Abstract:
An improved via arrangement for a bonding pad structure is disclosed comprising an array of vias surrounded by a line via. The line via provides a barrier to cracks in the dielectric layer encompassing the via array. Although cracks are able to spread relatively unhindered between the vias of the via array, they are blocked by the line via and thus can not spread to neighboring regions of the chip or wafer. The line via can be provided in a variety of shapes and dimensions, to suit a desired application. Additionally, due to its substantially uninterrupted length, the line via provides added strength to the bond pad.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates generally to semiconductor integrated circuit processing and more particularly to bond pad structures that minimize inter-metal dielectric cracking. 
       BACKGROUND OF THE INVENTION 
       [0002]    Bonding pads are the interfaces between the integrated circuits contained in semiconductor chips and the chip package. A large number of bonding pads is required to transmit power, ground and impute/output signals to the chip devices. It is thus important that the bonding pad yield be sufficiently high to ensure a high per chip yield. 
         [0003]    A typical bonding pad structure consists of metal layers, emanating from the terminals of a chip device, separated by inter-metal dielectric (IMD) layers that are often silicon oxide. Metal vias pass through the IMD layers to connect the metal layers. Wires are bonded to a bonding metal pattern and to the chip package forming electrical connections between the chip and the package. A passivation layer covers the surface, except over the bonding sites, to seal the chip from contaminants and to provide scratch protection. 
         [0004]    One mode of failure of the bonding pad relates to the peeling of the wire from the metal pattern due to forces exerted especially during the bonding process. Another failure mode that has been observed relates to bonding pad peel back, where forces imparted during wire bonding may cause a delaminating of one or more of the underlying layers. Another failure mode involves cracking of the IMD material. 
         [0005]    A conventional bond pad  1  for an integrated circuit (IC) wafer is illustrated in  FIGS. 1A and 1B . A pair of bond pad metal layers  2 A, B are connected by an array of conductive vias  10 . The bond pad metal layers  2 A, B are separated by a layer of dielectric material  12 , within which the vias  10  are disposed. During manufacturing, such as IC probe testing and during package assembly wire-bonding processes, external forces are applied to the bond pad  1 . These forces may cause cracks  12  to form in the dielectric material  12  between the vias  10 . Because the propagation path for these cracks  14  is largely uninhibited, the cracks  14  often extend to the area  16  outside the bond pad. Such cracking can cause current leakage, interlayer shorts, corrosion and reduced reliability of the IC. Moreover, large cracks  14  may cause failure of the IC very early in the life stage of the product in which the IC is used. 
         [0006]    Thus, there is a need for an improved arrangement for metal vias that will minimize the chances for cracks to occur in the IMD, and where such cracks do occur, to minimize and/or limit their propagation. Such an arrangement should also be inexpensive to manufacture. 
       SUMMARY OF THE INVENTION 
       [0007]    A bonding pad structure is disclosed, comprising a first conductive material layer, a layer of dielectric material disposed over the first conductive material layer and a second conductive material layer. A plurality of conductive vias may be disposed within the layer of dielectric material, said conductive vias being in electrical contact with the first and second conductive material layers. Further, a line via may be disposed about a perimeter of said plurality of conductive vias, said line via disposed within said layer of dielectric material. 
         [0008]    A bonding pad is also disclosed, comprising first, second and third conductive material layers. The bonding pad may also comprise first and second layers of dielectric material, the first layer of dielectric material disposed between the first and second conductive material layers, and the second layer of dielectric material disposed between the second and third conductive material layers. A first plurality of conductive vias may be disposed within the first layer of dielectric material to electrically connect the first and second conductive material layers. A second plurality of conductive vias may be disposed within the second layer of dielectric material to electrically connect the second and third conductive material layers. A first line via may be disposed within said first layer of dielectric material, said first line via having an inner perimeter substantially surrounding said first plurality of conductive vias. Thus, arranged, cracks in said first layer of dielectric material are contained between said first and second conductive material layers and said inner perimeter of said first line via. 
         [0009]    A method of forming a bonding pad is also disclosed, comprising: providing a semiconductor wafer; forming a first dielectric layer over the wafer; forming a first conductive material layer over the first dielectric layer; forming a second dielectric layer over the first conductive material layer; patterning the second dielectric layer to form a plurality of openings therein, said plurality of openings comprising a central array of openings and a line opening substantially surrounding said central array of openings; providing conductive material within said plurality of openings; and providing a second conductive material layer over said second dielectric layer and said conductive material within said plurality of openings; wherein cracks in said second dielectric layer are contained between said first and second conductive material layers and an inner perimeter of said conductive material disposed within said line opening. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    These and other features and advantages of the present invention will be more fully disclosed in, or rendered obvious by, the following detailed description of the preferred embodiment of the invention, which is to be considered together with the accompanying drawings wherein like numbers refer to like parts, and further wherein: 
           [0011]      FIGS. 1A and 1B  illustrate conventional via patterns of a typical bonding pad showing propagated cracks in the inter-metal dielectric (IMD) layer; 
           [0012]      FIGS. 2A and 2B  are cross-section and plan views, respectively, of an exemplary semiconductor wafer incorporating the novel bond pad and line via arrangement; 
           [0013]      FIG. 3  is a cross-section view of a multilayer bonding pad implementing the novel line via arrangement; 
           [0014]      FIG. 4  is a cross-section view of a multilayer bonding pad implementing an alternative line via arrangement between successive metal layers. 
       
    
    
     DETAILED DESCRIPTION 
       [0015]    According to an embodiment of the present invention, disclosed herein is a design for a bonding pad using an array of vias, the arrangement of which minimizes cracking of IMD material that often occurs during wafer handling and processing. 
         [0016]    Referring to  FIGS. 2A and 2B , the novel bonding pad  20  comprises a pair of bond pad metal layers  22 A,  22 B, with a layer of inter-metal dielectric (IMD)  24  disposed therebetween. A plurality of conductive vias  26  are disposed within the IMD layer  12 , and form individual electrical contacts between the bond pad metal layers  22 A, B. Additionally, a conductive line via  28  is disposed about the perimeter of the plurality of vias  26 . In addition to forming an electrical contact between the bond pad metal layers, the line via  28  encompasses the vias  26  to form an isolation barrier that prevents propagation of cracks  30  in the IMD layer  24  that may occur during wire bond processing. Thus, even if a crack  30  initiates in the IMD layer  24 , it can only propagate as far as the line via  28 , and can not extend into the area outside the area of the bond pad  20 . 
         [0017]    Referring to  FIG. 3 , the basic elements of a multilayer bonding pad structure  32  are illustrated in  FIG. 3 , and consist of a plurality of metal layers  34  emanating from the terminals of a chip device (not shown), separated by IMD layers  36 . Each metal layer  34  may be electrically connected to an adjacent metal layer  34  by a plurality of conductive vias  38 , as well as by a line via  39  that surrounds the plurality of conductive vias  38  one that particular level. A passivation layer  40  covers the surface of the topmost metal layer  34 , except over the bonding site, to seal the chip  42  from contaminants and to provide scratch protection. Wires may be bonded directly to the topmost metal layer  34  at the bonding site, or they may be bonded to an intervening bonding metal pattern and to the chip package, thus forming electrical connections between the chip  42  and the package. 
         [0018]    As shown in  FIG. 3 , the inventive via and line via arrangement shown in  FIGS. 2A ,  2 B can be implemented between any two adjacent levels of metal  34  in such a multilevel bonding pad  32 . The crack resistance properties of the via arrangement may be most effectively utilized when disposed between the top two metal layers. 
         [0019]    In addition to providing a barrier to IMD crack propagation, the line vias  39  may provide enhanced resistance to stresses arising during chip packaging processes. In contrast to typical bonding pads in which pad compressive strength is provided only by the square vias  38 , the line via  39  lends substantial strength to the bonding pad due to its uninterrupted length surrounding the plurality of vias  38 . Thus, the line via  39  may have a size and shape selected to maximize both the electrical connection between the contacted metal layers, and to maximize the strength of the bond pad to resist cracking and other damage due to stresses imposed during manufacture. In one embodiment, the line via  39  may have a width “LVW” of from about 0.5 times to about 2 times the width “VW” of via  38 . A minimum offset “LVO” between the line via  39  and the nearest via  38  may be about the same as the spacing “VO” between adjacent vias  38 . It will be appreciated that although the illustrated embodiment shows a line via  39  having a square shape, other shapes can also be provided. 
         [0020]    Additionally, although the embodiment illustrated in  FIG. 3  shows a line via  39  disposed between each of the metal layers  34 , it may be desirable to employ only a single line via  39  between the top two metal layers and to employ only square vias between the remaining metal layers. Further, where line vias  39  are provided on multiple levels (as in  FIG. 3 ), it may be desirable to offset the line vias  39  of adjacent levels as shown in  FIG. 4  to further enhance the strength of the bonding pad  32 . 
         [0021]    The line via layout is, as previously noted, designed to separate the IMD  36  of the bonding pad  32  from the remainder of the wafer or device, so that when the openings are filled with conductive material, the vias  38  are surrounded by a conductive-material filled line via  39 . Thus, a simplified high strength via arrangement may be provided which also limits IMD crack sizes to the diagonal dimension of the line via  39 . As previously noted, although a rectilinear line vias  39  is shown in  FIG. 2B , other shapes may also be provided. 
         [0022]    It will also be appreciated that although the dielectric layers  36  are each shown as being singularly deposited layers, one or more of these layers  36  could be a composite dielectric layer. Such a composite layer may relieve internal stress in the dielectric, since such internal stresses can contribute to cracking in the dielectric layer. A non-limiting example of such composite dielectric layers include dual oxide layers, in which one of the composite layers is formed using a high density plasma (HDP) process, and a second of the composite layers is formed using Plasma Enhanced Tetraethylorthosilicate (PETEOS). 
         [0023]    A method of forming the disclosed via and line via arrangement is also disclosed. The method can be carried out by first providing a pre-processed electronic substrate  44  and depositing a dielectric material thereon to form a dielectric layer  36 . A metal layer  34  may be formed within the dielectric layer  36 , followed by the deposition of another dielectric layer  36 . A plurality of openings may be formed in the dielectric layer  36 , and these openings may then be filled with a conductive material to form an array of vias  38 . The openings may be square or rounded to form square or rounded conductive vias. Further, a ring-shaped opening may be provided in the dielectric layer  36 . This ring shaped opening may surround the other openings so that when the ring-shaped opening is filled with conductive material a line array  39  is formed around the array of vias  38  (see  FIG. 2A ). 
         [0024]    In one embodiment, filling of the vias  38 ,  39  may be accomplished using a W plug process. Alternatively, Al plug, Cu plug or silicide plug processes may also be used. Following the filling of the vias  38  and line via  39  with conductive material, chemical-mechanical polishing (CMP) may be used to planarize the surface. 
         [0025]    As will be appreciated, the process of forming a metal layer  34 , dielectric layer  36 , vias  38  and line vias  39  may then be repeated as desired to form a multilayer bond pad structure such as that illustrated in  FIG. 3 . Bonding metal patterns may then be deposited on the top surface of the top most metal layer  34 . Wires may then be bonded to the bonding metal patterns. 
         [0026]    While the foregoing invention has been described with reference to the above embodiments, various modifications and changes can be made without departing from the spirit of the invention. Accordingly, all such modifications and changes are considered to be within the scope and range of equivalents of the appended claims.