Abstract:
A copper bonding compatible bond pad structure and associated method is disclosed. The device bond pad structure includes a buffering structure formed of regions of interconnect metal and regions of non-conductive passivation material, the buffering structure providing buffering of underlying layers and structures of the device.

Description:
The present application claims priority to, and is continuation of U.S. patent application Ser. No. 12/541,881 filed on Aug. 13, 2009 now U.S. Pat. No. 8,148,256, which is a divisional patent application of, U.S. patent application Ser. No. 11/444,977 filed on 31 May 2006 now U.S. Pat. No. 7,598,620 and having Franois Hebert and Anup Bhalla listed as inventors. The aforementioned patent applications are incorporated by reference herein. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention generally relates to bond pad structures and methods of bonding semiconductor devices to substrates and more particularly to a copper bonding compatible bond pad structure and a method of bonding copper bonding wires to a semiconductor device without damaging device package layers and underlying device structures. 
     Conventional bonding methods utilize either Al or Au bonding wires to connect the semiconductor device to a substrate such as a leadframe. Al suffers the disadvantage of having high resistance while Au is increasingly expensive. 
     Cu bonding wires have been considered an inexpensive alternative to Al and Au bonding wires. Cu is inexpensive, readily available, and has low resistance. As such, fewer Cu bonding wires are generally required. However, Cu bonding wires are harder than either Al or Au bonding wires and their use presents challenges not satisfactorily overcome by the prior art. 
     As Cu and Cu alloys are harder than conventional bonding wires, bonding using Cu and Cu alloy bonding wires may result in damage to the semiconductor device or to package layers forming a device bond pad. With reference to  FIG. 1 , an exemplary prior art semiconductor device  100  includes a substrate  110  having a semiconductor device (not shown) formed therein. Substrate  110  may be formed of Si and the semiconductor device may include a power MOSFET. A TiNi barrier metal layer  120  is disposed under an Al, AlCu or AlSiCu electrode metal layer  130 . A bond pad  140  may be formed by patterning a passivation layer  150  formed of oxynitride or silicon rich oxynitride. Bond pad  140  may include a MOSFET source bond pad. 
     A Cu bond wire  200  is shown in  FIG. 2  and  FIG. 3  bonded to the bond pad  140 . As shown in  FIG. 3 , the Cu bond wire  200  has penetrated the electrode metal layer  130  and partially penetrated the barrier metal layer  120 . Damage to the barrier metal layer  120  can result in junction leakage and/or device failure over time. In an extreme case (not shown), the Cu bond wire  200  may completely penetrate the barrier metal layer  120  and damage the semiconductor device. 
     To address this problem, prior art techniques use a very thick electrode metal layer  130 . Typical thicknesses are much greater than 3 micron and typically 6 microns. This technique disadvantageously increases material and manufacturing costs making the patterning of fine lines in the device interconnects very difficult. 
     There is therefore a need in the art for a copper bonding compatible bond pad structure and associated method that does not damage the barrier metal layer or underlying device structures. There is a further need in the art for a bond pad structure and associated method that achieves low contact resistance. There is also a need in the art for a bond pad structure and associated method that can be achieved at no additional processing cost. 
     SUMMARY OF THE INVENTION 
     The present invention overcomes the limitations of the prior art by providing a copper bonding compatible bond pad structure and associated method wherein the Cu bonding wire is buffered from the barrier metal layer. This buffering is accomplished by a buffering structure formed in the bond pad. The buffering structure includes regions of electrode metal and regions of dielectric passivation material which serve to buffer the Cu bonding wire and protect the barrier metal layer. The buffering structure is formed by patterning and etching the dielectric passivation layer when forming the bond pad. 
     In accordance with one aspect of the invention, a device bond pad includes a buffering structure formed of regions of interconnect metal and regions of non-conductive passivation material, the buffering structure providing buffering of underlying layers and structures of the device. 
     In accordance with yet another aspect of the invention, a method of forming a Cu bonding compatible bond pad structure includes the steps of (a) determining a buffering structure pattern, (b) patterning the buffering structure pattern on a dielectric passivation layer, and (c) processing the buffering structure pattern to create a buffering structure in the bond pad. Cu bonding compatible bond pad structure comprising: 
     In accordance with still another aspect of the invention, a Cu bonding compatible bond pad structure includes a buffering structure formed of regions of interconnect metal and regions of non-conductive passivation material, wherein the regions of non-conductive passivation material are formed from a dielectric passivation layer and the regions of interconnect metal are formed on an electrode interconnect metal layer underlying the dielectric passivation layer 
     There has been outlined, rather broadly, the more important features of the invention in order that the detailed description thereof that follows may be better understood, and in order that the present contribution to the art may be better appreciated. There are, of course, additional features of the invention that will be described below and which will form the subject matter of the claims appended herein. 
     In this respect, before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of design and to the arrangement of components or process steps set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein, as well as the abstract, are for the purpose of description and should not be regarded as limiting. 
     As such, those skilled in the art will appreciate that the conception upon which this disclosure is based may readily be utilized as a basis for the designing of other methods and systems for carrying out the several purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent methods and systems insofar as they do not depart from the spirit and scope of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross sectional view of a prior art bond pad; 
         FIG. 2  is a top view of a Cu bonding wire attached to the bond pad of  FIG. 1 ; 
         FIG. 3  is a cross sectional view of the Cu bonding wire shown in  FIG. 2 ; 
         FIG. 4  is a top view of a buffering structure in accordance with the invention; 
         FIG. 5  is a cross sectional view of the buffering structure of  FIG. 4  in accordance with the invention; 
         FIG. 6  is a cross sectional view of a Cu bonding wire attached to the buffering structure of  FIG. 4  in accordance with the invention; and 
         FIG. 7  is a flow chart of a method of forming a buffering structure in accordance with the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following detailed description is of the best modes of carrying out the invention. The description is not to be taken in a limiting sense, but is made merely for the purpose of illustrating the general principles of the invention, since the scope of the invention is best defined by the appended claims. 
     The present invention generally provides a Cu bonding compatible bond pad structure that buffers bonding damage. A buffering structure is formed in the bond pad when the bond pad is patterned on the dielectric passivation layer deposited and formed on a semiconductor device surface. The buffering structure may include regions of electrode interconnect metal and regions of non-conductive passivation material, the passivation material being patterned in the shape of dots, squares, rectangles, stripes, grid structures, zigzags, chevrons, waves or any other shape or configuration. 
     With reference to  FIG. 4 ,  FIG. 5 , and  FIG. 6 , a Cu bonding compatible bond pad structure  400  includes a buffering structure  410  formed in the bond pad structure  400 . The buffering structure  410  includes regions  415  of exposed electrode metal of an electrode metal layer  420  and regions  417  of non-conductive passivation material of a passivation layer  460 . Regions  417  may include dots, squares, rectangles, stripes, grid structures, zigzags, chevrons, waves or any other shape or configuration. The electrode metal layer  420  may comprise a layer of AlCu or AlSiCu. The electrode metal layer  420  is formed over a TiNi barrier metal layer  430 . 
     Upon bonding of a Cu bonding wire  450  to the bond pad structure  400 , the AlCu or AlSiCu of the electrode metal layer  420  will be squeezed by the pressure of the Cu bonding wire  450  and flow in a plurality of directions within the buffering structure  410  around, under and over the regions  417  of the patterned passivation material, depending upon the configuration of the regions  415  and  417 . Some of the regions  417  may be pushed into the AlCu or AlSiCu of the electrode metal layer  420  to provide a buffer or cushion to the Cu bonding wire  450  and keep the Cu bonding wire  450  away from the barrier metal layer  430  and a semiconductor device  440 . 
     The pattern and width and spacing of the regions  417  of the patterned passivation material and of the regions  415  of exposed electrode metal can be optimized depending upon the metal of the bonding wire and the bonding conditions. Furthermore, an aspect ratio or pattern density and related dimensions and shapes of the regions  415  and  417  can be optimized to minimize the impact on the contact resistance of the bond. More regions  417  of the patterned passivation material relative to the regions  415  of exposed electrode metal (a higher aspect ratio) may provide for greater barrier layer and underlying device structure protection. Less regions  417  relative to the regions  415  (a lower aspect ratio) may provide for lower contact resistance. Additionally, groupings of regions  415  and  417  can also be utilized in order to limit any stress and movement on the passivation layer  460 . 
     A method of forming a Cu bonding compatible bond pad structure in accordance with the invention may include patterning the buffering structure  410  in the bond pad  400 . With reference to  FIG. 7 , a method generally designated  700  includes a step  720  in which the pattern of a buffering structure is determined. The buffering structure pattern may provide for an optimized aspect ratio. The buffering structure pattern is then patterned onto a dielectric passivation layer in a step  730 . Finally, the pattern is etched in a step  740  to create the buffering structure. The buffering structure includes regions of exposed electrode metal of an electrode metal layer and regions of non-conductive passivation material. 
     The present invention advantageously provides for a Cu bonding compatible bond pad structure that buffers Cu bonding damage to the barrier metal layer and the semiconductor device. The bond pad structure can be obtained at no additional processing cost by patterning the passivation layer to create the buffering structure. The buffering structure provides for low contact resistance. 
     It should be understood, of course, that the foregoing relates to preferred embodiments of the invention and that modifications may be made without departing from the spirit and scope of the invention as set forth in the following claims.