WO2005101499A2

WO2005101499A2 - Methods of forming solder bumps on exposed metal pads and related structures

Info

Publication number: WO2005101499A2
Application number: PCT/US2005/012029
Authority: WO
Inventors: J. Daniel Mis
Original assignee: Unitive International Limited
Priority date: 2004-04-13
Filing date: 2005-04-12
Publication date: 2005-10-27
Also published as: US20050245066A1; US7358174B2; WO2005101499A3; TW200603698A

Abstract

A method of forming an electronic structure may include providing a substrate having a metal pad thereon. A conductive barrier layer may be formed on a first portion of the metal pad, and a second exposed portion of the metal pad may be free of the conductive barrier layer. In addition, an interconnection structure may be provided on the conductive barrier layer with the conductive barrier layer being between the interconnection structure and the metal pad. Moreover, the interconnection structure and the conductive barrier layer may include different materials. Related structures are also discussed.

Description

METHODS OF FORMING SOLDER BUMPS ON EXPOSED METAL PADS AND RELATED STRUCTURES

Related Application [0001] This application claims the benefit of priority from U.S. Provisional Patent Application No. 60/561,863 filed on April 13, 2004, the disclosure of which is hereby incorporated herein by reference in its entirety.

Field Of The Invention [0002] The present application relates to the field of electronics, and more particularly, to methods of forming interconnection bumps and related structures.

Background Of The Invention [0003] C4 (Controlled-Collapse Chip Connection) is used to connect IC (integrated circuit) chips to substrates in electronic packages. Moreover, C4 is a flip-chip technology in which the interconnections may be provided using relatively small solder balls on the chip surface. Because it is an area array, C4 technology may provide relatively high densities for chip interconnections. [0004] C4 technology has been used since the 1960s and has proven reliable in the semiconductor field. Historically, PbSn (lead-tin) solder has been evaporated through a metal mask. In the 1990s, electrochemical fabrication of C4 interconnections was introduced. See, for example, M. Datta, et al., "Electrochemical Fabrication of Mechanically Robust PbSn Interconnections", J. Electrochem. Soc, 142, 3779 (1995), U.S. Pat. No. 5,162,257 to Yung, and WO 96/30933, the disclosures of which are hereby incorporated herein in their entirety by reference. Electroplating may be more extendible than evaporation to small C4-pad dimensions, and may provide closer pad spacing, larger wafers, and/or lower-melting solders (having a higher content of Sn). [0005] U.S. Patent No. 5,937,320 discusses barrier layers for electroplated PbSn eutectic solder joints. An electrochemically fabricated C4 interconnection may have a barrier layer between the electroplated tin-rich solder bump and the ball-limiting metallurgy that protects the terminal metal in the ball-limiting metallurgy from attack by the Sn in the solder. The barrier layer may be electroplated through the same photoresist mask as the solder and thus may not require a separate patterning step. A thin layer of electroplated nickel may serve as a reliable barrier layer between a copper-based ball- limiting metallurgy and a tin-lead (PbSn) eutectic C4 ball. U.S. Patent No. 6,622,907 discusses a sacrificial seed layer process for forming C4 solder balls. The disclosures of U.S. Patent No. 5,937,320 and U.S. Patent No. 6,622,907 are hereby incorporated herein in their entirety by reference.

Summary [0006] According to embodiments of the present invention, methods of forming an electronic structure may include providing a substrate having a metal pad thereon. A conductive barrier layer may be formed on a first portion of the metal pad with a second exposed portion of the metal pad remaining free of the conductive barrier layer. In addition, an interconnection structure may be provided on the conductive barrier layer so that the conductive barrier layer is between the interconnection structure and the metal pad and so that the interconnection structure and the conductive barrier layer include different materials. [0007] More particularly, forming the conductive barrier layer may include forming a conductive seed layer on the metal pad and on the substrate. The conductive barrier layer may be selectively formed on a portion of the conductive seed layer on the first portion of the metal pad so that a second portion of the seed layer on the second portion of the metal pad is free of the conductive barrier layer. The second portion of the seed layer may then be removed from the second portion of the metal pad after selectively forming the conductive barrier layer. Moreover, removing the second portion of the seed layer may include etching the second portion of the seed layer using an etch chemistry that etches at least a portion of the conductive seed layer preferentially with respect to the conductive barrier layer and the metal pad. [0008] The exposed second portion of the metal pad may surround the conductive barrier layer, or a portion of the conductive barrier layer may extend beyond an edge of the metal pad. In addition, an insulating passivation layer may be formed on the substrate surrounding the metal pad, with the insulating passivation layer extending on an edge portion of the metal pad so that the second portion of the metal pad is exposed between the conductive barrier layer and the insulating passivation layer. A portion of the conductive barrier layer may also extend on a portion of the insulating passivation layer. In addition or in alternatives, a center of the conductive barrier layer may be substantially aligned with respect to a center of the metal pad, or a center of the conductive barrier layer may be substantially offset with respect to a center of the metal pad. [0009] A second metal pad may also be provided on the substrate, and the first and second metal pads may be spaced apart. A second conductive barrier layer may also be formed on a portion of the second metal pad, and an alignment of the first conductive barrier layer relative to the first metal pad may be different than an alignment of the second conductive barrier layer relative to the second metal pad. For example, the first conductive barrier layer may be substantially aligned relative to the first metal pad, and the second conductive barrier layer may be substantially offset relative to the second metal pad. In an alternative, the first conductive barrier layer may be substantially offset in a first direction relative to the first metal pad, and the second conductive barrier layer may be substantially offset in a second direction relative to the second metal pad, and the first and second directions may be different. [0010] • The interconnection structure may include a solder bump and/or a copper post. In addition, the metal pad may include aluminum, copper, gold, and/or alloys thereof, the conductive barrier layer may include nickel, copper, and/or alloys thereof, and the interconnection structure may include solder and/or copper. The metal pad may include aluminum, and the conductive barrier layer may include nickel. [0011] According to additional embodiments of the present invention, an electronic structure may include a substrate having a metal pad thereon. A conductive barrier layer may be on a first portion of the metal pad with a second exposed portion of the metal pad being free of the conductive barrier layer. An interconnection structure may be provided on the conductive barrier layer so that the conductive barrier layer is between the interconnection structure and the metal pad and so that the interconnection structure and the conductive barrier layer include different materials. [0012] For example, the exposed second portion of the metal pad may surround the conductive barrier layer, or a portion of the conductive barrier layer may extend beyond an edge of the metal pad. In addition, an insulating passivation layer on the substrate may surround the metal pad, and the insulating passivation layer may extend on an edge portion of the metal pad so that the second portion of the metal pad is exposed between the conductive barrier layer and the insulating passivation layer. Moreover, a portion of the conductive barrier layer may extend on a portion of the insulating passivation layer. A center of the conductive barrier layer may be substantially aligned with respect to a center of the metal pad, or a center of the conductive barrier layer may be substantially offset with respect to a center of the metal pad. [0013] In addition, a second metal pad may be provided on the substrate with the first and second metal pads being spaced apart, and a second conductive barrier layer may be provided on a portion of the second metal pad. More particularly, an alignment of the first conductive barrier layer relative to the first metal pad may be different than an alignment of the second conductive barrier layer relative to the second metal pad. The first conductive barrier layer may be substantially aligned relative to the first metal pad, and the second conductive barrier layer may be substantially offset relative to the second metal pad. In an alternative, the first conductive barrier layer may be substantially offset in a first direction relative to the first metal pad, and the second conductive barrier layer may be substantially offset in a second direction relative to the second metal pad with the first and second directions being different. [0014] The interconnection structure may include a solder bump and/or a copper post, and a seed layer may be provided between the conductive barrier layer and the metal pad, with the seed layer and the conductive barrier layer including different materials. The metal pad may include aluminum, copper, gold, and/or alloys thereof; the conductive barrier layer may include nickel, copper, and/or alloys thereof; and the interconnection structure may include solder and/or copper. More particularly, the metal pad may include aluminum and the conductive barrier layer may include nickel. [0015] According to still additional embodiments of the present invention, methods of forming an electronic structure may include providing a substrate having a metal pad thereon. An underbump metallurgy layer may be formed on a surface of the metal pad with the metal pad being between the underbump metallurgy layer and the substrate. A barrier layer may be formed on the underbump metallurgy layer with the underbump metallurgy layer being between the barrier layer and the metal pad. Moreover, an entirety of the barrier layer may be conformal with respect to the surface of the metal pad, and the barrier layer and the underbump metallurgy layers may include different materials. In addition, a solder bump may be formed on the barrier layer with the barrier layer being between the solder bump and the underbump metallurgy layer, and the barrier layer and the solder bump may include different materials. [0016] According to yet additional embodiments of the present invention, methods of forming an electronic structure may include providing a substrate having a metal pad thereon. An underbump metallurgy layer may be formed on a surface of the metal pad with the metal pad being between the underbump metallurgy layer and the substrate. A barrier layer may be formed on the underbump metallurgy layer with the underbump metallurgy layer being between the barrier layer and the metal pad, and the barrier layer and the underbump metallurgy layer may include different materials. Moreover, a solder bump may be formed on the barrier layer with the barrier layer being between the solder bump and the underbump metallurgy layer. The barrier layer and the solder bump may include different materials, and a portion of the metal pad may be exposed adjacent to the underbump metallurgy layer, the barrier layer, and the solder bump. [0017] According to more embodiments of the present invention, an electronic structure may include a substrate having a metal pad thereon and an underbump metallurgy layer on a surface of the metal pad with the metal pad being between the underbump metallurgy layer and the substrate. A barrier layer may be provided on the underbump metallurgy layer with the underbump metallurgy layer being between the barrier layer and the metal pad. Moreover, an entirety of the barrier layer may be conformal with respect to the surface of the metal pad, and the barrier layer and the underbump metallurgy layers may include different materials. In addition, a solder bump ^• may be provided on the barrier layer with the barrier layer being between the solder bump and the underbump metallurgy layer, and the barrier layer and the solder bump may include different materials. [0018] According to still more embodiments of the present invention, an electronic structure may include a substrate having a metal pad thereon and an underbump metallurgy layer on a surface of the metal pad with the metal pad being between the underbump metallurgy layer and the substrate. A barrier layer may be provided on the underbump metallurgy layer with the underbump metallurgy layer being between the barrier layer and the metal pad, and the barrier layer and the underbump metallurgy layer may include different materials. In addition, a solder bump may be provided on the barrier layer with the barrier layer being between the solder bump and the underbump metallurgy layer. The barrier layer and the solder bump may include different materials, and a portion of the metal pad may be exposed adjacent to the underbump metallurgy layer, the barrier layer, and the solder bump.

Brief Description Of The Drawings [0019] Figures 1A-C are cross-sectional views illustrating steps of forming electronic structures according to embodiments of the present invention. [0020] Figures 2A-C are cross-sectional views illustrating steps of forming electronic structures according to additional embodiments of the present invention. [0021] Figures 3A-B are cross-sectional views illustrating steps of forming electronic structures according to still additional embodiments of the present invention. [0022] Figures 4A-C are cross-sectional views illustrating steps of forming electronic structures according to yet additional embodiments of the present invention. [0023] Figures 5, 6, and 7 are plan views of electronic structures according to embodiments of the present invention. [0024] Figure 8 is a cross-sectional view illustrating a plurality of interconnection structures on a substrate according to embodiments of the present invention. [0025] Figure 9 is a plan view illustrating an array of interconnection structures according to embodiments of the present invention. [0026] Figures 10A-B are respective plan and cross-sectional views illustrating a plurality of interconnection structures on a substrate according to embodiments of the present invention. Detailed Description [0027] The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. [0028] In the drawings, the thickness of layers and regions are exaggerated for clarity. It will also be understood that when an element such as a layer, region or substrate is referred to as being on another element, it can be directly on the other element or intervening elements may also be present. In contrast, if an element such as a layer, region or substrate is referred to as being directly on another element, then no other intervening elements are present. Similarly, when an element such as a layer, region or substrate is referred to as being coupled or connected to/with another element, it can be directly coupled or connected to/with the other element or intervening elements may also be present. In contrast, if an element such as a layer, region or substrate is referred to as being directly coupled or connected to/with another element, then no other intervening elements are present. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items. The symbol "/" is also used as a shorthand notation for "and/or". [0029] Furthermore, relative terms, such as beneath, upper, lower, top, and/or bottom may be used herein to describe one element's relationship to another element as illustrated in the figures. It will be understood that relative terms are intended to encompass different orientations of the device in addition to the orientation depicted in the figures. For example, if the device in one of the figures is turned over, elements described as below other elements would then be oriented above the other elements. The exemplary term below, can therefore, encompasses both an orientation of above and below. [0030] It will be understood that although the terms first and second are used herein to describe various regions, layers and/or sections, these regions, layers and/or sections should not be limited by these terms. These terms are only used to distinguish one region, layer or section from another region, layer or section. Thus, a first region, layer or section discussed below could be termed a second region, layer or section, and similarly, a second region, layer or section could be termed a first region, layer or section without departing from the teachings of the present invention. Like numbers refer to like .elements throughout. [0031] The terminology used herein is for the purpose of describing particular embodiments only and is hot intended to be limiting of the invention. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and/or "comprising," when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. As used herein, the term "laterally" refers to a direction parallel to a surface of a substrate or die on which solder has been plated. [0032] Unless otherwise defined, all terms (including 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. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. [0033] When forming a solder bump on an existing device (input/output) pad, the device (input/output) pad may be sealed with an underbump metallurgy and/or passivation layer so that portions of the device pad are protected from the solder bump and/or from the environment. Such a structure, however, may result in a solder bump with a dimension larger than an exposed portion of the device pad. Accordingly, shorts between adjacent solder bumps may occur during reflow if the solder bumps extend laterally taking on a super-hemispheric profile. [0034] A size of an exposed portion of an input/output pad may be reduced by forming and patterning an additional passivation layer thereon. In an alternative, an input/output pad may be reconfigured using a redistribution layer. Use of an additional passivation layer and/or a redistribution layer, however, may increase cost and/or complexity. [0035] Methods and structures according to some embodiments of the present invention may provide a solder bump with dimensions smaller than an exposed portion of the device pad on which the solder bump is formed. Accordingly, bumping on tighter pitch designs may be provided without requiring forming an additional passivation layer on the device pad before bumping. [0036] According to first embodiments of the present invention illustrated in the cross-sectional views of Figures 1 A and IB, a substrate 101 may be provided with a metal pad 103 thereon wherein the metal pad 103 is free of any passivation layer thereon. The substrate 101 may be an integrated circuit substrate including integrated circuit devices therein, and the metal pad 103 may provide electrical connection with integrated circuit devices of the substrate 101. More particularly, an exposed surface of the metal pad 103 may comprise aluminum, gold, copper, and/or alloys thereof. [0037] An underbump metallurgy (seed) layer 105 may then be formed on the metal pad 103 and on the substrate 101 to facilitate subsequent electroplating. The underbump metallurgy (seed) layer 105 may include an adhesion layer adjacent the substrate 101 and metal pad 103 and a conduction layer on the adhesion layer opposite the substrate 101 and metal pad 103. More particularly, the adhesion layer may include titanium-tungsten (TiW), and the conduction layer may include copper (Cu), Silver (Ag), gold (Au), Palladium (Pd), and/or alloys thereof. The underbump metallurgy (seed) layer 105 may also include an intermediate layer between adhesion and conduction layers, and the intermediate layer may include titanium (Ti) and/or titanium nitride (TiN). [0038] A plating stencil (mask) 107 is then formed on the underbump metallurgy (seed) layer 105, and a hole 108 in the plating stencil 107 exposes portions of the underbump metallurgy (seed) layer 105. More particularly, the hole 108 exposes an area of the underbump metallurgy (seed) layer 105 that is less than an area of the metal pad 103 so that portions of the metal pad 103 extend beyond boundaries of the hole 108 as shown in Figure 1 A. The plating stencil (mask) 107, for example, may be a layer of an organic or inorganic photo-imagable material such as photoresist, and the hole may be formed using photolithography. More particularly, the plating stencil (mask) 107 may be formed by spinning or laminating the material on the underbump metallurgy (seed) layer 105, baking the material, selectively exposing the material to radiation (such as light), and developing the material to form the hole 108. In addition or in an alternative, the plating stencil (mask) 107 may be formed using electro-deposition. [0039] A barrier layer 109 may then be selectively formed (such as by plating) on portions of the underbump metallurgy (seed) layer 105 exposed through the hole 108. The barrier layer 109, for example, may include nickel, copper, and/or alloys thereof. After plating the barrier layer 109, a solder bump 111 is plated in the hole 108 on the barrier layer 109. The solder bump 111 may include an alloy such as a tin-lead (SnPb) solder, or the solder bump 111 may be lead free. [0040] Once the barrier layer 109 and the solder bump 111 are plated, the plating stencil (mask) 107 can be removed as shown in Figure IB. As further shown in Figure IB, portions of the underbump metallurgy (seed) layer 105 not covered by the barrier layer 109 and/or solder bump 111 may be removed, and the solder bump 111 may be subjected to reflow to provide a solder ball. For example, exposed portions of the underbump metallurgy (seed) layer 105 may be removed using an etch chemistry that removes the underbump metallurgy (seed) layer selectively with respect to the barrier layer 109. Accordingly, the patterned underbump metallurgy (seed) layer 105 may be undercut with respect to the barrier layer 109. [0041] More particularly, the underbump metallurgy (seed) layer 105 may be removed using an etch chemistry that removes at least a remaining portion of the underbump metallurgy (seed) layer 105 selectively with respect to the metal pad 103.. For example, peroxide (H O₂) may be used to remove a TiW adhesion layer of the underbump metallurgy (seed) layer 105 selectively with respect to an aluminum (or other) pad metal 103. Reflow of the solder bump 111 may be performed after removing a ^• solder wettable conduction layer of the underbump metallurgy (seed) layer 105 but before removing a solder non- wettable adhesion layer of the underbump metallurgy (seed) layer 105 so that the solder bump 111 does not spread across exposed portions of the metal pad 103. [0042] In an alternative, the metal pad 103 may include a solder non-wettable metal (such as aluminum) on a surface thereof so that reflow of the solder bump 111 may be performed after removing the underbump metallurgy (seed) layer 105 without the solder bump 111 spreading across exposed portions of the metal pad 103. In another alternative, reflow of the solder bump 111 may be performed without flux to maintain an oxide thereon so that the solder bump 111 does not spread across an exposed wettable surface such as a conduction layer of the underbump metallurgy (seed) layer 105 (before removing exposed portions of the underbump metallurgy layer) or the metal pad 103 (after removing exposed portions of the underbump metallurgy layer). Reflow of the solder bump 111 may be performed above a liquidus temperature of the solder bump 111, or reflow of the solder bump 111 may not exceed a liquidus temperature of the solder bump 111. In yet another alternative, the solder bump 111 may not be subjected to reflow. [0043] As shown in Figure IB, central portions of the metal pad 103 may be covered by the remaining portions of the underbump metallurgy (seed) layer 105, the barrier layer 109, and the solder bump 111. Edge portions of the metal pad 103, however, may remain exposed after forming the barrier layer 109 and the solder bump 111, and/or after reflowing the solder bump 111. [0044] As further shown in Figures 1 A and IB, the metal pad 103 may be considered to be "above" a surface of the substrate because an entirety of the metal pad 103 may be exposed before forming the underbump metallurgy (seed) layer 105, the barrier layer 109, and the solder bump 111. Accordingly, a surface portion of the substrate 101 may include an insulating passivation layer, and a hole and/or conductive via through the passivation layer may provide electrical coupling between the metal pad 103 and an electronic circuit(s) of the substrate 101. According to some embodiments shown in Figure IB, an entirety of the patterned underbump metallurgy (seed) layer 105 and an entirety of the barrier layer 109 may be conformal with respect to the metal pad 103 such that neither extends beyond an edge of the metal pad. According to other embodiments shown in the cross-sectional views of Figures IB and IC, portions of the patterned underbump metallurgy (seed) layer 105 and the barrier layer 109 (shown in the cross-sectional view of Figure IC) may extend beyond edges of the metal pad 103 while other portions of the patterned underbump metallurgy (seed) layer and barrier layer (shown in the cross-sectional view of Figure IB) are set back from edges of the metal pad. [0045] If the metal pad 103 is square and each of the patterned underbump metallurgy layer 105, the barrier layer 109, and the solder bump 111 are maintained within the metal pad 103,'the solder bump 111 may have a circular footprint as shown, for example, in Figure 5. In other embodiments, Figure IC may be a cross-sectional view taken at an angle with respect to the cross-section of Figure IB. As shown in Figure IC, portions of the patterned underbump metallurgy (seed) layer 105, the barrier layer 109, and the solder bump 111 may extend beyond the metal pad 103 onto the substrate 103. If the metal pad 103 is square when viewed from the top, and the cross-sections of Figures IB and IC are at an angle of 45 degrees with respect to each other, the solder bump 111 may have a circular footprint as shown, for example, in Figure 6. If the metal pad 103 is square when viewed from the top, and the cross-sections of Figures IB and IC are at an angle of 90 degrees with respect to each other, the solder bump 111 may have an oval footprint as shown, for example in Figure 7. [0046] In alternatives, the underbump metallurgy (seed) layer 105 may be patterned using the barrier layer 109 without the solder bump 111. The barrier layer 109, for example, may be selectively formed (such as by plating) on the underbump metallurgy (seed) layer 105, and portions of the underbump metallurgy (seed) layer 105 exposed by the barrier layer 109 may be selectively removed. After exposed portions of the underbump metallurgy (seed) layer 105 have been selectively removed, a solder bump or other interconnection structure may be provided on the barrier layer 109. For example, a solid preformed solder structure may be placed on the barrier layer 109, and/or the barrier layer 109 may be bonded with a solder structure on a second substrate. [0047] In addition or in an alternative, a conductive post (such as a copper post) may be provided on the barrier layer 109 instead of the solder bump 111 or between the barrier layer 109 and the solder bump 111. A conductive posit may be selectively formed on the barrier layer 109 (such as by plating using plating stencil 107) before selectively removing exposed portions of the underbump metallurgy (seed) layer 105, and/or a conductive post may be placed on the barrier layer 109 after selectively removing exposed portions of the underbump metallurgy (seed) layer 105. A solder structure may then be formed on the conductive post, and/or a solid preformed solder structure may be placed on the conductive post. In an alternative, the conducive post may be bonded with a solder structure on a second substrate. [0048] According to second embodiments of the present invention illustrated in the cross-sectional views of Figures 2A and 2B, a substrate 201 may be provided with a metal pad 203 and an inorganic dielectric passivation layer 204 (such as silicon oxide layer) thereon. For example, the inorganic passivation layer 204 may be formed over the substrate 201 and the metal pad 203 and then patterned to expose portions of the metal pad 203. The substrate 201 may be an integrated circuit substrate including integrated circuit devices therein, and the metal pad 203 may provide electrical connection with integrated circuit devices of the substrate 201. More particularly, an exposed surface of the metal pad 203 may comprise aluminum, gold, copper, and/or alloys thereof. [0049] An underbump metallurgy (seed) layer 205 may then be formed on the metal pad 203 and on the inorganic passivation layer 204 to facilitate subsequent electroplating. The underbump metallurgy (seed) layer 205 may include an adhesion layer adjacent the passivation layer 204 and metal pad 203 and a conduction layer on the adhesion layer opposite the passivation layer 204 and metal pad 203. More particularly, the adhesion layer may include titanium-tungsten (TiW), and the conduction layer may include copper (Cu), Silver (Ag), gold (Au), Palladium (Pd), and/or alloys thereof. The underbump metallurgy (seed) layer 205 may also include an intermediate layer between adhesion and conduction layers, and the intermediate layer may include titanium (Ti) and/or titanium nitride (TiN). [0050] A plating stencil (mask) 207 is then formed on the underbump metallurgy (seed) layer 205, and a hole 208 in the plating stencil 207 exposes portions of the underbump metallurgy (seed) layer 205. More particularly, the hole 208 exposes an area of the underbump metallurgy (seed) layer 205 that is less than an area of the metal pad 203 exposed by the passivation layer 204 so that portions of the metal pad 203 exposed by the passivation layer 204 extend beyond boundaries of the hole 208 as shown in Figure 2A. The plating stencil (mask) 207, for example, may be a layer of an organic or inorganic photo-imagable material such as photoresist, and the hole may be formed using photolithography. More particularly, the plating stencil (mask) 207 may be formed by spinning or laminating the material on the underbump metallurgy (seed) layer 205, baking the material, selectively exposing the material to radiation (such as light), and developing the material to form the hole 208. In addition or in an alternative, the plating stencil (mask) 207 may be formed using electro-deposition. [0051] A barrier layer 209 may then selectively formed (such as by plating) on portions of the underbump metallurgy (seed) layer 205 exposed through the hole 208. The barrier layer 209, for example, may include nickel, copper, and/or alloys thereof. After plating the barrier layer 209, a solder bump 211 is plated in the hole 208 on the barrier layer 209. The solder bump 211 may include an alloy such as a tin-lead (SnPb) solder, or the solder bump 211 may be lead free. [0052] Once the barrier layer 209 and the solder bump 211 are plated, the plating stencil (mask) 207 can be removed as shown in Figure 2B. As further shown in Figure 2B, portions of the underbump metallurgy (seed) layer 205 not covered by the barrier layer 209 and/or solder bump 211 may be removed, and the solder bump 211 may be subjected to reflow to provide a solder ball. For example, exposed portions of the underbump metallurgy (seed) layer 205 may be removed using an etch chemistry that removes the underbump metallurgy (seed) layer selectively with respect to the barrier layer 209. Accordingly, the patterned underbump metallurgy (seed) layer 205 may be undercut with respect to the barrier layer 209. [0053] More particularly, the underbump metallurgy (seed) layer 205 may be removed using an etch chemistry that removes at least a remaining portion of the underbump metallurgy (seed) layer 205 selectively with respect to the metal pad 203. For example, peroxide (H O₂) may be used to remove a TiW adhesion layer of the underbump metallurgy (seed) layer 205 selectively with respect to an aluminum (or other) pad metal 203. Reflow of the solder bump 211 may be performed after removing a solder wettable conduction layer of the underbump metallurgy (seed) layer 205 but before removing a solder non- wettable adhesion layer of the underbump metallurgy (seed) layer 205 so that the solder bump 211 does not spread across exposed portions of the metal pad 203. [0054] In an alternative, the metal pad 203 may include a solder non-wettable metal (such as aluminum) on a surface thereof so that reflow of the solder bump 211 may be performed after removing the underbump metallurgy (seed) layer 205 without the solder bump 211 spreading across exposed portions of the metal pad 203. In another alternative, reflow of the solder bump 211 may be performed without flux to maintain an oxide thereon so that the solder bump 211 does not spread across an exposed wettable surface such as a conduction layer of the underbump metallurgy (seed) layer 205 (before removing exposed portions of the underbump metallurgy layer) or the metal pad 203 (after removing exposed portions of the underbump metallurgy layer). Reflow of the solder bump 211 may be performed above a liquidus temperature of the solder bump 211, or reflow of the solder bump 211 may not exceed a liquidus temperature of the solder bump 211. In yet another alternative, the solder bump 211 may not be subjected to reflow. [0055] As shown in Figure 2B, edge portions of the metal pad 203 may be covered by the passivation layer 204, and central portions of the metal pad 203 may be covered by the remaining portions of the underbump metallurgy (seed) layer 205, the barrier layer 209, and the solder bump 211. Portions of the metal pad 203 between the passivation layer 204 and the patterned underbump metallurgy layer 205, however, may remain exposed after forming the barrier layer 209 and the solder bump 211, and/or after reflowing the solder bump 211. [0056] As further shown in Figures 2A and 2B, the metal pad 203 may be considered to be "below" or "beneath" a surface of the substrate because portions of the metal pad 203 may be covered by the passivation layer 204 before forming the underbump metallurgy (seed) layer 205, the barrier layer 209, and the solder bump 211. Stated in other words, the passivation layer 204 may be considered as a part of the substrate. According to some embodiments shown in Figure 2B, an entirety of the patterned underbump metallurgy (seed) layer 205 and an entirety of the barrier layer 209 may be conformal with respect to the metal pad 203 such that neither extends beyond an edge of the metal pad or onto the passivation layer. According to other embodiments shown in the cross-sectional views of Figure 2B and 2C, portions of the patterned underbump metallurgy (seed) layer 205 and the barrier layer 209 (shown in the cross- sectional view of Figure 2C) may extend to and/or overlap the passivation layer 204 while other portions of the patterned underbump metallurgy (seed) layer and barrier layer (shown in the cross-sectional view of Figure 2B) are set back from the passivation layer. [0057] If the metal pad 203 is square and each of the patterned underbump metallurgy layer 205, the barrier layer 209, and the solder bump 211 are maintained within the metal pad 203,' the solder bump 211 may have a circular footprint as shown, for example, in Figure 5. In other embodiments, Figure IC may be a cross-sectional view taken at an angle with respect to the cross-section of Figure IB. As shown in Figure IC, portions of the patterned underbump metallurgy (seed) layer 205, the barrier layer 209, and the solder bump 211 may extend beyond the metal pad 203 onto the passivation layer 204. If the metal pad 203 is square when viewed from the top, and the cross-sections of Figures IB and IC are at an angle of 45 degrees with respect to each other, the solder bump 211 may have a circular footprint as shown, for example, in Figure 6. If the metal pad 203 is square when viewed from the top, and the cross-sections of Figures IB and IC are at an angle of 90 degrees with respect to each other, the solder bump 211 may have an oval footprint as shown, for example in Figure 7. [0058] In alternatives, the underbump metallurgy (seed) layer 205 may be patterned using the barrier layer 209 without the solder bump 211. The barrier layer 209, for example, may be selectively formed (such as by plating) on the underbump metallurgy (seed) layer 205, and portions of the underbump metallurgy (seed) layer 205 exposed by the barrier layer 209 may be selectively removed. After exposed portions of the underbump metallurgy (seed) layer 205 have been selectively removed, a solder bump or other interconnection structure may be provided on the barrier layer 209. For example, a solid preformed solder structure may be placed on the barrier layer 209, and/or the barrier layer 209 may be bonded with a solder structure on a second substrate. [0059] In addition or in an alternative, a conductive post (such as a copper post) may be provided on the barrier layer 209 instead of the solder bump 211 or between the barrier layer 209 and the solder bump 211. A conductive post may be selectively formed on the barrier layer 209 (such as by plating using plating stencil 207) before selectively removing exposed portions of the underbump metallurgy (seed) layer 205, and/or a conductive post may be placed on the barrier layer 209 after selectively removing exposed portions of the underbump metallurgy (seed) layer 205. A solder structure may then be formed on the conductive post, and/or a solid preformed solder structure may be placed on the conductive post. In an alternative, the conducive post may be bonded with a solder structure on a second substrate. [0060] According to third embodiments of the present invention illustrated in the cross-sectional views of Figures 3 A and 3B, a substrate 301 may be provided with a metal pad 303 and an inorganic dielectric passivation layer 304a (such as silicon oxide layer) and an organic passivation layer 304b (such as polyimide) thereon. For example, the inorganic passivation layer 304a may be formed over the substrate 301 and the metal pad 303 and then patterned to expose portions of the metal pad 303. The organic passivation layer 304b may then be formed on the inorganic passivation layer 304a and on the metal pad 303 and patterned to expose portions of the metal pad 303. [0061] The substrate 301 may be an integrated circuit substrate including integrated circuit devices therein, and the metal pad 303 may provide electrical connection with integrated circuit devices of the substrate 301. More particularly, an exposed surface of the metal pad 303 may comprise aluminum, gold, copper, and/or alloys thereof. [0062] An underbump metallurgy (seed) layer 305 may then be formed on the metal pad 303 and on the organic passivation layer 304b to facilitate subsequent electroplating. The underbump metallurgy (seed) layer 305 may include an adhesion layer adjacent the organic passivation layer 304b and metal pad 303 and a conduction layer on the adhesion layer opposite the organic passivation layer 304b and metal pad 303. More particularly, the adhesion layer may include titanium-tungsten (TiW), and the conduction layer may include copper (Cu), Silver (Ag), gold (Au), Palladium (Pd), and/or alloys thereof. The underbump metallurgy (seed) layer 305 may also include an intermediate layer between adhesion and conduction layers, and the intermediate layer may include titanium (Ti) and/or titanium nitride (TiN). [0063] A plating stencil (mask) 307 is then formed on the underbump metallurgy (seed) layer 305, and a hole 308 in the plating stencil 307 exposes portions of the underbump metallurgy (seed) layer 305. More particularly, the hole 308 exposes an area of the underbump metallurgy (seed) layer 305 that no greater than an area of the metal pad 303 exposed by the organic passivation layer 304b so that portions of the underbump metallurgy (seed) layer 305 exposed by the hole 308 do not extend over the organic passivation layer 304b as shown in Figure 3 A. The plating stencil (mask) 307, for example, may be a layer of an organic or inorganic photo-imagable material such as photoresist, and the hole may be formed using photolithography. More particularly, the plating stencil (mask) 307 may be formed by spinning or laminating the material on the underbump metallurgy (seed) layer 305, baking the material, selectively exposing the material to radiation (such as light), and developing the material to form the hole 308. In addition or in an alternative, the plating stencil (mask) 307 may be formed using electro- deposition. [0064] A barrier, layer 309 may then be selectively formed (such as by plating) on portions of the underbump metallurgy (seed) layer 305 exposed through the hole 308. The barrier layer 309, for example, may include nickel, copper, and/or alloys thereof. After plating the barrier layer 309, a solder bump 311 is plated in the hole 308 on the barrier layer 309. The solder bump 311 may include an alloy such as a tin-lead (SnPb) solder, or the solder bump 311 may be lead free. [0065] Once the barrier layer 309 and the solder bump 311 are plated, the plating stencil (mask) 307 can be removed as shown in Figure 3B. As further shown in Figure 3B, portions of the underbump metallurgy (seed) layer 305 not covered by the barrier layer 309 and/or solder bump 311 may be removed, and the solder bump 311 may be subjected to reflow to provide a solder ball. For example, exposed portions of the underbump metallurgy (seed) layer 305 may be removed using an etch chemistry that removes the underbump metallurgy (seed) layer selectively with respect to the barrier layer 309. Accordingly, the patterned underbump metallurgy (seed) layer 305 may be undercut with respect to the barrier layer 309. [0066] More particularly, the underbump metallurgy (seed) layer 305 may be removed using an etch chemistry that removes at least a remaining portion of the underbump metallurgy (seed) layer 305 selectively with respect to the metal pad 303 and/or the organic passivation layer 304b. For example, peroxide (H₂O₂) may be used to remove a TiW adhesion layer of the underbump metallurgy (seed) layer 305 selectively with respect to an aluminum (or other) pad metal 303. Reflow of the solder bump 311 may be performed after removing a solder wettable conduction layer of the underbump metallurgy (seed) layer 305 but before removing a solder non-wettable adhesion layer of the underbump metallurgy (seed) layer 305 so that the solder bump 311 does not spread across exposed portions of the metal pad 303. [0067] In an alternative, the metal pad 303 may include a solder non-wettable metal (such as aluminum) on a surface thereof so that reflow of the solder bump 311 may be performed after removing the underbump metallurgy (seed) layer 305 without the solder bump 311 spreading across exposed portions of the metal pad 303. In another alternative, reflow of the solder bump 311 may be performed without flux to maintain an oxide thereon so that the solder bump 311 does not spread across an exposed wettable surface such as a conduction layer of the underbump metallurgy (seed) layer 305 (before removing exposed portions of the underbump metallurgy layer) or the metal pad 303 (after removing exposed portions of the underbump metallurgy layer). In still another alternative, the organic passivation layer 304b may act as a solder dam to confine the solder bump 311 during reflow. [0068] Reflow of the solder bump 311 may be performed above a liquidus temperature of the solder bump 311, or reflow of the solder bump 311 may not exceed a liquidus temperature of the solder bump 311. In yet another alternative, the solder bump 311 may not be subjected to reflow. [0069] As shown in Figure 3B, edge portions of the metal pad 303 may be covered by the organic passivation layer 304b, and central portions of the metal pad 303 may be covered by the remaining portions of the underbump metallurgy (seed) layer 305, the barrier layer 309, and the solder bump 311. According to particular embodiments of the present invention, an entirety of the surface of the metal pad 303 may be covered by the passivation layers 304a-b and the barrier layer. The barrier layer 309 and/or remaining portions of the underbump metallurgy (seed) layer 305, however, may not extend onto the organic passivation layer 304b. An integrity of the patterned underbump metallurgy (seed) layer 305, the barrier layer 309, and/or the solder bump 311 may thus be enhanced by not providing portions thereof on the potentially flexible organic passivation layer 304b. In an alternative, portions of the metal pad 303 between the passivation layer 304b and the patterned underbump metallurgy layer 305 may remain exposed after foπning the barrier layer 309 and the solder bump 311, and/or after reflowing the solder bump 311. [0070] As further shown in Figures 3 A and 3B, the metal pad 303 may be considered to be "below" or "beneath" a surface of the substrate because portions of the metal pad 303 may be covered by the passivation layers 304a and or 304b before forming the underbump metallurgy (seed) layer 305, the barrier layer 309, and the solder bump 311. Stated in other words, the passivation layers 304a and/or 304b may be considered as a part of the substrate. [0071] As shown in Figure 3B, the solder bump 311 may extend beyond the barrier layer 309 in a dimension parallel to the substrate after reflow. Accordingly, the solder bump 311 may partially overlap portions of the passivation layer 304b. If the passivation layer 304b exposes a square portion of the metal pad 303 and the barrier layer 309 and solder bump 311 are plated in a circular or oval hole 308 on a circular or oval portion of the metal pad 303, the solder bump 311 may overlap portions of the passivation layer 304b in some areas, and portions of the metal pad 303 may remain exposed in other areas, as illustrated, for example, in Figure 6 and/or Figure 7. According to some embodiments shown in Figure 3B, an entirety of the patterned underbump metallurgy (seed) layer 305 and an entirety of the barrier layer 309 may be conformal with respect to the metal pad 303 such that neither extends beyond an edge of the metal pad or onto the passivation layer. According to other embodiments shown in Figures 3B, portions of the patterned underbump metallurgy (seed) layer 305 and the barrier layer 309 (not shown in the cross-sectional view of Figure 3C) may extend to and/or overlap the passivation layers 704b and/or 704a while other portions of the patterned underbump metallurgy (seed) layer and barrier layer are set back from the passivation layer. [0072] In alternatives, the underbump metallurgy (seed) layer 305 may be patterned using the barrier layer 309 without the solder bump 311. The barrier layer 309, for example, may be selectively formed (such as by plating) on the underbump metallurgy (seed) layer 305, and portions of the underbump metallurgy (seed) layer 305 exposed by the barrier layer 309 may be selectively removed. After exposed portions of the underbump metallurgy (seed) layer 305 have been selectively removed, a solder bump or other interconnection structure may be provided on the barrier layer 309. For example, a solid preformed solder structure may be placed on the barrier layer 309, and/or the barrier layer 309 may be bonded with a solder structure on a second substrate. [0073] In addition or in an alternative, a conductive post (such as a copper post) may be provided on the barrier layer 309 instead of the solder bump 311 or between the barrier layer 309 and the solder bump 311. A conductive post may be selectively formed on the barrier layer 309 (such as by plating using plating stencil 307) before selectively removing exposed portions of the underbump metallurgy (seed) layer 305, and/or a conductive post may be placed on the barrier layer 309 after selectively removing exposed portions of the underbump metallurgy (seed) layer 305. A solder structure may then be formed on the conductive post, and/or a solid preformed solder structure may be placed on the conductive post. In an alternative, the conducive post may be bonded with a solder structure on a second substrate. [0074] According to fourth embodiments of the present invention illustrated in the cross-sectional views of Figures 4A and 4B, a substrate 401 may be provided with a metal pad 403 and an inorganic dielectric passivation layer 404a (such as silicon oxide layer) and an organic passivation layer 404b (such as polyimide) thereon. For example, the inorganic passivation layer 404a and the organic passivation layer 404b may be formed over the substrate 401 and the metal pad 403. Both the inorganic and organic passivation layers 404a-b may then be patterned using a single masking step to expose portions of the metal pad 403. [0075] The substrate 401 may be an integrated circuit substrate including integrated circuit devices therein, and the metal pad 403 may provide electrical connection with integrated circuit devices of the substrate 401. More particularly, an exposed surface of the metal pad 403 may comprise aluminum, gold, copper, and/or alloys thereof. [0076] An underbump metallurgy (seed) layer 405 may then be formed on the metal pad 403 and on the passivation layers 404a-b to facilitate subsequent electroplating. The underbump metallurgy (seed) layer 405 may include an adhesion layer adjacent the passivation layers 404a-b and metal pad 403 and a conduction layer on the adhesion layer opposite the passivation layers 404a-b and metal pad 403. More particularly, the adhesion layer may include titanium-tungsten (TiW), and the conduction layer may include copper (Cu), Silver (Ag), gold (Au), Palladium (Pd), and/or alloys thereof. The underbump metallurgy (seed) layer 405 may also include an intermediate layer between adhesion and conduction layers, and the intermediate layer may include titanium (Ti) and/or titanium nitride (TiN). [0077] A plating stencil (mask) 407 is then formed on the underbump metallurgy (seed) layer 405, and a hole 408 in the plating stencil 407 exposes portions of the underbump metallurgy (seed) layer 405. More particularly, the hole 408 exposes an area of the underbump metallurgy (seed) layer 405 that is less than an area of the metal pad 403 exposed by the passivation layers 404a-b so that portions of the underbump metallurgy (seed) layer 405 exposed by the hole 408 do not extend over the passivation layers 404a-b as shown in Figure 4A. The plating stencil (mask) 407, for example, may be a layer of an organic or inorganic photo-imagable material such as photoresist, and the hole may be formed using photolithography. More particularly, the plating stencil (mask) 407 may be formed by spinning or laminating the material on the underbump metallurgy (seed) layer 405, baking the material, selectively exposing the material to radiation (such as light), and developing the material to form the hole 408. In addition or in an alternative, the plating stencil (mask) 407 may be formed using electro-deposition. [0078] A barrier layer 409 may then be selectively formed (such as by plating) on portions of the underbump metallurgy (seed) layer 405 exposed through the hole 408. The barrier layer 409, for example, may include nickel, copper, and/or alloys thereof. After plating the barrier layer 409, a solder bump 411 is plated in the hole 408 on the barrier layer 409. The solder bump 411 may include an alloy such as a tin-lead (SnPb) solder, or the solder bump 411 may be lead free. [0079] Once the barrier layer 409 and the solder bump 411 are plated, the plating stencil (mask) 407 can be removed as shown in Figure 4B. As further shown in Figure 4B, portions of the underbump metallurgy (seed) layer 405 not covered by the. barrier layer 409 and/or solder bump 411 may be removed, and the solder bump 411 may be subjected to reflow to provide a solder ball. For example, exposed portions of the underbump metallurgy (seed) layer 405 may be removed using an etch chemistry that removes the underbump metallurgy (seed) layer selectively with respect to the barrier layer 409. Accordingly, the patterned underbump metallurgy (seed) layer 405 may be undercut with respect to the barrier layer 409. [0080] More particularly, the underbump metallurgy (seed) layer 405 may be . removed using an etch chemistry that removes at least a remaining portion of the underbump metallurgy (seed) layer 405 selectively with respect to the metal pad 403 and/or the organic passivation layer 404b. For example, peroxide (H₂O₂) may be used to remove a TiW adhesion layer of the underbump metallurgy (seed) layer 405 selectively with respect to an aluminum (or other) pad metal 403. Reflow of the solder bump 411 may be performed after removing a solder wettable conduction layer (such as copper) of the underbump metallurgy (seed) layer 405 but before removing a solder non-wettable adhesion layer (such as TiW) of the underbump metallurgy (seed) layer 405 so that the solder bump 411 does not spread across exposed portions of the metal pad 403. [0081] In an alternative, the metal pad 403 may include a solder non-wettable metal (such as aluminum) on a surface thereof so that reflow of the solder bump 411 may be performed after removing the underbump metallurgy (seed) layer 405 without the solder bump 411 spreading across exposed portions of the metal pad 403. In another alternative, reflow of the solder bump 411 may be performed without flux to maintain an oxide thereon so that the solder bump 411 does not spread across an exposed wettable surface such as a conduction layer of the underbump metallurgy (seed) layer 405 (before removing exposed portions of the underbump metallurgy layer) or the metal pad 403 (after removing exposed portions of the underbump metallurgy layer). Reflow of the solder bump 411 may be performed above a liquidus temperature of the solder bump 411, or reflow of the solder bump 411 may not exceed a liquidus temperature of the solder bump 411. In yet another alternative, the solder bump 411 may not be subjected to reflow. [0082] As shown in Figure 4B, edge portions of the metal pad 403 may be covered by the passivation layers 404a-b, and central portions of the metal pad 403 may be covered by the remaining portions of the underbump metallurgy (seed) layer 405, the barrier layer 409, and the solder bump 411. Portions of the metal pad 403 between the passivation layers 404a-b and the patterned underbump metallurgy layer 405, however, may remain exposed after forming the barrier layer 409 and the solder bump 411, and/or after reflowing the solder bump 411. [0083] As further shown in Figures 4A and 4B, the metal pad 403 may be considered to be "below" or "beneath" a surface of the substrate because portions of the metal pad 403 may be covered by the passivation layers 404a and/or 404b before foπning the underbump metallurgy (seed) layer 405, the barrier layer 409, and the solder bump 411. Stated in other words, the passivation layers 404a and/or 404b may be considered as a part of the substrate. According to some embodiments shown in Figure 4B, an entirety of the patterned underbump metallurgy (seed) layer 405 and an entirety of the barrier layer 409 may be conformal with respect to the metal pad 403 such that neither extends beyond an edge of the metal pad or onto the passivation layer. According to other embodiments shown in the cross-sectional views of Figures 4B and 4C, portions of the patterned underbump metallurgy (seed) layer 405 and the barrier layer 409 (shown in the cross-sectional view of Figure 4C) may extend to and/or overlap the passivation layers 404a and/or 404b while other portions of the patterned underbump metallurgy (seed) layer and barrier layer (shown in the cross-sectional view of Figure 4B) are set back from the passivation layer(s). [0084] If the exposed portion of the metal pad 403 is square and each of the patterned underbump metallurgy layer 405, the barrier layer 409, and the solder bump 411 are maintained within the exposed portion of the metal pad 403, the solder bump 411 may have a circular footprint as shown, for example, in Figure 5. In other embodiments, Figure IC may be a cross-sectional view taken at an angle with respect to the cross- section of Figure IB. As shown in Figure IC, portions of the patterned underbump metallurgy (seed) layer 405, the barrier layer 409, and the solder bump 411 may extend beyond the metal pad 403 onto the passivation layers 404a and 404b. If the metal pad 403 is square when viewed from the top, and the cross-sections of Figures IB and IC are at an angle of 45 degrees with respect to each other, the solder bump 411 may have a circular footprint as shown, for example, in Figure 6. If the metal pad 403 is square when viewed from the top, and the cross-sections of Figure^'s IB and IC are at an angle of 90 degrees with respect to each other, the solder bump 411 may have an oval footprint as shown, for example in Figure 7. [0085] In alternatives, the underbump metallurgy (seed) layer 405 may be patterned using the barrier layer 409 without the solder bump 411. The barrier layer 409, for example, may be selectively formed (such as by plating) on the underbump metallurgy (seed) layer 405, and portions of the underbump metallurgy (seed) layer 405 exposed by the barrier layer 409 may be selectively removed. After exposed portions of the underbump metallurgy (seed) layer 405 have been selectively removed, a solder bump or other interconnection structure may be provided on the barrier layer 409. For example, a solid preformed solder structure may be placed on the barrier layer 409, and/or the barrier layer 409 may be bonded with a solder structure on a second substrate. [0086] In addition or in an alternative, a conductive post (such as a copper post) may be provided on the barrier layer 409 instead of the solder bump 411 or between the barrier layer 409 and the solder bump 411. A conductive post may be selectively formed on the barrier layer 409 (such as by plating using plating stencil 407) before selectively removing exposed portions of the underbump metallurgy (seed) layer 405, and/or a conductive post may be placed on the barrier layer 409 after selectively removing exposed portions of the underbump metallurgy (seed) layer 405. A solder structure may then be formed on the conductive post, and/or a solid preformed solder structure may be placed on the conductive post. In an alternative, the conducive post may be bonded with a solder structure on a second substrate. [0087] As shown in the top view of Figure 5, edge portions of a metal pad 503 may be covered by a passivation layer 504, such as a passivation layer including one or more organic and/or inorganic dielectric layers. Moreover, a solder bump 511 may be formed on a central portion of the metal pad 503 according to embodiments of the present invention such that portions of the metal pad 503 are exposed between the passivation layer 504 and the solder bump 511. As discussed above with respect to Figures 1 A-B, 2A-B, 3 A-B, and 4A-B, an underbump metallurgy layer, a barrier layer, and/or a conductive post may be provided between the solder bump 511 and the metal pad 503, but the underbump metallurgy layer, the barrier layer, and/or the conductive post are not visible in the top view of Figure 5. The structure of Figure 5, for example, may be provided as discussed above with respect to Figures 1 A-B, 2A-B, 3A-B, and/or 4A-B. As discussed above, a conductive post (such as a copper post) may be provided in addition to or instead of the solder bump 711. [0088] As shown in the top view of Figure 6, edge portions of a metal pad 603 may be covered by a passivation layer 604, such as a passivation layer including one or more organic and/or inorganic dielectric layers. Moreover, a round solder bump 611 may be formed on a central portion of the metal pad 603 according to embodiments of the present invention such that portions of the metal pad 603 are exposed between the passivation layer 604 and the solder bump 611. As discussed above with respect to Figures 1 A-B, 2A-B, 3A-B, and 4A-B, an underbump metallurgy layer, a barrier layer, and/or a conductive post may be provided between the solder bump 611 and the metal pad 603, but the underbump metallurgy layer, the barrier layer, and/or the conductive post are not visible in the top view of Figure 6. In the structure of Figure 6, portions of the solder bump, the underbump metallurgy layer, the barrier layer, and/or the conductive post may extend to and/or overlap the passivation layer 604 while other portions of the solder bump 611, the underbump metallurgy layer, the barrier layer, and/or the conductive post are set back from the passivation layer 604. The structure of Figure 6, for example, may be provided as discussed above with respect to Figures 1 A-B, 2 A-B, 3A-B, and 4A-B. As discussed above, a conductive post (such as a copper post) may be provided in addition to or instead of the solder bump 711. [0089] As shown in the top view of Figure 7, edge portions of a metal pad 703 may be covered by a passivation layer 704, such as a passivation layer including one or more organic and/or inorganic dielectric layers. Moreover, an oval solder bump 711 may . be formed on a central portion of the metal pad 703 according to embodiments of the present invention such that portions of the metal pad 703 are exposed between the passivation layer 704 and the solder bump 711. As discussed above, an underbump metallurgy layer, a barrier layer, and/or a conductive post may be provided between the solder bump 711 and the metal pad 703, but the underbump metallurgy layer, the barrier layer, and/or the conductive post are.not visible in the top view of Figure 7. In the structure of Figure 7, portions of the solder bump, the underbump metallurgy layer, the barrier layer, and/or the conductive post may extend to and/or overlap the passivation layer 704 while other portions of the solder bump 711, the underbump metallurgy layer, the barrier layer, and/or the conductive post are set back from the passivation layer 704. More particularly, portions of the patterned underbump metallurgy (seed) layer, the barrier layer, and/or the conductive post may extend to and/or overlap the passivation layer 704 while other portions of the patterned underbump metallurgy (seed) layer, barrier layer, and/or conductive post are set back from the passivation layer. The structure of Figure 7, for example; may be provided as discussed above with respect to Figures 1 A-B, 2A-B, 3A-B, and 4A-B. As discussed above, a conductive post (such as a copper post) may be provided in addition to or instead of the solder bump 711. [0090] As shown in the cross-sectional view of Figure 8, solder bumps 811 provided according to embodiments of the present invention may allow a closer placement of metal pads 803 and solder bumps 811 to provide a tighter pitch on integrated circuit device 821. More particularly, the solder bumps 811 can be provided on central portions of the metal pads 803 -with portions of the metal pads 803 exposed adjacent to the solder bumps 811. Accordingly, shorting of adjacent solder bumps 811 can be reduced. Moreover, an additional passivation layer is not required to confine the solder within the central portion of the metal pad 803. [0091] As discussed above, the metal pads 803 are provided on substrate 801, and a passivation layer 804 may extend onto edge portions of the metal pads 803. The underbump metallurgy (seed) layer 805, the barrier layer 809, and the solder bump 811 may be formed as discussed above with regard to Figures 1 A-B, 2 A-B, 3 A-B, and/or 4A- B. In some embodiments, edge portions of the metal pads 803 may be free of the passivation layer 804 as discussed above with respect to Figures 1 A-B. [0092] Moreover, the metal pads 803 may be provided in staggered rows to further increase a pitch or density of the solder bumps 811 and/or to provide larger solder bumps 811 on the substrate 801. For example, metal pads 803 may be arranged in a checker board pattern as illustrated in the top view of Figure 9. A likelihood of shorts between solder bumps 811 may be reduced if one or more solder bumps 811 extends beyond the exposed portion of the respective metal pad 803 over the passivation layer 804. [0093] Figure 1 OA is a plan view of an electronic substrate including a plurality of interconnection structures on a substrate according to additional embodiments of the present invention, and Figure 10B is a cross-sectional view taken along section line I-I' of Figure 10A. In particular, portions of a plurality of metal pads 1003a-c may be exposed through a passivation layer 1004 on substrate 1001. As shown, edge portions of the metal pads 1003a-c may be covered by the passivation layer 1004. In other embodiments, edge portions of the metal pads 1003a-c may be free of the passivation layer 1004. Moreover, patterned seed layers 1005a-c and barrier layers 1009a-c may be provided between respective solder bumps lOlla-c and metal pads 1003a-c. Moreover, the passivation layer 1004 may include one or more orgnanic and/or inorganic dielectric layers. [0094] The structures of Figures 10 A-B may be formed as discussed above with regard to Figures 1 A-C, 2A-C, 3 A-B, and/or 4A-C. For example, a continuous underbump metallurgy (seed) layer may be formed on the passivation layer 1004 and metal pads 1003a-c to provide an electroplating electrode, and a plating stencil may be formed on the continuous underbump metallurgy (seed) layer. The plating stencil, for example, may expose circular areas of the continuous underbump metallurgy (seed) layer at least portions of which are on respective metal pads 1003a-c. The barrier layers -1009a-c can then be selectively formed (such as by plating) on exposed portions of the continuous underbump metallurgy layer. The plating stencil can then be removed, and portions of the continuous underbump metallurgy (seed) layer exposed by the barrier layers 1009a-c can be removed to provide the patterned underbump metallurgy (seed) layers 1005a-c. [0095] The solder bumps lOlla-c can be formed on the barrier layers, for example, by plating before removing the plating stencil and before removing exposed portions of the underbump metallurgy (seed) layer. In other embodiments, solid preformed solder structures may be placed on the barrier layers 1009a-c, and or the barrier layer 1009a-c may be bonded with solder structures on a second substrate. In still - other embodiments, conductive posts (such as copper posts) may be provided on the barrier layers 1009a-c instead of the solder bumps lOlla-c or between the barrier layers 1009a-c and the solder bumps lOlla-c. Conductive posts may be selectively formed on the barrier layers 1009a-c (such as by plating using the plating stencil) before selectively removing exposed portions of the continuous underbump metallurgy (seed) layer, and/or conductive posts may be placed on the barrier layers 1009a-c after selectively removing exposed portions of the continuous underbump metallurgy (seed) layer. Solder structures may then be formed on the conductive posts, and/or solid preformed solder structures may be placed on the conductive posts. In an alternative, the conducive posts may be bonded with solder structures on a second substrate. [0096] As shown in Figures 10A and 10B, relative placements of barrier layers 1009a-c solder bumps lOlla-c on respective metal pads 1003a-c may vary. For example, the barrier layer 1009b and solder bump 1011b may be substantially centered with respect to metal pad 1003b, while the barrier layers 1009a and 1009c and the solder bumps 1011a and 1001c may be offset in different directions relative to the metal pads 1003a and 1003b. Accordingly, barrier layers, solder bumps, and/or other interconnections structures may be redistributed with respect to metal pads without requiring redistribution lines and/or patterning thereof. [0097] Embodiments of the present invention may thus allow forming a solder bump on a metal input/output pad without completely sealing the metal input/output pad with the patterned underbump metallurgy (seed) layer, the barrier layer, and/or passivation. The patterned underbump metallurgy (seed) layer and the barrier layer may thus be contained within exposed portions of the metal input/output pad and/or portions of the underbump metallurgy (s,eed) layer and the barrier layer may extend beyond exposed portions of the metal input/output pad. For example, portions of an insulating passivation layer may extend between the metal input/output pad and edge portions of the underbump metallurgy (seed) layer and barrier layer, while other portions of the insulating passivation layer may be separated from the underbump metallurgy (seed) layer and the barrier layer by exposed portions of the metal input/output pad therebetween. Accordingly, the resulting solder bump may be smaller than an exposed portion of the corresponding metal input/output pad in one or more dimensions without requiring another passivation step. Accordingly, solder bumps can be formed on more closely spaced pads without requiring an additional passivation layer and with reduced risk of electrical shorts therebetween. [0098] While the present invention has been particularly shown and described with reference to embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims and their equivalents.

Claims

That Which Is Claimed Is:

1. A method of forming an electronic structure, the method comprising: providing a substrate having a metal pad thereon and an insulating layer surrounding the metal pad; forming a conductive barrier layer on a first portion of the metal pad, wherein a second exposed portion of the metal pad is free of the conductive barrier layer and free of the insulating layer; and providing an interconnection structure on the conductive barrier layer, wherein the conductive barrier layer is between the interconnection structure and the metal pad and wherein the interconnection structure and the conductive barrier layer include different materials.

2. A method of forming an electronic structure according to Claim 1 wherein forming the conductive barrier layer comprises, forming a conductive seed layer on the metal pad and on the insulating layer, selectively forming the conductive barrier layer on a portion of the conductive seed layer on the first portion of the metal pad so that a second portion of the seed layer on the second portion of the metal pad is free of the conductive barrier layer, and after selectively forming the conductive barrier layer, removing the second portion of the seed layer from the second portion of the metal pad.

3. A method according to Claim 2 wherein removing the second portion of the seed layer comprises etching the second portion of the seed layer using an etch chemistry that etches at least a portion of the conductive seed layer preferentially with respect to the conductive barrier layer and the metal pad.

4. A method according to Claim 1 wherein the exposed second portion of the metal pad surrounds the conductive barrier layer.

5. A method according to Claim 1 wherein a portion of the conductive barrier layer extends beyond an edge of the metal pad.

6. A method according to Claim 1 wherein the insulating layer extends on an edge portion of the metal pad opposite the substrate so that the second portion of the metal pad is exposed between the conductive barrier layer and the insulating layer.

7. A method according to Claim 1 wherein a portion of the conductive barrier layer extends on a portion of the insulating layer.

8. A method according to Claim 1 wherein a center of the conductive barrier layer is substantially aligned with respect to a center of the metal pad.

9. A method according to Claim 1 wherein a center of the conductive barrier layer is substantially offset with respect to a center of the metal pad.

10. A method according to Claim 1 further comprising: providing a second metal pad on the substrate, wherein the first and second metal pads are spaced apart; and forming a second conductive barrier layer on a portion of the second metal pad, wherein an alignment of the first conductive barrier layer relative to the first metal pad is different than an alignment of the second conductive barrier layer relative to the second metal pad.

11. A method according to Claim 10 wherein the first conductive barrier layer is substantially aligned relative to the first metal pad and wherein the second conductive barrier layer is substantially offset relative to the second metal pad.

12. A method according to Claim 10 wherein the first conductive barrier layer is substantially offset in a first direction relative to the first metal pad and wherein the second conductive barrier layer is substantially offset in a second direction relative to the second metal pad and wherein the first and second directions are different.

13. A method according to Claim 1 wherein the interconnection structure includes a solder bump and/or a copper post.

14. A method according to Claim 1 wherein the metal pad includes aluminum, copper, gold, and/or alloys thereof, wherein the conductive barrier layer includes nickel, copper, and/or alloys thereof, and wherein the interconnection structure includes solder and/or copper.

15. A method according to Claim 1 wherein the metal pad includes aluminum and the conductive barrier layer includes nickel.

16. A method according to Claim 1 wherein at least a portion of the metal pad is on a portion of the insulating layer so that a surface of the metal pad opposite the substrate is free of the insulating layer.

17. An electronic structure comprising: a substrate having a metal pad thereon and an insulating layer surrounding the metal pad; a conductive barrier layer on a first portion of the metal pad, wherein a second exposed portion of the metal pad is free of the conductive barrier layer and free of the insulating layer; and an interconnection structure on the conductive barrier layer, wherein the conductive barrier layer is between the interconnection structure and the metal pad and wherein the interconnection structure and the conductive barrier layer include different materials.

18. An electronic structure according to Claim 17 wherein the exposed second portion of the metal pad surrounds the conductive barrier layer.

19. An electronic structure according to Claim 17 wherein a portion of the conductive barrier layer extends beyond an edge of the metal pad.

20. An electronic structure according to Claim 17 wherein the insulating layer extends on an edge portion of the metal pad opposite the substrate so that the second portion of the metal pad is exposed between the conductive barrier layer and the insulating layer.

21. An electronic structure according to Claim 17 wherein a portion of the conductive barrier layer extends on a portion of the insulating layer.

22. An electronic structure according to Claim 17 wherein a center of the conductive barrier layer is substantially aligned with respect to a center of the metal pad.

23. An electronic structure according to Claim 17 wherein a center of the conductive barrier layer is substantially offset with respect to a center of the metal pad.

24. An electronic structure according to Claim 17 further comprising: a second metal pad on the substrate, wherein the first and second metal pads are spaced apart; and a second conductive barrier layer on a portion of the second metal pad, wherein an alignment of the first conductive barrier layer relative to the first metal pad is different than an alignment of the second conductive barrier layer relative to the second metal pad.

25. An electronic structure according to Claim 24 wherein the first conductive barrier layer is substantially aligned relative to the first metal pad and wherein the second conductive barrier layer is substantially offset relative to the second metal pad.

26. An electronic structure according to Claim 24 wherein the first conductive barrier layer is substantially offset in a first direction relative to the first metal pad and wherein the second conductive barrier layer is substantially offset in a second direction relative to the second metal pad and wherein the first and second directions are different.

27. An electronic structure according to Claim 17 wherein the interconnection structure includes a solder bump and or a copper post.

28. An electronic structure according to Claim 17 further comprising: a seed layer between the conductive barrier layer and the metal pad, wherein the seed layer and the conductive barrier layer include different materials.

29. An electronic structure according to Claim 17 wherein the metal pad includes aluminum, copper, gold, and/or alloys thereof, wherein the conductive barrier layer includes nickel, copper, and/or alloys thereof, and wherein the interconnection structure includes solder and/or copper.

30. An electronic structure according to Claim 17 wherein the metal pad includes aluminum and the conductive barrier layer includes nickel.

31. An electronic structure according to Claim 17 wherein at least a portion of the metal pad is on a portion of the insulating layer so that a surface of the metal pad opposite the substrate is free of the insulating layer.

32. A method of forming an electronic structure, the method comprising: providing a substrate having a metal pad thereon; forming an underbump metallurgy layer on a surface of the metal pad wherein the metal pad is between the underbump metallurgy layer and the substrate; forming a barrier layer on the underbump metallurgy layer wherein the underbump metallurgy layer is between the barrier layer and the metal pad, wherein an entirety of the barrier layer is conformal with respect to the surface of the metal pad, and wherein the barrier layer and the underbump metallurgy layers comprise different materials; and forming a solder bump on the barrier layer wherein the barrier layer is between the solder bump and the underbump metallurgy layer, and wherein the barrier layer and the solder bump comprise different materials.

33. A method of forming an electronic structure, the method comprising: providing a substrate having a metal pad thereon; forming an underbump metallurgy layer on a surface of the metal pad wherein the metal pad is between the underbump metallurgy layer and the substrate; forming a barrier layer on the underbump metallurgy layer wherein the underbump metallurgy layer is between the barrier layer and the metal pad, and wherein the barrier layer and the underbump metallurgy layer comprise different materials; and forming a solder bump on the barrier layer wherein the barrier layer is between the solder bump and the underbump metallurgy layer, wherein the barrier layer and the solder bump comprise different materials, and wherein a portion of the metal pad is exposed adjacent to the underbump metallurgy layer, the barrier layer, and the solder bump.

34. An electronic structure comprising: a substrate having a metal pad thereon; an underbump metallurgy layer on a surface of the metal pad wherein the metal pad is between the underbump metallurgy layer and the substrate; a barrier layer on the underbump metallurgy layer wherein the underbump metallurgy layer is between the barrier layer and the metal pad, wherein an entirety of the barrier layer is conformal with respect to the surface of the metal pad, and wherein the barrier layer and the underbump metallurgy layers comprise different materials; and a solder bump on the barrier layer wherein the barrier layer is between the solder bump and the underbump metallurgy layer, and wherein the barrier layer and the solder bump comprise different materials.

35. An electronic structure comprising: a substrate having a metal pad thereon; an underbump metallurgy layer on a surface of the metal pad wherein the metal pad is between the underbump metallurgy layer and the substrate; a barrier layer on the underbump metallurgy layer wherein the underbump metallurgy layer is between the barrier layer and the metal pad, and wherein the barrier layer and the underbump metallurgy layer comprise different materials; and a solder bump on the barrier layer wherein the barrier layer is between the solder bump and the underbump metallurgy layer, wherein the barrier layer and the solder bump comprise different materials, and wherein a portion of the metal pad is exposed adjacent to the underbump metallurgy layer, the barrier layer, and the solder bump.