature above 400° C. before depositing the dielectric to desorb contaminants.
11. The method of claim 9 , wherein the dielectric is deposited with the substrate tilted by a small angle relative to a predominant ion flux in the deposition chamber to reduce back-deposition of the sealing material.
12. The method of claim 1 , further comprising:
etching through the sealing layer to expose a metal ground ring adjacent to the chamber; and
depositing a conductive layer on the sealing layer and ground ring to electrically ground the microshell.
13. The method of claim 12 , further comprising:
depositing a semiconductor layer over the conductive layer to structurally reinforce the microshell.
14. The method of claim 13 , wherein the semiconductor layer comprises germanium to form a germanosilicide.