DETAILED DESCRIPTION OF THE INVENTION

A Spring Contact Element

[0094] FIGS. 1 A- 1 C corresponding to FIGS. 1 A- 1 C of the aforementioned U.S. Patent Application No. U.S. patent application Ser. No. 08/852,152 illustrate fabricating a plurality (one of many shown) of spring contact elements 120 on an electronic component 102 . Generally, a number of insulating layers having openings formed therein are aligned and “seeded” with a layer of conductive material. A mass of conductive material can then be formed (or deposited) in the seeded opening(s), such as by electroplating (or CVD, sputtering, electroless plating, etc.). After the insulating layers are removed, the masses can function as free-standing spring contact structures 120 which extend not only vertically above the surface of the component 102 , but also laterally from the location whereat they are mounted. In this manner, the spring contact structures are readily engineered to be compliant in both the Z-axis as well as in the x-y plane (parallel to the surface of the component).

[0095] FIG. 1A illustrates an exemplary technique for fabricating one of a plurality of microelectronic contact structures 120 on a substrate 102 . The substrate 102 , for example, may be an active electronic component, including semiconductor devices, including semiconductor devices resident on a semiconductor wafer (not shown). More generally, the substrate can be a variety of materials. This can be a passive device, such as an interposer or space transformer, or an active device such as a semiconductor device. The material of the substrate might be ceramic or silicon, among other choices. In general, a preferred substrate is one which is amenable to processing under typical semiconductor fabrication conditions.

[0096] The substrate 102 has a plurality (one of many shown) of areas 112 on its surface whereat the spring contact elements 120 will be fabricated. In the case of the substrate 102 being an electronic component (such as a semiconductor device), an area 112 preferably would be a terminal (such as a bond pad) of the electronic component.

[0097] Generally, a number (three shown) of patterned masking layers 104 , 106 and 108 are applied onto the surface of the substrate. The layers are patterned to have openings (as shown) aligned with the area 112 , and the openings are sized and shaped so that an opening in a one layer (e.g., 108 , 106 ) extends further from the area 112 than an opening in an underlying layer (e.g., 106 , 104 , respectively). In other words, the first layer 104 has an opening which may be directly over the area 112 . A portion of the opening in the second layer 106 is aligned over at least a portion of the opening in the first layer 104 and, conversely, a portion of the first layer 104 extends under a portion of the opening in the second layer 106 . Similarly, a portion of the opening in the third layer 108 is aligned over at least a portion of the opening in the second layer 106 and, conversely, a portion of the second layer 106 extends under a portion of the opening in the third layer 108 . The bottom portion of a given overall opening is directly over the selected area 112 and its top portion is elevated from its bottom portion. In one preferred embodiment, the top portion is laterally offset from the area 112 .

[0098] As discussed in greater detail hereinbelow, and as discussed in greater detail in the aforementioned U.S. patent application Ser. No. 08/819,464, a conductive metallic material is deposited into the opening, and the masking layers are removed, resulting in a free-standing contact structure having been fabricated directly upon the substrate with its base end secured to the substrate 102 at the area 112 and its free end extending both above the surface of the substrate and laterally-displaced from the area 112 .

[0099] If required, such as for electroplating, a very thin (e.g., 4500 Å) “seed” layer of conductive material 114 such as titanium/tungsten (TiW) may be deposited into the openings. Then, a mass of conductive metallic material (e.g., nickel) 120 can be deposited by electroplating into the openings.

[0100] FIGS. 1B and 1C illustrate a resulting spring contact element 120 having its base end 122 adjacent the area 112 , and its free-end (tip) 124 elevated in the z-axis above the surface of the substrate 102 as well as laterally offset in the x-axis and y-axis from the base end 122 .

[0101] As best viewed in FIG. 1 C, the contact element 120 will react pressure applied in the z-axis at its tip end 124 , as indicated by the arrow 132 , such as would result from making a temporary pressure electrical connection with a terminal (not shown) of another electronic component (not shown). Compliance in the z-axis ensures that contact force (pressure) will be maintained, and also accommodates non-planarities (if any) between terminals (not shown) on the other electronic component (not shown). Such temporary electrical connections are useful for making temporary connections to the electronic component 102 , such as for performing burn-in and/or testing of the component 102 .

[0102] The tip end 124 is also free to move compliantly in the x- and y-directions, as indicated by the arrows 134 and 136 , respectively. This would be important in the context of joining (by soldering, or brazing, or with a conductive adhesive) the tip end 124 to a terminal (not shown) of another electronic component (not shown) which has a different coefficient of thermal expansion than the substrate (component) 102 . Such permanent electrical connections are useful for assemblies of electronic components, such as a plurality of memory chips (each of which is represented by the substrate 102 ) to another electronic component such as an interconnection substrate such as a printed circuit board (“PCB”; not shown).

[0103] The plurality of spring contact elements 120 can be fabricated with very precise dimensions and very precise spacing from one another. For example, tens of thousands of such spring contact elements 120 are readily precisely fabricated on a corresponding number of terminals on semiconductor devices which are resident on a semiconductor wafer (not shown).

[0104] In this manner, there has been shown a method of fabricating spring contact elements ( 120 ) directly on a substrate ( 102 ) such as an electronic component, such as a semiconductor device which may be resident on a semiconductor wafer, by applying at least one layer of masking material ( 104 , 106 , 108 ) on a surface of the substrate ( 102 ) and patterning the masking layer to have openings extending from areas ( 112 ) on the substrate to positions which are spaced above the surface of the substrate and which also may be laterally and/or transversely offset from the areas 112 ); by optionally seeding ( 114 ) the openings; by depositing at least one layer of a conductive metallic material into the openings; and by removing the masking material so that the remaining conductive metallic material forms free-standing contact elements extending from the surface of the substrate, each contact element having a base end which is secured to a one of the areas of the substrate and having a tip end for making an electrical connection to a terminal of an electronic component.

[0105] The structures (spring contact elements) 120 are principally, preferably entirely, metallic, and may be formed (fabricated) as multilayer structures. Suitable materials for the one or more layers of the contact structures include but are not limited to:

[0106] nickel, and its alloys;

[0107] copper, cobalt, iron, and their alloys;

[0108] gold (especially hard gold) and silver, both of which exhibit excellent current-carrying capabilities and good contact resistivity characteristics;

[0109] elements of the platinum group;

[0110] noble metals;

[0111] semi-noble metals and their alloys, particularly elements of the palladium group and their alloys; and

[0112] tungsten, molybdenum and other refractory metals and their alloys. Nickel and nickel alloys are particularly preferred.

[0113] In cases where a solder-like finish is desired, tin, lead, bismuth, indium and their alloys can also be used.

Another Spring Contact Element

[0114] FIGS. 2 A- 2 C corresponding to FIGS. 3 A- 3 C of the aforementioned U.S. patent application Ser. No. 08/852,152 are schematic illustrations of spring contact elements 200 and 250 (compare 120 ) fabricated according to the techniques of the present invention.

[0115] The spring contact element 200 of FIGS. 2A and 2B has a base end portion 202 , a contact (tip) end portion 204 , a main body portion 206 therebetween, an overall length “L” and an overall height “H”. As illustrated, the main body portion 206 is offset a distance “d2” in a one direction from the base end portion 202 , and is offset a distance “d1” in another direction from the contact end portion 304 .

[0116] As best viewed in the top schematic view of FIG. 2 B, the contact element 200 can be provided with a widthwise taper “α” so that it is narrower (width “w2“) at its contact end 204 than at its base end 202 (width “w1”)

[0117] FIG. 2C is a schematic representation of a similar (to the contact element 200 ) spring contact element 250 that has a base end portion 252 (compare 202 ), a contact (tip) end portion 254 (compare 204 ), and a main body portion 256 (compare 206 ) therebetween. In this example, the contact element 250 can be provided with a thickness taper “β” so that it is thinner (thickness “t2”) at its contact end 254 than at its base end 252 (thickness “t1”)

Exemplary Dimensions

[0118] The spring contact elements of the present invention are particularly well suited to making interconnections between microelectronic components. Suitable dimensions for the spring contact element are (in mils, unless otherwise specified): 2

[0119] These dimensions are illustrative, and are not meant to limit in any way the scope of the claims. Dimensions outside these ranges may be useful according to various choices readily made by one skilled in the art.

[0120] The technique described hereinabove and resulting spring contact elements 120 , 200 and 250 are viable, but somewhat limited in that:

[0121] (a) it is necessary to apply three masking layers ( 104 , 106 , 108 ), one atop the other, and pattern each masking layer with openings registering with openings in previously-applied layers;

[0122] (b) the entire resulting spring contact element is of uniform composition (e.g., of one or more metallic layers throughout its construction);

[0123] (c) there is no “tip feature” (described in greater detail hereinbelow) associated therewith.

Another Spring Contact Element

[0124] FIGS. 3 A- 3 C corresponding to FIGS. 1A, 1D and 1 E, respectively, of the aforementioned U.S. patent application Ser. No. 08/802,054 and its counterpart PCT patent application number US97/08271, and illustrate an elongate resilient (spring) contact element 300 that is suitable for attachment as a free-standing structure to an electronic component.

[0125] The structure 300 is elongate, has two ends 302 and 304 , a central portion 306 therebetween, and has an overall longitudinal length of “L” between the two ends. The length “L” is in the range of 10-1000 mils, such as 40-500 mils or 40-250 mils, preferably 60-100 mils.

[0126] The end 302 is a “base” whereat the contact element 300 will be mounted to an electronic component (not shown). The end 304 is a “free-end” (tip) which will effect a pressure connection with another electronic component (e.g., a device-under-test, not shown).

[0127] The structure 300 has an overall height of “H”. The height “H” is in the range of 4-40 mils, preferably 5-12 mils. (1 mil=0.001 inches=about 25 microns)

[0128] As best viewed in FIG. 3 A, the structure is “stepped”. The base portion 302 is at a first height, the tip 304 is at another height, and a middle (central) portion 306 is at a third height which is between the first and second heights. Therefore, the structure 300 has two “standoff” heights, labeled “d1” and “d2” in the figure. In other words, the spring contact element 300 has two “steps”, a step up from the contact end 304 to the central body portion 306 , and a further step up from the central body portion 306 to the base end 302 .

[0129] In use, the structure is often used as a resilient contact member to allow a mechanical and electrical connection between a second electronic device and the substrate upon which the structure is mounted. When the structure is engaged, a pressure connection moves the tip 304 closer to the substrate (not shown), thus diminishing height “H”. The distances d1 and d2 can be chosen to allow displacement of tip 304 by a sufficient amount to provide the desired contact. The contact force will be influenced by the resilience of the structure as it resists compression when brought into contact with the second electronic device. The design and the resiliency of the central portion will influence how much the central portion can flex near the tip 304 versus near the base 302 .

[0130] The standoff height “d1”, which is the “vertical” (as viewed in FIG. 3A ) distance between the tip 304 and the central portion 306 , is selected in part to prevent bumping of the structure (contact element) with a surface of a component being contacted by the tip end 304 .

[0131] In use, the standoff height “d2”, which is the “vertical” (as viewed in FIG. 3A ) distance between the base 302 and the central portion 306 , is selected in part to allow the beam (contact element) to bend and be displaced toward the surface of a substrate to which the element is attached.

[0132] The dimensions for the standoff heights “d1” and “d2” are:

[0133] “d1” is in the range of 3-15 mils, preferably approximately 7 mils±1 mil; and

[0134] “d2” is in the range of 0-15 mils, preferably approximately 7 mils±1 mil. In the case of “d2” being 0 mil, the structure would be substantially planar (without the illustrated step) between the central portion 306 and the base portion 302 .

[0135] In use, the structure 300 is intended to function as a cantilever beam, and is preferably provided with at least one taper angle, in a manner such as was discussed with respect to FIGS. 2B and 2C .

[0136] In contrast to the spring contact structures 120 , 200 and 250 described hereinabove, the tip end 304 of the spring contact structure 300 is preferably provided with an integral protruding topological “tip feature” 308 , for example in the geometric form of a pyramid, to aid in effecting pressure connection to a terminal of an electronic component (not shown).

[0137] The spring contact structure 300 is principally, preferably entirely, metallic, and may be formed (fabricated) as a multilayer structure, suitably employing, for its layers the materials listed hereinabove for layers of other contact structures.

[0138] FIG. 3B shows an enlarged view of the contact end 304 of the contact structure 300 . In this enlarged view it can be seen that the tip feature 308 is suitably quite prominent, projecting a distance “d3“, in the range of 0.25-5 mils, preferably 3 mils, from the bottom (as viewed) surface of the contact end of the spring contact element, and is suitably in the geometric shape of a pyramid, a truncated pyramid, a wedge, a hemisphere, or the like.

[0139] The resulting contact structure has an overall height “H” which is approximately the sum of “d1”, “d2” (and “d3”) plus the thickness of the central body portion when the contact structure is not compressed.

[0140] The various dimensions set forth for the spring contact element 300 are in the ranges set forth hereinabove for the spring contact elements 200 and 250 (except for the dimension “d3” which is relevant only to the contact element 300 ).

[0141] Another dimension is of interest—namely, the width and length (i.e., footprint) of the overall tip end ( 304 ). In instances where the tip end is expected to make contact with a terminal of an electronic component which is recessed (e.g., a bond pad of a semiconductor device which has passivation material surrounding the bond pad), it may be desirable to ensure that the footprint of the tip end is sufficiently small to make such contact, for example, less than 4 mils by 4 mils. It is particularly useful to make the footprint of the contact end relatively small, for example, 10 microns or even 2 or 3 microns square, to make a penetrating contact feature which will tend to penetrate miscellaneous contaminants on the surface of a contact.

[0142] It is desirable that the tip feature 308 is of sufficient height (d3) to make contact with a terminal, which may be recessed below the surface of the second electronic component. Generally speaking, the selection of an appropriate tip end design will be dictated by the peculiarities of the given application. For example, for contacting bond pads on silicon devices, the tip end design illustrated in FIG. 3B would likely be most appropriate. For contacting C4 bumps, the tip end design illustrated in FIG. 3C (described hereinbelow) would likely be most appropriate.

[0143] FIG. 3C illustrates an alternate embodiment of a spring contact structure wherein separate and distinct (discrete) contact tip structures 328 , such as are described in the aforementioned PCT/US96/08107 can be mounted to the contact end portions 304 of the spring contact elements, such as by brazing 330 thereto. This provides the possibility of the contact tip structure 328 having a different metallurgy, than the spring contact element ( 300 ). For example, the metallurgy of the spring contact element ( 300 ) is suitably targeted at its mechanical (e.g., resilient, spring) characteristics and its general capability to conduct electricity, while the metallurgy of a contact tip structure 328 mounted thereto is appropriately targeted to making superior electrical connection with a terminal of an electronic component being contacted and, if needed, can have superior wear-resistance.

[0144] According to an aspect of the invention, processes such as photolithography are employed to fabricate the spring contact elements of the present invention with tolerances, both of the springs themselves and with regard to the relative locations of a plurality of springs, suitable for use as interconnections in the context of fine-pitch microelectronics.

Mounting and Contacting Spring Contact Elements

[0145] FIGS. 4 A- 4 C, corresponding to FIGS. 4 A- 4 C of the aforementioned U.S. patent application Ser. No. 08/802,054 and its counterpart PCT patent application number US97/08271, illustrate a technique wherein a plurality (two of many shown) of contact structures 402 (compare 120 , 200 , 250 , 300 ) have been fabricated on a sacrificial substrate 404 . The base end portions of the contact structures 402 are brought into contact with a corresponding plurality of terminals 406 on an electronic component 408 , whereupon the base end portions are suitably joined by soldering, brazing or with a conductive adhesive 410 to the terminals 406 .

[0146] It is within the scope of this invention that any suitable technique and/or material for affixing the base end portions of the contact structures ( 402 ) to terminals of an electronic component be employed, including brazing, welding (e.g., spot welding), soldering, conductive epoxy, tacking the contact structure in any suitable manner to the terminal and securely affixing the contact structure to the terminal by plating (e.g., electroplating), and the like.

[0147] The sacrificial substrate 404 is then removed, in any suitable manner, such as by chemical etching or heating), resulting in an electronic component 408 having a plurality (two of many shown) of spring contact elements 402 affixed thereto, as illustrated in FIG. 4B .

[0148] As is evident in FIG. 4B, a plurality of elongate spring contact elements can be mounted to an electronic component having a plurality of terminals on a surface thereof. Each spring contact element has a base end and a contact end opposite the base end, and is mounted by its base end to a corresponding terminal of the electronic component. The contact end of each spring contact element extends above the surface of the electronic component to a position which is laterally offset from its base end.

[0149] FIG. 4C illustrates an application for the spring contact elements 420 wherein the spring contact elements have been mounted in the manner described with respect to FIG. 4B to a space transformer component ( 408 ) of a probe card assembly (not shown) so that the tip features (compare 308 ) at their contact ends (compare 304 ) make pressure connections with terminals 422 of an electronic component 420 such as a semiconductor device which may or may not be resident on a semiconductor wafer. As described hereinabove, it is within the scope of this invention that separate and discrete contact tip structures ( 328 ) be affixed to the contact end portions of the spring contact elements.

[0150] It is within the scope of this invention that the substrate (component) to which the structures 402 are mounted, for example the component 408 illustrated in FIG. 4C is active electronic components, such as memory devices or ASICs.

[0151] It is also within the scope of the invention, as is illustrated in FIG. 4 C, that the component or substrate to which the structures (e.g., 402 ) are mounted can be provided with a contiguous (as illustrated) or segmented ground plane to control impedance. Such a ground plane may comprise a plurality of ground lines 412 aligned directly underneath the structures 402 , but sufficient clearance for the tip of the structure to deflect must be assured. Alternatively, the ground plane 412 can be covered with an insulating layer. Another approach would be to dispose ground plane lines 414 on the surface of the substrate 408 slightly (such as 1 mil, in the x-axis) offset from directly underneath the structures 402 , and laying parallel to the structure 402 .

Multilayer Structures

[0152] FIGS. 5 A- 5 D, corresponding to FIGS. 2 A- 2 D of the aforementioned U.S. patent application Ser. No. 08/819,464 illustrate an exemplary technique for prefabricating metallic structures 520 which suitably are components of a microelectronic contact structure on a sacrificial substrate 502 . In this example, a silicon substrate (wafer) 502 having a top (as viewed) surface is used as the sacrificial substrate.

[0153] A layer 504 of titanium is deposited (e.g., by sputtering) onto the top surface of the silicon substrate 502 , and suitably has a thickness of approximately 250 Å (1 Å=0.1 nm=10 ⁻¹⁰ m). A layer 506 of aluminum is deposited (e.g., by sputtering) atop the titanium layer 504 , and suitably has a thickness of approximately 20,000 Å. The titanium layer 504 is optional and serves as an adhesion layer for the aluminum layer 506 . A layer 508 of copper is deposited (e.g., by sputtering) atop the aluminum layer 506 , and suitably has a thickness of approximately 5,000 Å.

[0154] A layer 510 of masking material (e.g., photoresist) is deposited atop the copper layer 508 , and suitably has a thickness of approximately 2 mils. The masking layer 510 is processed in any suitable manner to have a plurality (three of many shown) of holes (openings) 512 extending through the photoresist layer 510 to the underlying copper layer 508 . For example, each hole 512 may be 6 mils in diameter, and the holes 512 may be arranged at a pitch (center-to-center) of 10 mils. The sacrificial substrate 502 has, in this manner, been prepared for fabricating a plurality of contact tip structures at what are “lithographically-defined” locations on the sacrificial substrate 502 , within the holes 512 . Exemplary metallic structures 520 may be formed, as follows.

[0155] A layer 514 of nickel is deposited, such as by plating, within the holes 512 , onto the copper layer 508 , and suitably has a thickness of approximately 1.0-1.5 mils. Optionally, a thin layer (not shown) of a noble metal such as rhodium can be deposited onto the copper layer 508 prior to depositing the nickel. Next, a layer 516 of gold is deposited, such as by plating, onto the nickel 514 . The multilayer structure of nickel and gold (and, optionally, rhodium) will serve as a pre-fabricated metallic structure suitable for use as one or more of the components of multipart, assembled spring contact elements which are described in greater detail hereinbelow.

[0156] Next, as illustrated in FIG. 5 B, the photoresist 510 is stripped away (using any suitable solvent), leaving a plurality of pre-fabricated metallic structures 520 sitting atop the copper layer 508 . Next, the exposed (i.e., not covered by contact tip structures 520 ) portion of the copper layer 508 is subjected to a quick etch process, thereby exposing the aluminum layer 506 . As will be evident, aluminum is useful in subsequent steps, since aluminum is substantially non-wettable with respect to most solder and braze materials.

[0157] It bears mention that it is preferred to pattern the photoresist with additional holes (not shown, comparable to 512 ) within which “ersatz” metallic structures 522 may be fabricated in the same process steps employed to fabricate the actual metallic structures 520 . These ersatz structures 522 will serve to uniformize the aforementioned plating steps ( 514 , 516 ) in a manner that is well known and understood, by reducing abrupt gradients (non-uniformities) from manifesting themselves across the surface being plated. Such structures ( 522 ) are typically referred to in the field of plating as “robbers”.

[0158] In this manner, a plurality of metallic structures 520 have successfully been pre-fabricated on a sacrificial substrate 502 , awaiting subsequent joining to terminals of electronic components or to other metallic structures. Optionally, as part of the pre-fabrication of metallic structures (alternatively, immediately prior to joining the metallic structures 520 to terminals or other metallic structures, solder or brazing paste (“joining material”) 524 is deposited onto the top (as viewed) surfaces of the metallic structures 520 . (There is no need to deposit the paste onto the tops of the ersatz structures 522 ). This is implemented in any suitable manner, such as with a stainless steel screen or stencil or by automated dispensing of solder paste, as is known in the art. A typical paste (joining material) 524 would contain gold-tin alloy (in a flux matrix) exhibiting, for example, 1 mil spheres (balls).

[0159] The metallic structures 520 , as fabricated upon and resident upon a sacrificial substrate 502 , constitute a product in and of themselves.

[0160] As described in the aforementioned U.S. patent application Ser. No. 08/819,464, the metallic structures 520 may be contact tip structures suitable for joining to ends of free-standing resilient contact structures resident on an electronic component, in which case the sacrificial substrate 502 with contact tip structures 520 resident thereon is brought to bear upon tips (free ends) of exemplary elongate interconnection elements extending from a substrate which may be an electronic component.

[0161] As shown in FIG. 5 C, the contact tip structures 520 (only two contact tip structures are shown in the view of FIG. 5 D, for illustrative clarity) are aligned with the tips (distal ends) of interconnection elements 552 extending from a surface of an electronic component 554 , using standard flip-chip techniques (e.g., split prism), and the assembly is passed through a brazing furnace (not shown) to reflow the joining material 524 , thereby permanently joining (e.g., brazing) the prefabricated contact tip structures 520 to the ends of the interconnection elements 532 .

[0162] During the reflow process, the exposed aluminum layer ( 506 ), being non-wettable, prevents solder (i.e., braze) from flowing between the contact tip structures 520 , i.e., prevents solder bridges from forming between adjacent contact tip structures.

[0163] In addition to this anti-wetting function of the aluminum layer 506 , the aluminum layer 506 also serves to provide a release mechanism. Using a suitable etchant, the aluminum is preferentially (to the other materials of the assembly) etched away, and the silicon sacrificial substrate 502 simply “pops” off, resulting in a substrate or electronic component 554 having “tipped” interconnection elements 552 , each having a prefabricated tip structure 520 , as illustrated in FIG. 5D . (Note that the joining material 524 has reflowed as “fillets” 525 on end portions of the interconnection elements 552 .)

[0164] In a final step of the process, the residual copper ( 508 ) is etched away, leaving the contact tip structures 520 with nickel (or rhodium, as discussed hereinabove) exposed for making reliable electrical pressure connections to terminals (not shown) of other electronic components (not shown).

[0165] It is within the scope of the invention that the brazing (soldering) paste ( 524 ) is omitted, and in its stead, alternating layers of gold and tin in a eutectic ratio are plated onto the interconnection elements ( 552 ) prior to mounting the contact tip structures ( 520 ) thereto. In a similar manner, eutectic joining layers can be plated onto the contact tip structures ( 520 ) prior to joining with the interconnection elements ( 552 ).

[0166] Since the contact tip structures ( 520 ) are readily fabricated to be coplanar and of uniform thickness, the resulting “tipped” interconnection elements ( FIG. 5D ) will have tips (i.e., the exposed surfaces of the contact tip structures) which are substantially coplanar. The electronic component (e.g., 554 ) to which the interconnection elements (e.g., 552 ) are mounted may be an ASIC, a microprocessor, a component (e.g., space transformer component) of a probe card assembly, and the like.

A Multilayer Structure and a Release Mechanism

[0167] FIG. 6 corresponds to FIG. 4A of the aforementioned U.S. patent application Ser. No. 08/819,464 and illustrates a useful (e.g., preferred) technique for forming a multilayer metallic component for a spring contact structure in (or on) a sacrificial substrate, in the following manner, using a thin aluminum layer (foil) 600 as the sacrificial substrate:

[0168] provide a temporary backing 602 , such as a plastic sheet, for the foil 600 , to increase the structural integrity of the foil (this backing layer 602 can also act as a plating barrier/mask);

[0169] pattern the face (top, as viewed) of the foil 600 with a thin (approximately 3 mil) layer of photoresist 604 , or the like, leaving (or creating) openings 616 at locations whereat it is desired to form multilayer metallic components of spring contact structures;

[0170] deposit (such as by plating) a thin (approximately 100 microinch (μ″)) layer 606 of hard gold onto the foil 600 , within the openings 616 in the photoresist 604 ;

[0171] deposit (such as by plating) a very thin (approximately 5-10 μ″) layer (“strike”) of copper 608 onto the layer of hard gold (it should be understood that such a copper strike is useful but optional, and is provided principally to assist in subsequent plating of the previous gold layer 606 );

[0172] deposit (such as by plating) a relatively thick (approximately 2 mil) layer 610 of nickel onto the copper strike 608 (or, if there is not copper strike, onto the layer 606 of hard gold); and

[0173] deposit (such as by plating) a thin (approximately 100 μ″) layer 612 of soft gold onto the nickel.

[0174] This results in a multilayer structure 620 (compare 520 ), which is readily joined to either a terminal of an electronic component (not shown) or to another component of a spring contact structure (not shown). The multilayer structure 620 has, as its principal layers, a hard gold surface ( 606 ) for contacting (e.g., making pressure connections to) terminals of electronic components (not shown) making the structure 620 particularly useful as a tip component of a spring contact element, a nickel layer ( 610 ) providing strength, and a soft gold layer ( 612 ) which is readily bonded to (joinable to) a terminal of an electronic component or to another component of a spring contact structure.

[0175] Regarding depositing the materials for the structure 620 into the openings 616 of the masking material 604 atop the sacrificial substrate, it should be noted that the sacrificial substrate itself (e.g., 600 ), or one or more of the blanket layers deposited thereon serve to electrically connect the openings to one another, thereby facilitating the use of electroplating processes to deposit the multiple metallic layers of the structure 620 .

[0176] In use, the structures 620 can be joined to terminals of electronic components or to other structures in the manner(s) described with respect to FIGS. 4A, 5C and 5 D, and the aluminum sacrificial substrate 600 can be removed by means of chemical etching (e.g., with potassium-hydroxide).

Another Multilayer Structure and another Release Mechanism

[0177] FIG. 7 corresponds to FIG. 4B of the aforementioned U.S. patent application Ser. No. 08/819,464 and illustrates another technique for making components of microelectronic contact structures and releasing them from the sacrificial substrate upon which they are formed. The technique is not dependent on chemical etching (compare FIG. 6 ) to release the metallic structures from the sacrificial substrate.

[0178] As mentioned hereinabove, a “plain” (i.e., no active devices resident thereupon) silicon wafer can be used as the sacrificial substrate upon which the post/beam/tip components of spring contact elements of the present invention may be fabricated. An exemplary metallurgy is set forth hereinabove ( FIG. 6 ), wherein by using a suitable chemical selective etching process, the components of spring contact elements can be released from the sacrificial substrate.

[0179] It is within the scope of this invention that an appropriate metallurgy in conjunction with heat can be used to release the components of the spring contact elements from the sacrificial substrate, rather than by using chemical etching. For example, as illustrated by FIG. 7 :

[0180] Step 1 . Etch a pit (one of one or more shown) 702 into a silicon (sacrificial) substrate 704 at a location (one of several shown) whereat it is desired to have a topological feature on a contact tip structure. As discussed hereinbelow, etching of silicon can be self-limiting.

[0181] Step 2 . Apply a patterned masking layer 706 (e.g., photoresist) onto the surface of the silicon (sacrificial) substrate 704 . An opening 708 in the masking layer is at a corresponding location where a corresponding tip component 720 will be fabricated.

[0182] Step 3 . Deposit (such as by sputtering) a thin layer 710 of a non-wettable (as will be evident) material such as tungsten (or titanium-tungsten) onto the substrate, within the opening 708 of the masking layer 706 .

[0183] Step 4 . Deposit (such as by sputtering) a thin layer 712 of a non-wetting material such as plateable lead (or indium) onto the thin tungsten layer, within the opening 708 of the masking layer 706 .

[0184] Step 5 . Fabricate a tip component 720 having one or more layers within the opening 708 of the masking layer 706 , in the manner described hereinabove (e.g., with respect to FIG. 6 ).

[0185] Step 6 . Reflow (using heat) a tip component 720 onto an end of a beam component (not shown) in the manner described hereinabove. During reflow, the thin layer 712 will melt and ball up. For example, tungsten ( 710 ) is not wettable with respect to lead ( 712 ). This will cause the tip component 720 to be released from the sacrificial substrate 704 .

[0186] Optionally, a second layer of non-wettable material (e.g., tungsten) can be applied over the layer 712 , between layer 712 and tip component 720 . Said material will become part of the resulting contact tip structure, unless it is removed (e.g., by etching). In some cases, lead will not ball up (e.g., lead tends to wet nickel), in which cases it may be desired to deposit additional layers such as lead, then tungsten, then lead, to ensure proper release of the contact tip structures from the sacrificial substrate.

[0187] Optionally, another layer of material which will ball up when heated (e.g., lead, indium) can be applied over the second layer of non-wettable material (e.g., tungsten). Any residual lead on the surface of the resulting contact tip structure is readily removed, or may be left in place. Alternatively, a layer of a “barrier” material can be deposited between the second layer of material which will ball up and the first layer (e.g., rhodium) of the resulting tip component 720 . The “barrier” material may be tungsten, silicon nitride, molybdenum, or the like.

Another Multilayer Structure

[0188] FIGS. 8 A- 8 F correspond to FIGS. 5 A- 5 F of the aforementioned U.S. patent application Ser. No. 08/819,464 and illustrate a technique for forming metallic structures having pyramid or truncated pyramid tip features on a sacrificial substrate which is a silicon wafer.

[0189] FIG. 8A illustrates a first step in the technique, wherein a layer 804 of masking material, such as photoresist, is applied to the surface of the silicon substrate 802 , and is patterned to have a plurality (two of many shown) of openings 806 extending to the surface of the silicon substrate 802 . The openings 806 are preferably square, measuring approximately 1-4 mils, such as 2.5 mils on a side. However, the openings may be rectangular, or may have other geometric shapes.

[0190] Next, as illustrated in FIG. 8 B, the silicon substrate 802 is etched to form a like plurality (one of many shown) of pyramid-shaped depressions 808 in the silicon substrate 802 . Such etching of silicon will tend to be self-limiting, as the etching proceeds along the crystal plane at 54.74° for (100) silicon. In other words, the depression will extend to a depth which is defined (dictated) by the size of the opening 806 and the nature of the silicon substrate 802 . For example, with a square opening 2.5 mils per side, the depth of the depression will be approximately 2 mils. Ultimately, depression 808 will become a contact feature integrally formed upon the resulting contact tip structure to be formed on the silicon substrate. This is preferably a photolithographic process, so that the size and spacing of the opening 806 and feature 808 will be extremely precise. Tolerances of microns (10 ⁻⁶ meters) are readily attained.

[0191] Next, as illustrated in FIG. 8 C, the masking material 804 is removed, and a new masking layer 814 (compare 804 ), such as photoresist, is applied to the surface of the silicon substrate 802 and is patterned to have a plurality (one of many shown) of openings 816 (compare 806 ) extending to the surface of the silicon substrate 802 . The openings 816 are larger than the openings 806 , and are generally aligned therewith. (A typical opening 816 is over a depression 808 .) An exemplary opening 816 is a rectangle suitably measuring approximately 7 mils (across the page, as shown) by 8-30 mils (into the page, as shown). Ultimately, an opening 816 will be filled with conductive material forming the body of a contact tip structure, being pre-fabricated on the sacrificial substrate 802 . This is also preferably a photolithographic process, but the size and spacing of these openings 816 need not be as precise as previous openings 806 . Tolerances on the order of up to 1 mil (0.001 inch) are generally acceptable.

[0192] Next, as illustrated by FIG. 8C, a multilayer contact tip structure 820 is built up within the opening 816 , with a pyramid-shaped tip feature 830 extending from a surface thereof. In this example, the multilayer buildup is suitably:

[0193] first deposit (apply) a release mechanism 822 such as has been described hereinabove (e.g., a multilayer buildup of lead/tungsten/lead);

[0194] then deposit a relatively thin layer 824 of rhodium or tungsten (or ruthenium, or iridium, or hard nickel or cobalt or their alloys, or tungsten carbide), such as 0.1-1.0 mils thick;

[0195] then deposit a relatively thick layer 826 of nickel, cobalt or their alloys;

[0196] finally deposit a relatively thin layer 828 of soft gold, which is readily brazed to.

[0197] In this manner, a plurality of elongate contact tip structures 820 can be fabricated, each having a projecting pyramid-shaped contact (tip) feature 830 projecting from a surface thereof. It is this projecting contact feature that is intended to make the actual contact with a terminal (not shown) of an electronic component (not shown)(see FIG. 4C ).

[0198] As shown in FIG. 8D (and evident in FIGS. 8C, 8E and 8 F), the pyramid-shaped contact feature 830 is suitably polished (abraded) off, preferably at a level indicated by the dashed line 834 , which will configure the pyramid-shaped feature as a truncated pyramid-shaped feature. The relatively small flat end shape (e.g., a square measuring a few tenths of a mil on a side), rather than a truly pointed end shape, will tend to be sufficiently “sharp” to make reliable pressure connections with terminals (not shown) of electronic components (not shown). This configuration will tend to wear better than a truly pointed feature for making repeated pressure connections to a large number of electronic components, such as would be expected in an application of the tipped interconnection elements of the present invention for probing (e.g., testing silicon device wafers).

[0199] Another advantage of polishing off the point of the contact feature 830 is that the second layer of the multilayer buildup can be exposed for making contact with a terminal (not shown) of an electronic component (not shown). For example, this layer can be of a material with superior electrical characteristics, such as rhodium. Or, it can be a material with superior wear characteristics, such as titanium-tungsten. One preferred material is palladium alloyed with cobalt. Other palladium alloys also are preferred.

[0200] FIG. 8E illustrates the elongate contact tip structure 820 of the present invention joined to an end of an elongate interconnection element 840 . FIG. 8F illustrates a plurality of elongate contact tip structures 820 of the present invention, each joined to a contact bump 832 of a membrane probe 834 . In these exemplary applications, the contact tip structures 820 having projecting topological contact features 830 provide:

[0201] a distinct metallurgy;

[0202] a distinct contact topology (topography);

[0203] tightly controlled positional tolerances; and

[0204] if desired, a degree of pitch spreading.

[0205] Regarding effecting pitch spreading, it can be seen in FIG. 8F that the contact tip structures can be arranged so that the spacing between the contact features 830 is greater (as shown) or lesser (not shown) than the spacing of the contact balls 832 .

[0206] Generally, in use, the “tipped” interconnection element is mounted to a first electronic component, and the apex (top, as viewed in FIGS. 8E and 8F ) portion of the pyramid effects an electrical connection to a terminal (not shown) of a second electronic component (not shown).

[0207] As mentioned above, by prefabricating contact tip structures (e.g., 820 ) with topological contact features (e.g., 830 ) on a surface thereof, it is possible to achieve extremely high positional precision for the pressure connection to be made, without requiring a comparable degree of precision in either the body portion of the contact tip structure or the interconnection element to which it is joined.

Joining Components Together

[0208] There have been described hereinabove some techniques for joining prefabricated contact tip structures (e.g., 328 , 520 , 820 to ends of spring contact elements, elongate interconnection elements or contact bumps membrane probe (e.g., 304 , 552 , 840 , 832 ).

[0209] FIGS. 9 A- 9 C correspond to FIGS. 7C, 7D and 7 F, respectively, of the aforementioned U.S. patent application Ser. No. 08/819,464 and illustrate another embodiment of making a contact structure and joining it to an electronic component.

[0210] FIGS. 9 A- 9 C illustrate a technique for fabricating contact tip structures which are elongate and which, in use, will function as cantilever (plated cantilevered beam) spring contact elements, and mounting same to terminals of electronic components. These techniques are particularly well suited to ultimately mounting spring contact elements to electronic components such as semiconductor devices, space transformer substrates of probe card assemblies, and the like.

[0211] FIG. 9A illustrates a sacrificial substrate 902 such as a silicon wafer, into a surface of which one or more trenches 904 are etched. The trench 904 is illustrative of a surface texture ‘template’ for the contact tip structure 920 which will be fabricated on the sacrificial substrate 902 . The layout (spacing and arrangement) of the trenches 904 can be derived from (e.g. replicate or “mirror”) the bond pad layout of a semiconductor die (not shown) which is ultimately (in use) intended to be contacted (e.g., probed). For example, the trenches 904 can be arranged in a row, single file, down the center of the sacrificial substrate. Many memory chips, for example, are fabricated with a central row of bond pads (“lead on center” or LOC).

[0212] A hard “field” layer 906 has been deposited upon the surface of the sacrificial substrate 902 , including into trench 904 . Another layer 908 , such as of a plateable material, can optionally be deposited over the field layer 906 , if the field layer is of a material which is not amenable to plating such as tungsten-silicide, tungsten, or diamond. (If, as will be evident from the discussion hereinbelow, the layer 906 is difficult to remove, it may be applied by selective deposition (e.g., patterning through a mask), to avoid such removal.)

[0213] A masking material 910 , such as photoresist, is applied to define an opening 916 for the fabrication of plated cantilever tip structure 920 . The opening 916 in the masking layer 910 extends to cover the trench 904 . Next, a relatively thick (e.g., 1-3 mils) layer 912 of a spring alloy material (such as nickel and its alloys) is optionally deposited (such as by plating), over which a layer 914 of material such as soft gold is deposited which is amenable to brazing or soldering, in the event that the spring alloy is not easy to bond, solder or braze to. The spring alloy layer 912 is deposited by any suitable means such as plating, sputtering or CVD. Another preferred spring alloy is palladium and its alloys, particularly palladium-cobalt.

[0214] Next, as shown in FIG. 9 B, the masking material 910 is stripped (removed), along with that portion of the layers ( 906 and 908 ) which underlie the masking material 910 , resulting in an elongate contact tip structure 920 having been fabricated upon the sacrificial substrate 902 . Each elongate contact tip structure 920 has a tip portion 922 (directly over a corresponding one of the trenches 904 ), a base portion 924 , and an intermediate portion 926 between the tip and base portions 922 and 924 .

[0215] A plurality of such structures 920 may be staggered (oriented left-right-left-right), so that although their tip portions ( 922 ) are all aligned in a row (corresponding, e.g., to a central row of bond pads on a semiconductor device), their base portions 924 are oriented opposite one another. In this manner, the spacing between the base portions 924 of the contact tip structures 920 is at a greater (coarser) pitch (spacing) than the tip portions 922 .

[0216] As mentioned hereinabove with respect to the spring contact structures 200 and 250 is that the intermediate portion 926 can be tapered, from narrowest at the (contact) tip portion 922 to widest at the base portion 924 . This feature provides for controllable, determinate amount of deflection of the tip portion 922 when the base portion 924 is rigidly mounted to a terminal of an electronic component such as a space transformer of a probe