All Wired Up: In Step 2, the donor die is set face down on top of the host die. The surfaces of each die have been precisely smoothed and chemically treated so that the two dies form a covalent bond [see inset, top left] that is structurally identical to those in bulk silicon. A via, or hole, is then dry etched into the back side of the donor die. The via reaches down and through the bond pad, where that chip's global interconnects have been routed. The new annular via extends all the way through to the redirect layer wiring on the host die.

In Step 3, the sides of the annular via are coated with insulating material, usually silicon dioxide [see inset, upper right]. Then metal is deposited in the hole to create a wire that reaches all the way from the back side of the donor chip to the redirect layer wiring in the host. Now global signals can flow between the two chips and to and from the rest of the device in which the 3-D IC is put.