The present invention relates generally to integrated circuit devices that include one or more programmable fuse elements. More particularly, the present invention relates to fuse structures in integrated circuits and techniques for programming integrated circuits by electrically altering the conductive state of one or more such fuse structures.
The use of fuses in integrated circuits is well known in the art. U.S. Pat. No. 3,792,319 discloses an early example of a polycrystalline silicon fusible link, which is "blown" or programmed by passing electrical current through the fusible link. Fuses that are programmed by selective irradiation are also known in the art. For example, U.S. Pat. No. 4,503,315 discloses a fuse that is programmed by exposure to a laser beam.
A common application for such fuses is the deselection of rows or columns of memory cells in dynamic random access memories (DRAMs) or static random access memories (SRAMs) that contain a defective memory cell and the substitution of respective redundant rows or columns. U.S. Pat. No. 5,771,195 discloses such a technique.
Since the introduction of polycrystalline silicon (or "polysilicon") fuses, improvements have been made in electrically programmable fuses. U.S. Pat. No. 5,789,970 discloses a composite fuse structure of silicide and polysilicon that includes PN junctions in the polysilicon layer for increasing the resistance of the fuse in the programmed state. A discontinuity is formed in the silicide over one of the PN junctions causing a large increase in resistance from the unprogrammed state to the programmed state. A further improvement is achieved by the present invention.