Indented lid for encapsulated devices and method of manufacture
View Patent ↗A method for providing improved gettering in a vacuum encapsulated device is described. The method includes forming a plurality of small indentation features in a device cavity formed in a lid wafer. The gettering material is then deposited over the indentation features. The indentation features increase the surface area of the getter material, thereby increasing the volume of gas that the getter material can absorb. This may improve the vacuum maintained within the vacuum cavity over the lifetime of the vacuum encapsulated device.
1. A method for forming an encapsulated device, comprising:
forming at least one indentation feature on at least a portion of a surface of at least one of two substrates;
forming a getter material over the indentation feature;
forming a device on at least one of the two substrates; and
coupling the two substrates with an adhesive substance including embedded rigid particles, wherein the embedded rigid particles define a minimum separation between the substrates to define a cavity encapsulating the device, wherein the adhesive substance is at least one of a glass frit, an epoxy and a metal alloy, and wherein the embedded rigid particles are substantially spherical electrically non-conducting particles of at least about 10 microns in diameter, and wherein the embedded rigid particles define a separation between two surfaces forming the cavity.
2. The method of claim 1 , wherein forming the at least one indentation feature comprises forming at least one of a blind hole, a groove, a post and a trench on at least a portion of a surface of the cavity.
3. The method of claim 1 , further comprising:
forming a cavity in at least one of the two substrates;
aligning the substrates such that the cavity is located over the device; and
evacuating the cavity.
4. The method of claim 3 , further comprising:
singulating the devices.
5. The method of claim 3 , further comprising:
adding a gas to the evacuated cavity, wherein the gas comprises at least one of sulfur hexafluoride (SF 6 ), helium (He), nitrogen (N 2 ), argon (Ar), and neon (Ne).
6. The method of claim 1 , wherein forming the at least one indentation feature further comprises forming the at least one indentation feature using at least one of deep reactive ion etching, wet etching, ion milling, dry etching, stamping, molding, electroplating and ion beam deposition.
7. The method of claim 2 , wherein a characteristic dimension of the at least one indentation feature is at least about ten times smaller than a width of the device cavity.
8. The method of claim 1 , wherein at least one substrate comprises a substantially flat wafer of at least one of glass, Kovar, Invar, silicon, metal, and ceramic.
9. The method of claim 1 , wherein coupling step comprises forming a substantially hermetic seal between the two substrates.
10. The method of claim 1 , wherein a layer of getter material comprises at least one of zirconium, titanium, vanadium, niobium, tantalum and iron, and is between about 0.5 μm and about 3 μm thick.
11. The method of claim 1 , wherein the device comprises at least one of a MEMS actuator, a MEMS sensor, and an infrared device and an integrated circuit.
12. The method of claim 1 , wherein one of the substrates on which the device is formed comprises at least one of silicon, gallium arsenide, glass, quartz, ceramic and metal, and the other substrate is a substantially flat lid wafer comprising at least one of glass, Kovar, Invar, silicon, metal, and ceramic.
13. The method of claim 1 , wherein the separation defined by the rigid particles alone forms the cavity enclosing the device and provides a clearance for the device.
14. The method of claim 1 , wherein the adhesive substance comprises at least one of glass frit and a metal alloy.
15. The method of claim 1 , wherein the adhesive substance comprises AuIn x , wherein x is about 2.
16. The method of claim 1 , wherein the embedded particles comprise at least one of alumina, silica, diamond, glass and sapphire spheres of at least about 10 μm diameter, providing a cavity with a clearance of at least about 10 μm.
17. The method of claim 1 , wherein a top of the cavity is formed by a flat surface of a lid wafer and a bottom surface of the cavity is formed by a device wafer on which the device is formed, and the sides of the cavity are formed by the adhesive substance.
18. The method of claim 1 , wherein forming the at least one indentation feature comprises forming at least one blind hole having a diameter of between about 5 microns and 10 microns, and a depth of about 8 microns to about 20 microns.
19. An apparatus for performing the method of claim 1 , comprising:
means for forming at least one indentation feature on at least a portion of a surface of at least one of two substrates;
means for forming a getter material over the at least one indentation feature;
means for forming a device on at least one of the two substrates; and
means for bonding two substrates with an adhesive substance including embedded rigid particles, wherein the embedded rigid particles define a minimum separation between the substrates to define a cavity encapsulating the device, wherein the adhesive substance is at least one of a glass frit, an epoxy and a metal alloy, and wherein the embedded rigid particles are substantially spherical electrically non-conducting particles of at least about 10 microns in diameter, and wherein the embedded rigid particles define a separation between two surfaces forming the cavity.