Abstract:
A copper fuse structure for integrated circuit employs two copper pads formed over a semiconductor substrate. The two copper pads are electrically insulated by dielectrics. An aluminum line is utilized to cover and electrically connect the two copper pads.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     The present invention relates to a semiconductor structure in integrated circuit (IC). More particularly, the present invention relates to a copper fuse of semiconductor structure for IC. 
     2. Description of Related Art 
     As the design rule of the semiconductor process approaches or is less than 0.18 μm, copper gradually replaces aluminum as an interconnect in the metallization process since copper has lower resistance that can reduce RC delay. However, copper easily reacts with the oxygen in the surroundings to form a thin copper oxide on its surface, which leads to the failure of electrical contact. As a result, it is difficult to substitute copper for aluminum when forming a fuse in an IC as, in the IC industry, at the current line width. 
     SUMMARY OF THE INVENTION 
     The invention provides a structure of a copper fuse in an IC, by which structure RC delay is reduced. 
     As embodied and broadly described herein, the invention provides a structure of a copper fuse for an IC, which fuse includes two copper pads formed on a semiconductor substrate where the copper pads are isolated from each other with dielectrics. A metal line formed over the semiconductor substrate covers the two metal pads wherein one end of the metal line is connected to one of the two copper pads and the other end of the metal line is connected to the other of the two copper pads. A passivation layer formed over the semiconductor substrate covers the two copper pads. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. In the drawings, 
     FIG. 1 is a schematic, cross-sectional view illustrating a structure of a copper fuse according to one preferred embodiment of this invention; and 
     FIG. 2 is a schematic, top view of FIG. 1, where the cross-sectional view along the line I—I is shown in FIG.  1 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIG. 1, after the formation of a MOS device and contact (not shown), a tungsten plug is subsequently formed in the device region  100   a  of an IC structure. Such metallization processes as wiring line and vias are carried out by damascene, for example, where the wiring lines and the vias are isolated from with dielectrics  102 . Thereafter, a passivation layer  104   a  is deposited and then patterned by photolithography to form a pad window such that a metal pad  106   a  made of copper, for example, is exposed. A barrier layer  108   a  such as TiN or TaN is formed on the metal pad layer  106   a . An aluminum layer  110   a  is formed and patterned to complete the wire bonding process of the device region  100   a  for the back-end process of the IC. 
     Referring to FIG.  1  and FIG. 2 simultaneously, a copper fuse set up in the peripheral region  100   b  is first to form two metal copper pads  106   b  in the dielectrics  102 . The two copper pads  106   b  connected to corresponding devices (not shown) are formed by damascene, for example, when the metal pad  106   a  is formed. Thereafter, the passivation layer  104   b  is formed when the passivation layer  104   a  is formed in order to cover the two copper pads  106   b . The passivation layer  104   b  can be silicon oxide/silicon nitride, for example. As the passivation layer  104   a  in the device region  100   a  is patterned, photolithography is also employed to form an opening  112  in the passivation layer  104   b  so that the two copper pads are exposed. A barrier layer  108   b  such as TiN or TaN formed by sputtering is then formed on the copper pads  106   b . A metal layer  110   b  is formed by sputtering to cover the copper pads  106   b  to electrically connect the two copper pads  106   b . The barrier layer  108   b  is used to improve the adhesion of the copper pads  106   b  and the metal layer  110   b,  and the metal layer  110   b  can be aluminum, for example. Thereafter, the metal layer  110   b  and the barrier layer  108   b  are patterned to form parallel fuses, as shown in FIG.  2 . One end of the metal layer  110   b  is connected to one copper pad  106   b  and the other end of the metal layer  1106   b  is connected to the other copper pad  106   b.    
     The two copper pads  106   b  and the metal line  110   b  constitute the copper fuse structure of the preferred embodiment in the invention. The copper pads  106   b  are electrically insulated and electrically connected by the metal layer  110   b.  Therefore, when any one of the fuses in FIG. 2 must be disconnected, the metal line  110   b  can be blown off by laser power such that the copper pads  106   b  can be prevented from being damaged. 
     The copper pads  106   b  in this embodiment is covered by the passivation layer  104   b  and the metal layer  110   b  so that the copper pads  106   b  are isolated from the air. When the back end process is complete, the copper pads  106   b  are not exposed. Therefore, oxidation on the surface of the copper pads  104   b  can be avoided. In addition, the copper pads are used as a portion of the fuses, thereby reducing RC delay. 
     Moreover, the process to form the copper fuses in this embodiment is compatible with the back-end process of the device region  100   a  for IC structure. Thus, the manufacturing cost does not increase. 
     The copper fuse structure utilizes an aluminum metal line to cover and electrically connect to the two copper pads. The copper pads serve as a part of the fuses to reduce RC delay, and in addition, the fuse is disconnected by blowing off the aluminum line. Moreover, the aluminum line and the passivation layer covering the copper pads is capable of preventing the copper pads from being oxidized by air. 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.