Abstract:
A slot design for a metal interconnect line comprising a metal interconnect including at least two metal sub-interconnect lines that intersect to form an intersection area. At least one of the metal sub-interconnect lines having elongated slots formed therein with the elongated slots each having an axis extending through the intersection area. The intersection area having an effective cross-sectional area that is at least equal to the effective cross-sectional area of at least one of the metal sub-interconnect lines having elongated slots formed therein.

Description:
FIELD OF THE INVENTION 
   The present invention relates generally to semiconductor fabrication and more specifically to slot designs for metal interconnects. 
   BACKGROUND OF THE INVENTION 
   The purpose of slots in wide copper metal structures is to release thermal stress and reduce dishing effects during copper chemical mechanical polishing (CMP). 
   U.S. Pat. No. 6,251,786 B1 to Zhou et al. describes a dual damascene process with reduced dishing. 
   U.S. Pat. No. 6,358,831 B1 to Liu et al. describes a bonding pad process that reduces dishing. 
   U.S. Pat. No. 6,258,711 B1 to Laursen describes a metal planarization process. 
   U.S. Pat. No. 6,294,471 B1 to Tseng describes a chemical mechanical process (CMP) for a conductive structure. 
   SUMMARY OF THE INVENTION 
   Accordingly, it is an object of one or more embodiments of the present invention to provide an improved slot design for a metal interconnect line. 
   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 slot design for a metal interconnect line comprises a metal interconnect including at least two metal sub-interconnect lines that intersect to form an intersection area. At least one of the metal sub-interconnect lines having elongated slots formed therein with the elongated slots each having an axis extending through the intersection area. The intersection area having an effective cross-sectional area that is at least equal to the effective cross-sectional area of at least one of the metal sub-interconnect lines having elongated slots formed therein. 

   
     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: 
       FIG. 1  schematically illustrates a wide copper, elongated slot design known to the inventors. 
       FIG. 2  schematically illustrates a first preferred embodiment of the present invention. 
       FIG. 3  schematically illustrates an enlarged view of a first preferred embodiment of  FIG. 2  having no slots in the intersection area. 
       FIG. 4  schematically illustrates a second preferred embodiment of the present invention having square slots in checkerboard design in the intersection area. 
       FIG. 5  schematically illustrates a third preferred embodiment of the present invention having square slots in diamond design in the intersection area. 
       FIGS. 6 and 7  schematically illustrate alternate intersection areas. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Process Known to the Inventors—Not To Be Considered Prior Art 
   As shown in  FIG. 1  in a design known to the inventors and not to be considered as prior art for the instant invention, copper interconnect design  16  includes a bond pad  15  connected to wide copper interconnect lines (interconnects)  20 ,  22  each having a slot design having respective elongated slots  13 ,  14 . 
   Interconnects  20 ,  22  intersect as at  10  with the elongated slots  14  of interconnect  22  continuing into the intersection area  12 . Intersection area  12  is defined by intersection boundaries and as shown in  FIG. 1 , intersection area is a corner area defined by corner boundaries  17 ,  18 . Elongated slots  14  of interconnect  22  crossing over corner boundary  18  and into corner area  12 . This design known to the inventors incurs up to about 90% burn-in open failure rate from current crowding and induced inhomogeneous current flow within the corner area  12 . 
   With a current flow direction  7 , the effective cross-sectional area in region “B” within intersection  10  (width 9 times the thickness of film “t”) is less than the effective cross-sectional area in region “A”_of interconnect  20  adjacent intersection  10  ((widths 11, 11′, 11″ and 11′″) times the thickness of film t). This creates the problem of current crowding and further, because the paths in region B isn&#39;t distributed uniformly, it induces inhomogeneous current flow. 
   First Embodiment—No Slots or Other Openings 
     FIG. 2  illustrates the first embodiment of the present invention wherein a copper interconnect design  100  on a chip  101  includes a bond pad  106  and one or more metal interconnect lines (interconnects)  108  and may include one or more dummy metal regions  102 ,  104 . Dummy metal regions  102 ,  104  are preferably comprised of copper, aluminum, gold or silver and are more preferably copper. Bonding pad  106  and metal interconnects  108  are preferably comprised of copper, aluminum, gold or silver and are more preferably copper. 
   Metal interconnect(s)  108  include substantially straight metal sub-interconnect lines (sub-interconnects)  120 ,  130  that intersect at approximately 90° angles to form intersection areas  110  defined by intersection boundaries  114 ,  112 . As shown in  FIG. 2  (and  FIGS. 3  to  5 ) the intersection areas  110  are corner areas  110  defined by corner boundaries  112 ,  114  that segregate corner areas  110  from the intersecting metal sub-interconnects  120 ,  130 . Metal interconnect(s)  108  and metal sub-interconnects  120 ,  130  are preferably comprised of copper, aluminum, gold or silver and are more preferably copper as will be used hereafter for illustrative purposes. 
   As shown in FIG.  2  and more clearly shown in  FIG. 3  (an enlargement of the corner area of  FIG. 2 ) copper sub-interconnects  120 ,  130  each (at least one) include respective elongated slots  122 ,  132  formed therein and, in the first embodiment of the present invention, none of the slots  122 ,  132  extend past the respective corner boundaries  112 ,  114  and into the corner areas  110 ; and no other opening(s) is/are formed within the corner area  110  of copper interconnect  108  so that the corner area  110  has an unbroken surface. 
   As one skilled in the art would understand, the upper surface unit area of corner area  110  is greater than the upper surface unit area of the sub-interconnects  120 ,  130  having elongated slots  122 ,  132 ; and the effective cross-sectional unit area of corner area  110  is greater than the effective cross-sectional unit area of each of the sub-interconnect  120 ,  130  having elongated slots  122 ,  132 . Thus with a current flow direction  107 , there is no current crowding and the current distribution is homogeneous. 
   Elongated slots  122 ,  132  each have a width of preferably from about 6000 to 30,000 Å and more preferably from about 10,000 to 15,000 Å. 
   Second Embodiment—Checkerboard Pattern Square Slot Openings  140   
   As shown in  FIG. 4 , which is the same structure as that shown in  FIG. 3  with the addition of square slot openings  140  formed within the intersection area/corner area  110  that are each aligned with each set of respective intersecting axes  150 ,  160  of elongated slots  122 ,  132  to form a ‘checkerboard’ pattern. 
   Square slot openings  140  each are preferably from about 6000 to 30,000 Å and more preferably from about 10,000 to 15,000 Å on a side. 
   With a current flow direction  117 , the effective cross-sectional area in region “D” within intersection  110  is essentially equal to the effective cross-sectional area in region “C”_of interconnect  130  adjacent intersection  110 . Therefore there is no problem of current crowding and further, because the paths in region D are distributed uniformly, homogeneous current flow results. 
   Third Embodiment—Diamond Pattern Square Slot Openings  170   
   As shown in  FIG. 5 , which is the same structure as that shown in  FIG. 3  with the addition of square slot openings  170  formed within the intersection area/corner area  110  in a diamond pattern Each of the square slot openings  170  are aligned with the selected intersecting axes  150 ,  160  of elongated slots  122 ,  132  to form a diamond pattern as shown. 
   Square slot openings  170  each are preferably from about 6000 to 30,000 Å and more preferably from about 10,000 to 15,000 Å on a side. 
   With a current flow direction  127 , the effective cross-sectional area in region “F” within intersection  110  ((widths 113+113+115)×t) is greater than the effective cross-sectional area in region “E”_of interconnect  130  adjacent intersection  110  ((widths 131+131+131+131+131)×t). Therefore there is no problem of current crowding and because the paths in region F are distributed roughly uniformly, homogeneous current flow results. 
   It is noted that while the second and third embodiments of the present invention disclose square slot openings  140 ,  170  arranged in respective checkerboard and diamond patterns, such square slot opening  140 ,  170  may form other overall patterns within the intersections of axes  150 ,  160  within intersection area/corner area  110 . 
   While the individual slot openings  140 ,  170  have been illustrated as having a square shape as that shape is more efficiently formed at the select points of intersection of the axes of the respective elongated slots  132 ,  122 , the slot openings  140 ,  170  themselves may have other shapes rather than square, such as circular, oval, diamond, rectangular, irregular, etc., as long as slot openings  140 ,  170  are restricted to the areas defined by the intersection of respective axes  150 ,  160  (and do not cross the respective intersection boundaries/corner boundaries  112 ,  114 ). 
   Slot openings  140 ,  170  are restricted to the areas defined by the intersection of respective axes  150 ,  160  so as to limit their overall size. The individual slot opening  140 ,  170  are more preferably square in shape because that is the easiest shape to form. 
     FIGS. 6 and 7  show alternate metal interconnects  108  wherein the sub-interconnects  120 ,  130  may intersect in a T-pattern forming an intersection area  110 ′ defined by intersection boundaries  112 ′,  114 ′, as shown in  FIG. 6 ; or in a cross-pattern forming an intersection area  110 ″ defined by intersection boundaries  112 ″,  114 ″, as shown in FIG.  7 . 
   While  FIGS. 6 and 7  specifically illustrate the more preferred slotless/openless intersection areas  110 ′,  110 ″, the respective intersection areas  110 ′,  110 ″ may have the second embodiment checkerboard pattern (preferred), the third embodiment diamond pattern (preferred), or other alternate patterns (less preferred). Whether a slotless/openless intersection area  110 ′,  110 ″ is selected, the second embodiment checkerboard pattern is selected or the third embodiment diamond pattern is selected, the design creates similar homogeneous current distribution and the absence of current crowding as discussed in the first, second and third embodiments above. 
   Regardless of which of the three embodiments or alternatives disclosed herein are employed in accordance with the present invention, homogeneous current flow in the intersection areas/corner areas  110  is realized with much less product burn-in failure rate. The product burn-in open failure rate is improved to preferably from about 25 to 0% and more preferably about 0%. 
   ADVANTAGES OF THE PRESENT INVENTION 
   The advantages of one or more embodiments of the present invention include: 
   1. homogeneous current flow in corner areas; and 
   2. reduced burn-in open failure rate. 
   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.