System and method for providing access to an encapsulated device
View Patent ↗A method for providing access to a feature on a device wafer, and located outside an encapsulation region is described. The method includes forming a cavity in the lid wafer, aligning the lid wafer with the device wafer so that the cavity is located substantially above the feature, and removing material substantially uniformly from the bottom surface of the lid wafer, until an aperture is formed at the cavity, over the feature on the device wafer. By removing material from the lid wafer in a substantially uniform manner, difficulties with the prior art procedure of saw cutting, such as alignment and debris generation, are avoided.
1. An encapsulated device formed on a device wafer, comprising:
a lid wafer aflixed to the device wafer, having an encapsulating lid cavity located in the lid wafer substantially over the device, the encapsulating lid cavity having an inner surface and an exterior outer surface, the exterior outer surface defined by a top surface and sidewalls formed in the lid wafer, wherein the sidewalls extend from the top surface to a bonding surface of the lid wafer, and wherein the sidewalls are substantially non-parallel along substantially an entire length of the sidewalls.
2. The encapsulated device of claim 1 , wherein the lid wafer includes a wall of the encapsulation cavity having a thickness in a region substantially over the device of less than about 400 μm.
3. The encapsulated device of claim 1 , further comprising: a feature on the device wafer associated with the encapsulated device, but located outside the encapsulating cavity of the lid wafer.
4. The encapsulated device of claim 1 , wherein the feature is at least one probe pad electrically coupled to the device.
5. The encapsulated device of claim 1 , wherein the lid wafer comprises at least one of silicon, glass, quartz, ceramic, sapphire, and metal, and the encapsulated device comprises an encapsulated MEMS device.
6. The encapsulated device of claim 2 , wherein the sidewalls of the lid wafer outside the encapsulation cavity and a line parallel to a surface of the lid wafer define an angle of about 55 degrees.
7. The encapsulated device of claim 2 , wherein the entire lengths of the sidewalls of the lid wafer outside the encapsulation cavity are non-parallel, and formed by wet etching the lid wafer.
8. The encapsulated device of claim 4 , wherein the probe pad comprises a gold layer about 7 microns thick.
9. The encapsulated device of claim 1 , wherein the device wafer is a substantially whole, unsingulated wafer.
10. The encapsulated device of claim 1 , where the depth of the encapsulating cavity is about 75 μm.
11. The encapsulated device of claim 1 , wherein a thickness of the lid wafer in the region directly over the device is less than about 150 μm.
12. The encapsulated device of claim 1 , wherein the substantially non-parallel sidewalls defining the exterior outer surface of the encapsulating cavity are symmetric about an axis substantially through the middle of the device.
13. The encapsulated device of claim 1 , wherein a thickness of the sidewalls of the encapsulating cavity are thicker at the top surface than at the bonding surface of the lid wafer.
14. The encapsulated device of claim 3 , further comprising at least one aperture in the lid wafer directly over the feature associated with the device.
15. The encapsulated device of claim 14 , wherein the aperture has substantially non-parallel sidewalls.
16. The encapsulated device of claim 15 , wherein the sidewalls of the aperture form an angle of about 55 degrees with a line parallel to another surface of the lid wafer.