Single crystal fuse on air in bulk silicon
View Patent ↗An integrated eFUSE device is formed by forming a silicon “floating beam” on air, whereupon the fusible portion of the eFUSE device resides. This beam extends between two larger, supporting terminal structures. “Undercutting” techniques are employed whereby a structure is formed atop a buried layer, and that buried layer is removed by selective etching. Whereby a “floating” silicide eFUSE conductor is formed on a silicon beam structure. In its initial state, the eFUSE silicide is highly conductive, exhibiting low electrical resistance (the “unblown state of the eFUSE). When a sufficiently large current is passed through the eFUSE conductor, localized heating occurs. This heating causes electromigration of the silicide into the silicon beam (and into surrounding silicon, thereby diffusing the silicide and greatly increasing its electrical resistance. When the current source is removed, the silicide remains permanently in this diffused state, the “blown” state of the eFUSE.
1. An integrated floating-beam eFUSE device, comprising:
a raised silicon structure, said structure comprising a beam portion joining two spaced-apart terminal portions;
silicide formed on a top surface of the raised silicon structure, said silicide extending across the beam portion;
an air gap underlying the beam portion; and
an oxide fill material surrounding the raised structure, substantially without intruding into undercut areas beneath the raised structure, for stabilizing the raised structure while leaving the air gap substantially intact.
2. An eFUSE device according to claim l, wherein the raised silicon structure is single-crystal epitaxially grown silicon.
3. An eFUSE device according to claim 1 , wherein the silicide on the beam portion initially creates a low-resistance conductive pathway between silicide on the two terminal portions in an initial “unblown” state of the eFUSE device.
4. An eFUSE device according to claim 3 , wherein electromigration of silicide on the beam portion into the raised silicon structure produces a high-resistance pathway between silicide on the two terminal portions in a subsequent “blown” state of the eFUSE device.
5. An eFUSE device according to claim 1 , wherein said terminal portions are completely supported by a surrounding dielectric material.
6. An eFUSE device according to claim 5 , wherein the dielectric material is silicon dioxide.
7. An eFUSE device according to claim 1 , wherein said terminal portions are partially supported by an underlying doped implantation layer.
8. An eFUSE device according to claim 1 , further comprising:
an overlying dielectric material; and
contact structures extending through the overlying dielectric to form electrical contact with silicide on the two terminal portions.