Abstract:
An integrated circuit and a fuse therefore are disclosed. The integrated circuit fuses includes a plurality of terminals coupled by a fuse element, wherein the fuse element is located in a non-last metal layer and/or wherein each terminal is fully-landed on an upper surface of a wire of the fuse element. As a result, there is no explosion that causes damage to surrounding material. In addition, use of the wet etchant allows positioning of a fuse in any metal layer including any non-last metal layer, thus increasing design possibilities.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This continuation application claims priority to co-pending U.S. patent application Ser. No. 10/604,011, entitled INTEGRATED CIRCUIT FUSE AND METHOD OF OPENING, filed on Jun. 20, 2003, the contents of which are hereby incorporated by reference in their entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The present invention relates generally to integrated circuits, and more particularly, to an integrated circuit fuse. 
     2. Related Art 
     Back-end-of-line (BEOL) modifications are common in integrated circuit (IC) manufacture. One mechanism for making changes to an IC is to open a fuse that has been built into the IC. One widely used approach to opening a fuse is using a laser to destroy a fuse wire. Laser blown fuses have the advantage of allowing only selected fuses to be blown without the use of a chrome-on-glass mask. In operation, an infrared laser is used to heat a element to the point where it is destroyed, opening the wiring path. 
     One disadvantage of this approach, however, is that the destruction of the element is explosive and oftentimes causes damage to surrounding materials, e.g., insulator. Conventionally, damage to surrounding materials is inadequate to harm the delicate wiring at lower levels, which could cause IC failure. In many newer applications, however, very large elements, e.g., wide and tall, are provided at the last level to accommodate better power distribution. Unfortunately, larger elements result in larger fuses that require more laser energy to open, and thus cause more damage to surrounding materials. Accordingly, there is now a higher risk of damage to the delicate wiring used at the lower levels and a higher risk of IC failure. 
     Another disadvantage of current fuse technology is the necessity to place the fuses in the last metal layer, which limits design possibilities. 
     In view of the foregoing, there is a need for a method of opening an IC fuse that does not damage surrounding areas, and allows for non-last metal layer positioning of the fuse. 
     SUMMARY OF THE INVENTION 
     The invention includes an integrated circuit, and a fuse therefore. The integrated circuit fuses includes a plurality of terminals coupled by a fuse element, wherein the fuse element is located in a non-last metal layer and/or wherein each terminal is fully-landed on an upper surface of a wire of the fuse element. As a result, there is no explosion that causes damage to surrounding material. In addition, use of the wet etchant allows positioning of a fuse in any metal layer including any non-last metal layer, thus increasing design possibilities. 
     As a result, there is no explosion that causes damage to surrounding material. In addition, use of the wet etchant allows positioning of a fuse in any any non-last metal layer, thus increasing design possibilities. 
     A first aspect of the invention is directed to a method for opening an integrated circuit fuse, the method comprising the steps of: generating at least one opening to a fuse element that couples a plurality of terminals; and wet etching the fuse element to open the fuse. 
     A second aspect of the invention is directed to an integrated circuit fuse comprising: a plurality of terminals coupled by a fuse element; wherein the fuse element is located in a non-last metal layer. 
     A third aspect of the invention is directed to an integrated circuit comprising: a fuse including a plurality of terminals coupled by a fuse element; wherein the fuse element is located in a non-last metal layer. 
     A fourth aspect of the invention is directed to an integrated circuit fuse comprising: a plurality of terminals coupled by a fuse element; wherein each terminal is fully-landed on a wire of the fuse element. 
     A fifth aspect of the invention is directed to an integrated circuit comprising: an opened fuse area including a metal liner of a fuse element, the fuse element having been removed to generate the opened fuse area, the metal liner being intact immediately adjacent to, and in non-contact, with a plurality of terminals. 
     The foregoing and other features of the invention will be apparent from the following more particular description of embodiments of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The embodiments of this invention will be described in detail, with reference to the following figures, wherein like designations denote like elements, and wherein: 
         FIG. 1  shows one embodiment of an integrated circuit fuse according to the invention. 
         FIG. 2  shows a flow diagram of a method for opening the fuse of  FIG. 1 . 
         FIGS. 3-7  show steps of the method of  FIG. 2 . 
         FIG. 8  shows a perspective cross-sectional view of an opened fuse area generated according to the method of  FIGS. 3-7 . 
         FIG. 9  shows an alternative embodiment of an integrated circuit fuse according to the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference to the accompanying drawings,  FIG. 1  is cross-sectional view of an integrated circuit (IC)  8  including one embodiment of an IC fuse  10  according to the invention. IC fuse  10  includes a plurality of terminals  13  coupled by a fuse element  16 . In the  FIG. 1  embodiment, fuse element  16  is provided in the form of a horizontal wire  12  that couples terminals  13 , which each include a stud  14  and a horizontal wire  18 . In the  FIG. 1  embodiment, terminals  13  are also located in the same layer. It is understood that each wire  18  continues on in a direction perpendicular to the page, i.e., into and/or out of the page. Each stud  14  is provided as a vertical wire and couples at least one respective wire  18  to fuse element  16 . Each stud  14  and wire  18  includes a metal liner  24  of, for example, tantalum, tungsten, titanium nitride, or any other liner metal used for such purposes. Each stud  14  is fully-landed on a wire  12  of fuse element  16 . That is, each metal liner  24  is on top of wire  12  of fuse element  16 , and does not contact a metal liner  17  that surrounds at least a portion of fuse element  16 . 
     Fuse element  16  is shown located in a penultimate metal layer  20 , but may be located in any non-last metal layer. In addition, while wires  18  are shown in a last metal layer  22 , they may be located in any metal layer. In one embodiment, element  16 , wires  18  and studs  14  are all made of copper. However, other materials such as aluminum are also possible. 
     Terminals  13  are surrounded by an insulator  26 , which is typically some type of glass, e.g., silicon oxide. A thin diffusion barrier or cap  28  of, for example, silicon nitride (SiN) or silicon carbide (SiC), is also typically provided on top of fuse element  16 . A final insulating passivation layer  30  is also shown. Passivation layer  30  may include silicon dioxide, silicon nitride, silicon carbide or a combination thereof, and may consist of sublayers (not all shown) including, for example, a thin diffusion barrier  32  on top of wires  18 . Passivation layer  30  may also include a polyimide or other polymeric layer(s). Diffusion barrier  32  may include, for example, SiN, SiC or other diffusion barrier material. 
     Referring to  FIG. 2 , a flow diagram of a method for opening IC fuse  10  is shown.  FIGS. 3-7  illustrate the steps of the method. Steps S 1 -S 4  (or steps S 1 -S 6 ), as will be described below, collectively generate at least one opening  50  ( FIG. 5 ) to fuse element  16 . Referring to  FIGS. 2 and 3 , in step S 1 , a layer  40  is deposited on passivation layer  30 . In one embodiment layer  40  is a photoresist. In this case in step S 2 , photoresist  40  is exposed using laser light  42  of the proper wavelength to generate at least one opening area  44 . In one embodiment, ultraviolet laser light is used. In this manner, laser equipment similar to the more conventional infrared laser fuse opening equipment may continue to be used, and only certain fuses can be targeted for opening. In an alternative embodiment, layer  40  may be provided as a polymer that ablates upon exposure to laser light  42  to generate at least one opening area  44 . Referring to  FIGS. 2 and 4 , in step S 3 , layer  40  is developed or opened to leave an opening  46  where each opening area  44  (not shown) was generated. Steps S 1 -S 3 , collectively, apply a layer  40  to define an opening area  44  ( FIG. 4 ). 
     Referring to  FIGS. 2 and 5 , in step S 4 , at least one opening  50  is generated by etching, such as reactive ion etching (RIE), to remove passivation layer  30  and insulator  26  beneath each photoresist opening  46 , i.e., in the areas where there is no photoresist  40 . As noted earlier, passivation layer  30  and insulator  26  may include sublayers, each of which are removed by etching. In any case, etching chemistry can be altered as necessary during the course of operation to remove all layers and stop on diffusion barrier  28  on top of wire  12  of fuse element  16 . If no diffusion barrier  28  is provided, each opening  50  fully extends to wire  12  of fuse element  16 . However, if diffusion barrier  28  is provided, the process includes step S 6 , described below. 
     Referring to  FIGS. 2 and 5 , in step S 5 , the remaining photoresist  40  (or polymer if used) is stripped, for example, by an oxygen plasma or any other now known or later developed method. 
     Referring to  FIGS. 2 and 6 , in step S 6 , if a diffusion barrier  28  is provided, it is removed such that each opening  50  fully extends to wire  12  of fuse element  16 . Removal of any diffusion barrier  28  may be made, for example, by reactive ion etching. If wire  12  of fuse element  16  is provided as copper, etching may occur in a non-oxygen plasma to prevent corrosion to fuse wire  16 . Steps S 1 -S 5 , or steps S 1 -S 6 , collectively, generate at least one opening  50  to fuse element  16 . 
     Referring to  FIGS. 2 and 6 , in step S 7 , wet etching  52  is used to remove, i.e., dissolve, wire  12  of fuse element  16 . Wet etchant  52  may be any of various aggressive wet etches suitable for wire  12  material. Wet etchant  52  cuts under terminals  14  and dissolves wire  12  of fuse element  16  therebetween. Since terminals  13  are fully-landed on wire  12  of fuse element  16 , once the fuse wire is removed, the circuit is open. The resulting open fuse is shown in  FIGS. 7 and 8 . In the case where wire  12  of fuse element  16  is copper, wet etchant  52  may include at least one of sulfuric acid, aqueous ammonium persulfate, hydrogen peroxide and water. Wet etchant  52  can act sideways so that fuse element  16  can be completely dissolved. Terminals  13  will not be affected by wet etchant  52  because they are surrounded on the sides (studs  14  and wires  18 ) and bottom (wires  18 ) by metal liner  24 , which is not affected by wet etchant  52 . Note, however, metal liner  17  material, as shown in  FIG. 8 , is not on top of fuse element  16  and, therefore, does not prevent wet etching of fuse element  16 . As shown, one opening  50  is generated to each side of terminals  13 . It should be recognized, however, that any number of openings  50 , including one, may be generated depending on the required space for wet etchant  52 , e.g., how much wet etchant  52  is required, where it is required, venting required, etc. It should also be recognized that the shape of each opening  50  may be adjusted to address different situations, e.g., opening  50  may be semi-circular, elongated, etc. 
     Referring to  FIG. 8 , IC  8  including an opened fuse area  100  generated according to the above method is shown. Opened fuse area  100  includes a metal liner  17  of a fuse element  16  (not actually shown) that has been removed to generate the opened fuse area. Metal liner  17  is intact immediately adjacent to, and in non-contact, with plurality of terminals  13 .  FIG. 8  illustrates how terminals  13  were fully-landed on fuse element  16 , now removed, such that once fuse element  16  is removed, terminals  13  no longer make contact with fuse element  16  or a metal liner  17  thereof. Since the above method is non-damaging to everything except wire  12  of fuse element  16 , metal liner  17  remains intact immediately adjacent terminals  13 , as opposed to having been explosively removed. 
     It should be recognized that the particular IC fuse  10  shown is only illustrative and that the invention may include any IC fuse  10  having a fuse element  16  in any non-last metal layer. It should also be recognized that IC fuse  10  is only one of many possible layouts for wiring, and that fuse element  16  may be provided in different designs (shapes) and appropriate openings made to allow wet etchant  52  access to any location of the fuse wire. For example, one alternative embodiment is shown in  FIG. 9 . 
     In the  FIG. 9  embodiment, a vertical fuse  110  including a fuse element  116  including a horizontal fuse wire  112  and a fuse vertical stud  148  may be provided in a vertical fashion between two substantially horizontal terminals  13 A,  13 B. In this case, a higher terminal  13 A includes a horizontal wire  118 A and a terminal vertical stud  114 , and a lower terminal  113 B includes a horizontal wire  1118 B. In this case, only one terminal  13 A requires a terminal vertical stud  114  for horizontal wire  118 A since fuse element  116  includes its own fuse vertical stud  148  extending to horizontal wire  1118 B. A single opening  150  is provided such that a wet etchant (not shown) may remove fuse element  116  including wire  112  and vertical stud  148 . Vertical stud  114  of terminal  13 A must be fully landed on wire  112  of fuse element  116 , as described above, to prevent shorting from a liner  124  of terminal  13 A to a liner  117  of fuse element  116  when vertical fuse  110  is opened. Fuse vertical stud  148  may be directly below terminal vertical stud  114  or offset as shown. Fuse vertical stud  148 , however, does not necessarily need to be fully landed on horizontal wire  118 B. The above-described structure may be provided in any layers desired so long as opening  150  can reach fuse element  116 . In view of the foregoing, the invention should not be limited to any particular design. 
     While this invention has been described in conjunction with the specific embodiments outlined above, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, the embodiments of the invention as set forth above are intended to be illustrative, not limiting. Various changes may be made without departing from the spirit and scope of the invention as defined in the following claims.