Abstract:
In interconnect fabrication (e.g. a damascene process), a conductive layer is formed over a substrate with holes, and is polished to provide interconnect features in the holes. To prevent erosion/dishing of the conductive layer at the holes, the conductive layer is covered by a sacrificial layer (possibly conformal) before polishing; then both layers are polished. Initially, before polishing, the conductive layer and the sacrificial layer are recessed over the holes, but the sacrificial layer is polished at a lower rate to result in a protrusion of the conductive layer at a location of each hole. The polishing can continue to remove the protrusions and provide a planar surface.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 15/066,238, filed Mar. 10, 2016, incorporated herein by reference, which is a continuation of U.S. patent application Ser. No. 14/814,344, filed Jul. 30, 2015, incorporated herein by reference, which is a continuation of U.S. patent application Ser. No. 14/199,181, filed Mar. 6, 2014, incorporated herein by reference, now U.S. Pat. No. 9,123,703, which is a division of U.S. patent application Ser. No. 13/168,839, filed Jun. 24, 2011, titled “SYSTEMS AND METHODS FOR PRODUCING FLAT SURFACES IN INTERCONNECT STRUCTURES”, incorporated herein by reference, now U.S. Pat. No. 8,728,934. 
    
    
     INCORPORATION BY REFERENCE 
     All publications, including patents and patent applications, mentioned, in this specification are herein incorporated by reference in their entirety to the same extent as if each individual publication was specifically and individually indicated to be incorporated by reference. 
     FIELD OF THE INVENTION 
     The present invention relates generally to semiconductor device and methods pertaining to their manufacture. More specifically, the present invention relates to devices and methods for reducing/eliminating dishing defects in interconnect structures. 
     BACKGROUND OF THE INVENTION 
     Semiconductor chips are fabricated on suitable flat substrate wafers, such as GaAs, diamond coated substrates, silicon carbide, silicon wafers, etc. After making the active devices, a series of steps are performed to connect the various devices with highly conducting wiring structures, so they can have communication with each other to perform logic operations. These wiring structures or interconnect structures are essentially a skeletal network of conducting materials, typically metals in a matrix of dielectric materials. In high performance devices and to improve device density and yield, it is imperative to minimize topographic features within the interconnect layers for any given device and across the entire substrate. One common method of forming these high performance interconnect layers is the damascene process. 
     Multiple types of damascene structures are known, however the single and dual damascene are the most common. In single damascene, each metal or via layer is fabricated in a series of operations, while in dual damascene, a metal level and a via level are fabricated in a similar operation. Of these two, the dual damascene step is often preferred because of lower cost and higher device performance. 
     In the dual damascene process, a suitable substrate with or without devices is coated with a suitable resist layer. The resist layer is imaged to define desirable patterns by lithographic methods on the substrate. Cavities are etched on the patterned substrates typically by reactive ion etching methods, RIE. The patterned substrate is then coated with a suitable barrier/seed layer prior to overfilling the cavities with a suitable metal, typically copper by electro-deposition from a superfilling plating bath chemistry. 
     The damascene process is repeated to form the many layers of interconnect. As a result of the discontinuity in the properties (difference in mechanical properties, polishing rates, etc) of the metal and insulator, and their respective interactions with the polishing pad, polishing slurry, and other process parameters produces erosion in high metal pattern density features and dishing in large metal structures. The higher the metal pattern density, the higher the erosion, similarly, the larger the size of the metal cavity, the worse the gravity of the dishing defect. These deleterious defects cause shorting defects in subsequent levels, reducing device yield. 
     Similar results are observed in cross section topographic profiles of polished TSV structures. The center of the vias are typically lower than the surface of the insulators. 
     One of the consequences of dishing in the interconnect structures is poor flatness of the conductor and much higher pressures are typically needed to bond devices to the dished substrate or for wafer to wafer bonding. One method used to improve wafer to wafer bonding is to selectively recess the dielectric layer, so that the copper structures are protruding above the insulator surface prior to the bonding operation. This operation adds additional cost to the technology and is a source of defect when not properly implemented. Also, the poor flatness on the conductor surface often produces defect bonds, when the said surface is bonded or attached to other devices or substrates. 
     Other attempts to reduce the impact of these defects have lead to the incorporation of dummy dielectric features within large copper structures in dual damascene feature for chip interconnects. This approach has been helpful, but it has also increased mask design complexity and the associated loss of freedom of structure placement on the modified pads. 
     SUMMARY OF THE DISCLOSURE 
     In one embodiment, a method of forming a semiconductor interconnect structure is provided, comprising forming a cavity in a substrate, depositing a barrier layer on the cavity and on a first surface of the substrate, depositing a conductor on the barrier layer and inside the cavity, depositing a conductive sacrificial layer on the conductor, and removing portions of the conductive sacrificial layer, the conductor, and the barrier layer from the first surface until the conductor inside the cavity is angled greater than or equal to zero with respect to the first surface of the substrate. 
     In some embodiments, the removing step comprises removing portions of the conductive sacrificial layer, the conductor, and the barrier layer until the conductor inside the cavity comprises a planar surface that is coplanar with the first surface of the substrate. In other embodiments, the removing step comprises removing portions of the conductive sacrificial layer, the conductor, and the barrier layer until the conductor inside the cavity comprises a substantially convex surface that extends above the first surface of the substrate. 
     In one embodiment of the method, the conductor comprises copper. 
     In an additional embodiment, the removing step comprises a chemical mechanical polishing process. In another embodiment, the removing step comprises an ECMP process. 
     In some embodiments of the method, the depositing a conductive sacrificial layer step further comprises electrolessly or electrolytically depositing a conductive sacrificial layer on the conductor. 
     In one embodiment, a corrosion rate of the conductive sacrificial layer is less than a corrosion rate of the conductor. In another embodiment, a polishing rate of the conductive sacrificial layer is less than a polishing rate of the conductor. 
     In some embodiments, the conductive sacrificial layer comprises a material selected from the group of Ni, Ni alloys, NiP, NiB, NiW, NiWB, NiCoP, NiMoP, NiGa nickel-tungsten, cobalt alloys, CoP, CoWP, CMoP, copper alloys, copper-tungsten, Cu—Ga, and Cu—In. 
     In additional embodiments of the method, the depositing a conductive sacrificial layer step further comprises depositing a conductive sacrificial layer having a thickness ranging from approximately 3 nm to 300 nm on the conductor. Alternatively in another embodiment, the depositing a conductive sacrificial layer step further comprises depositing a conductive sacrificial layer having a thickness ranging from approximately 5 nm to 50 nm on the conductor. In some embodiments, the conductive sacrificial layer comprises a conformal layer. In another embodiment, the conductive sacrificial layer comprises an electroplated metal. 
     Another method of forming a semiconductor device is provided, comprising depositing a barrier layer on a substrate comprising at least one cavity, depositing a conductor on the barrier layer to overfill the at least one cavity, depositing a conductive sacrificial layer on the conductor, and removing the conductive sacrificial layer, the conductor, and the barrier layer from portions of the substrate adjacent to the at least one cavity to form an interconnect structure. 
     In some embodiments, the interconnect structure comprises a flat surface that is co-planar with a top surface of the substrate. In other embodiments, the interconnect structure comprises a top surface that angles upwards from a first surface of the substrate. 
     In some embodiments, the interconnect structure comprises a damascene structure. In other embodiments, the interconnect structure comprises a through-silicon via structure or interposer. 
     In one embodiment of the method, the removing the conductive sacrificial layer step further comprises removing the conductive sacrificial layer, the conductor, and the barrier layer or adhesion, layer or coupling layer from portions of the substrate adjacent to the at least one cavity until the conductor within the interconnect structure forms a substantially convex surface. 
     In another embodiment of the method, the removing the conductive sacrificial layer step further comprises removing the conductive sacrificial layer, the conductor, and the barrier layer from portions of the substrate adjacent to the at least one cavity until the conductor within the cavity forms a flat surface. 
     Another method of forming a semiconductor interconnect structure is provided, comprising forming a cavity in a substrate, depositing a barrier layer on the cavity and on a first surface of the substrate, depositing a conductor on the barrier layer, or adhesion layer or coupling layer inside the cavity, depositing a conductive sacrificial layer on the conductor, and removing portions of the conductive sacrificial layer, the conductor, and the barrier layer from the first surface until the conductor inside the cavity comprises a planar surface that is coplanar with the first surface of the substrate. 
     A semiconductor structure is also provided, comprising a substrate, and an interconnect structure disposed on the substrate, the interconnect structure having a top planar surface that is coplanar with the substrate. 
     In some embodiments, the interconnect structure comprises a damascene structure. In other embodiments, the interconnect structure comprises a TSV structure. In other embodiments, the substrate is an interposer. In one embodiment, the substrate and structure is a flat display panel. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A-1F  illustrate one method of forming a semiconductor interconnect structure. 
         FIGS. 2A-2G  illustrate another method of forming a semiconductor interconnect structure. 
         FIGS. 3A-3E  illustrate yet another method of forming a semiconductor interconnect structure. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIGS. 1A-1F  illustrate a conventional method and approach for forming a damascene structure on a semiconductor device  100 .  FIG. 1A  illustrates a substrate  102  having cavities  104   a ,  104   b , and  104   c  formed in the substrate below a top or first surface  106  of the substrate. The cavities can be formed by any process known in the art, such as by coating the substrate with a suitable resist layer, imaging the resist layer to define lithographic patterns on the substrate, and etching the cavities on the patterned substrate, such as with a reactive ion etching (RIE) method. The substrate can comprise any suitable wiring substrate, semiconductor, or non-semiconductor substrate used in devices, packages, or flat panels. Such substrate can be, for example, wafers, silicon wafers, glass, glass ceramic, ceramics, sapphire, interposer substrate, or wiring boards, for example.  FIG. 1A  illustrates the formation of both single damascene ( 104   b ) and dual damascene ( 104   a  and  104   c ) structures. 
     Referring to  FIG. 1B , a barrier/seed layer, or a platable adhesion or coupling layer  108  can be deposited on the substrate, including on the top surface of the substrate and on the side and bottom walls of cavities  104   a - 104   c . After application of the barrier/seed layer, a conductor  110  can be deposited on the barrier/seed layer  108  to overfill the cavities, as shown in  FIG. 1C . In one embodiment, the conductor comprises copper and is deposited on the barrier layer and inside the cavities by electro-deposition from a superfilling plating bath chemistry. In other embodiments, the conductor comprises aluminum, nickel, tungsten, copper tungsten alloy. 
     Next, the conductor coated substrate can be removed/polished to remove excess conductor and barrier/seed layer from the semiconductor device. In some embodiments, this process is achieved with a chemical-mechanical polishing (CMP) or electro-chemical-mechanical polishing (ECMP) device.  FIG. 1D  illustrates the remaining conductor portions as interconnect structures  112   a - 112   e  within the cavities (e.g., within cavities  104   a - 104   c ), after the removing or polishing step. It should be noted that in the conventional interconnect formation process described thus far, the interconnect structures, as shown in  FIG. 1D , comprise concave or “dished” top surfaces. More specifically, the conductor dips or curves down from the edge of the substrate into the cavity. 
       FIG. 1E  illustrates a close-up view of interconnect structure  112   a  from  FIG. 1D  contained within circle  1 E- 1 E, and more clearly shows the dishing described above in  FIG. 1D . Referring to  FIG. 1E , it is clear that the interconnect structure  112   a  dishes or curves downward from interface between the barrier layer  108  and the substrate  102 . This is further illustrated by referencing imaginary dashed line  114 , which extends from top surface  106  of the substrate  102 . As shown by angle θ, the surface of the conductor inside the cavity is angled less than zero with respect to the first or top surface  106  of the substrate  102 . Generally speaking, the center of the interconnect structures are recessed to be lower than the top surface of the substrate and lower than the edges of the interconnect structures. 
     In an alternative embodiment,  FIG. 1F  illustrates dishing defects of interconnect structures  112   a - 112   c  in through-silicon via (TSV) structures. The formation of the TSV structures with a substrate  102 , cavities, a barrier layer  108 , and interconnect structures  112   a - 112   c  can be similar to as described above with respect to the damascene process. 
     A method of reducing or eliminating dishing defects on substrates will now be described. Referring now to  FIG. 2A , a semiconductor device  200  comprises a suitable substrate  202 , barrier/seed layer  208 , and conductor  210 . As shown in the figure, the barrier/seed layer and the conductor are both deposited in cavities formed in the substrate. The methods of forming the cavities and depositing the barrier/seed and conductor layers can be the same as they are described above with respect to  FIGS. 1A-1C . 
     In contrast to the conventional approach, the present method further includes the step of depositing a conductive sacrificial layer  216  on the conductor  210  prior to the removing/polishing step. In one embodiment of this invention, the sacrificial material is coated on the conductor material after the gap filling process. In another embodiment, the sacrificial material is coated over the conductor after thermal treatment of the conductor to stabilize the grain size or structure of the coated conductor. 
     Referring again to  FIG. 2A , the conductive sacrificial layer  216  can be a material dissimilar to the conductor  210  upon which it is deposited. For example, in embodiments where the conductor  210  comprises copper, the conductive sacrificial layer  216  can comprise any conductive material except for copper. 
     In some embodiments, a corrosion rate or dissolution/polishing rate of the conductive sacrificial layer  216  is lower than that of the conductor  210 . In other embodiments, the conductive sacrificial layer  216  can be electrolessly deposited on the conductor  210 . In additional embodiments, the conductive sacrificial layer  216  can comprise Ni, Ni alloys, NiP, NiB, NiW, NiWB, NiCoP, NiMoP, NiGa nickel-tungsten, cobalt alloys, copper-tungsten, CoP, CoWP, CMoP, or any other similar suitable materials. In yet another embodiment, the conductive sacrificial layer can have a thickness ranging from approximately 3 nm to 300 nm on the conductor, or more specifically, can have a thickness ranging from approximately 5 nm to 50 nm on the conductor. In another embodiment, the conductive sacrificial layer can comprise a low dielectric constant material. In other embodiments, the conductive sacrificial layer comprises a conformal layer, or an electroplated metal. In other embodiments, more than one sacrificial layer may be coated. 
     After depositing the conductive sacrificial layer on the conductor, portions of the conductive sacrificial layer  216 , the conductor  210 , and the barrier layer  208  can be removed or polished, such as with a CMP or ECMP process.  FIG. 2B  illustrates the semiconductor device  200  after an intermediate polish with a CMP machine. In  FIG. 213 , only portions of the conductive sacrificial layer remain, illustrated as portions  218   a ,  218   b , and  218   c . Also shown, some portions of the conductor  210  have been polished away.  FIG. 2C  illustrates the semiconductor device  200  after additional polishing. In  FIG. 2C , a thin layer of conductor  210  still remains over the barrier layer  208 , and the portions of the conductor over the cavities resemble a convex or domed surface, as shown. The conductive sacrificial layer has been completely removed by this stage in the process. 
     Further polishing/removing of portions of the conductive sacrificial layer is illustrated in  FIG. 2D . As illustrated, portions of the conductive sacrificial layer, the conductor, and the barrier layer have been removed from the top surface of the substrate so that the conductor inside each of the cavities (e.g., interconnect structures  212   a ,  212   b , and  212   c ) each resemble a convex surface that extends above the top surface  206  of the substrate. In  FIG. 2D , the conductive sacrificial layer, the conductor, and the barrier layer have been removed from portions of the substrate adjacent to each of the interconnect structures. 
       FIG. 2E  illustrates a close-up view of the interconnect structure  212   a  from  FIG. 2D  contained within circle  2 E- 2 E, and more clearly shows the domed or upwardly curved surface described above in  FIG. 2D . Referring to  FIG. 2E , it is clear that the interconnect structure  212   a  curves upward from the interface between the barrier layer  208  and the substrate  202 . This is further illustrated by referencing imaginary dashed line  220 , which is angled upwards from top surface  206  of the substrate  202 . As shown by angle θ, the surface of the conductor inside the cavity is angled upwards greater than zero with respect to the first or top surface  206  of the substrate  202 . Generally speaking, the center of the interconnect structures are raised to be higher than the top surface of the substrate. The interconnect structures formed and illustrated in  FIGS. 2D-2E  can be any type of damascene interconnect structure, such as a single or dual damascene structure. 
     In the embodiment described above, polishing/removing portions of the conductive sacrificial layer, the conductor, and the barrier layer can result in the formation of an interconnect structure resembling a convex or domed surface, where an angle of the surface of the conductor inside the cavity is greater than zero with respect to the top surface of the substrate. However, in some embodiments, polishing/removing the conductor can result in the ideal flat or co-planar interconnect structure.  FIGS. 2F and 2G  illustrate the method step of removing portions of the conductive sacrificial layer, the conductor, and the barrier layer from the top surface of the substrate until the conductor inside the cavity is angled equal to zero with respect to the top surface, or alternatively, until the conductor inside the cavity comprises a planar surface that is coplanar with the top surface of the substrate. This method step results in a semiconductor structure that comprises a substrate and an interconnect structure disposed on the substrate, where the interconnect structure has a top planar surface that is coplanar with the substrate. 
       FIG. 2F  shows interconnect structures  212   a ,  212   b , and  212   c  having top surfaces that are co-planar or substantially co-planar with top surface  206  of the substrate  202 , and  FIG. 2G  illustrates a close up view of interconnect structure  212   a  and its flat top surface. 
       FIGS. 3A-3E  illustrate methods for forming semiconductor devices  300  with TSV structures having flat/co-planar top surfaces, or alternatively, having top surfaces that are angled upwards greater than or equal to zero with respect to the top surface of the substrate. The method steps for forming these TSV structures are substantially similar to the method steps described above in  FIGS. 2A-2G . 
     Referring to  FIG. 3A , a substrate  302  includes a barrier/seed layer, adhesion layer or coupling layer  308 , a conductor  310 , and a conductive sacrificial layer  316  disposed on the conductor. In  FIG. 3B , a portion of the conductive sacrificial layer and the conductor have been polished/removed, leaving only portions  318   a ,  318   b , and  318   c  of conductive sacrificial layer remaining. In  FIG. 3C , further polishing/removal of the conductive sacrificial layer and the conductor has left only a thin layer of conductor over the barrier/seed layer, as well as slightly domed surfaces over the cavities. Further polishing/removal of the conductor and barrier/seed layer can result in the domed interconnect structures  312   a ,  312   b , and  312   c  with top surfaces angled at greater than zero with respect to the top surface  306  of the substrate, as shown in  FIG. 3D , or alternatively, can result in the domed interconnect structures  312   a ,  312   b , and  312   c  with flat or co-planar top surfaces, as shown in  FIG. 3E . The interconnect structures formed and illustrated in  FIGS. 3D-3E  can be any type of TSV interconnect structure. Additionally, the methods described herein can be used with any of the interconnect structures described in U.S. application Ser. Nos. 12/221,204, or 12/646,836, both of which are incorporated herein by reference. 
     In some embodiments of the invention described above, the interconnect structures manufactured with the methods described herein form a metal level within a substrate. In other embodiments, the interconnect structures form a via level within a substrate. 
     In some embodiments, the pattern substrate herein known as the first material, is coated with a second material and the second material may be a coupling layer or an adhesive layer or a barrier/seed layer or their various combinations. The third material coated over the second material and may fill or overfill the cavities in the first material. A fourth material deposited by wet deposition methods such as electroless or electrolytic film may be coated over the third material. The removal rate of the fourth material been less than that of the third material and during the planarization step to remove unwanted materials, the presence of the fourth material cause a substantial co-planar topography across the substrate. 
     As for additional details pertinent to the present invention, materials and manufacturing techniques may be employed as within the level of those with skill in the relevant art. The same may hold true with respect to method-based aspects of the invention in terms of additional acts commonly or logically employed. Also, it is contemplated that any optional feature of the inventive variations described may be set forth and claimed independently, or in combination with any one or more of the features described herein. Likewise, reference to a singular item, includes the possibility that there are plural of the same items present. More specifically, as used herein and in the appended claims, the singular forms “a,” “and,” “said,” and “the” include plural referents unless the context clearly dictates otherwise. It is further noted that the claims may be drafted to exclude any optional element. As such, this statement is intended to serve as antecedent basis for use of such exclusive terminology as “solely,” “only” and the like in connection with the recitation of claim elements, or use of a “negative” limitation. Unless defined otherwise herein, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The breadth of the present invention is not to be limited by the subject specification, but rather only by the plain meaning of the claim terms employed.