Abstract: A method is described for progressively forming a fuse access opening for laser trimming in an integrated circuit with improved control of dielectric thickness over the fuse. A dielectric layer is formed over the fuse and a polysilicon layer is then patterned over the fuse to form a first etch stop. An ILD layer is added and a second etch stop is formed in a first metal layer on the ILD layer over the first etch stop. The second etch stop serves to protect the ILD layer over the fuse from being etched by an ARC over etch during the via etching in a first IMD layer. A first portion of the laser access window is formed during the via etching of the first IMD layer. The second etch stop is then removed by the second metal patterning etch, exposing the ILD layer over the first etch stop at it's original thickness. A passivation layer is deposited and patterned to form access openings to bonding pads as well as to further open the laser access window to the first etch stop.

Abstract: A method is described for progressively forming a fuse access openings in integrated circuits which are built with redundancy and use laser trimming to remove and insert circuit sections. The fuses are formed in a polysilicon layer and covered by one or more relatively thin insulative layers. An etch stop is patterned over the fuse in a higher level polysilicon layer or a first metallization layer. Additional insulative layers such as inter-metal dielectric layers are then formed over the etch stop. A first portion of the laser access window is then etched during the via etch for the top metallization level. The etch stop prevents removal of the insulation subjacent to it. Cumulative thickness non-uniformities in the relatively thick upper insulative layers are thus removed from the fuse window. The etch stop is removed during patterning of the top level metallization.