Elastic interface for wafer bonding apparatus
View Patent ↗An apparatus for bonding a lid wafer to a device wafer includes an elastic interface having a first surface and a second surface. Relieved areas may be created in the elastic interface by removing at least some of the elastic material of the interface, leaving a mesh with nodes. Raised areas may be disposed on the nodes in staggered positions on the first surface relative to the second surface. The bonding pressure deflects the raised features on the first surface in one direction and the raised features on the second surface in another direction. The restoring force of the mesh transmits the pressure through the interface and to a lid wafer and a device wafer, to bond the lid wafer to the device wafer.
1. A wafer bonding tool, comprising:
a movable pressure chuck and a wafer support device;
a single sheet of elastic material having a first surface and
a second surface on a side opposite the first surface, wherein the single sheet is disposed between the pressure chuck and the wafer support device; and
a plurality of raised features disposed on the first and second surfaces, with the raised features on the first surface disposed in a staggered position with respect to the raised features on the second surface.
2. The wafer bonding tool of claim 1 , wherein the raised features on the first surface are disposed on every other node, and the raised features on the second surface are disposed on every intervening node.
3. The wafer bonding tool of claim 1 , further comprising at least one of beryllium copper, shim stock and spring steel.
4. The wafer bonding tool of claim 1 , wherein the raised features of the elastic interface have a height of between about 0.1 mm and 0.3 mm relative to at least one of the first and the second surface, and a width of about 1 mm.
5. The wafer bonding tool of claim 1 , wherein the relieved areas are substantially square, with a width of about 3 mm.
6. The wafer bonding tool of claim 1 , wherein the elastic sheet has a total thickness of about 0.5 mm.
7. The wafer bonding tool of claim 1 , wherein a pitch between the raised features varies across a diameter of the elastic interface.
8. The wafer bonding tool of claim 1 , further comprising:
a pressure device generating pressure; and
a heat source.
9. The wafer bonding tool of claim 8 , wherein the elastic sheet is disposed between the pressure device and a two-wafer assembly.
10. The wafer bonding tool of claim 9 , wherein the wafer support device supports the two-wafer assembly.
11. The wafer bonding tool of claim 10 , wherein elastic sheet is disposed between the two-wafer assembly and the wafer support device.
12. The wafer bonding tool of claim 8 , wherein the elastic sheet can accommodate at least about 50 μm of flatness non-uniformity across a six inch diameter wafer.
13. The wafer bonding tool of claim 9 , further comprising a voltage source for applying a voltage across the two-wafer assembly.
14. The wafer bonding tool of claim 9 , wherein the two-wafer assembly compnses:
at least one substantially circular device wafer, upon which devices are disposed; and
a substantially circular lid wafer coupled to the substantially circular device wafer, wherein the raised features on the elastic sheet are configured to deliver pressure from the pressure chuck to the lid wafer and device wafer in the wafer bonding tool.
15. The wafer bonding tool of claim 1 , wherein the raised features are circles disposed on the nodes of the mesh of the elastic sheet.
16. The wafer bonding tool of claim 1 , wherein the pitch between the nodes of the elastic sheet varies smoothly across the diameter of the elastic sheet.