Abstract:
An apparatus for electrically testing a semiconductor device is disclosed. The apparatus comprises a probe card comprising a probe, wherein the probe comprises a probe tip. Further, the probe tip comprises a foot with an arbitrarily sized cross-section and an apex with an arbitrarily sized cross-section, wherein the cross-section of the foot is wider than the cross-section of the apex.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
       [0001]    The present application is a divisional of, claims the benefit of and priority to U.S. application Ser. No. 14/178,171, Attorney Docket ATST—U0078.US, filed Feb. 11, 2014, entitled “METHODS TO MANUFACTURE SEMICONDUCTOR TIPS”, and hereby incorporated by reference in its entirety, which claims the benefit of and priority to U.S. Provisional Application No. 61/936,480, filed Feb. 6, 2014, which is incorporated by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    Embodiments of the present disclosure relate generally to the field of semiconductor probe tips for semiconductor testing and more specifically to the field of semiconductor probe tip fabrication with an arbitrarily small apex cross-section and an arbitrarily wide foot cross-section. 
       BACKGROUND 
       [0003]    Several desirable attributes for a probe tip include, but are not limited to: an adequate level of structural robustness, a small apex cross-section-to-tip-height ratio, and a small apex area. An adequate level of structural robustness may provide some immunity to the range of tangential or shear forces encountered during normal operation. A small apex cross-section-to-tip-height ratio may assist with the placement of the probe tip and avoid unnecessary contact with ancillary structures surrounding the electrical feature of interest on the semiconductor die (e.g., a contact pad or solder bump). Finally, a small apex area may increase local pressure and ease any required scratching of oxide layers over the electrical structures of interest and facilitate the penetration of metallic surfaces. 
         [0004]    In light of these desired design features, a possible probe tip shape that meets these desirable attributes may include a conical or pyramid shape. In other words, a desirable probe tip shape may define a volume with a large base, providing mechanical robustness to shear forces, and a small apex for efficient scratching of metal oxides and penetration of metallic surfaces. 
         [0005]    Such conical or pyramid-shaped probe tips may be manufactured utilizing molds. However, such manufacturing methods based upon the use of a defined mold and its subsequent filling (e.g., electro-deposition or electroplating) suffer from limitations pertaining to the types of geometries that can be achieved during the definition of the mold itself, especially when the mold is the result of a photolithographic process. Although photolithographic processes can provide molds of an arbitrary shape and height, they typically yield molds with straight sidewalls, essentially oriented along an axis perpendicular to the surface underneath. Cone, truncated cone, or pyramid shapes are generally more difficult to achieve via photolithography alone. 
       SUMMARY OF THE INVENTION 
       [0006]    This present invention provides a solution to the challenges inherent in manufacturing semiconductor probe tips. In a method according to one embodiment of the present invention, a method for manufacturing a semiconductor probe tip with an arbitrarily small apex cross-section and an arbitrarily wide foot cross-section is disclosed. In one embodiment, a metallic structure is formed in a cavity with one conductive sidewall. The cavity with a conductive sidewall may be formed from a plurality of cavities to allow the formation of the metallic structure with an arbitrarily sized small apex cross-section and an arbitrarily sized wide foot cross-section. 
         [0007]    In a method according to one embodiment of the present invention, a method for forming a semiconductor probe tip is disclosed. The method comprises depositing a first copper layer onto exposed electrically conductive areas of a wafer. The first copper layer surrounds a non-conductive polymer structure on the wafer. The non-conductive polymer structure is removed to form a primary cavity in the first copper layer. The wafer and the primary cavity are coated with a polymer layer. Regions of the polymer layer are removed to form a secondary cavity within and alongside the primary cavity. A metal layer is deposited on exposed electrically conductive areas of the wafer and within bounds of the secondary cavity. 
         [0008]    In one exemplary embodiment, the method further comprises removing the polymer layer and depositing a second copper layer to cover exposed electrically conductive areas of the wafer, the first copper layer, and the metal layer. The second copper layer is planarized so that an upper surface of the first copper layer is substantially exposed. Planarizing the second copper layer removes any of the metal layer above the upper surface of the first copper layer. The first and second copper layers are selectively etched to reveal a remaining portion of the metal layer. The remaining portion of the metal layer comprises a semiconductor probe tip. A cross-section of an apex of the semiconductor probe tip is narrower than a cross-section of a foot of the semiconductor probe tip. 
         [0009]    In an apparatus according to one embodiment of the present invention, the apparatus comprises a probe card comprising a probe. The probe comprises a probe tip. The probe tip comprises a foot with an arbitrarily sized cross-section, and an apex with an arbitrarily sized cross-section. The cross-section of the foot is wider than the cross-section of the apex. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    The present invention will be better understood from the following detailed description, taken in conjunction with the accompanying drawing figures in which like reference characters designate like elements and in which: 
           [0011]      FIG. 1  illustrates an exemplary schematic cross-section of a semiconductor probe tip in accordance with an embodiment of the present invention; 
           [0012]      FIGS. 2, 3, 4, and 5  illustrate exemplary schematic cross-sections of a semiconductor device illustrating the formation of a primary cavity during a process for fabricating a semiconductor probe tip in accordance with an embodiment of the present invention; 
           [0013]      FIGS. 6 and 7  illustrate exemplary schematic cross-sections along line A-A of  FIG. 8  of a semiconductor device illustrating the formation of a secondary cavity during a process for fabricating a semiconductor probe tip in accordance with an embodiment of the present invention; 
           [0014]      FIG. 8  illustrates an exemplary top-down view of the primary cavity and the secondary cavity of  FIG. 7  during the process for fabricating a semiconductor probe tip in accordance with an embodiment of the present invention; 
           [0015]      FIGS. 9, 10, 11, 12, and 13  illustrate exemplary schematic cross-sections of a semiconductor device illustrating the formation of a metallic structure in the primary and secondary cavities of  FIG. 7  during the process for fabricating a semiconductor probe tip in accordance with an embodiment of the present invention; 
           [0016]      FIG. 14  illustrates an exemplary three-dimensional view of a semiconductor probe tip in accordance with an embodiment of the present invention; and 
           [0017]      FIG. 15  illustrates an exemplary flow diagram, illustrating the steps to an exemplary process for forming a semiconductor probe tip in accordance with an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0018]    Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. While the invention will be described in conjunction with the preferred embodiments, it will be understood that they are not intended to limit the invention to these embodiments. On the contrary, the invention is intended to cover alternatives, modifications and equivalents, which may be included within the spirit and scope of the invention as defined by the appended claims. Furthermore, in the following detailed description of embodiments of the present invention, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, it will be recognized by one of ordinary skill in the art that the present invention may be practiced without these specific details. In other instances, well-known methods, procedures, components, and circuits have not been described in detail so as not to unnecessarily obscure aspects of the embodiments of the present invention. The drawings showing embodiments of the invention are semi-diagrammatic and not to scale and, particularly, some of the dimensions are for the clarity of presentation and are shown exaggerated in the drawing Figures. Similarly, although the views in the drawings for the ease of description generally show similar orientations, this depiction in the Figures is arbitrary for the most part. Generally, the invention can be operated in any orientation. 
       NOTATION AND NOMENCLATURE 
       [0019]    Some portions of the detailed descriptions, which follow, are presented in terms of procedures, steps, logic blocks, processing, and other symbolic representations of operations on data bits within a computer memory. These descriptions and representations are the means used by those skilled in the data processing arts to most effectively convey the substance of their work to others skilled in the art. A procedure, computer executed step, logic block, process, etc., is here, and generally, conceived to be a self-consistent sequence of steps or instructions leading to a desired result. The steps are those requiring physical manipulations of physical quantities. Usually, though not necessarily, these quantities take the form of electrical or magnetic signals capable of being stored, transferred, combined, compared, and otherwise manipulated in a computer system. It has proven convenient at times, principally for reasons of common usage, to refer to these signals as bits, values, elements, symbols, characters, terms, numbers, or the like. 
         [0020]    It should be borne in mind, however, that all of these and similar terms are to be associated with the appropriate physical quantities and are merely convenient labels applied to these quantities. Unless specifically stated otherwise as apparent from the following discussions, it is appreciated that throughout the present invention, discussions utilizing terms such as “processing” or “accessing” or “executing” or “storing” or “rendering” or the like, refer to the action and processes of a computer system, or similar electronic computing device, that manipulates and transforms data represented as physical (electronic) quantities within the computer system&#39;s registers and memories and other computer readable media into other data similarly represented as physical quantities within the computer system memories or registers or other such information storage, transmission or display devices. When a component appears in several embodiments, the use of the same reference numeral signifies that the component is the same component as illustrated in the original embodiment. 
         [0021]    As discussed herein, there are many challenges inherent in manufacturing a conical or pyramid-shaped probe tip through photolithographic techniques alone. For example, following conventional photolithography techniques, an apex of a probe tip may be formed that is not that much narrower than the probe tip&#39;s foot. Such exemplary probe tip structures are generally two dimensional structures that are extruded in a third direction. When a photoresist window or cavity is filled with a metal to form the probe tip, the probe tip will be shaped as a cube or a rectangular shape (following the same dimensions as the cavity in the photoresist). In other words, there are tradeoffs: if a probe tip is designed to have a large surface area at the foot (to provide robustness to the probe tip and a generous amount of gluing surface between the probe tip foot and an underlying surface), the resulting apex that contacts an electrical feature of interest will have approximately the same cross-section as the base, and such a cross-section may be too large for the apex. 
         [0022]    This present invention provides a solution to the increasing challenges inherent in manufacturing semiconductor probe tips. Various embodiments of the present disclosure provide an exemplary probe tip with a foot with an arbitrarily wide cross-section and an apex with an arbitrarily narrow cross-section. The cross-section of the apex may be narrower than the cross-section of the foot. Embodiments of the present invention, as discussed herein, circumvent the previously mentioned limitations by using a manufacturing process capable of producing probe tips with arbitrarily small apex and arbitrarily large feet. As discussed in detail herein, arbitrary dimensions for the foot and the apex are provided through manufacturing steps that utilize a primary cavity and a secondary cavity, and where a sidewall of the secondary cavity comprises a conductive surface. 
         [0023]    As discussed in detail below, the resulting mold or cavity will comprise a conductive sidewall, with the remaining sidewalls non-conductive. In other words, in addition to the bottom of the cavity, one of the sidewalls will also be conductive. Therefore, during an exemplary electroplating process, a metal layer may grow from the bottom of the cavity, directly on the conductive portions of substrate, as well as on the conductive sidewall of the cavity. As discussed herein, when one of the four sides of a photoresist cavity is replaced with a conductive material, an exemplary electroplating process may grow a metal layer from the bottom of the photoresist cavity as well as from the conductive sidewall of the cavity. In one embodiment, such a metal layer will form a contiguous, L-shaped metal layer. 
         [0024]    As discussed herein, an exemplary tip  100  is a part of a probe that engages mechanically with a semiconductor chip, and under favorable circumstances, establishes electrical contact with the semiconductor chip for the duration of the test. In one embodiment, the tip  100  will mechanically engage with electrical structures on the semiconductor chip, such as pads and solder bumps. In one embodiment, an apex  102  of the tip  100  refers to a distal part of the tip  100 , that is, a part of the tip  100  that engages with a semiconductor chip. A foot  104  of the tip  100  refers to a proximal part of the tip  100 , that is, a part of the tip  100  that is mechanically attached to the rest of the probe. In one embodiment, a structure of interest, such as an electrical pad may be recessed and surrounded by a wall of dielectric or passivation material. Therefore, in one embodiment, an apex  102  may have a sufficient height above a foot  104  to ensure that as the apex  102  penetrates an opening in a dielectric or passivation layer of several microns surrounding an electrical structure of interest, the apex  102  will be able to engage with a surface of the electrical structure of interest without the foot  104  coming into contact with the surrounding dielectric or passivation layers. 
         [0025]      FIGS. 2-7  illustrate exemplary cross-sectional views of a fabrication process for manufacturing an exemplary semiconductor probe tip. In  FIG. 2 , a polymer structure  201  and a conductive layer  202   b  are formed on a wafer  202   a . In one embodiment, a wafer  202   a  refers to a slice of semiconductor or insulating material, such as silicon, ceramic or glass. In one embodiment, the wafer  202   a  may be coated with one or more conductive layers  202   b , including but not limited to: gold, copper, and nickel. The wafer  202   a  and the conductive layers  202   b  may be collectively referred to as a substrate  202 . 
         [0026]    In one embodiment, the polymer structure  201  is made of a non-conductive polymer. In one embodiment, the polymer structure  201  is fabricated using photolithographic techniques. Conditions of the photolithographic process may generally influence the verticality of sidewalls  204  of the polymer structure  201 . For example, the sidewalls  204  may form an angle as small as 80 degrees and as large as 100 degrees with a surface of the substrate  202 . As discussed herein, the polymer structure  201  may be any arbitrary shape and size as determined through exemplary photolithographic process steps. Depending on the requirements of the application, one or more similar structures may be built simultaneously. 
         [0027]    As illustrated in  FIG. 3 , a layer of copper (Cu)  301  may be deposited onto the conductive layers  202   b  of the substrate  202 . Using electroplating techniques, it is possible to restrict the growth of copper to regions of the substrate  202  that are electrically conductive and directly exposed to the plating process that is devoid of polymer structures, such as the polymer structure  201 . As illustrated in  FIG. 3 , during the electroplating processing, a copper layer  301  is deposited on any electrically conductive surface (e.g., the conductive layers  202   b  of the substrate  202 ), such that the copper layer  301  surrounds the polymer structure  201 . 
         [0028]      FIG. 4  illustrates a cross-sectional view of an exemplary copper layer  401  after the original copper layer  301  (illustrated in  FIG. 3 ) has been subjected to a planarization process. In one embodiment, the planarization process may utilize one or more techniques such as polishing, lapping or fly-cutting. Such planarization processes may be used to control and define a thickness  403  of the copper layer  401 . 
         [0029]    As illustrated in  FIG. 5 , the polymeric structure  201 , illustrated in  FIGS. 2-4 , may be removed, leaving a negative space  501  with a predictable size and shape. In  FIG. 5 , the negative space  501  is indicated with a dotted line. In one embodiment, the negative space  501  replicates with a desired level of fidelity a shape and size of the removed polymer structure  201 . Hereinafter, the negative space  501  is also referred to as a primary cavity  501 . 
         [0030]    As illustrated in  FIG. 6 , the substrate  202 , the copper layer  401 , and the primary cavity  501  may be coated with a polymer layer  601 . In one example, the polymer of choice may be a photosensitive epoxy with a level of viscosity chosen so as to fill-up the primary cavity  501 , as well as resulting in a coating substantially flat. As illustrated in  FIG. 6 , the polymer layer responds with a plastic flow so as to fill the primary cavity  501  on the exposed conductive surface of the substrate  202 . 
         [0031]    As illustrated in  FIG. 7 , regions of the polymer  601  may be removed, using, for example, a photolithographic process, leaving a second negative space  701 , also referred to as a secondary cavity  701 . The secondary cavity  701  is represented in  FIG. 7  with a dashed line (with the primary cavity  501  still represented by a dotted line). In one embodiment, illustrated in  FIG. 7 , the bounds of the secondary cavity  701  extend geographically from a location situated within the bounds of the primary cavity  501 , to a location situated on the copper regions  401  surrounding the primary cavity  501 . As illustrated in  FIG. 7 , a left-hand sidewall of the secondary cavity  701  is a sidewall  603  of the polymer layer  601 , while a right-hand sidewall of the secondary cavity  701  is a right-hand step comprising a portion of the copper layer  401  and a sidewall  605  of the polymer layer  601 . Therefore, as illustrated in  FIG. 7 , while the left-hand sidewall of the secondary cavity  701  comprises a non-conductive sidewall (formed from sidewall  603  of the polymer layer  601 ), the right-hand sidewall of the secondary cavity  701  comprises a conductive portion (formed from the copper layer  401 ) and a non-conductive portion (formed from the sidewall  605  of the polymer layer  601 ). 
         [0032]    While  FIG. 7  illustrates a cross-section of an exemplary primary cavity  501  and secondary cavity  701 ,  FIG. 8  illustrates a top-down view of a possible geometry  801  for the secondary cavity  701 , represented by a solid line, and a possible geometry  802  of the primary cavity  501 , represented by double dashed lines. In one embodiment, the cross-section illustrated in  FIG. 7 , is taken at line A-A in  FIG. 8 . 
         [0033]    As illustrated in  FIG. 8 , portions of the primary cavity  501  that remain buried under the polymer  601  are defined by the double dashed lines  802  and the solid line  801 . In other words, the portions of the primary cavity  501  that are buried under the polymer layer  601  lie between the outline of the exemplary geometry  802  of the primary cavity  501  and the outline of the exemplary geometry  801  of the secondary cavity  701 . As illustrated in  FIG. 8 , the buried portion  803  of the primary cavity  501  is shaded. 
         [0034]    As illustrated in  FIG. 9 , after the secondary cavity  701  has been formed, a metal layer  901  may be deposited into the primary cavity  701 . In one embodiment, as illustrated in  FIG. 9 , a metal layer  901  is deposited on the substrate  202 . As illustrated in  FIG. 9 , the metal layer  901  is deposited on an exposed portion of the conductive layer  202   b  of the substrate  202 . Using electroplating, it is possible to limit a growth of the electroplated material to only regions of the wafer  202  within the bounds of the secondary cavity  701 . 
         [0035]    As illustrated in  FIG. 9 , it is therefore possible to grow a continuous metal structure  901  which extends from the bottom of a portion of the primary cavity  501  (as defined by the secondary cavity  701 ), continues along one or more sections of the sidewalls of the primary cavity  501 , as well as on regions of the copper layer  401  that surrounds the primary cavity  501 . Using electroplating, it is also possible to control the nature, composition, and thickness of the metal layer  901 . In one exemplary embodiment, the metal layer  901  is made out of rhodium, nickel, gold, or nickel/rhodium. In another embodiment, the metal layer  901  is comprised of two or more layers of similar or dissimilar materials. As illustrated in  FIG. 9 , the electroplating may deposit a metal layer  901  on the exposed conductive layer  202   b  of the substrate  202 , a sidewall of the copper layer  401 , and along an exposed portion of a top surface of the copper layer  401 . In one exemplary embodiment, as illustrated in  FIG. 9 , the metal layer  901  comprises a contiguous S-shape. 
         [0036]    As illustrated in  FIG. 10 , after the metal layer  901  has been formed, the polymer layer  601  (that was used to form the secondary cavity  701 ) may be removed. In one embodiment, the polymer layer  601  is removed with a solvent. 
         [0037]    As illustrated in  FIG. 11 , a layer of copper  1101  may be deposited to coat the remaining exposed conductive surfaces. As illustrated in  FIG. 11 , the electroplating deposits a copper layer  1101  over the original copper layer  401 , over an exposed portion of the conductive layer  202   b  of the substrate  202 , and over the metal layer  901 . In one embodiment, the layer of copper  1101  is deposited by submerging the semiconductor device into a plating solution of copper to encapsulate the substrate  202  and exposed layers in a copper layer  1101 . 
         [0038]    As illustrated in  FIG. 12 , after the copper layer  1101  has been deposited, the copper layer  1101  and the metal layer  901  may be subjected to a planarization process. In one embodiment, an upper surface of the copper layer  1101  is subjected to planarization techniques, such as lapping, polishing, and/or grinding. The above described planarization process continues until an upper surface of the first copper layer  401  is substantially exposed and only a portion of the copper layer  1101  remains as a second copper layer  1201  around the metal layer  901 , but below the upper surfaces of the first copper layer  401 . As illustrated in  FIG. 12 , after the planarization process, the copper layer  1101  has been removed from above the copper layer  401 . As illustrated in  FIG. 12 , in one embodiment, a portion of the metal layer  901  deposited above the first copper layer  401  is also removed during the planarization process. 
         [0039]    As illustrated in  FIG. 13 , after the copper layer  1101  and the metal layer  901  have been planarized as illustrated in  FIG. 12 , the first copper layer  401  and the second copper layer  1201  may be selectively etched to reveal what remains of the metal layer  901 . In one embodiment, the remaining metal layer  901  comprises a probe tip  1301  with an L-shaped configuration. In one embodiment, the probe tip  1301  is a contiguous L-shaped structure. As illustrated in  FIG. 13 , the probe tip  1301  comprises a foot  1302  and an apex  1303 . As also illustrated in  FIG. 13 , a side  1304  of the tip  1301  represents a vertical section of the tip  1301  and defines an apex  1303  height above the foot  1302 . 
         [0040]      FIG. 14  illustrates an exemplary three-dimensional rendering of one possible probe tip geometry that may be achieved using the process described herein. As illustrated in  FIG. 14 , and discussed herein, an exemplary probe tip  1400  comprises a foot  1401  with a large cross-section for mechanical robustness and an apex  1402  with a small cross-section for enhanced probing capability. The foot in-plane geometry  1403 , illustrated in  FIG. 14 , is defined by the secondary cavity  701 , as illustrated in  FIGS. 7 and 8 . A thickness of the foot  1401  may be defined by controlling an electro-deposition process that deposits the metal layer  901 . As discussed herein, an apex in-plane geometry  1404  may be defined during the fabrication process leading to the creation of the secondary cavity  701 , as illustrated in  FIGS. 7 and 8 . In one embodiment, an apex cross-section  1404  width may range from a few microns to several tens of microns. As also illustrated in  FIG. 14 , a height  1405  of the apex  1402  above the foot  1401  of the probe tip  1400  may be defined by an amount of material deposited during the metal deposition step, as well as by a selected thickness of the first copper layer  401 . 
         [0041]    As discussed herein, the height of the apex  1402  above the foot  1401  may be selected to ensure that the apex  1402  is able to adequately engage a target electrical contact, pad, or solder bump without interference from the foot  1401 . In one embodiment, a location of interest in a semiconductor device that will be engaged by a probe tip  1400  may be covered by an oxidized layer. In one embodiment, the location of interest may also be surrounded by a wall of oxidized material. Therefore, as discussed herein, the height  1405  of the apex  1402  above the foot  1401  needs to be sufficient so that the foot  1401  of the probe tip does not contact the oxidized material. 
         [0042]      FIG. 15  illustrates exemplary steps to a process for fabricating a probe tip with a contiguous L-shape, using exemplary lithographic processes. In step  1502  of  FIG. 15 , a non-conductive polymer structure is formed on a wafer. In one embodiment, the non-conductive polymer structure is a rectangular shape. In one embodiment, the wafer comprises a substrate and a layer of conductive material. 
         [0043]    In step  1504  of  FIG. 15 , a first copper layer is deposited on exposed electrically conductive areas of the wafer. As discussed herein, the first copper layer will not be deposited onto the non-conductive polymer structure. In step  1506  of  FIG. 15 , an upper surface of the copper layer is planarized. 
         [0044]    In step  1508  of  FIG. 15 , the polymeric structure is removed to form a primary cavity in the first copper layer. In one embodiment, the primary cavity comprises a conductive bottom side and four conductive sidewalls. 
         [0045]    In step  1510  of  FIG. 15 , the wafer and first copper layer are coated with a polymer layer. In step  1512  of  FIG. 15 , portions of the polymer layer are removed to form a secondary cavity. In one embodiment, the secondary cavity begins in the primary cavity and extends up a sidewall of the first copper layer and onto a top surface of the first copper layer. 
         [0046]    In step  1514  of  FIG. 15 , a metal layer is deposited on the surface of the wafer and within the bounds of the secondary cavity. In one embodiment, the metal layer is deposited using metal deposition processes such as electroplating. Therefore, as also illustrated in  FIG. 9 , the metal layer will only be deposited on exposed electrically conductive surfaces. Therefore, as illustrated in  FIG. 9 , the metal layer will be formed as an S-shaped layer covering the exposed bottom of the secondary cavity, the single conductive sidewall of the secondary cavity, and the exposed portion of the first copper layer. 
         [0047]    In step  1516  of  FIG. 15 , the polymer layer used to form the secondary cavity is removed. In step  1518  of  FIG. 15 , a second copper layer is deposited to coat any exposed electrically conductive surfaces. As illustrated in  FIG. 11 , the first copper layer  401 , the exposed portion of the conductive layer  202   b  of the substrate  202 , and the metal layer  901  are covered by the second copper layer  1101 . In step  1520  of  FIG. 15 , the surface of the second copper layer  1101  is planarized so that an upper surface of the first copper layer  401  is substantially exposed and a portion of the metal layer above the first copper layer  401  is removed. 
         [0048]    In step  1522  of  FIG. 15 , the first and second copper layers  401 ,  1101  are removed by selectively etching to reveal the metal layer  901  with a contiguous L-shape. 
         [0049]    Although certain preferred embodiments and methods have been disclosed herein, it will be apparent from the foregoing disclosure to those skilled in the art that variations and modifications of such embodiments and methods may be made without departing from the spirit and scope of the invention. It is intended that the invention shall be limited only to the extent required by the appended claims and the rules and principles of applicable law.