Abstract:
A method of fabricating a bonding pad anchoring structure comprising the following steps. Providing a substrate. Forming a series of grated metal layers over the substrate separated by an interleaving series of via plug layers having via plugs electrically connecting respective at least a portion of adjacent grated metal layers. The series of grated metal layers having an uppermost grated metal layer. Forming an uppermost via plug layer over the uppermost grated metal layer. The uppermost via plug layer having via plugs. Forming a bonding pad layer over the uppermost via plug layer so that the uppermost via plugs within the uppermost via plug layer electrically connect the bonding pad layer to at least a portion of the uppermost grated metal layer whereby the bonding pad layer is securely bonded to the substrate.

Description:
This application is a division of U.S. Ser. No. 10/243,910 filed Sep. 13, 2002 now U.S. Pat No. 6,955,981. 

   FIELD OF THE INVENTION 
   The present invention relates generally to semiconductor fabrication and more specifically to processes of fabricating pad structures. 
   BACKGROUND OF THE INVENTION 
   Poor bondability of bonding pads is a continuing issue to low-k Intermetal dielectric (IMD) layers. Pad peeling and craters have been found during wire bonding processes and post-testing. Mechanical stress also degrades performance. 
   For example,  FIG. 1  illustrates a conventional N level bonding pad  10  with metal via anchors  12  (through IMD layer  11 ) anchoring and electrically connecting N level bonding pad  10  to N-1 level metal layer  14 . Bonding wire  20  is electrically affixed to N level bonding pad  10  as at  22 . 
   Metal via plugs  16  (through IMD layer  15 ) electrically connect N-1 level metal layer  14  to N-2 level metal layer  18 .  FIG. 2  is a cross-section of  FIG. 1  taken along line  2 - 2  of  FIG. 1 , illustrating that the N- 1  level, etc., metal layer  14  is a solid sheet layer. This structure suffers from the above described shortfalls. 
   U.S. Pat. No. 6,258,715 B1 to Yu et al. describes plugs under bonding pads to improve adhesion. 
   U.S. Pat. No. 6,236,114 B1 to Huang et al. describes a bonding pad with extra vias. 
   U.S. Pat. No. 5,923,088 to Shiue et al. describes a bonding pad structure with via plugs thereunder. 
   U.S. Pat. No. 5,739,587 to Sato describes another bonding pad structure with via plugs thereunder. 
   SUMMARY OF THE INVENTION 
   Accordingly, it is an object of one or more embodiments of the present invention to provide an improved method of anchoring a bonding pad. 
   Other objects will appear hereinafter. 
   It has now been discovered that the above and other objects of the present invention may be accomplished in the following manner. Specifically, a substrate is provided. Forming a series of grated metal layers over the substrate separated by an interleaving series of via plug layers having via plugs electrically connecting respective at least a portion of adjacent grated metal layers. The series of grated metal layers having an uppermost grated metal layer. Forming an uppermost via plug layer over the uppermost grated metal layer. The uppermost via plug layer having via plugs. Forming a bonding pad layer over the uppermost via plug layer so that the uppermost via plugs within the uppermost via plug layer electrically connect the bonding pad layer to at least a portion of the uppermost grated metal layer whereby the bonding pad layer is securely bonded to the substrate. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be more clearly understood from the following description taken in conjunction with the accompanying drawings in which like reference numerals designate similar or corresponding elements, regions and portions and in which: 
       FIGS. 1 and 2  schematically illustrate a prior art bonding pad anchoring structure with  FIG. 2  being a cross-section of  FIG. 1  along line  2 - 2 . 
       FIGS. 3 to 7  schematically illustrate a preferred embodiment of the present invention with  FIG. 4  being a cross-section of  FIG. 3  along line  4 - 4 ;  FIG. 5  being a cross-section of  FIG. 3  along line  5 - 5 ;  FIG. 6  being a cross-section of  FIG. 3  along line  6 - 6 ; and  FIG. 7  being a cross-section of  FIG. 3  along line  7 - 7 . 
       FIGS. 8A ,  8 B, and  8 C schematically illustrate a plan view of a bonding pad anchored by the method of the present invention. 
       FIGS. 9A ,  9 B, and  9 C schematically illustrate a plan view of an alternate bonding pad anchored by the method of the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Unless otherwise specified, all structures, layers, steps, methods, etc. may be formed or accomplished by conventional steps or methods known in the prior art. 
   As shown in  FIG. 3 , bonding pad anchoring structure  130  includes an uppermost metal layer M 8 , i.e. bonding pad  100  with a bonding wire  120  affixed to bonding pad  100  as at  122 . Uppermost metal layer M 8  need not be grated. 
   Metal V 7  via plugs  102  formed through intermetal dielectric (IMD) layer  101  electrically connect M 8  bonding pad  100  to M 7  metal layer  104  formed through dielectric layer  103 . Bonding pad  100  may be a solid sheet of metal or may be grated as are the underlying metal layers  104 ,  108 ,  112 . As shown in  FIG. 4 , M 7  metal layer  104  is grated and comprises spaced apart metal lines  104 ′. 
   Metal V 6  via plugs  106  formed through IMD layer  105  electrically connect M 7  metal layer  104  to M 6  metal layer  108  formed through low-k dielectric layer  107 . As shown in  FIG. 5 , M 6  metal layer  108  is also grated and comprises spaced apart metal lines  108 ′. As shown in  FIG. 7 , metal V 6  via plugs  106  (as are metal V 7  via plugs  102 , metal V 5  via plugs  110  and all underlying metal via plugs) are located at the intersection of the adjacent V 7  metal layer  102  metal lines  102 ′ and V 6  metal layer  108  metal lines  108 ′. 
   As shown in  FIGS. 3 and 5 , M 6  metal layer  108  metal lines  108 ′ may be rotated at a ninety degree (90°) relative to M 7  metal layer  104  metal lines  104 ′. This 90° rotation creates more interface between the metal and the low-k material in the lattice. 
   If current degradation is a problem due to the 90° rotation, M 6  metal layer  105  metal lines  105 ′ may be substantially parallel relative to M 7  metal layer  104  metal lines  104 ′. 
   Metal V 5  via plugs  110  formed through IMD layer  109  electrically connect M 6  metal layer  108  to M 5  metal layer  112  formed through low-k dielectric layer  109 . As shown in  FIG. 6 , M 5  metal layer  112  is also grated and comprises spaced apart metal lines  112 ′. As shown in  FIGS. 3 and 6 , M 5  metal layer  112  metal lines  112 ′ may be rotated at a ninety degree (90°) relative to M 6  metal layer  108  metal lines  108 ′. This 90° rotation again creates more interface between the metal and the low-k material in the lattice. 
   Again, if current degradation is a problem due to the 90° rotation, M 5  metal layer  112  metal lines  112 ′ may be substantially parallel relative to M 6  metal layer  108  metal lines  108 ′. 
   Additional metal via plugs/metal layers may be formed down to V 1  and M 1  layers (not shown) within structure  140 . Structure  40  is understood to possibly include a semiconductor wafer or substrate, active and passive devices formed within the wafer, conductive layers and dielectric layers (e.g., inter-poly oxide (IPO), intermetal dielectric (IMD), etc.) formed over the wafer surface. The term “semiconductor structure” is meant to include devices formed within a semiconductor wafer and the layers overlying the wafer. 
   Each such additional lower metal layers are each comprised of spaced metal lines that may be either rotated substantially 90° relative to the immediately overlying metal layer or may be substantially parallel relative to the immediately overlying metal layer as shown and described herein. 
   The metal layers  100 ,  104 ,  108 ,  112 , etc. the metal via plugs  102 ,  106 ,  110 , etc. are preferably comprised of copper, aluminum, gold, tungsten (W) or titanium (Ti) and are more preferably copper. IMD layers  101 ,  105 ,  109  are preferably comprised of low-k material such as FSG, SiLK, nanoglass, Black Diamond™ (a product of Applied Materials of Santa Clara, Calif.), or a porous dielectric material. IMD layers  101 ,  105 ,  109  preferably have a dielectric constant (k) of less than about 3.2. IMD layers  101 ,  105 ,  109  each have a thickness of preferably from about 2000 to 10,000 Å and more preferably from about 4000 to 8000 Å. 
   Dielectric layers  103 ,  107 ,  111  are preferably comprised of low-k material such as FSG, SiLK, nanoglass, Black Diamond™ (a product of Applied Materials of Santa Clara, Calif.), or a porous dielectric material. Dielectric layers  103 ,  107 ,  111  preferably have a dielectric constant (k) of less than about  3 . 0 . Dielectric layers  103 ,  107 ,  111  each have a thickness of preferably from about 2000 to 30,000 Å and more preferably from about 2500 to 10,000 Å. 
   Metal lines  104 ′,  108 ′,  112 ′ (and any underlying metal lines) have a width of preferably from about 10,000 to 50,000 Å and more preferably from about 20,000 to 30,000 Å and are spaced apart preferably from about 10,000 to 50,000 Å and more preferably from about 10,000 to 30,000 Å. The widths and spacing of the metal lines  104 ′,  108 ′,  112 ′ (and any underlying metal lines) are adjustable to accommodate the differing low-k materials comprising IMD layers  101 ,  105 ,  109  (and any underlying IMD layers). 
   The grating of metal lines  104 ′,  108 ′,  112 ′ (and any underlying metal lines) achieves good bondability and eliminates any mechanical stress issue. Since the metal lines  104 ′,  108 ′,  112 ′ (and any underlying metal lines) are adjacent to IMD, the main energy of the bonding wire  120  is absorbed upon the periphery of the metal lines  104 ,  108 ,  112  just as if the metal layers  104 ,  108 ,  112  (and any underlying metal lines) were solid sheets and can be absorbed by the multiple peripheries. Further, chemical mechanical polishing (CMP) dishing effects are reduced using the grating structure of the metal lines  104 ′,  108 ′,  112 ′ (and any underlying metal lines). The lattice structure of the bonding pad anchoring structure  130  of the present invention improves the mechanical properties of the overall structure  130  akin to reinforced concrete. 
   In tests, the novel bonding pad anchoring structure  130  of the present invention produced about a 96% bonding yield and is admirable suited for 0.13 μm rule and beyond. 
   A First Bonding Pad  100  — FIGS. 8A ,  8 B, and  8 C 
     FIGS. 8A ,  8 B, and  8 C illustrate a plan view, i.e. a top down view, of one preferred structure of the bonding pad  100  having an outer metal ring  202  and a non-continuous series of spaced-apart, equal length grated metal lines  204 . The outer metal ring  202  and grated metal lines  204  may comprise copper, aluminum, gold, tungsten, any other suitable material, and/or combinations thereof. In the present embodiment, the outer metal ring  202  and grated metal lines  204  comprise copper. Disposed in between the outer metal ring  202  and grated metal lines  204  may be low-k dielectric materials, such as FSK, SiLK, nanoglass, Black Diamond™ (a product of Applied Materials of Santa Clara, Calif.), a porous dielectric material, any other suitable low-k dielectric material, and /or combinations thereof. The grated metal lines  204  may be spaced apart at varying widths or equal widths, and the widths may be adjusted to accommodate differing low/k dielectric materials disposed between. 
   The bonding pad  100  illustrated in  FIG. 8C  may be used in other IMD layers  101 ,  105 , 109 . 
   A Second Bonding Pad  100  — FIGS. 9A ,  9 B, and  9 C 
     FIGS. 9A ,  9 B, and  9 C illustrate a plan view, i.e. a top down view, of another preferred structure of the bonding pad  100  having an outer metal ring  302  and a non-continuous series of spaced-apart, equal length, staggered grated metal lines  304 ,  306 . The outer metal ring  202  and grated metal lines  204  may comprise copper, aluminum, gold, tungsten, titanium, any other suitable material, and/or combinations thereof. In the present embodiment, the outer metal ring  202  and grated metal lines  204  comprise copper. Disposed in between the outer metal ring  202  and grated metal lines  204  may be a low-k dielectric material, such as FSG, SiLK. nanoglass, Black Diamond™ (a product of Applied Materials of Santa Clara, Calif.), a porous dielectric material, any other suitable low-k dielectric material, and/or combinations thereof. The grated metal lines  204  may be spaced apart at varying widths or equal widths, and the widths may be adjusted to accommodate differing low-k dielectric materials disposed between. 
   The bonding pad  100  illustrated in  FIG. 9C  may be used in other IMD layers  101 ,  105 ,  109 . 
   According to a variation, one or more of the series of grated metal layers  104 ,  108  and  112  could have an outer metal ring and a series of non-continuous, spaced apart grated metal lines. 
   Advantages of the Present Invention 
   The advantages of one or more embodiments of the present invention include:
         1. bonding pad bondability is improved;   2. mechanical stress due to the bonding wire is greatly reduced;   3. any metal cup dishing effect is automatically attenuated;   4. the package (pkg) level thermal property is improved; and   5. the peeling process issue is automatically resolved.       

   While particular embodiments of the present invention have been illustrated and described, it is not intended to limit the invention, except as defined by the following claims.