Abstract:
A structure and method for monitoring extrusion failures. The structure includes: a test wire having first and second ends; first and second vias contacting first and second ends of the test wire; a first monitor structure electrically isolated from the test wire and surrounding a periphery of the test wire; and a second monitor structure over the test wire, the second monitor structure electrically isolated from the test wire, the second monitor structure extending over at least the first end of the test wire.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to the field of integrated circuits; more specifically, it relates to methods and structures for detection of metal extrusions associated with electromigration in high-current density settings. 
       BACKGROUND OF THE INVENTION 
       [0002]    In modern integrated circuits, devices such as transistors formed in a semiconductor substrate are interconnected by wires formed in interlevel dielectric (ILD) layers into circuits. At high current densities, the metal in the wires can migrate in the direction of electron flow building up at the anode end of the wire to the point where the buildup of metal causes delamination of the interlevel dielectric layers and extrusion of metal from the end of the wire. These extrusions can short to adjacent wires causing circuit failures. The remedy is to make wires wider and/or thicker to reduce current density, however wider lines use more integrated circuit chip real estate and makes dense wiring schemes more difficult if not impossible. The data gathered from extrusion monitors enables the use of wires of minimum wire cross-sectional areas in the integrated circuit. 
         [0003]    Currently, the industry uses electromigration or extrusion test structures to monitor this failure mechanism. However, current monitors only can detect fails, which extend laterally to adjacent wires in the same ILD layer. However, extrusions that extend vertically and short to wires in upper or lower ILD layers are not detected. Therefore, there is a need for an extrusion monitor that can detect vertical as well as lateral extrusions. 
       SUMMARY OF THE INVENTION 
       [0004]    A first aspect of the present invention is a structure, comprising: an electrically conductive test wire formed in a first dielectric layer over a top surface of a substrate, a bottom surface of the test wire facing the top surface of the substrate, the test wire having first and second ends, a top surface of the test wire opposite the bottom surface of the test wire; an electrically conductive first monitor structure formed in the first dielectric layer, a bottom surface of the first monitor structure facing the top surface of the substrate, the first monitor structure electrically isolated from the test wire, the first monitor structure surrounding a periphery of the test wire; an electrically conductive second monitor structure formed in a second dielectric layer over the first dielectric layer, a bottom surface of the second monitor structure facing a top surface of the test wire, the second monitor structure electrically isolated from the test wire, the second monitor structure extending over the first end of the test wire; and electrically conductive first and second vias either (i) located between the top surface of the substrate and the test wire, the first via physically and electrically contacting the bottom surface of the test wire at the first end and the second via physically and electrically contacting the bottom surface of the test wire at the second end or (ii) located between the test wire and the second monitor structure, the first via physically and electrically contacting the top surface of the test wire at the first end and the second via physically and electrically contacting the top surface of the test wire at the second end. 
         [0005]    A second aspect of the present invention is a method, comprising: forming an electrically conductive test wire formed in a first dielectric layer over a top surface of a substrate, a bottom surface of the test wire facing the top surface of the substrate, the test wire having first and second ends, a top surface of the test wire opposite the bottom surface of the test wire; forming an electrically conductive first monitor structure formed in the first dielectric layer, a bottom surface of the first monitor structure facing the top surface of the substrate, the first monitor structure electrically isolated from the test wire, the first monitor structure surrounding a periphery of the test wire; forming an electrically conductive second monitor structure formed in a second dielectric layer over the first dielectric layer, a bottom surface of the second monitor structure facing a top surface of the test wire, the second monitor structure electrically isolated from the test wire, the second monitor structure extending over the first end of the test wire; and forming electrically conductive first and second vias either (i) located between the top surface of the substrate and the test wire, the first via physically and electrically contacting the bottom surface of the test wire at the first end and the second via physically and electrically contacting the bottom surface of the test wire at the second end or (ii) located between the test wire and the second monitor structure, the first via physically and electrically contacting the top surface of the test wire at the first end and the second via physically and electrically contacting the top surface of the test wire at the second end. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    The features of the invention are set forth in the appended claims. The invention itself, however, will be best understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings, wherein: 
           [0007]      FIG. 1A  is a top view and  FIGS. 1B ,  1 C and  1 D are cross sectional views through respective lines  1 B- 1 B,  1 C- 1 C and  1 D- 1 D of an extrusion monitor structure according to a first embodiment of the present invention; 
           [0008]      FIG. 2  is an exploded top view of the electrically conductive structures in each ILD layer of the extrusion monitor of  FIGS. 1A ,  1 B,  1 C and  1 D; 
           [0009]      FIG. 3A  is a top view and  FIGS. 3B ,  3 C and  3 D are cross sectional views through respective lines  3 B- 3 B,  3 C- 3 C and  3 D- 3 D of an alternative wiring scheme for the extrusion monitor structure according to the first embodiment of the present invention; 
           [0010]      FIG. 4A  is an exploded top view of the electrically conductive structures in each ILD layer of the extrusion monitor of  FIGS. 3A ,  3 B,  3 C and  3 D; 
           [0011]      FIGS. 4B ,  4 C and  4 D are top views of alternative constructions for a layer of the extrusion monitor illustrated in  FIG. 4A ; 
           [0012]      FIG. 5A  is a top view and  FIGS. 5B ,  5 C and  5 D are cross sectional views through respective lines  5 B- 5 B,  5 C- 5 C and  5 D- 5 D of an extrusion monitor structure according to a second embodiment of the present invention; 
           [0013]      FIG. 6  is an exploded top view of the electrically conductive structures in each ILD layer of the extrusion monitor of  FIGS. 5A ,  5 B,  5 C and  5 D; 
           [0014]      FIG. 7A  is a top view and  FIGS. 7B ,  7 C and  7 D are cross sectional views through respective lines  7 B- 7 B,  7 C- 7 C and  7 D- 7 D of an alternative wiring scheme for the extrusion monitor structure according to a second embodiment of the present invention; 
           [0015]      FIG. 8  is an exploded top view of the electrically conductive structures in each ILD layer of the extrusion monitor of  FIGS. 7A ,  7 B,  7 C and  7 D; 
           [0016]      FIG. 9  is an exploded top view of the electrically conductive structures in each ILD layer of the extrusion monitor of a modified version of the first embodiment of the present invention; 
           [0017]      FIG. 10  is an exploded top view of the electrically conductive structures in each ILD layer of the extrusion monitor of a modified version of the second embodiment of the present invention; 
           [0018]      FIG. 11  is an exploded top view of the electrically conductive structures in each ILD layer of the extrusion monitor of another modified version of the first embodiment of the present invention; 
           [0019]      FIG. 12  is an exploded top view of the electrically conductive structures in each ILD layer of the extrusion monitor of another modified version of the second embodiment of the present invention; 
           [0020]      FIG. 13A  is a top view and  FIGS. 13B ,  13 C and  13 D are cross sectional views through respective lines  13 B- 13 B,  13 C- 13 C and  13 D- 13 D of an extrusion monitor structure according to alternative wiring schemes of the present invention; 
           [0021]      FIG. 14  is an exploded top view of the electrically conductive structures in each ILD layer of the extrusion monitor of  FIGS. 13A ,  13 B,  13 C and  13 D. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0022]    Descriptions of electromigration extrusions and the mechanism of electromigration extrusions are given in U.S. Pat. No. 7,119,545 to Ahsan et al., which is hereby included by reference in its entirety. 
         [0023]      FIG. 1A  is a top view and  FIGS. 1B ,  1 C and  1 D are cross sectional views through respective lines  1 B- 1 B,  1 C- 1 C and  1 D- 1 D of an extrusion monitor structure according to a first embodiment of the present invention. In  FIGS. 1A ,  1 B,  1 C and  1 D, formed on a top surface of a substrate  100  is a first interlevel dielectric layer (ILD)  105 , formed on a top surface of the first ILD layer is a second ILD layer  110  and formed on a top surface of the second ILD layer is a third ILD layer  115 . Formed in second ILD layer  110  is an electrically conductive and rectangular ring-shaped first extrusion monitor structure  120  having integrally formed connector wires  125 A and  125 B at opposite ends of the ring. First extrusion monitor  120  completely surrounds a perimeter of an electromigration test wire  130  also formed in second ILD layer  110 . Electrically conductive wires  135 A and  135 B formed in first ILD layer  105  are connected to opposite ends of electromigration test wire  130  through respective vias  140 A and  140 B formed in second ILD layer  110 . Formed in third ILD layer  115  are second and third extrusion monitor structures  145 A and  145 B formed over respective opposite ends of electromigration test wire  130  and having integrally formed connector wires  150 A and  150 B. 
         [0024]    In one example, wires  135 A and  135 B, vias  140 A and  140 B, test wire  130  and first, second and third extrusion monitors  120 ,  145 A and  145 B are damascene structures. In one example, test wire  130  and vias  140 A and  140 B are dual damascene structures and wires  135 A and  135 B, and first, second and third extrusion monitors  120 ,  145 A and  145 B are damascene structures. 
         [0025]    A damascene process is one in which wire trenches or via openings are formed in a dielectric layer, an electrical conductor of sufficient thickness to fill the trenches is deposited on a top surface of the dielectric, and a chemical-mechanical-polish (CMP) process is performed to remove excess conductor and make the surface of the conductor co-planar with the surface of the dielectric layer to form damascene wires (or damascene vias). When only a trench and a wire (or a via opening and a via) is formed the process is called single-damascene. 
         [0026]    A dual-damascene process is one in which via openings are formed through the entire thickness of a dielectric layer followed by formation of trenches part of the way through the dielectric layer in any given cross-sectional view. All via openings are intersected by integral wire trenches above and by a wire trench below, but not all trenches need intersect a via opening. An electrical conductor of sufficient thickness to fill the trenches and via opening is deposited on a top surface of the dielectric and a CMP process is performed to make the surface of the conductor in the trench co-planar with the surface of the dielectric layer to form dual-damascene wires and dual-damascene wires having integral dual-damascene vias. 
         [0027]    In either damascene or dual damascene wires, the conductor may be formed by forming a liner (i.e. a conformal layer that does not fill the trench) on the sidewalls and bottom of the trench and filling the remaining space in the trench with a core conductor. 
         [0028]    In one example, wires  135 A and  135 B, vias  140 A and  140 B, test wire  130  and first, second and third extrusion monitors  120 ,  145 A and  145 B may comprise gold (Au), aluminum (Al), copper (Cu), silver (Ag), alloys of Au, alloys of Al, alloys of Cu, alloys of Ag, tantalum (Ta), tantalum nitride (TaN), titanium (Ti), titanium nitride (TiN) or combinations thereof. Wires  135 A and  135 B, vias  140 A and  140 B, test wire  130  and first, second and third extrusion monitors  120 ,  145 A and  145 B may comprise a liner of TiN on a liner of Ti on a core of Al or may comprise a liner of Ta on a liner of TaN on a core of Cu. 
         [0029]    In one example, ILD layers  105 ,  110 , and  115  independently comprise a material selected from the group consisting of silicon dioxide (SiO 2 ), silicon nitride (Si 3 N 4 ), silicon carbide (SiC), silicon oxy nitride (SiON), silicon oxy carbide (SiOC), organosilicate glass (SiCOH), plasma-enhanced silicon nitride (PSiN x ) NBLok (SiC(N,H)) or combinations thereof. In one example, ILD layers  105 ,  110 , and  115  independently comprise low K (dielectric constant) material selected from the group consisting of hydrogen silsesquioxane polymer (HSQ), methyl silsesquioxane polymer (MSQ), SiLK™ (polyphenylene oligomer) manufactured by Dow Chemical, Midland, Tex., Black Diamond™ (methyl doped silica or SiO x (CH 3 ) y  or SiC x O y H y  or SiOCH) manufactured by Applied Materials, Santa Clara, Calif., organosilicate glass (SiCOH), and porous SiCOH, other low K materials and combinations thereof. A low K dielectric material has a relative permittivity of less than 4.0. 
         [0030]    A horizontal direction is a direction in a plane parallel to a top surface of substrate  100  and a vertical direction is a direction perpendicular to the top surface of the substrate. Horizontal extrusions of sufficient length extending from an end of test line  130  will short to first extrusion monitor  120  and vertical extrusions of sufficient length extending from an end of test line  130  will short to second or third extrusion monitors  145 A or  145 B. In use, while a current is forced through test line  130  a leakage current between test line  130  and first extrusion monitor  120 , second extrusion monitor  145 A and third extrusion monitor  145 B is measured. When an extrusion short occurs, there is a dramatic increase in the leakage current. Leakage currents between each of first, second and third extrusion monitors  120 ,  145 A and  145 B may be monitored separately, individually or in combination. 
         [0031]      FIG. 2  is an exploded top view of the electrically conductive structures in each ILD layer of the extrusion monitor of  FIGS. 1A ,  1 B,  1 C and  1 D. In all exploded views described in the present invention, conductive structures are shown in order from an uppermost structure (top of the drawing) furthest from the substrate to a lowermost structure (bottom of the page) closest to the substrate and the dashed lines and crosses indicate how the conductive structures are aligned to each other. In  FIG. 2 , wires  135 A and  135 B, vias  140 A and  140 B, test wire  130  and first, second and third extrusion monitors  120 ,  145 A and  145 B are aligned to each other. In one example, edges  146 A,  147 A and  148 A of second extrusion monitor  145 A are aligned to the top surface of substrate  100  directly over respective edges  121 ,  122  and  123  of first extrusion monitor  120  and edges  146 B,  147 B and  148 B of third extrusion monitor  145 B are aligned directly over respective edges  121 ,  124  and  123  of first extrusion monitor  120  when viewed from  FIG. 1A . Note edges  121  are aligned to both edges  146 A and  146 B and edges  123  are aligned to both edges  148 A and  148 B. Edge to edge alignment of vertically stacked structures is defined by edges of the stacked structures being in a same plane that is perpendicular to the top surface of the substrate on which the structures are stacked. Alternatively, any or all of edges  146 A,  147 A,  148 A,  146 B,  147 B and  148 B may extend past respective edges  121 ,  122 ,  123  and  124  when viewed from  FIG. 1A . 
         [0032]      FIG. 3A  is a top view and  FIGS. 3B ,  3 C and  3 D are cross sectional views through respective lines  3 B- 3 B,  3 C- 3 C and  3 D- 3 D of an alternative wiring scheme for the extrusion monitor structure according to the first embodiment of the present invention. In  FIGS. 3A and 3C  it can be that connector wires  150 A and  150 B (see  FIG. 1A ) are not present and that second and third extrusion monitors  145 A and  145 B are electrically connected to first extrusion monitor  120  by vias  155 A 1 ,  155 A 2 ,  155 B 1  and  155 B 2 . In one example, second and third extrusion monitors  145 A and  145 B and vias  155 A 1 ,  155 A 2 ,  155 B 1  and  155 B 2  are damascene structures. In one example, second extrusion monitor  145 A and vias  155 A 1 ,  155 A 2  are a dual damascene structure and third extrusion monitor  145 B and vias  155 B 1 ,  155 B 2  are a dual damascene structure. 
         [0033]      FIG. 4A  is an exploded top view of the electrically conductive structures in each ILD layer of the extrusion monitor of  FIGS. 3A ,  3 B,  3 C and  3 D. In  FIG. 4A , it can be seen two vias are supplied for each of second and third extrusion monitors  145 A and  145 B, but any number from one via to as many vias as will fit may be used. 
         [0034]      FIGS. 4B ,  4 C and  4 D are top views of alternative constructions for a layer of the extrusion monitor illustrated in  FIG. 4A . In  FIG. 4B  multiple vias  155 C 1  are substituted for vias  155 A 1  and  155 A 2  for second extrusion monitor  145 A. There would be corresponding multiple vias or via bars associated with third extrusion monitor  145 B. In  FIG. 4C  via bars  155 D 1  and D 2  are substituted for vias  155 A 1  and  155 A 2  for second extrusion monitor  145 A. There would be a corresponding pair of via bars associated with third extrusion monitor  145 B. In  FIG. 4D , a U-shaped via  155 E is substituted for vias  155 A 1  and  155 A 2  for second extrusion monitor  145 A. There would be a corresponding U-shaped via associated with third extrusion monitor  145 B. In the alternatives illustrated in  FIGS. 4B ,  4 C and  4 B, the structures may be damascene or dual-damascene. The structures illustrated in  FIGS. 4B ,  4 C and  4 D provide more monitor area for a potential extrusion to contact. 
         [0035]      FIG. 5A  is a top view and  FIGS. 5B ,  5 C and  5 D are cross sectional views through respective lines  5 B- 5 B,  5 C- 5 C and  5 D- 5 D of an extrusion monitor structure according to a second embodiment of the present invention and  FIG. 6  is an exploded top view of the electrically conductive structures in each ILD layer of the extrusion monitor of  FIGS. 5A ,  5 B,  5 C and  5 D. In  FIGS. 5A ,  5 B,  5 C,  5 D and  6 , second and third extrusion monitors  145 A and  145 B (see  FIG. 1A ) which were essentially plates, are replaced with respective multiple extrusion monitor bars  160 A and  160 B located over opposite ends of electromigration test wire  130 . Each bar  160 A is electrically connected to first extrusion monitor  120  by at least one via  165 A (though two are shown, one at each end of each bar  160 A) only one via  165 A to each extrusion monitor bar  160 A will suffice. Each extrusion monitor bar  160 B is electrically connected to first extrusion monitor  120  by at least one via  165 B (though two are shown, one at each end of each extrusion monitor bar  160 B) only one via  165 B to each extrusion monitor bar  160 B will suffice. Further, via bars  155 D 1  and  155 D 2  of  FIG. 4C  or U-shaped via bar  155 E of  FIG. 4D  may be substituted for vias  165 A (or  165 B). Extrusion monitor bars  160 A and vias  165 A (or via bars  155 D 1  and  155 D 2 , or U-shaped via bar  155 E) may be damascene or dual damascene structures. Extrusion monitor bars  160 A and  160 B and associated vias may comprise any of the materials described supra for second and third extrusion monitors  145 A and  145 B. 
         [0036]    The use of bars instead of plates has the advantageous of allowing optical inspection of the underlying electromigration test wire during failure analysis and of more closely duplicating actual wiring of functional circuits thus providing more accurate failure data. 
         [0037]      FIG. 7A  is a top view and  FIGS. 7B ,  7 C and  7 D are cross sectional views through respective lines  7 B- 7 B,  7 C- 7 C and  7 D- 7 D of an alternative wiring scheme for the extrusion monitor structure according to a second embodiment of the present invention and  FIG. 8  is an exploded top view of the electrically conductive structures in each ILD layer of the extrusion monitor of  FIGS. 7A ,  7 B,  7 C and  7 D. In  FIGS. 7A ,  7 B,  7 C,  7 D and  8 , vias  165 A and  165 B of  FIGS. 5A ,  5 B,  5 C,  5 D and  6  have been replaced with an integrally formed wires  166 A and  168 A and connection wire  170 A connecting all extrusion monitor bars  160 A and integrally formed wires  166 B and  168 B and connection wire  170 B connecting all extrusion monitor bars  160 B. 
         [0038]      FIG. 9  is an exploded top view of the electrically conductive structures in each ILD layer of the extrusion monitor of a modified version of the first embodiment of the present invention.  FIG. 9  is similar to  FIG. 4A  except second and third extrusion monitors  145 A and  145 B are replaced by a single upper extrusion monitor  175  and the electrical connections to upper extrusion monitor plate  175  are not shown. Electrical connections to upper extrusion monitor plate  175  may be made using an integrally formed wire similar to wire  150 A of  FIG. 2  or by any of the via schemes illustrated in  FIGS. 4B ,  4 C and  4 D. The position of these connections is indicated in  FIG. 9 . Upper extrusion monitor plate  175  and associated vias (if any) may comprise any of the materials described supra for second and third extrusion monitors  145 A and  145 B. In one example, edges  176 ,  177 ,  178  and  179  of upper extrusion monitor plate  175  are aligned to respective edges  121 ,  122 ,  123  and  124  of first extrusion monitor  120 . In the example of  FIG. 9 , upper extrusion monitor plate  175  completely overlays first extrusion monitor  120  and electromigration test wire  130  and when viewed from above. 
         [0039]      FIG. 10  is an exploded top view of the electrically conductive structures in each ILD layer of the extrusion monitor of a modified version of the second embodiment of the present invention.  FIG. 10  is similar to  FIG. 6  except the two sets of multiple extrusion monitor bars  160 A and  160 B (see  FIG. 6 ) are replaced by a single set of multiple upper extrusion monitor bars  180  and the electrical connections to each of the upper extrusion monitor bars are not shown. Electrical connections to the set of upper extrusion monitor bars  180  may be made using an integrally formed wire similar to wire  170 A of  FIG. 7A  or by any of the via schemes illustrated in  FIGS. 4B ,  4 C and  4 D including placing a ring via similar to first extrusion monitor  120  between the first extrusion monitor and the set of upper extrusion monitor bars  180 . The position of these connections is indicated in  FIG. 10 . The set of upper extrusion monitor bars  180  and associated vias (if any) may comprise any of the materials described supra for second and third extrusion monitors  145 A and  145 B. In one example, edges  181 ,  182 ,  183  and  184  of the set of upper extrusion monitor bars  180  are aligned to respective edges  121 ,  122 ,  123  and  124  of first extrusion monitor  120 . In the example of  FIG. 10 , the perimeter of extrusion monitor bars  180  completely overlays first extrusion monitor  120  and electromigration test wire  130  and when viewed from above. 
         [0040]      FIG. 11  is an exploded top view of the electrically conductive structures in each ILD layer of the extrusion monitor of another modified version of the first embodiment of the present invention.  FIG. 11  is similar to  FIG. 9 , except a lower extrusion monitor plate  185 A is positioned under (but isolated from) electromigration test wire  130 . Additionally slots  190 A and  190 B, are provided to allow electrical connection between wires  135 A and  135 B and vias  140 A and  140 B. Note wires  135 A and  13 B are now in the same wiring level as lower extrusion monitor plate  185 A. Electrical connections to lower extrusion monitor plate  185 A may be made using an integrally formed wire similar to wire  150 A of  FIG. 2  or by any of the via schemes illustrated in  FIGS. 4B ,  4 C and  4 D. The position of these connections to lower extrusion monitor plate  185 A is indicated in  FIG. 11 . Lower extrusion monitor plate  185 A and associated vias (if any) may comprise any of the materials described supra for second and third extrusion monitors  145 A and  145 B. In one example, edges  186 ,  187 ,  188  and  189  of lower extrusion monitor plate  185 A are aligned to respective edges  121 ,  122 ,  123  and  124  of first extrusion monitor  120 . In the example of  FIG. 11 , upper extrusion monitor plate  175  completely overlays first extrusion monitor  120  and electromigration test wire  130  and lower extrusion monitor plate  185 A when viewed from above. 
         [0041]      FIG. 12  is an exploded top view of the electrically conductive structures in each ILD layer of the extrusion monitor of another modified version of the second embodiment of the present invention.  FIG. 12  is similar to  FIG. 11 , except a set of multiple lower extrusion monitor bars  205  and  210  are positioned under (but isolated from) electromigration test wire  130 . Note wires  135 A and  135 B are now in the same wiring level as lower extrusion monitor bars  205  and  210 . Electrical connections to the set of multiple lower extrusion monitor bars  205  and  210  may be made using an integrally formed wire similar to wire  150 A of  FIG. 2  or by any of the via schemes illustrated in  FIGS. 4B ,  4 C and  4 D. The position of these connections to the set of multiple lower extrusion monitor bars  205  and  210  is indicated in  FIG. 12 . The set of multiple lower extrusion monitor bars  205  and  210  and associated vias (if any) may comprise any of the materials described supra for second and third extrusion monitors  145 A and  145 B. In one example, edges  211 ,  212 ,  213  and  214  of the set of multiple lower extrusion monitor bars  205  and  210  are aligned to respective edges  121 ,  122 ,  123  and  124  of first extrusion monitor  120 . In the example of  FIG. 12 , the perimeter of extrusion monitor bars  180  completely overlays first extrusion monitor  120 , electromigration test wire  130  and lower extrusion monitor bars  205  and  210  when viewed from above. 
         [0042]      FIG. 13A  is a top view and  FIGS. 13B ,  13 C and  13 D are cross sectional views through respective lines  13 B- 13 B,  13 C- 13 C and  13 D- 13 D of an extrusion monitor structure according to alternative wiring schemes of the present invention and  FIG. 14  is an exploded top view of the electrically conductive structures in each ILD layer of the extrusion monitor of  FIGS. 13A ,  13 B,  13 C and  13 D.  FIGS. 13A ,  13 B,  13 C,  13 D and  14 , are similar to  FIGS. 1A ,  1 B,  1 C,  1 D and  2  except second and third extrusion monitor structures  145 A and  145 B have been replaced with are second and third extrusion monitor structures  195 A and  195 B having respective slots  205 A and  205 B in order to allow wires  135 A and  135 B to be formed in the same wiring level as second and third extrusion monitor structures  195 A and  195 B. Note, the dielectric layers that the various conductive elements are formed in are now one level closer to substrate  100 . The principle of wiring scheme illustrated (i.e. contact to electromigration test wire  130  through vias  220 A and  220 B from above rather than from below) in  FIGS. 13A ,  13 B,  13 C,  13 D and  14  may be applied to any of the embodiments of the present invention. For the embodiments of  FIGS. 11 and 12 , the geometry of upper and lower extrusion monitor structures are swapped. 
         [0043]    Thus, the embodiments of the present invention provide extrusion monitors that can detect vertical as well as lateral extrusions. 
         [0044]    The description of the embodiments of the present invention is given above for the understanding of the present invention. It will be understood that the invention is not limited to the particular embodiments described herein, but is capable of various modifications, rearrangements and substitutions as will now become apparent to those skilled in the art without departing from the scope of the invention. For example, the combinations of the various extrusion monitor structures may be used together in conjunction with a single electromigration test wire. For example, the various extrusion monitor structures illustrated as over the electromigration test wire may be placed under or both over and under the electromigration test wire in any combination. For example, a first via at a first end of an electromigration wire may physically and electrically contact a bottom surface of the wire, while a second via at a second end of the wire may physically and electrically contact a top surface of the wire. Therefore, it is intended that the following claims cover all such modifications and changes as fall within the true spirit and scope of the invention.