Abstract:
The present invention provides bond pads structures between semiconductor integrated circuits and the chip package with enhanced resistance to fracture and improved reliability. Mismatch in the coefficient of temperature expansion (CTE) among the materials used in bond structures induces stress and shear on them that may result in fractures within the back end dielectric stacks and cause reliability problems of the packaging. By placing multiple metal pads which are connected to the bond pad through multiple metal via, the adhesion between the bond pads and the back end dielectric stacks is enhanced.

Description:
RELATED APPLICATIONS 
     This application is a divisional of U.S. patent application Ser. No. 11/559,130, filed Nov. 13, 2006. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to semiconductor structures, and particularly, to bonding pad structures. 
     BACKGROUND OF THE INVENTION 
     In the semiconductor industry, a bond pad refers to a contiguous metal pad typically formed out of the last layers of metal during a semiconductor manufacturing sequence. A bond pad is typically large enough to accommodate the bottom portion of a solder ball. A bond pad structure refers to a structure containing such a bond pad and surrounding or attached structure, which as a whole helps accommodate the solder ball. 
     Once the fabrication of integrated circuit elements on a semiconductor substrate is completed, the semiconductor substrate is diced and packaged in a bonding process. Bond pads provide a structure for electrical connection between the fabricated integrated circuit elements and the package. Typically, one end of an interconnection wire is bonded to a bond pad and the other end is bonded to the next level of integration, which is typically an inner lead of the package. In a typical bonding process, multiple interconnection wires are utilized to connect each of the electrically active pads to one of the inner leads of the package. 
     A typical bond pad structure contains an exposed large piece of metal on which a bonding wire is attached with a solder ball. During the operation of the chip, the temperature of the chip rises, thereby raising the temperature of the bonding structure including the bonding pad and the solder ball. Due to the differences in the coefficients of thermal expansion (CTE), the bonding structure is subjected to shear and stress. These may cause cracks in the bonding structure causing electrical failure of the bonding pad or slow degradation and reliability problems due to ingress of ambient atmosphere, especially moisture into the chip. Wakharkar et al., “Materials Technologies for Thermomechanical Management of Organic Packages,” Vol. 09, Issue 04, November 2005, pp. 309-324” discusses various aspects of reliability due to chip-package interaction (CPI). 
     Therefore, mechanical strength of the bonding structure that is sufficient to withstand the stress and shear during the operational lifetime of a chip is of utmost importance in the design of a bonding structure. To establish the reliability of a particular bond structure, it is customary in the semiconductor industry to subject the bond structures to rigorous stress routines and measure their failure rate. The standard method of testing the mechanical strength of a bonding structure is known as “JEDEC Standard” and is widely used in the semiconductor industry. 
     Many designs to enhance the mechanical strength of the bonding structure are known. As an example, U.S. Pat. No. 6,365,970 to Tsai et al.; U.S. Pat. No. 5,739,587 to Sato; and U.S. Pat. No. 5,700,735 to Shiue et al. utilize multiple layers of metals and via plugs. These structures utilize multiple layers of metals connected with via plugs in the bonding pad area to mechanically strengthen the bonding structures. One disadvantage of this approach is the lack of availability of the bonding pad area for wiring purposes. In other words, since multiple metal levels are filled with structures that are part of the bond structure, no other electrical structure such as metal wiring can be built within the same space. Thus, metal wiring is severely limited under the bond pad. 
     An alternative approach in the prior art that maximizes the available space for wiring under the bond pad is also known. Instead of utilizing multiple layers of metal, only the top level of metal is utilized for the bond pad. An electrical connection from the bond pad to lower metal levels is provided through an extension of the bond pad and vias attached to a lower level metal wire. The area below the bond pad is available for electrical wiring. If electrical wiring is not needed under the bond pad, the area in the lower level under the bond pads may be filled with metal fills to facilitate a chemical mechanical planarization (CMP) process. 
     It has been discovered during the process of the present invention that the above structure with one level of metal for the bond pads is prone to fracture when subjected to reliability stress. While the structure above provides maximum flexibility for wiring, the mechanical strength of the structure is not sufficient to provide a reliable structure under stress. 
     Therefore, the need exists to provide a bond pad structure that provides sufficient mechanical strength while still providing as much flexibility in metal wiring under the bond pad structure as possible. 
     SUMMARY OF THE INVENTION 
     The present invention addresses the needs described above and provides a bond pad structure with enhanced mechanical strength. Specifically, the present invention aims to increase the mechanical strength of a bond pad structure compared to the prior art that maximizes the available space for wiring under a bond pad. 
     The present invention also provides as much free space as possible under a bond pad structure to facilitate the ease of design for wiring purposes. 
     Furthermore, the present invention provides a bond pad structure that facilitates easy manufacture of the structure without excessive burden on process control. Specifically, the present invention seeks to place metal fills as necessary under a bond pad structure to reduce dishing during a chemical mechanical polishing process during the manufacture of the structure. 
     While this disclosure uses specific materials to describe the invention, it should be recognized that functionally equivalent material may be substituted for any of the material described below. 
     In accordance with one aspect of the present invention, multiple first metal vias are placed within the “pad area”, that is, within the boundaries of a first metal pad, or a bond pad, and adjoined to the bond pad from below. Each of the multiple first metal vias are connected to mutually disjoined multiple metal pads, herein referred to as “multiple metal pads,” which are located below the multiple first metal vias. Each of the multiple metal pads are confined within the metal level immediately below the level of the bond pad itself. 
     In this inventive structure, not only does the bottom surface of the bond pad itself adhere to the insulating layer immediately below, but the walls of the multiple first metal vias and all the surfaces of the multiple metal pads not adjoining the multiple first metal vias also adhere to the dielectrics surrounding them. The area of adhesion between the dielectric material in the back end of the line film stack and the contiguous and conducting extension of the bond pad, including the bond pad itself, the multiple first metal vias, and the multiple metal pads, is increased significantly. 
     In accordance with another aspect of the present invention, the use of metal wiring in the area within the metal levels below the bond pad is enabled to provide enhanced flexibility in metal wiring. The metal wiring may be utilized to pass current from another part of the semiconductor chip through the area containing the bond pad to yet another part of the semiconductor chip. The area not utilized by the multiple metal pads or by the metal wiring may be filled with metal fills to facilitate the chemical mechanical planarization process during the manufacturing. Alternatively, if the area below the bond pad is not utilized, metal fills only may be utilized to facilitate the CMP process. 
     While small portions of the multiple pads may actually be located outside the pad area, the multiple metal pads and the multiple first metal vias landing on them are substantially within the pad area to minimize the adverse impact on the wiring. The multiple metal pads may be confined exclusively within the peripheral area, defined as the area within the pad area and along the periphery of the bond pad, or they may be confined exclusively within the center area, defined as the remainder of the center area after excluding the peripheral area. Alternatively, the multiple metal pads may be distributed across the pad area, both within the peripheral area and within the center area. 
     In accordance with yet another aspect of the present invention, a portion of the pad area within the metal level below the bond pad, wherein the multiple metal pads are located, may be utilized to electrically connect the bond pad to the integrated circuit elements on the chip and to provide enhanced flexibility in metal wiring. The use of additional metal wire connected to the bond pad has the advantage of reducing the resistance of the electrical path from the bond pad, thereby reducing a voltage drop between the bond pad and the integrated circuit elements. 
     In this case, the unused portion of the pad area within the metal level below the bond pad may also be utilized for a second set of metal wires for passing current from another part of the semiconductor chip through the pad area within the metal level below the bond pad to yet another part of the semiconductor chip. If some unused area still remains in the pad area within the metal level below the bond pad, metal fills may optionally be used to facilitate the CMP process. 
     According to still another aspect of the present invention, multiple first metal vias are placed within the “pad area”, that is, within the boundaries of a first metal pad, or a bond pad, and adjoined to the bond pad from below. Each of the multiple first metal vias are connected to one of mutually disjoined multiple metal stacks, herein referred to as “vertical alternating stacks,” wherein third metal pads and second metal vias are alternately adjoined to one another. When two components of a vertical alternating stack are adjoined, they are always adjoined vertically, that is, one on top of another. The top of each of the vertical alternating stack is a third metal pad which adjoins the bottom of at lease one of the multiple first metal vias. All components within each vertical alternating stack are electrically connected to one another. 
     Not only does the bottom surface of the bond pad itself adhere to the insulating layer immediately below in this structure, but the walls of the multiple first metal vias and surfaces of all the vertical alternating stacks not adjoining the multiple first metal vias also adhere to the dielectrics surrounding them. The area of adhesion between the dielectric material in the back end of the line film stack and the contiguous and conducting extension of the bond pad, including the bond pad itself and the multiple vertical alternating stacks, is increased significantly. 
     A portion of pad area within the metal level below the bond pad, wherein the multiple metal pads are located, may be utilized to electrically connect the bond pad to the integrated circuit elements on the chip and to provide enhanced flexibility in metal wiring in this structure. Also, the unused portion of the pad area within the metal level below the bond pad may also utilized for a second set of metal wires for passing current from another part of the semiconductor chip through the pad area within the metal level below the bond pad to yet another part of the semiconductor chip. If some unused area still remains in the pad area within the metal level below the bond pad, metal fills may optionally be used to facilitate the CMP process. 
     The adhesion between the bond structures according to the various aspects of the present invention is superior to prior art structures without any via below a bond pad while the flexibility of wiring is better than prior art structures wherein the bond pad structure occupies multiple levels of metal layers. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of a top-down view of a bond pad structure according to the prior art. 
         FIG. 2  is a schematic diagram of a cross-sectional view of a bond pad structure in  FIG. 1  in the direction A-A′. 
         FIG. 3  is a scanning electron micrograph (SEM) of a structure according to the prior art showing a fracture induced during the preconditioning of JEDEC level 3 test. 
         FIG. 4  is a magnified view of the scanning electron micrograph (SEM) in  FIG. 3  of the area with the fracture. 
         FIG. 5  is a schematic diagram of a top-down view of a bond pad structure according to a first embodiment of the present invention. 
         FIG. 6  is a schematic diagram of a cross-sectional view of a bond pad structure in  FIG. 5  in the direction B-B′. 
         FIG. 7  is a schematic diagram of a top-down view of a bond pad structure according to a second embodiment of the present invention. 
         FIG. 8  is a schematic diagram of a cross-sectional view of a bond pad structure in  FIG. 7  in the direction B-B′. 
         FIG. 9  is a schematic diagram of a top-down view of a bond pad structure according to a third embodiment of the present invention. 
         FIG. 10  is a schematic diagram of a cross-sectional view of a bond pad structure in  FIG. 9  in the direction B-B′. 
         FIG. 11  is a schematic diagram of a top-down view of a bond pad structure according to a fifth embodiment of the present invention. 
         FIG. 12  is a schematic diagram of a cross-sectional view of a bond pad structure in  FIG. 11  in the direction B-B′. 
         FIG. 13  is a schematic diagram of a top-down view of a bond pad structure according to a seventh embodiment of the present invention. 
         FIG. 14  is a schematic diagram of a cross-sectional view of a bond pad structure in  FIG. 13  in the direction B-B′. 
         FIG. 15  is a schematic diagram of a top-down view of a bond pad structure according to an eighth embodiment of the present invention. 
         FIG. 16  is a schematic diagram of a top-down view of a bond pad structure according to a ninth embodiment of the present invention. 
         FIG. 17  is a schematic diagram of a cross-sectional view of a bond pad structure in  FIG. 13  in the direction B-B′. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Before describing the present invention in detail, a discussion of a prior art bond pad structure is provided. The purpose of this discussion is to clearly illustrate the fundamental difference between the prior art and the present invention. 
     Referring to  FIG. 1 , a schematic top-down view of a prior art bond pad structure  100  is provided wherein a bond pad  150 , a bond pad extension  151 , a portion of a metal wire  120  that is electrically connected to the bond pad  150  and to the bond pad extension  151  through two vias  156  are shown. Also shown are the opening  161  in a passivation layer  160  (not shown in  FIG. 1 ) and in a photosensitive polyimide layer  170  (not shown in  FIG. 1 ) as well as the periphery  181  of a barrier liner material  180  (not shown in  FIG. 1 ). A metal fill  121  within the area of the bond pad extension  151  is shown as well as multiple metal fills  123  within the area of the pad  150 , or the “pad area.” 
       FIG. 2  is a schematic cross-sectional view of the prior art bond pad structure  100  along the line labeled A-A′ in  FIG. 1 . A first insulating layer  110 , which is the topmost insulating layer from the underlying back end of the line stack, contains the metal wire  120  as well as the metal fill  121  under the bond pad extension  151  and the metal fills  123  contained within the pad area. While additional metal fills are not specifically shown under the bond pad  150 , they maybe placed in the same level as the metal fill  121  shown in  FIG. 2 . Disposed on top of the first insulating layer  110  is a second insulating layer  135 , which in turn comprises a cap layer  130 , and an insulating dielectric layer  140 . A bond pad  150  and the bond pad extension  151  are disposed on top of the second insulating layer  135 . A via  156 , which is filled with metal and electrically connects the bond pad extension  151  and the metal wire  120  insulating layer, is disposed within an opening in the second insulating layer  135  and the cap layer  130 . A passivation layer  160  and a photosensitive polyimide layer  170  are disposed over the bond pad  150 , the bond pad extension  151 , or the second insulation layer  135 . The opening  161  in the passivation layer  160  and a photosensitive polyimide layer  170  is also shown. The barrier liner material  180  and its periphery  181  and the solder is disposed over the opening  161 . A solder ball  190  is disposed on the barrier liner material  180 . 
     In the course of experiments leading to the present invention, the prior art bond pad structures schematically represented by  FIGS. 1-2  were manufactured and placed under reliability stress conditions. Specifically, these samples were subjected to the JEDEC level 3 testing wherein each package formed using a bonding process on the bond pads is subjected to preconditioning and then tested for functionality for the next 168 hours. In other words, certification at JEDEC level 3 testing means that the package can operate for 168 hours after being subjected to preconditioning. The preconditioning method for level 3 JEDEC testing is 192 hours of exposure to 60% relative humidity at 30 degree Celsius. 
     Some of the samples showed structural fails after the preconditioning stress.  FIG. 3  shows a scanning electron micrograph (SEM)  300  of a cross-section of one of the samples that failed after the preconditioning stress. With a rotation of a solder ball  390 , or a “C4 ball,” due to the shear and stress during the preconditioning, the underlying back end of the line stack  310  separated from the solder ball  390  causing a crack  399  between them. The location of the crack is schematically shown in  FIG. 2  as a dotted line  199 . 
       FIG. 4  shows a magnified SEM  400  of the SEM  300  shown in  FIG. 3 , wherein the structures surrounding the crack  499  are shown in more detail. A first insulating layer  410 , which is the topmost insulating layer in the back end of the line stack (not fully shown in  FIG. 4 ) and is a TEOS (Tetra Ethyl Orthosilicate; (C 2 H 5 O) 4 Si) based FSG (Fluorosilicate Glass) in this SEM, contains metal fills  423  in the pad area. The metal fills  423  are made of copper in this case. One part of a stack, consisting of a portion  430  of a cap layer, which in turn contains an NBLoK (Nitrided Barrier Low K: nitrogen doped silicon carbide (SiN X C Y H Z ) as exemplified in U.S. Pat. No. 7,009,280) and a nitride layer, and a portion  440  of a second insulating layer, is attached to the first insulating layer  410  above. Another part of the same stack, consisting of a different portion  431  of the cap layer and a different portion  441  of the second insulating layer, is attached to an aluminum alloy  450  below. A crack  499  between the two parts of the same stack is clearly visible and is located between the first dielectric  410  above and the aluminum alloy  450  below. The aluminum alloy  450  comprises a liner stack and aluminum in this particular case. The liner stack is made of tantalum nitride (TaN), titanium (Ti), and titanium nitride (TiN). Below the aluminum alloy  450  is a passivation layer  460 , of which a crack is visible in this SEM  400 . The passivation layer  460  is a stack of oxide and nitride in this case. Below the passivation layer  460  is a polyimide layer  470 . Part of the solder ball  490  is also seen. 
     Clearly, the mechanical strength of this structure was not sufficient to prevent the delamination of the bond pad structure from the underlying back end of the line dielectric material during the preconditioning. As shall be seen below, the present invention strengthens the mechanical strength of a bond pad structure to prevent fails as seen in  FIGS. 3-4 . 
     According to a first embodiment of the present invention, a first bond pad structure  500  is described in  FIGS. 5-6 .  FIG. 5  is a schematic top-down view, while  FIG. 6  is a schematic cross-sectional view along the line B-B′ in  FIG. 5 . The first bond pad structure  500  has a first metal pad  550 , which is a bond pad, in the first layer of the structure. The area inside the periphery of the first metal pad  550  is referred to as the “pad area.” Only one contiguous first metal pad is necessary for the formation of one of the first bond pad structure  500 . The first metal pad  550  is made of metal, and preferably a stack of a liner material and an aluminum alloy. A bond pad extension  551 , adjoining the bond pad  550 , built on the same level as a bond pad  550 , and consisting of the same material as the bond pad, may optionally be constructed as well. The liner material may comprise a stack of tantalum nitride (TaN), titanium (Ti), and titanium nitride (TiN) or an alternate stack of metals with good adhesion property to the underlying dielectric material 
     The first bond pad structure  500  according to the first embodiment of the present invention contains a first insulating layer  535  disposed underneath the first metal pad  550  and extends at least over the entire pad area. The bottom surface of the first metal pad  550  adjoins the top surface of the first insulating layer  535 . In  FIG. 6 , the first insulting layer  535  comprises a stack of an insulating dielectric layer  540  disposed on top of a cap layer  530 , both of which are insulators. Preferably, the insulating dielectric layer  540  is chosen from a silicon oxide layer, a silicon nitride layer, and a doped silicon oxide layer such as a fluorosilicate glass (FSG). Preferably, the cap layer  530  is chosen from a BLoK layer (a Barrier Low K layer as exemplified in U.S. Pat. No. 6,632,478), an NBLoK layer, and a silicon nitride layer. Alternatively, the first insulating layer  535  may comprise a single layer of insulating material or even a stack of more than two insulating materials. 
     The first bond pad structure  500  according to the first embodiment of the present invention contain multiple first metal vias  552  through the first insulating layer  535  and are located within the pad area. The top surface of each of the multiple first metal vias  552  adjoins a portion of the bottom surface of the first metal pad  550 , or the bond pad. Optionally, metal vias  556  may be utilized to connect the bond pad extension  551  to a portion of a metal wire  520  below. Preferably, the first metal vias  552  and the first metal pad  550  are aluminum alloys. Most preferably, the first metal vias  552  and the first metal pad  550  are formed at the same time as a stack containing a liner material and aluminum. 
     The first bond pad structure  500  according to the first embodiment of the present invention contains multiple metal pads  522  disposed underneath the first insulating layer  535 , and overlapping at least a portion of the pad area, and not adjoined to one another. The multiple metal pads  522  are located beneath the multiple first metal vias  552  and adjoin the bottom surface of at least one of the multiple first metal vias  552 . The multiple metal pads  522  are placed within a second insulating layer  510  disposed below the first insulating layer  535  such that at least a portion of the top surface of the second insulating layer  510  adjoins a portion of the bottom surface of the first insulating layer  535 . Preferably, the multiple metal pads  522  are contained within the pad area to reduce the area from which further metal wiring needs to be excluded. Optionally, metal fills  521  may be placed under the bond pad extension  551 . Preferably, the multiple metal pads  522  are copper alloys. Most preferably, the multiple metal pads  522  contain a liner material and copper. 
     Furthermore, the location of the multiple first metal vias  552  is limited in the first embodiment of the present invention. To qualify this limitation some definitions are presented below: 
     The center point  555  of the first metal pad  550  is defined as follows. For each of the points within the top surface of the first metal pad, the maximum distance to the periphery of the first metal pad is measured. In other words, each point within the first metal pad is assigned a number which corresponds to the maximum distance to the periphery, or the boundary, of the first metal pad  550 . The point that achieves the minimum number among all the numbers assigned to the points within the first metal pad is defined as the center point  555  of the first metal pad  550 . 
     To define a boundary  557 , each point on the periphery of the bond pad  550  is hypothetically connected by a straight line to the center point  555 . At a fixed percentage of the distance between 15% and 85% measured from the center point  555 , each of the hypothetical straight lines is terminated. The set of all the terminated points define the boundary  557 . 
     The pad area of the first metal pad  550  is divided into two areas, a peripheral area  559  located between the periphery of the bond pad  550  and the boundary  557 , and a center area  558  confined within the boundary  557 . While in all passages below, whenever the peripheral area is described as “an area inside and along edges of said first metal pad” or in similar wordings, the rigorous definition as described above applies. While different percentage numbers may be selected to define a boundary  557  for a given metal pad  550 , that is, any percentage between 15% and 85%, one boundary has one number for the selected percentage. 
     According to the first embodiment of the present invention, the center area  558  does not contain any second metal pad  522 . All the metal pads are confined within the peripheral area  559 . Consequently, all of the first metal vias  552  are also located within the peripheral area  559 . 
     The first bond pad structure  500  according to the first embodiment of the present invention may further contain a passivation layer  560 , which is disposed on the first metal pad  550 , the bond pad extension  551 , and the first insulating layer  535 . The passivation layer  560  blocks the ingress of moisture from the ambient environment into the integrated semiconductor elements below the first bond pad structure  500 . Preferably, the passivation layer  560  comprises a silicon nitride or a stack of dielectric material containing silicon nitride, such as a stack of silicon nitride and silicon oxide. Furthermore, a photosensitive polyimide (PSPI)  570  may be disposed on the passivation layer  560 . Alternatively, a different material that can be lithographically patterned and conducive to the bonding process may be utilized. 
     The first bond pad structure  500  according to the first embodiment of the present invention may further contain an opening  561  through both the passivation layer  560  and the PSPI  570 . Also, it may contain a barrier layer material  580  with the periphery  581  and disposed on top of the first metal pad  550  within the area of the opening  561 . A solder ball  590  may be placed on the barrier layer material  580 . 
     The second metal pads  522  have bottom surfaces, sidewall surfaces, and top surfaces that are not covered by the multiple first metal vias  552 . This increases the area of the interface between the first bond pad structure  500  and the surrounding insulating material. Furthermore, the bottom surfaces and the sidewall surfaces of the second metal pads  522  may have a liner material with good adhesion to the insulating material, as is typically the case in typical semiconductor processing flow. Therefore, the adhesion of the first bond pad structure  500  is significantly higher than that from the bond pad structure  100  in  FIGS. 1-2  known in the prior art, resulting in higher mechanical strength and improved reliability of the structure under stress. 
     Typical bond pads are made of an aluminum alloy while most of metal wiring within the back end of the line dielectric stack utilizes copper. The higher adhesion strength between copper and dielectric material than that between the aluminum alloy and dielectric material is utilized in the bond pad structure according to the present invention. 
     While the area of adhesion is significantly increased, a substantial portion of the area in the metal levels below the bond pad itself is still available for metal wiring. While the flexibility of metal wiring is less than that of a prior art bond pad structure without any vias below the bond pad and thus has maximal available wiring pace under the bond pad, considering that such a structure is prone to reliability issues, a moderate decrease in the flexibility of metal wiring is a fully warranted tradeoff in engineering. The advantage of the structure according to the present invention in maintaining good flexibility in wiring is apparent in comparison with other prior art structures. 
     According to the second embodiment of the present invention, a second bond pad structure  700  is described in  FIGS. 7-8 .  FIG. 7  is a schematic top-down view, while  FIG. 8  is a schematic cross-sectional view along the line B-B′ in  FIG. 7 . The second bond pad structure  700  according to the second embodiment of the present invention is similar to the first bond pad structure  500  according to the first embodiment of the present invention and shares many of the same features. Consequently, like elements between the first and the second embodiments of the present invention are numbered the same. Furthermore, in all of the additional embodiments to be described below, like elements between the described embodiment of the present invention and the first embodiment of the present invention share the same numbers in figures. 
     According to the second embodiment of the present invention, the center area  558  of the bond pad structure  700  does not contain any second metal pad  522 . All the metal pads are confined within the peripheral area  559 . All of the first metal vias  552  are also located within the peripheral area  559 . Furthermore, at least one metal structure that does not contact any of the first metal vias  552  is placed within the pad area and at the same level as the second metal pads  522 . The metal structure can be either first metal fills  523  or at least one first metal wire  525 . None of the first metal fills  523  or any of a portion of the first metal wires  525  is adjoined by any of the first metal vias  552 . In other words, there are no metal vias within the pad area that connect any of the metal fills  23  or any of a portion of the first metal wires  525  to the first metal pad  550  above. 
     Any of the first metal wires  525  may extend outside the pad area to make electrical connections to other components of the integrated circuit as necessary. The first metal wires  525  may be utilized to make electrical connections to various parts of the integrated circuit elements or to any other pad other than the bond pad  550 , or even to the bond pad  550  through secondary connections. However, there is no first metal via  552  that connects the bond pad  550  and any of the first metal wires  525  directly. 
     The second embodiment of the present invention enables the placement of first metal wires  525  under the first metal pad  550 , or the bond pad, to utilize the area for increased flexibility in wiring during the circuit layout compared to the first embodiment of the present invention. The unused areas after the placement of a portion of the first metal wires  525  are filled with first metal fills  523 . 
     According to a third embodiment of the present invention, a third bond pad structure  900  is described in  FIGS. 9-10 .  FIG. 9  is a schematic top-down view, while  FIG. 10  is a schematic cross-sectional view along the line B-B′ in  FIG. 9 . The second bond pad structure  900  according to the third embodiment of the present invention is similar to the first bond pad structure  500  according to the first embodiment of the present invention. 
     According to the third embodiment of the present invention, the peripheral area  559  of the bond pad structure  900  does not contain any second metal pad  522 . All the metal pads are confined within the center area  558 . Consequently, all of the first metal vias  552  are also located within the center area  559 . The third embodiment of the present invention shares the advantages of the first embodiment of the present invention with the difference being that the area that may be utilized for other purposes within the pad area and at the same level as the second metal pads  522  coincide with the peripheral area  559  instead of the center area  558 . 
     According to a fourth embodiment (not shown in figures) of the present invention, a fourth bond pad structure is derived from the third bond pad structure  900  in  FIG. 9 . All structural features according to the third embodiment of the present invention are also present in the fourth embodiment of the present invention as well. The additional features of the fourth embodiment compared to the features of the third embodiment are similar to the additional features of the second embodiment compared to the features of the first embodiment. For this reason, elements in  FIGS. 7-8  are used in this passage to describe the additional features of the fourth embodiment compared to the third embodiment of the present invention. According to the fourth embodiment of the present invention, at least one metal structure that does not contact any of the first metal vias  552  is placed within the pad area and at the same level as the second metal pads  522 . The metal structure can be either first metal fills  523  or at least one first metal wire  525 . None of the first metal fills  523 , nor any of a portion of the first metal wires  525  are adjoined by any of the first metal vias  552 . In other words, there are no metal vias within the pad area that connect any of the metal fills  23  or any of a portion of the first metal wires  525  to the first metal pad  550  above. 
     The fourth embodiment of the present invention enables the placement of first metal wires  525  under the first metal pad  550 , or the bond pad, to utilize the area for increased flexibility in wiring during the circuit layout compared to the first embodiment of the present invention. The unused areas after the placement of a portion of the first metal wires  525  are filled with first metal fills  523 . The difference between the fourth embodiment and the second embodiment of the present invention is whether the peripheral area  559  or the center area  558  is used for the placement of the second metal pads  552 . 
     According to a fifth embodiment of the present invention, a fifth bond pad structure  1100  is described in  FIGS. 11-12 .  FIG. 11  is a schematic top-down view, while  FIG. 12  is a schematic cross-sectional view along the line B-B′ in  FIG. 11 . The fifth bond pad structure  1100  according to the third embodiment of the present invention is similar to the first bond pad structure  500  according to the first embodiment of the present invention except that both the center area  558  and the peripheral area  559  are used for the placement of the second metal pads  552  in the fifth embodiment while only the peripheral area  559  is utilized for the placement of the second metal pads  552  in the first embodiment of the present invention. The fifth embodiment of the present invention enables an increase in the mechanical strength of the bond pad structure  1100  at the expense of flexibility in metal wiring in the same level as the second metal pads  522  compared to the first embodiment. 
     According to a sixth embodiment (not shown in figures) of the present invention, a sixth bond pad structure is derived from the fifth bond pad structure  1100  in  FIG. 11 . All structural features according to the fifth embodiment of the present invention are also present in the sixth embodiment of the present invention as well. As in the description of the fourth embodiment of the present invention above, elements in  FIGS. 7-8  are used in this passage. According to the sixth embodiment of the present invention, at least one metal structure that does not contact any of the first metal vias  552  is placed within the pad area and at the same level as the second metal pads  522 . The metal structure can be either first metal fills  523  or at least one first metal wire  525 . None of the first metal fills  523 , nor any of a portion of the first metal wires  525  are adjoined by any of the first metal vias  552 . In other words, there are no metal vias within the pad area that connect any of the metal fills  23  or any of a portion of the first metal wires  525  to the first metal pad  550  above. 
     The sixth embodiment of the present invention enables the placement of at least one first metal wire  525  under the first metal pad  550 , or the bond pad, to utilize the area for increased flexibility in wiring during the circuit layout. The unused areas after the placement of a portion of the first metal wires  525  are filled with first metal fills  523 . The difference between the sixth embodiment and the second or fourth embodiment of the present invention is whether both the peripheral area  559  and the center area  558  are used for the placement of the second metal pads  552  or only one of the two areas is used for the same purposes. 
     According to a seventh embodiment of the present invention, a seventh bond pad structure  1300  is described in  FIGS. 13-14 .  FIG. 13  is a schematic top-down view, while  FIG. 14  is a schematic cross-sectional view along the line B-B′ in  FIG. 13 . The seventh bond pad structure  1300  according to the seventh embodiment of the present invention shares all the elements of the first bond pad structure  500  according to the first embodiment of the present invention described above. In addition, at least one second metal wire  524  is placed within the pad area and at the same level as the second metal pads  522 . Any of the second metal wires  524  may extend outside the pad area to make electrical connections to other components of the integrated circuit as necessary. All of the second metal wires  524  is adjoined by at east one of the first metal vias  552  and electrically connected to the bond pad  550 . 
     The seventh embodiment of the present invention enables the use of the pad area at the same level as the second metal pads for wiring the bond pad  550  to the integrated circuit elements below. Alternatively, the second metal wires  524  may be used with existing wiring scheme to reduce the resistance of the circuit wiring path from the bond pad  550 . 
     According to an eighth embodiment of the present invention, an eighth bond pad structure  1500  is described in a schematic top-down view in  FIG. 15 . The eighth bond pad structure  1500  according to the present invention shares all the elements of the seventh bond pad structure  1300  according to the seventh embodiment. Furthermore, at least one metal structure that does not contact any of the first metal vias  552  is placed within the pad area and at the same level as the second metal pads  522 . The metal structure can be either first metal fills  523  or at least one first metal wire  525 . None of the first metal fills  523 , nor any of a portion of the first metal wires  525  are adjoined by any of the first metal vias  552 . In other words, there are no metal vias within the pad area that connect any of the metal fills  23  or any of a portion of the first metal wires  525  to the first metal pad  550  above. The structure and the functionality of the first metal wires  525  is exactly the same as described in any of the prior embodiments of the present invention. 
     The eighth embodiment of the present invention enables the placement of first metal wires  525  under the first metal pad  550 , or the bond pad, to utilize the area for increased flexibility in wiring during the circuit layout compared to the seventh embodiment of the present invention. The unused areas after the placement of a portion of the first metal wires  525  are filled with first metal fills  523 . 
     Table 1 below shows a list of enabled elements according to the first through eighth embodiments of the present invention in a tabular format. 
     
       
         
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 List of enabled elements according to the first through eighth embodiments of 
               
               
                 the present invention 
               
             
          
           
               
                   
                   
                 First metal 
                   
                   
                   
               
               
                   
                 First metal 
                 vias in 
                   
                   
                 Second 
               
               
                   
                 vias in center 
                 peripheral 
                 First metal 
                 First metal 
                 metal wires 
               
               
                 Enabled elements 
                 area 558 
                 area 559 
                 fills 523 
                 wires 525 
                 524 
               
               
                   
               
               
                 First embodiment 
                 No 
                 Yes 
                 No 
                 No 
                 No 
               
               
                 Second embodiment 
                 No 
                 Yes 
                 Yes 
                 Yes 
                 No 
               
               
                 Third embodiment 
                 Yes 
                 No 
                 No 
                 No 
                 No 
               
               
                 Fourth embodiment 
                 Yes 
                 No 
                 Yes 
                 Yes 
                 No 
               
               
                 Fifth embodiment 
                 Yes 
                 Yes 
                 No 
                 No 
                 No 
               
               
                 Sixth embodiment 
                 Yes 
                 Yes 
                 Yes 
                 Yes 
                 No 
               
               
                 Seventh embodiment 
                 No 
                 Yes 
                 No 
                 No 
                 Yes 
               
               
                 Eighth embodiment 
                 No 
                 Yes 
                 Yes 
                 Yes 
                 Yes 
               
               
                   
               
             
          
         
       
     
     According to a ninth embodiment of the present invention, a ninth bond pad structure  1600  is described in  FIGS. 16-17 .  FIG. 16  is a schematic top-down view, while  FIG. 17  is a schematic cross-sectional view along the line B-B′ in  FIG. 16 . Since all elements common with the other embodiments of the present invention are labeled with the same reference number and have the same structural and functional characteristics, only the key elements of the ninth embodiment of the present invention are described herein. 
     The first bond pad structure  500  has a first metal pad  550  and a first insulating layer  535 . Multiple first metal vias  552  through the first insulating layer  535  are located within the pad area wherein the top surface of each of the multiple first metal vias  552  adjoins a portion of the bottom surface of the first metal pad  550 , or the bond pad. 
     According to the ninth embodiment of the present invention, multiple third metal pads  502  and multiple second metal vias  507  are provided. Each of the third metal pads  502  may be placed in any metal level below the level of the first metal pad  550 . The distinction between third metal pads  502  and second metal pads  522  is made herein to point out that the third metal pads may be placed in any metal level below the level of the first metal pad  550  whereas the second metal pads  522  can be placed only in the metal level immediately below the level of the first metal pad  550 . Also, each of the second metal vias  505  may be placed between any two metal levels or even between a metal level and the semiconductor substrate. 
     However, each of the third metal pads  502  and each of the second metal vias is a part of one of the many vertical alternating stacks  595 , which is formed alternately adjoining third metal pads and second metal vias vertically such that the component for the top of each vertical alternating stack  595  is one of the third metal pads  502 . In other words, a vertical alternating stack comprises at least one of third metal pads  502  and at least one of second metal vias  507 . The stacking sequence of each of the vertical alternating stacks, counted from the top to bottom, begins with a third metal pad  502 , followed by a second metal via  507 , and alternates between one of the third metal pads  502  and one of the second metal vias  507  if more components are used. If the components of the alternating vertical stacks are listed from top to bottom, for example, an alternating vertical stack may consist of a third metal pad  502  and a second metal via  507 , a third metal pad  502  and a second metal via  507  and another third metal pad  502 , a third metal pad  502  and a second metal via  507  and another third metal pad  502  and another third metal via  507 , a third metal pad  502  and a second metal via  507  and another third metal pad  502  and another second metal via  507  yet another third metal pad, etc. The bottom of a sequence may terminate with a third metal pad  502  or a second metal via  507 . The bottom of a vertical alternating stack may terminate within a layer of back end of the line dielectric material, a shallow trench isolation, or the semiconductor substrate. 
     Optionally, at least one metal structure that does not contact any of the multiple metal vias  552  or any of the vertical alternating stacks  595  is placed within the pad area and at any level wherein any of the third metal pads  502  are located. The metal structure can be either second metal fills  503  or at least one third metal wire  505 . Once again, a distinction between embodiments of the present invention is made in that second metal fills and third metal wires in the ninth embodiment may be placed at any level wherein any of the third metal pads  502  are located whereas first metal fills and first metal wires in the prior embodiments can be placed only in the metal level immediately below the level of the first metal pad  550 . None of the second metal fills  503 , or any of a portion of the third metal wires  505  is adjoined by any of the first metal vias  552  or by any of the alternating vertical stacks  595 . In other words, there is no electrical connection between the bond pad  550  and either the second metal fills  503  or third metal wires  505 . 
     Any of the third metal wires  505  may extend outside the pad area to make electrical connections to other components of the integrated circuit as necessary. The third metal wires  505  may be utilized to make electrical connections to various parts of the integrated circuit elements or to any other pad other than the bond pad  550 , or even to the bond pad  550  through secondary connections. However, there is no first metal via  522  that connects the bond pad  550  and any of the first metal wires  505  directly. 
     Also, optionally, at least one fourth metal wire (not shown in  FIGS. 16-17 ) may be placed within the pad area and at the same level as any of the third metal pads  522 . Both structurally and functionally, the fourth metal wires are similar to the second metal wires  524  as described in the bond pad structure  1300  according to the seventh embodiment of the present invention in  FIGS. 13-14 . However, the fourth metal wires according to the ninth embodiment of the present invention may be placed in any level containing at least one of the third metal pads  522  whereas the second metal wires according to the seventh and eighth embodiments of the present invention limits the placement of the second metal wires to the metal level immediately below the level of the first metal pad  550 . Any of the fourth metal wires may extend outside the pad area to make electrical connections to other components of the integrated circuit as necessary. All of the fourth metal wires are directly or indirectly adjoined by at east one of the first metal vias  552  and electrically connected to the bond pad  550 . 
     A method of fabricating the bond pad structures in the various embodiments described above is now discussed. 
     Integrated circuit devices are first formed on a semiconductor substrate. A back end of the line stack is formed layer by layer above the integrated circuit devices by depositing insulator layers, etching of lines and vias in the insulator layers, filling the metal lines and vias with metal, and removing the excessive metal outside the metal lines and planarizing the surface for each layer of processing. 
     In the case of the ninth embodiment according to the present invention, the vertical alternating stacks  595  are formed within the back end of the line stack by forming third metal pads  502  in appropriate metal layers at the same time and using identical processing methods as when the metal wires in the same level are formed. Similarly, second metal vias  507  are formed at the same time and using identical processing methods as when other vias in the same level are formed. Proceeding in this manner, all components of the vertical alternating stacks  595  located below the second insulating layer  510  in the bond pad structure  1600  in  FIGS. 16-17  are formed. 
     For all embodiments of the present invention, a second insulating layer  510  is deposited over an underlying region of semiconductor device at this point. The underlying region may have a back end of the line stack, which in turn may comprise multiple insulator layers, metal line levels, and via levels as is necessary for the implementation of the ninth embodiment of the present invention as described above. The second metal pads  522 , any of the first metal fills  523 , any first metal wires  525 , and any second metal wires  524  according to the first through eighth embodiment of the present invention are lithographically patterned on the second insulating layer  510  by depositing a layer of photoresist, exposing it under a mask to a light source, and developing it. Alternatively, third metal pads  502  and any of the second metal fills  503 , third metal wires  505 , and fourth metal wires that are located within the bond pad structure  1600  in  FIGS. 16-17  according to the ninth embodiment of the present invention are lithographically patterned on the second insulating layer  510  in a similar manner. The lithographic pattern is then etched into the second insulating layer  510  by a reactive ion etch (RIE) process. 
     Vias located within the second insulating layer  510  are formed by lithographically patterning the vias followed by an etch process that transfers the pattern into the second insulating layer  510 . Patterning and etching of the vias may be performed prior to or after the etching of the pattern for the second metal pads  522  or the third metal pads  502  that are located within the second insulating layer  510 . In the ninth embodiment of the present invention, the second metal vias  507  that are located within the second insulating layer  510  are formed at the same time as the other vias located within the same level. 
     All the features in the metal level within the second insulating layer  510  are filled with a first conducting material. Specifically, according to the first through eighth embodiments of the present invention, the second metal pads  522 , any of the first metal fills  523 , any first metal wires  525 , and any second metal wires  524  are filled with the first conducting material. Alternatively, according to the ninth embodiment of the present invention, the third metal pads  502  and any of the second metal fills  503 , third metal wires  505 , and fourth metal wires that are located within the bond pad structure  1600  in  FIGS. 16-17  are filled with the first conducting material. The first conducting metal is preferably a stack of a liner material and a metal layer. Most preferably, the metal layer is made of copper. Preferably, the fill process fills both the metal lines and the metal vias at the same time, which is called a dual damascene process. 
     Any excess first conducting material above the top surface of the second insulating layer  510  is then removed by a chemical mechanical polish (CMP) process. 
     While the process for the manufacture of the structures within the second insulating layer  510  is described with a dual damascene process whether the metal lines be formed first or the vias be formed first, the same structures may alternatively be fabricated using a single damascene process, wherein the features in the via levels are produced first and the features in the metal line level are produced thereafter. This invention may be practiced both ways. 
     Thereafter, a first insulating layer  535  is deposited over the second insulating layer  510  and the metal structures filled with the first conducting material. Preferably, the first insulating layer  535  comprises a stack of a cap layer  530 , which is deposited first, and an insulating dielectric layer  540 , which is deposited after and on top of the cap layer  530 . 
     Another layer of photoresist is deposited over the first insulating layer  535 , exposed to a light source under a mask, and developed such that a pattern of multiple first metal vias  552  are formed on the photoresist. The pattern includes the features for first metal vias  552 . This pattern is etched into the first insulating layer  535  using a RIE process. The patterned part of the first insulating layer  535  is etched through and portions of the top surface of the metal structures are exposed. The resulting structure includes openings for the formation of the first metal vias  552 . Specifically, the exposed metal surfaces are those of the second metal pads  552  and any of the second metal wires  524  in the seventh or eighth embodiment of the present invention or those of the third metal pads  552  within the level of the second insulating layer  510  and any of the fourth metal wires in the ninth embodiment of the present invention. 
     Thereafter, a metal layer made of a second conducting material is deposited over the first insulating layer and inside the openings. Preferably, the second conducting material is an aluminum alloy. Most preferably, the second conducting material is a stack containing a liner material and aluminum. This deposition process forms a blanket film, which includes the first metal pad  550 , the first metal vias  552 , and an optional bond pad extension  551  as well as unwanted portions of the second conducting material elsewhere. 
     A third pattern containing a pattern for the first metal pad  550  and optionally, the bond pad extension  551  is formed by depositing yet another layer of photoresist, and exposing it to a light source under a mask containing the features for the first metal pad  550  and optional bond pad extension  551 . The unwanted portions of the second conducting material that are located outside the area of the first metal pad  550  and outside the area of the bond pad extension  551 , if any of the bond pad extension  551  is present, is then etched and removed. Thus, the shape of the first metal pad  550 , or a bond pad, is defined at this point. 
     Thereafter, a passivation layer  560  is deposited over the first metal pad  550  and over the second insulating layer  535 , followed by a deposition of a photosensitive polyimide layer  570  over the passivation layer  560 . The photosensitive polyimide layer  570  is then exposed to a light source under a mask that contains a pattern for an opening  561  over the first metal pad  550 . A portion of the passivation layer  560  and the photosensitive polyimide layer  570  is then removed from above the first metal pad  550  from within the area of the opening  561 . The opening  561  within the passivation layer  560  and the photosensitive polyimide layer  570  is smaller than the size of the first metal pad  550 . 
     While the invention has been described in terms of specific embodiments, it is evident in view of the foregoing description that numerous alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, the invention is intended to encompass all such alternatives, modifications and variations which fall within the scope and spirit of the invention and the following claims.