Abstract:
A method for improving the integrated circuits bonding firmness, whose principle is that after the later film is piled on top of the previous film, the upper surface of the later film will be affected by the previous film. Among the metal layers of the multi-level interconnection, the metal layer under and most close to the bond pad metal (the top metal layer of the multi-level interconnection) has a regular or an irregular layout pattern, which is under the predetermined regions serving as bond pad windows. These regular or irregular layout patterns result in a rough upper surface, and then improves the firmness of bond wires.

Description:
This application is a divisional of application Ser. No. 09/221,569 filed Dec. 29, 1998, now U.S. Pat. No. 6,444,295. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a method for improving integrated circuits bonding firmness and, more particularly, to regular or irregular layout patterns formed under bond pads. 
     2. Description of the Prior Art 
     As the increment of integration, the multi-level interconnection must be used for the coupling of internal circuits during the fabrication of semiconductor devices because that the single metal connect is not sufficient for using. In general, many semiconductor devices utilize bond pads and bond wires to form the electrically coupling between internal and external circuits. Because the bond pads are formed on the upper metal layer of the multi-level interconnection, the upper metal layer of the multi-level interconnection are usually called as “bond pad metal layer”. The formation of bond pads includes photolithography and etching processes to form bond pad windows in the passivation layer, which covers the devices formed previously, and then expose the predetermined areas located in the “bond pad metal layer”. After the bond pad windows are formed, thin wires are bonded into the bond pad windows to couple with the predetermined areas served as bond pads. 
     The bond wires are tensioned and sheared during the devices are packaged, which may cause the peeling of bond wires and thus bring about the failure of the devices. There are many prior arts to solve the foregoing problem. For example, the U.S. Pat. No. 5,695,592 (Dec. 9, 1997) entitled “Method of adhesively bonding mineral particles to support” or the U.S. Pat. No. 5,700,581 (Dec. 23, 1997) entitled “Solvent-free expoxy based adhesives for semiconductor chip attachment”. Another method is to modify the structure of bond pads for increasing firmness of bond wire. For example, the U.S. Pat. No. 5,686,762 (Nov. 11, 1997) titled “Semiconductor device with improved bond pads”. Among these methods, the U.S. Pat. No. 5,686,762 is described accompanied with the FIG.  1 . At least one opening is formed in the bonding surface of bond pads and the opening(s)  22  may recesses extending partially into the bonding surface or channels that extend entirely through the bond pad. This method increases the firmness of bond wire efficiently but additional steps are needed during the forming of opening(s)  22 . Such as an additional photomask of the opening(s)  22  pattern additional photolithography process removal of the photoresistor and etching processes process and so on. In FIG. 1, the object  12  is an internal circuit; the object  16  is the bond pad window; the object  18  is a passivation layer and the object  20  is an insulator layer. 
     The method disclosed in the present invention is easier than aforesaid methods, because additional steps or cost is not necessary for the present invention. The feature of the present invention is to make the bonding surface of metal layer under and most close to the bond pad layer (the top metal layer of multi-level interconnection) rough, which leads to improving the firmness of bond wire. The principle of roughness process is, under the predetermined regions serve as bond pads, to form a metal layer with regular or irregular layout patterns. It&#39;s worthy to note that the roughness process is be implemented in the meanwhile of the deposition of the metal layer under the bond pad layer. In other words, it doesn&#39;t require additional steps or cost because the photomasks of layout pattern and that of metal layer are the same one. 
     SUMMARY OF THE INVENTION 
     During the devices are packaged, the break of bond wires or the peeling of bond pads occurs frequently and thus result in the failure of the devices. In order to improve the firmness of bond wires, the present invention discloses a method, which makes the metal layer under and most close to the bond pad metal layer (the upper metal layer of multi-level interconnection) rough. The method of making rough is, under the bond pad metal, to form a metal layer with regular or irregular layout patterns to result in the undulation of upper surface. The bonding surface of later bond pads formed on the metal is affected by the undulation, and thus improves the firmness of bond wires. 
     The preferred embodiment of the present invention is described as follow: An internal circuit is formed on a substrate by conventional method. This internal circuit comprises several metal-oxide semiconductors (MOSs) or other semiconductor devices. An insulator layer is formed on the internal circuit and then several contact holes are formed in the insulator layer by photolithography and etching processes. Several plugs are formed in the contact holes and couple to the internal circuit. A composition layer is formed, which serves as a part of the multi-level interconnection. The composition layer is composed with at least one metal layer and at least one inter-metal dielectric layer (IMD), and each film of the composition layer is piled on top of each other. The bottom and the top of the composition layer are a metal layer and a dielectric layer, respectively. There are several vias and several via plugs in each inter-metal dielectric layer, and these via plugs serve to make the metal layers coupling to the internal circuit. It&#39;s worthy to note that, under the specific regions serving as bond pads, the top metal layer of the composition layer has a regular or an irregular layout pattern. 
     The method disclosed in the present invention is applied in multi-level interconnection. If the number of metal layers of the multi-level interconnection is 3, the number of metal layers of the composition layer is 2; the inter-metal dielectric layers (IMD) of the composition layer serve as insulation and whose number is 2, as well. 
     A bond pad layer is formed on the composition layer. Then a passivation layer is formed on the bond pad layer. The passivation layer serves to protect the internal circuit from moisture and alkali ions. Then by photolithography and etching processes; bond pad windows are formed in the passivation layer to expose the bond pad layer. Finally, the bond wires are bonded to the bond pads. 
     After the aforesaid steps are finished, a test machine was used to test the firmness of the bond wires. The test result reveals that no matter whether ball shear test or wire pull test, the bond pads using present invention satisfy the industrial standard (wire pull is 5 mg and ball shear is 30 mg) 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated as the same becomes better understood by reference to the following detailed description when taken in conjunction with the accompanying drawings, wherein 
     FIG. 1 is a cross section view of a bond pad structure of prior art. 
     FIG.  2 ( a ) is a cross section view of a bond pad structure of present invention. 
     FIG.  2 ( b ) is a simplified layout pattern of the present invention. 
     FIG.  3 ( a ) is the practical layout pattern of FIG.  2 ( b ), and FIGS.  3 ( b ) to ( t ) is the other layout patterns of present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A multi-level interconnection structure will be employed below to illustrate the preferred embodiment of present invention. Referring to FIG.  2 ( a ), an internal circuit  15  is formed on a substrate  10   a  by using conventional method. This internal circuit  15  comprises several metal-oxide semiconductors (MOSs) or other semiconductor devices. An insulator layer  100  is formed on the internal circuit  15  and then several contact holes  107  are formed in the insulator layer  100  by photolithography and etching processes. Several plugs  109  are formed in the contact holes  107  and couple with the internal circuit  15 . 
     Still referring to FIG.  2 ( a ), a composition layer  300  is formed, which serves as a part of the multi-level interconnection. The composition layer  300  is composed with at least one metal layer and at least one inter-metal dielectric layer (IMD). The bottom and the top of the composition layer  300  are the metal layer  310  and the dielectric layer  320 , respectively. There are a plurality of vias and a plurality of via plugs  350  in each inter-metal dielectric layer, which serve to make the metal layers of said composition layer  300  coupling to the internal circuit  15 . It&#39;s worthy to note that, in some specific regions of the surface, the upper metal layer  310  of the composition layer  300  includes a regular or an irregular layout pattern  600  formed thereon (as shown in FIG.  2 ( b )). The purpose of the layout pattern  600  is to form a rough upper surface and thus to increase the firmness of subsequent wire bonds  200  formed thereon. This process is referred to “the roughened process”, and the specific regions are under the regions  180  which serve as bond pads. 
     The reasons why the metal layer  310  is selected to proceed “the roughened process” are described as follow: Because the metal layer  310  is the layer under and most close to the bond pads  180 , the influence of the metal layer  310  on roughness of bond pads  180 &#39;s bonding surface is the most efficient than other layers. Another reason is that if forming the regular or irregular layout pattern  600  on bond pads  180 &#39;s bonding surface, thus will reduce of the area of bond pads  180  and also the performance of current-transmitting. 
     Still referring to FIG.  2 ( a ), a bond pad layer  500  is formed on the composition layer  300 . Then a passivation layer  160  is formed on the bond pad layer  500 . The passivation layer  160  serves to protect the internal circuit  15  from moisture and alkali ions. Then bond pad windows  170  are formed in the passivation layer  160  to expose the bond pads  180  by photolithography and etching processes. The dimensions of the bond pads  180  are 96×96 micrometer square as an example. Of course, other dimensions can be used. Finally, bond wires  200  are bonded to the bond pads  180  to couple to the external circuit (not shown). 
     In the present embodiment, the layout pattern  600  shown in FIG.  2 ( b ) is marked “pad-02”, which is simplified for showing the drawing simply. The practical pattern of pad-02 is shown in FIG.  3 ( a ) and also marked “pad-02”. The other layout patterns shown in FIGS.  3 ( b ) to ( t ) is marked “pad-04”•“pad-06” . . . . and “pad-40”, respectively. These layout patterns include: a matrix composed with a plurality of squares (serial numbers are “pad-02”•“pad-04” . . . “pad-22” and shown in FIG.  3 ( a ) to ( k )). The dimensions of squares belong to the same serial number are the same, but the dimensions of squares belong to different serial number are different from each other. A matrix composed with a plurality of round dots (serial number is “pad-24” and shown in FIG.  3 ( l )); A “#” shaped ditch (serial number is “pad-26” and shown in FIG.  3 ( m )); A cross shaped ditch (serial number is “pad-28” and shown in FIG.  3 ( n )); An irregular pattern composed with a plurality of squares with several dimensions (serial number is “pad-30” and shown in FIG.  3 ( o )); Patterns composed with a plurality of concentric rings (serial numbers are “pad-32”•“pad-34” and shown in FIGS.  3 ( p ) to ( q ), respectively) and irregular polygons (serial numbers is “pad-36” to “pad-40” and shown in FIGS.  3 ( r ) to ( t ), respectively). On the wafer  100   b  and  100   c , the above-mentioned steps forming bond pads  180  proceed repeatedly to make a comparison. It&#39;s worthy to note that the metal layers of present invention is a preferred embodiment, and other conductive materials suiting to serve as the multi-level interconnection are included in the scope of the present invention. 
     For comparing bond pads of the present invention with that of convention, in the meanwhile, a plurality of general bond pads are formed on the wafers named  100   a • 100   b  and  100   c  by conventional process. These general bond pads are marked serial numbers “pad-01”•“pad-03” . . . “pad-39” and whose total numbers are 20, too. Except forming the regular or irregular layout pattern, the remainder steps to form these general bond pads are the same with the forming process of bond pads  180  “pad-02”•“pad-04” . . . “pad-40”. 
     A test machine was utilized to exam the firmness of the bond wires. The test result listed in Table-1(a) and Table-1(b) reveal that no matter whether wire pull test or ball shear test, the bond pads of present invention (pad-02•pad-04 . . . pad-40) satisfy the industrial standard (wire pull is 5 mg and ball shear is 30 mg). Some bond pads of the present invention are more excellent than that of convention (pad-01•pad-03 . . . pad-39), and the test results of conventional bond pads are listed in Table-2(a) and Table-2(b), respectively. Hence it appears that the bond pads of the present invention are conducive to the firmness of bond wire. 
     
       
         
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 1(a) 
               
             
             
               
                   
               
               
                 The wire pull test of the present invention 
               
               
                 (unit:mg) 
               
             
          
           
               
                   
                 wafer 100a 
                 wafer 100b 
                 wafer 100c 
                 average 
               
               
                   
               
             
          
           
               
                 pad-02 
                 8.8 
                 9.3 
                 8.3 
                 8.80 
               
               
                 pad-04 
                 7.5 
                 9.9 
                 8.5 
                 8.63 
               
               
                 pad-06 
                 9.8 
                 11.0 
                 10.05 
                 10.43 
               
               
                 pad-08 
                 9.9 
                 9.9 
                 9.5 
                 9.77 
               
               
                 pad-10 
                 9.6 
                 9.4 
                 9.8 
                 9.60 
               
               
                 pad-12 
                 9.4 
                 8.7 
                 8.7 
                 8.93 
               
               
                 pad-14 
                 8.9 
                 9.5 
                 8.6 
                 9.00 
               
               
                 pad-16 
                 9.8 
                 9.3 
                 8.7 
                 8.93 
               
               
                 pad-18 
                 9.3 
                 9.5 
                 8.8 
                 9.20 
               
               
                 pad-20 
                 8.9 
                 9.1 
                 8.7 
                 8.90 
               
               
                 pad-22 
                 8.1 
                 9.0 
                 8.5 
                 8.53 
               
               
                 pad-24 
                 9.5 
                 9.8 
                 8.8 
                 9.37 
               
               
                 pad-26 
                 9.2 
                 9.1 
                 7.6 
                 8.63 
               
               
                 pad-28 
                 9.4 
                 8.9 
                 8.0 
                 8.77 
               
               
                 pad-30 
                 8.1 
                 8.2 
                 7.7 
                 8.00 
               
               
                 pad-32 
                 6.8 
                 7.4 
                 6.1 
                 6.77 
               
               
                 pad-34 
                 7.2 
                 7.7 
                 6.9 
                 7.27 
               
               
                 pad-36 
                 7.7 
                 6.1 
                 6.9 
                 6.90 
               
               
                 pad-38 
                 7.4 
                 7.0 
                 7.5 
                 7.30 
               
               
                 pad-40 
                 8.4 
                 7.9 
                 7.3 
                 7.86 
               
               
                   
               
             
          
         
       
     
     
       
         
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 1(a) 
               
             
             
               
                   
               
               
                 The ball shear test of the present invention 
               
               
                 (unit:mg) 
               
             
          
           
               
                   
                 wafer 100a 
                 wafer 100b 
                 wafer 100c 
                 average 
               
               
                   
               
             
          
           
               
                 pad-02 
                 46.9 
                 28.6 
                 26.3 
                 33.93 
               
               
                 pad-04 
                 41.2 
                 42.1 
                 36.2 
                 39.83 
               
               
                 pad-06 
                 42.1 
                 34.8 
                 45.8 
                 40.9 
               
               
                 pad-08 
                 44.2 
                 36.2 
                 63.2 
                 47.87 
               
               
                 pad-10 
                 37.1 
                 37.9 
                 46.7 
                 40.57 
               
               
                 pad-12 
                 43.5 
                 40.6 
                 37.3 
                 40.46 
               
               
                 pad-14 
                 38.8 
                 38.5 
                 49.4 
                 42.23 
               
               
                 pad-16 
                 35.4 
                 33.3 
                 35.8 
                 34.83 
               
               
                 pad-18 
                 36.5 
                 33.2 
                 37.9 
                 35.87 
               
               
                 pad-20 
                 32.2 
                 33.1 
                 32.0 
                 32.43 
               
               
                 pad-22 
                 32.4 
                 33.3 
                 30.5 
                 32.07 
               
               
                 pad-24 
                 30.6 
                 32.2 
                 31.0 
                 31.27 
               
               
                 pad-26 
                 36.0 
                 32.7 
                 30.1 
                 32.93 
               
               
                 pad-28 
                 34.2 
                 32.8 
                 30.0 
                 32.33 
               
               
                 pad-30 
                 34.8 
                 36.5 
                 29.5 
                 33.60 
               
               
                 pad-32 
                 32.1 
                 46.4 
                 38.6 
                 39.03 
               
               
                 pad-34 
                 30.6 
                 34.1 
                 35.5 
                 33.40 
               
               
                 pad-36 
                 38.5 
                 26.8 
                 38.5 
                 34.60 
               
               
                 pad-38 
                 35.1 
                 36.0 
                 30.1 
                 33.73 
               
               
                 pad-40 
                 30.2 
                 30.8 
                 33.1 
                 31.37 
               
               
                   
               
             
          
         
       
     
     
       
         
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 2(a) 
               
             
             
               
                   
               
               
                 The wire pull test of conventional bond pads 
               
               
                 (unit:mg) 
               
             
          
           
               
                   
                 wafer 100a 
                 wafer 100b 
                 wafer 100c 
                 average 
               
               
                   
               
             
          
           
               
                 pad-01 
                 10.2 
                 9.9 
                 9.1 
                 9.73 
               
               
                 pad-03 
                 8.3 
                 8.7 
                 7.3 
                 8.10 
               
               
                 pad-05 
                 9.0 
                 9.8 
                 9.4 
                 9.40 
               
               
                 pad-07 
                 10.0 
                 10.8 
                 9.2 
                 10.00 
               
               
                 pad-09 
                 10.1 
                 10.1 
                 9.8 
                 10.00 
               
               
                 pad-11 
                 10.0 
                 9.6 
                 9.7 
                 9.77 
               
               
                 pad-13 
                 9.2 
                 9.5 
                 9.3 
                 9.33 
               
               
                 pad-15 
                 9.0 
                 8.8 
                 8.8 
                 8.87 
               
               
                 pad-17 
                 9.3 
                 8.5 
                 8.9 
                 8.90 
               
               
                 pad-19 
                 9.9 
                 9.8 
                 9.3 
                 9.67 
               
               
                 pad-21 
                 9.8 
                 8.7 
                 7.8 
                 8.77 
               
               
                 pad-23 
                 8.0 
                 7.9 
                 9.7 
                 8.53 
               
               
                 pad-25 
                 9.1 
                 8.7 
                 8.7 
                 8.83 
               
               
                 pad-27 
                 8.9 
                 8.7 
                 8.9 
                 8.83 
               
               
                 pad-29 
                 7.9 
                 7.6 
                 7.5 
                 7.66 
               
               
                 pad-31 
                 7.3 
                 7.6 
                 5.3 
                 6.73 
               
               
                 pad-33 
                 8.4 
                 7.0 
                 6.1 
                 7.17 
               
               
                 pad-35 
                 7.3 
                 8.3 
                 5.5 
                 7.03 
               
               
                 pad-37 
                 6.9 
                 7.1 
                 5.4 
                 6.47 
               
               
                 pad-39 
                 7.2 
                 6.2 
                 7.7 
                 7.03 
               
               
                 average 
                 8.84 
                 8.665 
                 8.17 
                 8.558 
               
               
                   
               
             
          
         
       
     
     
       
         
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 2(b) 
               
             
             
               
                   
               
               
                 The ball shear test of conventional bond pads 
               
               
                 (unit:mg) 
               
             
          
           
               
                   
                 wafer 100a 
                 wafer 100b 
                 wafer 100c 
                 average 
               
               
                   
               
             
          
           
               
                 pad-01 
                 40.0 
                 40.0 
                 44.2 
                 41.53 
               
               
                 pad-03 
                 49.4 
                 39.8 
                 43.1 
                 44.1 
               
               
                 pad-05 
                 41.5 
                 36.1 
                 39.9 
                 39.17 
               
               
                 pad-07 
                 46.4 
                 33.4 
                 53.9 
                 44.57 
               
               
                 pad-09 
                 43.8 
                 37.2 
                 44.2 
                 41.73 
               
               
                 pad-11 
                 38.8 
                 43.7 
                 40.2 
                 40.90 
               
               
                 pad-13 
                 40.1 
                 41.0 
                 44.1 
                 41.73 
               
               
                 pad-15 
                 37.7 
                 41.5 
                 39.9 
                 39.70 
               
               
                 pad-17 
                 37.3 
                 32.3 
                 53.1 
                 40.90 
               
               
                 pad-19 
                 37.9 
                 37.2 
                 37.0 
                 37.36 
               
               
                 pad-21 
                 41.0 
                 40.1 
                 36.4 
                 39.17 
               
               
                 pad-23 
                 39.0 
                 40.1 
                 36.9 
                 38.67 
               
               
                 pad-25 
                 38.8 
                 40.5 
                 35.4 
                 38.23 
               
               
                 pad-27 
                 39.1 
                 40.0 
                 39.5 
                 39.53 
               
               
                 pad-29 
                 35.7 
                 40.9 
                 34.3 
                 36.97 
               
               
                 pad-31 
                 43.0 
                 47.6 
                 40.6 
                 43.73 
               
               
                 pad-33 
                 40.6 
                 43.6 
                 32.3 
                 38.83 
               
               
                 pad-35 
                 38.2 
                 42.1 
                 32.1 
                 37.47 
               
               
                 pad-37 
                 39.9 
                 37.4 
                 38.8 
                 38.70 
               
               
                 pad-39 
                 40.4 
                 33.0 
                 31.5 
                 34.97 
               
               
                 average 
                 40.430 
                 39.395 
                 39.870 
                 39.898 
               
               
                   
               
             
          
         
       
     
     As is understood by a person skilled in the art, the foregoing preferred embodiments of the present invention are illustrated of the present invention rather than limiting of the present invention. It is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims, the scope of which should be accorded the broadest interpretation so as to encompass all such modifications and similar structure.