Abstract:
An electrically programmable fuse comprising a cathode member, an anode member, and a link member, wherein the cathode member, the anode member, and the link member each comprise one of a plurality of materials operative to localize induced electromigration in the programmable fuse.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    This invention relates to semiconductor fuses, and particularly to electrically programmable semiconductor fuses. 
         [0003]    2. Description of Background 
         [0004]    Before our invention, electrically programmable fuses (eFuses) used in rerouting circuits typically include poly-silicon strips with a thin layer of silicide covering the top of the stripes. Passing current through the eFuse results in the electromigration of silicide material in the fuse. Electromigration refers the transport of material caused by the gradual movement of the ions in a conductor due to the momentum transfer between conducting electrons and diffusing metal atoms. The effect is more pronounced in applications where high direct current densities are used, such as in microelectronics and related structures. With respect to eFuse devices, electromigration results in a higher resistance in the eFuse, effectively making the eFuse act as an open circuit. Thus, a large current density is required to induce electromigration in these types of eFuses. The use of a large current may result in a rupture of the fuse link in the eFuse. 
       SUMMARY OF THE INVENTION 
       [0005]    The shortcomings of the prior art are overcome and additional advantages are provided through the provision of an electrically programmable Efuse, comprising, a cathode member, an anode member, and a link member connecting the cathode member and the anode member, wherein the cathode member, the anode member, and the link member include at least two materials of different resistivities so as to promote faster electromigration at a selected region of the fuse with respect to other regions of the fuse. 
         [0006]    An alternate exemplary embodiment of an electrically programmable fuse comprising a first layer of polysilicon disposed on a substrate defining an anode member, a link member, and a cathode member, and a second layer disposed on the first layer further defining the anode member, the link member and the cathode member, wherein the second layer comprises a first metal silicide and a second metal silicide. 
         [0007]    An exemplary alternate embodiment of an electrically programmable fuse comprising an anode member comprising a first metal disposed on a substrate and a second metal disposed on the first metal, a cathode member comprising the first metal disposed on the substrate and the second metal disposed on the first metal, a link member comprising the first metal disposed on the substrate, and a notch portion defined in part by the second metal of the anode member, the second metal of the cathode member and the link member. 
         [0008]    An exemplary alternate embodiment of an electrically programmable fuse comprising a first metal defining an anode member; and a second metal defining a link member and a cathode member, wherein the resistivities of the first and second metal are operative to induce electromigration in the first metal prior to the inducing electromigration in the second metal. 
         [0009]    Additional features and advantages are realized through the techniques of the present invention. Other embodiments and aspects of the invention are described in detail herein and are considered a part of the claimed invention. For a better understanding of the invention with advantages and features, refer to the description and to the drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    The subject matter, which is regarded as the invention, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other aspects, features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
           [0011]      FIG. 1A  illustrates a perspective view of one example of an eFuse. 
           [0012]      FIG. 1B  illustrates a perspective view of an example of an alternate embodiment of an eFuse. 
           [0013]      FIG. 1C  illustrates a perspective view of an example of an alternate embodiment of an eFuse. 
           [0014]      FIG. 2  illustrates a perspective view of an example of an alternate embodiment of an eFuse. 
           [0015]      FIG. 3  illustrates a perspective view of an example of an alternate embodiment of an eFuse. 
       
    
    
       [0016]    The detailed description explains the preferred embodiments of the invention, together with advantages and features, by way of example with reference to the drawings. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0017]    Systems and methods involving electrically programmable fuses are provided. Several exemplary embodiments are described. 
         [0018]    In this regard, an electrically programmable fuse (eFuse) may be used to reroute circuits in semiconductors. For example, typical semiconductors include logic that is permanently etched on a chip. This logic cannot usually be changed once the chip is etched. However, eFuses may be used to dynamically reprogram semiconductor chips while they are in use. 
         [0019]    Existing eFuses may include poly-silicon strips with a thin layer of silicide covering the top of the strips. Programming these eFuses requires passing a pulse of high current through the eFuse. The pulse of current induces a large gap in the conducting silicide layer caused by the electromigration of atoms in the metal. The gap in the conducting silicide layer may include an undesirable rupture in the fuse link portion of the eFuse. The resistance of the poly-silicon strip shifts from about 100 ohms to 1 kohm or greater, for example, in the programmed eFuse. The amount of resistance shift using this type of eFuse cannot be easily controlled because the programming process uses a large amount of power density in a short period of time (approximately 1 msec, for example). 
         [0020]    Thus, it is desirable to reduce the amount of power density required to program an eFuse, such that the amount of resistance shift is more controllable, and a rupture of the fuse link portion of the eFuse may be prevented. 
         [0021]      FIG. 1A  illustrates a perspective view of an exemplary embodiment of an eFuse. An eFuse  100  includes an anode member  102 , a cathode member  104 , and a link member  106  disposed on a substrate  112 . Substrate  112  may include a dielectric material such as SiCOH, for example. The link member  106  includes an anode portion  108  and a cathode portion  110 , and contacts the anode member  102  and the cathode member  104  at the distal ends of the link member  106 . 
         [0022]    In the illustrated embodiment, anode member  102 , the cathode member  104 , and the link member  106  each include two layers. The first (or lower) layer  114  is a polysilicon layer disposed on the substrate  112 . The second (or upper) layer  116  is a metal silicide layer that includes two different types of metal silicides such as those selected from titanium, cobalt, nickel, platinum and tungsten, for example. 
         [0023]    In the illustrated exemplary embodiment, the second layer  116  of the anode member  102  and the anode portion  108  of the link member  106  include a first type of metal silicide. The second layer  116  of the cathode member  104  and the cathode portion  110  of the link member  106  include of a second type of metal silicide. 
         [0024]    In operation, an eFuse is programmed by inducing a current through the fuse member that causes electromigration of the atoms in the fuse member. The electromigration causes the resistively of the eFuse to increase. The effective result is that the programmed eFuse acts as an open circuit. 
         [0025]    Electromigration may be determined by current density, temperature, and resistively of a material. Materials with higher resistively require less current density to induce electromigration. Thus, varying the resistivity of certain components of an eFuse allows less current density to be used to program the eFuse. Additionally, by locating materials of different resistivities in different areas of an eFuse, the location of the electromigration may be more easily controlled. 
         [0026]    In this regard, referring to the eFuse  100  of  FIG. 1A , for example, when current is passed from the cathode member  104  through the link member  106  to the anode member  102 , the temperature of the eFuse increases. The combination of higher temperature and current flow causes electromigration in the eFuse  100 . In the eFuse  100 , the top layer  116  includes two types of metal silicides. The first metal silicide located in the cathode member  104  and the cathode portion  110  of the link member  106  has a lower resistivity than the second metal silicide located in the anode member  102  and the anode portion  108  of the link member  106 . Thus, the current density for promoting electromigration in the anode portion  108  of the link member  106  is lower than the current density for promoting electromigration in the cathode portion  110 . As a result, electromigration occurs earlier in the anode portion  108 . 
         [0027]      FIG. 1B  illustrates a perspective view of an alternate exemplary embodiment of an eFuse  100 . The illustrated embodiment includes an anode member  102  electrically connected to a cathode member  104  via a link member  106 . The link member  106  includes an anode portion  108 , a cathode portion  110 , and a center portion  120 . The eFuse  100  includes a first layer  114  that is a polysilicon material disposed on a dielectric substrate  112 . 
         [0028]    A second layer  116  includes two types of metal silicides. The second layer  116  of the anode member  102  and the cathode member  104  comprise of a first metal silicide. The second layer  116  of the anode portion  108  of the link member  106  and the second layer  116  of the cathode portion  110  of the link member  106  also comprise of the first metal silicide. The second layer  116  of the  106  center portion  120  of the link member includes a second metal silicide. 
         [0029]    In operation, the center portion  120  of the eFuse  100  comprises a layer of metal silicide that has a higher resistivity than the other metal silicide portions of the eFuse  100 . When a current is applied across the link member  106 , the higher resistivity of the center portion  120  causes a higher temperature and a higher electromigration in the center portion  120  relative to the other portions of the eFuse  100 . Thus, the electromigration in the eFuse  100  is localized in the center portion  120 . 
         [0030]      FIG. 1C  illustrates an alternate embodiment of the eFuse  100 , the anode member&#39;s  102  and cathode member&#39;s  104  second layers comprise a first metal silicide. The second layer  116  of the link member  106  comprises a second metal silicide. 
         [0031]    In the illustrated alternate embodiment of eFuse  100  shown in  FIG. 1C , the entire metal silicide layer of the link portion  106  comprises a metal silicide with a higher resistivity than the metal silicide layers of the cathode member  104  and the anode member  102 . The relative difference in resistivities between the link member  106  and the cathode member  104  and anode member  106  results in electromigration occurring in the link member  106  prior to the cathode member  104  and the anode member  102 . 
         [0032]      FIG. 2  illustrates another alternate embodiment of an eFuse  200 . In the illustrated embodiment, an anode member  202 , a link member  206 , and a cathode member  204  are disposed on a dielectric substrate  212 . The anode member  202  comprises a first metal, and the link member  206  and cathode member  204  comprises a second metal. The metals may be any of a variety of suitable metals including metal nitride and metal silicide, for example. The second metal has a higher resistivity relative to the first metal. Thus, electromigration occurs in the second metal prior to the first metal. 
         [0033]      FIG. 3  illustrates an alternate embodiment of an eFuse  300 . The illustrated embodiment includes an anode member  302 , a link member  306 , and a cathode member  304 . The link member includes an anode portion  308 , a notch portion  322 , and a cathode portion  310 . 
         [0034]    The anode member  302 , the link member  306 , and the cathode member  304  include two layers. A first layer  314  is disposed on a substrate  312 , and comprises a first metal. A second layer  316  is disposed on the first layer  314  and comprises a second metal. The first layer  314  of the link member  306 , and the second layer  316  of the anode portion  308  and the cathode portion  310  of the link member  306  partially define the notch portion  322 . 
         [0035]    In operation, when current is induced across the link member  306 , current must flow under the notch portion  322 . Since the cross sectional area of the link member  306  is smaller under the notch portion  322  than the other portions of the link member  306 , the current crowds under the notch portion  322 . Thus, the effective resistivity of the area under the notch is greater than the other portions of the link member  306 . The resultant electromigration occurs under the notch portion  322  prior to the other portions of the eFuse  300 . This effect may be increased if the first and second metals have similar conductivities. 
         [0036]    While the preferred embodiment to the invention has been described, it will be understood that those skilled in the art, both now and in the future, may make various improvements and enhancements which fall within the scope of the claims which follow. These claims should be construed to maintain the proper protection for the invention first described.