Abstract:
A method of repairing hollow metal void defects in interconnects and resulting structures. After polishing interconnects, hollow metal void defects become visible. The locations of the defects are largely predictable. A repair method patterns a mask material to have openings over the interconnects (and, sometimes, the adjacent dielectric layer) where defects are likely to appear. A local metal cap is formed in the mask openings to repair the defect. A dielectric cap covers the local metal cap and any recesses formed in the adjacent dielectric layer.

Description:
FIELD OF THE INVENTION 
     The present invention generally relates to interconnect structures of microelectronic devices. In particular, the invention relates to methods of locally repairing a defect in an interconnect and the resulting structure. 
     BACKGROUND AND RELATED ART 
     Hollow metal is a type of defect found in metal interconnects of microelectronic devices. Hollow metal refers to voids at the surface of the metal line. The voids are detected after polishing the metal. Accordingly, hollow metal voids are different from voids formed by electromigration or stress migration because an interconnect having hollow metal has not experienced electric current or substantial heat cycles, respectively. 
     Void defects such as hollow metal are detrimental to both device performance, leading to electrical opens and reliability degradation, and manufacturability. Therefore, it is desirable to repair the defects. 
     SUMMARY 
     The general principal of the present invention is a method of repairing interconnects having a hollow metal void defect by a formation of a local metal cap. 
     In one embodiment, the method of repairing an interconnect includes forming a mask material over an interconnect post chemical mechanical polish (CMP), and opening the mask over a first portion of an interconnect and over a dielectric layer adjacent the first portion of the interconnect thereby forming a recess in the dielectric layer. The method continues by forming a local metal cap on the first portion of the interconnect and then forming a dielectric cap over the entire surface of the interconnect and adjacent dielectric layer. 
     Another embodiment provides a structure including an interconnect having a first portion, the first portion having a local metal cap. The structure also includes a dielectric layer adjacent the interconnect. The dielectric layer has a recess abutting the first portion of the interconnect. 
     In a further embodiment of the invention provides a structure including an interconnect having a first portion and a second portion, wherein the first portion has a local metal and the second portion lacks a local metal. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a top down view of two interconnects, one of which has a hollow metal void defect; 
         FIG. 1B  illustrates a cross section through a first interconnect having a hollow metal defect; 
         FIG. 1C  illustrates a cross section through a second interconnect lacking a hollow metal defect; 
         FIG. 2  is a flow chart of a method to repair hollow metal defects according to an embodiment of the present invention; 
         FIG. 3A  is a top down view of two interconnects after the masking step creates a first portion of the interconnects uncovered by the mask material according to an embodiment of the present invention; 
         FIG. 3B  illustrates a cross section through a first interconnect having a hollow metal defect of  FIG. 3A ; 
         FIG. 3C  illustrates a cross section through a second interconnect lacking a hollow metal defect of  FIG. 3A ; 
         FIG. 4A  is a top down view of two interconnects after the local metal cap step according to an embodiment of the present invention; 
         FIG. 4B  illustrates a cross section through a first interconnect of  FIG. 4A  having a hollow metal defect filled with local metal cap; 
         FIG. 4C  illustrates a cross section through a second interconnect of  FIG. 4A  lacking a hollow metal defect but receiving a local metal cap; 
         FIG. 5A  illustrates a cross section through a repaired first interconnect after forming a dielectric cap according to an embodiment of the present invention; 
         FIG. 5B  illustrates a cross section through a second interconnect lacking a hollow metal defect but receiving a local metal cap and a dielectric cap according to an embodiment of the present invention; 
         FIG. 6A  is a top down view of two interconnects that received a local repair method according to an embodiment of the present invention; 
         FIG. 6B  illustrates a cross section through a first interconnect having a hollow metal defect repaired according to an embodiment of the present invention; and 
         FIG. 6C  illustrates a cross section through a second interconnect lacking a hollow metal defect which received a repair method according to an embodiment of the present invention. 
     
    
    
     Other objects, aspects and advantages of the invention will become obvious in combination with the description of accompanying drawings, wherein the same number represents the same or similar parts in all figures. 
     DETAILED DESCRIPTION 
     A hollow metal defect is described in conjunction with  FIGS. 1A-C . A method to repair a hollow metal defect in an embodiment of the present invention includes patterning and etching a mask to form a first portion of the interconnect not covered by mask, forming a local metal cap to repair the defect, and forming a dielectric cap. The method is described in conjunction with  FIGS. 2-5 . In another embodiment of the invention, a structure having a locally repaired defect is described in conjunction with  FIGS. 6A-C . A detailed description of the invention is made in combination with the following embodiments. 
     Referring to  FIG. 1A  a top down view of a first interconnect  101  and second interconnect  102  embedded in a dielectric layer  115  is illustrated. The interconnects comprise a bulk conductor  105  and a liner  110 . The first interconnect  101  has a hollow metal defect  120 .  FIG. 1B  is a cross-section of an embodiment of the first interconnect  101 .  FIG. 1C  is a cross-section of an embodiment of the second interconnect  102 . 
     In  FIGS. 1A-C , the interconnects  101 / 102  are metal lines. The metal lines may be part of a dual damascene structure as depicted in  FIGS. 1B and 1C , or the interconnects  101 / 102  may be part of a single damascenes structure. In other embodiments, the interconnects may be single-damascene. Further embodiments may include single damascene vias, rather than metal lines. 
     Still referring to  FIGS. 1A  and C, the interconnects comprise a liner  110  which may be one or more layers which individually or in combination serve one or more of the following functions: adhesion promotion, and diffusion barrier. In a preferred embodiment, the liner  110  includes a TaN layer and Ta layer. In addition, the interconnects comprise a bulk conductor  105  which may be one or more layers. In a preferred embodiment, the bulk conductor includes copper and alloys such as copper aluminum and manganese. 
     The interconnects of  FIGS. 1A-C  are adjacent dielectric layer  115 . The dielectric layer can be a single layer or, more preferably, is a composite of several layers including adhesion layers or etch stop layers. For example, but not limiting the disclosure, the dielectric layer  115  can include a silicon dioxide layer and a carbon containing silicon oxide layer; the dielectric layer  115  can include several layers having different carbon contents; the dielectric layer  115  can include a nitrogen containing layer; the dielectric layer  115  can include a porous layer; the dielectric layer  115  can includes a spin on glass, e.g. SiLK. Preferably, the dielectric layer has a dielectric constant less than or equal to four. Preferably, the dielectric layer  115  is substantially co-planar with the interconnects  101 / 102 . 
     Finally,  FIGS. 1A  and B show a hollow metal void defect  120 . Hollow metal defects are missing portions (voids) of the bulk conductor  105 . In the figures, the hollow metal void  120  is shown at the end portion of the interconnect, a location where they are usually found. Typically, hollow metal defects  120  are found in minimally dimensioned structures, for example structures having a width less than 70 nm. Hollow metal voids  120  are also commonly found in via chain links A via chain link is a series of short interconnects with vias located at opposite line ends and electrically connected by an underneath metal line. The short lines are formed in a dense array to form millions of via links. Referring to  FIG. 1B , the hollow metal void  120  is illustrated in cross section. 
       FIG. 2  is a flow chart  200  of an embodiment of a method to repair hollow metal defects. The starting point  210  is providing interconnects after the CMP module, presumably at least one of the interconnects has a hollow metal defect. A masking step  220  covers all the interconnects except for openings made at location susceptible to hollow metal. A local metal cap step  230  forms a metal cap on the interconnects in the openings of the mask. A dielectric cap  240  step covers the mask material and the local metal cap. The steps are discussed in more detail below. 
       FIGS. 3A-C  describe a first step of an embodiment to repair the hollow metal defect void  120  of  FIGS. 1A-C . In  FIGS. 3A-C  a mask  140  if formed above the interconnects  101 / 102  and dielectric layer  115 . The mask  140  material is patterned and etched to expose a first portion  151  of the interconnects  101  and  102 . Due to overlay tolerances, patterning and etching the mask  140  also etches a portion of the dielectric layer  115  adjacent the first portion  151  of the interconnects  101 / 102  thereby forming a recess  130  in the dielectric layer  115 . The mask  140  material is preferably a dielectric layer containing nitrogen and or carbon. The mask  140  is from about 5 nm thick to about 100 nm and ranges there between. The etch is preferably a non-oxygen containing reactive ion etch chemistry, such as a fluorocarbon and inert element. However, any etch which does not appreciably etch the interconnects  101 / 102  is acceptable. 
     The first potions  151  of the interconnects  101 / 102  are the areas which are not covered by mask  140  material. Areas of the interconnects which are covered by the mask  140  material are referred to as second portions  152 . In  FIGS. 3A-3C , the first portions  151  for both the first  101  and second  102  interconnects are the right-hand side end portions of the interconnects, however, other configurations are also possible. For example, an individual interconnect can have multiple first portions  151 , meaning, interconnect  101  could also have an area not covered by mask  140  material on the left-hand side end portion, as well. In addition, all interconnects do not have to have a first portion  151 , meaning some interconnects could be completely covered by the mask  140  material. Numerous other configurations are also possible, including first portions at corners, intersections or other areas that are not end portions. 
     In  FIGS. 3A-C , both interconnects  101  and  102  have first portions  151  and associated recesses  130  in the dielectric layer  115  adjacent the first portions  151 . However, only one of the interconnects, first interconnect  101 , has a hollow metal void  120  defect. Creating first portions  151  in interconnects which lack defects will occur as the photolithography reticle is designed to expose areas in which a defect likely, but not necessarily, exists. 
     Referring to  FIGS. 4A-C , in a next step in the method of repairing a hollow metal defect, a local metal cap  125  is formed on the first portions  151  of the interconnects  101 / 102 . Preferably, the local metal cap  125  includes cobalt, for example, but not by limitation, CoWP. The local metal cap  125  could also include ruthenium (Ru) or manganese (Mn). Also preferably, the local metal cap  125  is formed by a selective process, for example, but not by limitation, electroless deposition. Other embodiments allow for a selective chemical vapor deposition (CVD) of cobalt and/or ruthenium local metal cap  125 . The local metal cap  125  is formed such that it substantially fills the hollow metal void  120 , here substantially filling includes hollow metal defects  120  which are about two-thirds filled. Overfilling of the hollow metal void  120  is also acceptable. However, because the local metal cap  125  also forms on the first portions  151  in which there is no hollow metal void  120 , it is preferable to keep the local metal cap  125  thinner rather than thicker. Specifically, in a preferred embodiment, the height of the local metal cap  125  does not exceed the height of the mask  140  material. If the local metal cap  125  does protrude significantly above the height of the mask  140  material, a touch up dielectric chemical mechanical polish (CMP) can be performed to planarize the local metal cap  125  with the mask  140 . 
     Referring to  FIGS. 5A  and B, first interconnect  101  and second interconnect  102  are respectively illustrated after formation of a dielectric cap  145 . Dielectric cap  145  can be the same or different material as mask  140  material. In a preferred embodiment, dielectric cap  145  comprises nitrogen, carbon or both. If needed, at this point a touch-up chemical mechanical polish (CMP) or other planarizing process can take place. Preferably, the dielectric cap  145  is conformal such that it fills recess  130  of the dielectric layer  115 . 
     Though not pictured, further interconnect layers can be formed above the first and second interconnects. The further interconnect layers may have a first via which lands, at least partially, on the local metal cap  125 , thus the first via lands a repaired interconnect rather than a void. In other areas, the further interconnect layer may have a second via which lands on a second portion of the interconnect  101 / 102  (where no local metal cap  125  exists). 
     An advantage of the method described above for repairing hollow metal-type defects, is that residual metal contamination is minimized by forming the metal cap through a mask. The resulting metal cap is localized rather than covering the entire surface of the interconnect. During selective deposition of the entire interconnect surface, often residual metal is left on top of the dielectric layer. In addition to being a contaminant that may interfere with subsequent processing steps, residual metal can lead to electrical shorts and early fails. In the present invention, depositing metal locally through a mask minimizes the formation of residual metal. 
     Referring to  FIGS. 6A-C , the interconnects of  FIGS. 1A-C  are shown after receiving a repair method according to an embodiment of the present invention.  FIG. 6A  is a top down view of first interconnect  101  and second interconnect  102  after repair but with mask  140  and dielectric cap  145  (shown in cross-sections  6 B and  6 C) removed for ease of viewing.  FIG. 6A  indicates the first portions  151  of the interconnects  101 / 102  which were not covered by mask material  140  and thus received the local metal cap  135 .  FIG. 6A  indicates second portions  152  of the interconnects  101 / 102  which are covered by the mask material  140  and thus do not have a local metal cap  140 . 
     Referring to  FIG. 6B , the first interconnect  101  which had the hollow metal defect is now repaired by having a local metal cap  125  substantially fill the defect. In the first portion  151  of interconnect  101 , above the local metal cap  125  is the dielectric cap  145 . The dielectric cap  145  also fills the recess  130  of dielectric layer  115 . In the second portion  152  of interconnect  101 , there is no local metal cap  125 , instead the mask  140  material is above the interconnect. In the second portion  152 , the mask  140  material is between the interconnect and the dielectric cap  145 . 
     Referring to  FIG. 6C , the second interconnect  102  which lacked the hollow metal defect still received the repair method, and thus it has a local metal cap  125  on top of the interconnect  102  in first portion. In the first portion  151  of interconnect  102 , above the local metal cap  125  is the dielectric cap  145 . The dielectric cap  145  also fills the recess  130  of dielectric layer  115 . In the second portion  152  of interconnect  102 , there is no local metal cap  125 , instead the mask  140  material is above the interconnect. In the second portion  152 , the mask  140  material is between the interconnect and the dielectric cap  145 . 
     An advantage of the present structure and method is that it is amenable to repairing hollow metal defects in areas that are susceptible to hollow metal defects, for example, via chains and line ends. 
     While the present invention has been described with reference to what are presently considered to be the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. On the contrary, the invention is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. The scope of the following claims is to be accorded the broadcast interpretation so as to encompass all such modifications and equivalent structures and functions.