Simultaneous wafer bonding and interconnect joining

1. A method of forming a microelectronic assembly comprising the steps of:

providing a microelectronic element having a major surface, and a dielectric layer and at least one bond pad exposed at the major surface, the microelectronic element containing a plurality of active circuit elements, wherein the dielectric layer is separated in a direction parallel to the major surface from the at least one bond pad by a gap;

providing a second element having a coefficient of thermal expansion of less than 10 ppm/° C., the second element having a major surface and a dielectric layer exposed at the major surface of the second element;

forming a first metal layer such that a first portion of the first metal layer overlies the at least one bond pad and a second portion of the first metal layer overlies the dielectric layer of the microelectronic element, the first and second portions being separated by the gap;

forming a second metal layer overlying the dielectric layer of the second element; and

joining the first metal layer with the second metal layer.

2. The method of claim 1 , wherein the steps of forming each include depositing a first stage including at least one of copper or aluminum onto at least one of the microelectronic element or the second element.

3. The method of claim 1 , wherein the microelectronic element is a chip, and the second element has an area substantially the same as an area of the chip.

4. The method of claim 1 , wherein the step of forming the first metal layer includes forming a metal over substantially the entire major surface of the microelectronic element, and further comprising the step of removing a portion of the metal such that the metal extends to a predetermined height above the major surface of the microelectronic element.

5. The method of claim 4 , further comprising removing the metal directly overlying the gap along the major surface of the microelectronic element.

6. The method of claim 5 , wherein the gap is large enough to provide a relief volume sufficient to compensate for a sum of the total variation in co-planarity of top surfaces of the first metal layer overlying the at least one bond pad and the dielectric layer on the microelectronic element, and the total variation in co-planarity of top surfaces of the second metal layer overlying the dielectric layer on the second element and at least one bond pad exposed at the major surface thereof.

7. The method of claim 1 , wherein the step of joining includes heating at least one of the first and second metal layers to a temperature between about 50 and 300° C.

8. The method of claim 1 , wherein at least one of the first and second metal layers includes at least a portion which is exothermic and thermally-activated through application of heat, and the step of joining includes heating the at least a portion of the exothermic metal layer to thermally activate such layer.

9. The method of claim 1 , wherein the second element is a microelectronic element containing a plurality of active circuit elements and includes at least one bond pad exposed at the major surface thereof.

10. The method of claim 9 , wherein at least one of the elements includes a through silicon via electrically connected with the at least one bond pads of such element and extending from the major surface of such element toward a second surface of such element remote from the major surface of such element.

11. The method of claim 10 , wherein a through silicon via extends through the microelectronic and second elements and is electrically connected with a bond pad of the microelectronic element and a bond pad of the second element.

12. The method of claim 9 , wherein the step of joining includes juxtaposing the at least one bond pad of the microelectronic element with the at least one bond pad of the second element and heating the first and second metal layers to a joining temperature.

13. The method of claim 9 , wherein the at least one bond pad on each of the elements includes a plurality of bond pads aligned in a plurality of rows.

14. The method of claim 9 , wherein the at least one bond pad on each of the elements includes a plurality of bond pads aligned adjacent a periphery of the respective major surface, and the dielectric layer overlies a central region of such major surface.

15. The method of claim 1 , wherein the dielectric layer of at least one of the elements is compressible to absorb any dimensional tolerances.

16. The method of claim 1 , wherein the height of the at least one bond pad above the major surface of the microelectronic element differs from the height of the dielectric layer above the major surface of the microelectronic element.

17. The method of claim 1 , wherein at least one of the steps of forming includes depositing a reflow metal, and the step of joining includes heating the reflow metal to a temperature that causes the reflow metal to melt.

18. The method of claim 17 , wherein the reflow metal is selected from the group consisting of tin, solder, indium, gold, and any combination thereof.

19. The method of claim 1 , wherein the steps of forming include depositing copper, and the step of joining includes applying heat and pressure between the elements such that the copper overlying the microelectronic element and the copper overlying the second element fuse together.

20. The method of claim 19 , further comprising forming a layer of gold on the copper overlying at least one of the elements, and the step of joining includes heating the gold to a temperature at which the gold diffuses into the copper.

21. The method of claim 1 , wherein the step of forming the first and second metal layers includes depositing a base metal and a layer of gold overlying the base metal, wherein the step of joining includes applying heat and pressure to the elements until the first and second metal layers fuse together.

22. A microelectronic assembly comprising:

a microelectronic element having a major surface, and a dielectric layer and at least one bond pad exposed at the major surface, the microelectronic element containing a plurality of active circuit elements;

a second element having a coefficient of thermal expansion of less than 10 ppm/° C., the second element having a major surface, and at least one bond pad and a dielectric layer exposed at the major surface thereof;

a first metal layer overlying the at least one bond pad and the dielectric layer of the microelectronic element, wherein a gap is formed in the first metal layer between the at least one bond pad and the dielectric layer;

a second metal layer overlying the at least one bond pad and the dielectric layer of the second element; and

wherein first portions of the first and second metal layers overlying the dielectric layers are joined together and second portions of the first and second metal layers overlying the at least one bond pads and being separate from the first portions are joined together so as to mechanically and electrically connect the microelectronic element with the second element.

23. The assembly of claim 22 , wherein the microelectronic element is a chip, and the second element has an area substantially the same as an area of the chip.

24. The assembly of claim 22 , wherein the gap is large enough to provide a relief volume sufficient to compensate for a sum of the total variation in co-planarity of the top surfaces of the first metal layer overlying the at least one bond pad and the dielectric layer on the microelectronic element, and the total variation in co-planarity of the top surfaces of the second metal layer overlying the at least one bond pad and the dielectric layer on the second element.

25. The assembly of claim 22 , wherein at least one of the first and second metal layers includes at least a portion which is exothermic and thermally-activated through application of heat.

26. The assembly of claim 22 , wherein the second element is a microelectronic element containing a plurality of active circuit elements.

27. The assembly of claim 26 , wherein at least one of the elements includes a through silicon via electrically connected with the at least one bond pads and extending from the major surface of such element toward a second surface of the element remote from the major surface.

28. The assembly of claim 27 , wherein a through silicon via extends through the microelectronic and second elements and is electrically connected with a bond pad of the microelectronic element and a bond pad of the second element.

29. The assembly of claim 26 , wherein the at least one bond pad on each of the elements includes an array of bond pads arranged in a plurality of rows.

30. The assembly of claim 26 , wherein the at least one bond pad on each of the elements includes a plurality of bond pads arranged adjacent a periphery of such element, and the dielectric layer overlies a central region of the major surface.

31. The assembly of claim 26 , wherein a gap is formed in the second metal layer between the at least one bond pad and the dielectric layer.

32. The assembly of claim 22 , wherein the dielectric layer of at least one of the elements is compressible to absorb any dimensional tolerances.

33. The assembly of claim 22 , wherein the height of the at least one bond pad above the major surface of the microelectronic element differs from the height of the dielectric layer above the major surface of the microelectronic element.

34. The assembly of claim 22 , wherein at least one of the metal layers includes a reflow metal selected from the group consisting of tin, solder, indium, gold, and any combination thereof.

35. The assembly of claim 34 , wherein each of the first and second metal layers includes a layer of metal which is wettable by the reflow metal, wherein the reflow metal overlies the wettable metal layer.

36. The assembly of claim 22 , wherein the first and second metal layers comprise copper.

37. The assembly of claim 36 , further comprising a layer of gold overlying at least one of the first and second metal layers.

38. The assembly of claim 22 , wherein the first and second metal layers do not directly overlie the respective major surfaces of the elements.

39. A system comprising an assembly according to claim 22 and one or more other electronic components electrically connected to the assembly.

40. A system as claimed in claim 39 further comprising a housing, the assembly and the other electronic components being mounted to the housing.

41. A microelectronic assembly comprising:

a microelectronic element having a major surface and a dielectric layer exposed at the major surface; and

a second element having a major surface and a dielectric layer exposed at the major surface of the second element;

the major surfaces of the microelectronic and second elements confronting one another with a plurality of metal elements disposed between the dielectric layers, the metal elements being electrically isolated from the microelectronic element,

wherein the metal elements join the microelectronic and second elements with one another,

wherein on each of the microelectronic element and the second element, a gap is formed along the major surface between one or more of the metal elements and an adjacent portion of the dielectric layer,

wherein the gap is large enough to provide a relief volume into which a reflowable metal can flow from between the dielectric layers of the microelectronic and second elements, the relief volume being sufficient to compensate for a sum of the total variation in co-planarity of top surfaces of the metal elements and the dielectric layer overlying the major surface of the microelectronic element, and the total variation in co-planarity of top surfaces of the metal elements and the dielectric layer overlying the major surface of the second element.

42. The assembly of claim 41 , wherein the second element has a coefficient of thermal expansion of less than 10 ppm/° C.

43. The assembly of claim 41 , wherein the microelectronic element contains a plurality of active circuit elements.

44. The assembly of claim 43 , wherein the second element is a microelectronic element containing a plurality of active circuit elements and includes at least one bond pad exposed at the major surface.

45. The assembly of claim 41 , wherein the microelectronic element is a chip, and the second element has an area substantially the same as an area of the chip.

46. The assembly of claim 41 , wherein the dielectric layer of at least one of the elements is compressible to absorb any dimensional tolerances.

47. A system comprising an assembly according to claim 41 and one or more other electronic components electrically connected to the assembly.

48. A system as claimed in claim 47 further comprising a housing, the assembly and the other electronic components being mounted to the housing.