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Publication numberUS20040065555 A1
Publication typeApplication
Application numberUS 10/434,289
Publication dateApr 8, 2004
Filing dateMay 7, 2003
Priority dateMay 7, 2002
Also published asUS20070163888, US20080210563, WO2003095713A1
Publication number10434289, 434289, US 2004/0065555 A1, US 2004/065555 A1, US 20040065555 A1, US 20040065555A1, US 2004065555 A1, US 2004065555A1, US-A1-20040065555, US-A1-2004065555, US2004/0065555A1, US2004/065555A1, US20040065555 A1, US20040065555A1, US2004065555 A1, US2004065555A1
InventorsGang Zhang
Original AssigneeUniversity Of Southern California
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Conformable contact masking methods and apparatus utilizing in situ cathodic activation of a substrate
US 20040065555 A1
Abstract
Electroplating processes (e.g. conformable contact mask plating and electrochemical fabrication processes) that include in situ activation of a surface onto which a deposit will be made are described. At least one material to be deposited has an effective deposition voltage that is higher than an open circuit voltage, and wherein a deposition control parameter is capable of being set to such a value that a voltage can be controlled to a value between the effective deposition voltage and the open circuit voltage such that no significant deposition occurs but such that surface activation of at least a portion of the substrate can occur. After making electrical contact between an anode, that comprises the at least one material, and the substrate via a plating solution, applying a voltage or current to activate the surface without any significant deposition occurring, and thereafter without breaking the electrical contact, causing deposition to occur.
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Claims(38)
I claim:
1. A method for activating a surface of a substrate onto which a metal will be deposited by electrodeposition, comprising:
(A) supplying a substrate onto which one or more depositions may have occurred, wherein the substrate has a surface to be activated prior to occurrence of a deposition of at least one additional material;
(B) contacting a plating solution and the substrate;
(C) contacting the plating solution and an activation anode; and
(D) applying a voltage or current between the activation anode and the substrate at a level and for a time such that at least partial activation of at least a portion of the substrate surface occurs without significant deposition of the at least one additional material occurring onto the surface, and thereafter without separating the substrate from the plating solution, applying a voltage or current between a deposition anode and the substrate at a level and for a time so as to cause deposition of the at least one additional material.
2. The process of claim 1 wherein the deposition anode comprises the activation anode.
3. The process of claim 1 wherein the deposition anode and the activation anode are different.
4. The process of claim 1 wherein the at least one additional deposition comprises a deposition of nickel.
5. The process of claim 4 wherein the at least portion of the substrate surface that is activated comprises nickel.
6. An electrochemical fabrication process for producing a three-dimensional structure from a plurality of adhered layers, the process comprising:
(A) depositing a first material onto the substrate to form a portion of a layer and depositing at least a second material to form another portion of the layer, wherein the substrate may comprise previously deposited material; and
(B) forming a plurality of layers such that each successive layer is formed adjacent to and adhered to a previously deposited layer, wherein said forming comprises repeating operation (A) a plurality of times;
wherein at least a plurality of the selective depositing operations comprise:
(1) contacting the substrate and a patterned mask having at least one opening;
(2) in presence of a plating solution, conducting an electric current between an anode and the substrate, which functions as a cathode, through the at least one opening in the mask, such that the selected one of the first or second deposition materials is deposited onto the substrate to form at least a portion of a layer; and
(3) separating the mask from the substrate;
 wherein for a plurality of layers, in the presence of a plating solution, applying a current between an activation anode and the substrate, which functions as a cathode, at such a level and for such a time that at least partial activation of at least a portion of a surface of the substrate occurs without significant deposition of material occurring, and then without separating the substrate and the plating solution, applying a current between a deposition anode and the substrate which functions as a cathode, at such a level so as to cause deposition of a desired one of the first or second materials.
7. The process of claim 18 additionally comprising:
(C) supplying a plurality of preformed masks, wherein each mask comprises a patterned dielectric material that includes at least one opening through which deposition can take place during the formation of at least a portion of a layer, and wherein each mask comprises a support structure that supports the patterned dielectric material; and
wherein the contacting of the substrate and the patterned mask comprise contacting a selected one of the preformed masks to the substrate.
8. The process of claim 18 wherein the contacting of the substrate and the patterned mask comprise forming and adhering a patterned mask to the substrate.
9. The process of claim 18 wherein the selected one and the desired one are the same.
10. The process of claim 18 wherein the selected one and the desired one are different.
11. The process of claim 6 wherein the deposition anode comprises the activation anode.
12. The process of claim 6 wherein the deposition anode and the activation anode are different.
13. The process of claim 6 wherein the deposition of the first or second material that occurs after activation comprises a deposition of nickel.
14. The process of claim 13 wherein the at least portion of the substrate surface that is activated comprises nickel.
15. An electrochemical fabrication process for producing a three-dimensional structure from a plurality of adhered layers, the process comprising:
(A) supplying at least one material to be deposited, wherein the at least one material has an effective deposition voltage that is higher than an open circuit voltage, and wherein a deposition control parameter is capable of being set to such a value that a voltage can be controlled to a value between the effective deposition voltage and the open circuit voltage such that no significant deposition occurs but such that surface activation of at least a portion of the substrate can occur;
(B) forming a plurality of layers by depositing one or more materials which include the at least one material, wherein each successive layer is formed adjacent to and adhered to a previously deposited layer,
wherein after making electrical contact between an anode and the substrate via a plating solution, setting the deposition control parameter to at least one value and for a time such that at least a portion of the surface of the substrate is activated without any significant deposition occurring, and thereafter without breaking the electrical contact, applying a current between the anode and the substrate such that deposition of the at least one material occurs,
wherein the deposition of the at least one material or a deposition of at least one other material comprises:
(1) contacting or placing in proximity a patterned mask having at least one opening and a substrate;
(2) in presence of a plating solution, conducting an electric current between an anode and the substrate, which functions as a cathode, through the at least one opening in the mask, such that one of the at least one deposition material or the other deposition material is deposited onto the substrate to form at least a portion of a layer, after which the mask is removed from the substrate.
16. The process of claim 15 wherein the deposition of the at least one material comprises a deposition of nickel.
17. The process of claim 15 wherein the at least portion of the substrate that is activated comprises a previous deposition of the at least one material.
18. The process of claim 17 wherein the deposition that occurs after activation comprises a deposition of nickel.
19. The process of claim 15 wherein the formation of each of a number of layers comprise at least one blanket deposition as well as the selective deposition wherein for a given layer the selectively deposited material is different from a material deposited by blanket deposition.
20. The process of claim 15 wherein the plurality of selective depositions comprise the deposition of a plurality of different materials.
21. The process of claim 15 wherein at least a portion of one layer is formed by a non-electroplating deposition process.
22. The process of claim 15 wherein a plurality of depositions occur during the formation of each of a number of layers wherein at least one of the depositions on each of the number of layers deposits copper and at least one of the other depositions on the number of layers deposits nickel.
23. The process of claim 15 wherein the selective depositing for each of a number of layers comprises at least two selective depositions.
24. The process of claim 15 wherein a number of the plurality of preformed mask share a common support structure.
25. The process of claim 15 wherein a number of the plurality of layers are each formed by depositing at least one structural material using at least one deposition and by depositing at least one sacrificial material by using at least one other deposition.
26. The process of claim 15 wherein at least a portion of the at least one sacrificial material is removed after formation of a plurality of layers to reveal a three-dimensional structure comprised of at least one structural material.
27. The process of claim 15 wherein, for each of a plurality of masks, the support for the conformable material for a mask comprises the anode involved in the deposition associated with the use of the mask.
28. The process of claim 15 wherein, for each of a plurality of masks, the support for the conformable material for a mask is a porous medium which does not act as the anode during a deposition associated with the use of the mask.
29. The process of claim 15 wherein different masks are used during the deposition associated with the formation of at least two different layers.
30. The process of claim 15 wherein the same mask is used during the deposition associated with the formation of at least two different layers.
31. The process of claim 15 wherein the separating of the selected preformed mask occurs without breaking contact with sidewalls of the material deposited through the at least one opening while deposition continues to occur such that a deposition thickness continues to increase such that it exceeds a height that would have been practical if the entire deposition would have been attempted without separating the mask during plating.
32. The process of claim 15 where a thickness of the conformable material of at least one selected mask is less than 100 μm and is more preferably less than 50 μm.
33. The process of claim 15 wherein the formation of at least a plurality of layers additionally comprises removing a portion of the deposited material from the substrate such that a desired surface level is obtained.
34. An electrochemical fabrication process for producing a three-dimensional structure from a plurality of adhered layers, the process comprising:
forming a plurality of layers, wherein each layer is formed from the deposition of one or more materials, and wherein each successive layer is formed adjacent to and adhered to a previously deposited layer, wherein said forming comprises:
(A) contacting the substrate and a patterned mask having at least one opening;
(B) in presence of a plating solution, conducting an electric current between an anode and the substrate, which functions as a cathode, through the at least one opening in the mask, such that the first deposition material is deposited onto the substrate to form at least a portion of a layer; and
(C) separating the mask from the substrate; and
wherein for a plurality of layers, in the presence of a plating solution, applying a current between an activation anode and the substrate, which functions as a cathode, at such a level and for such a time that at least partial activation of at least a portion of the substrate surface occurs without significant deposition of material occurring, and then without separating the substrate and the plating solution, applying a current between a deposition anode and the substrate, which functions as a cathode, at such a level so as to cause deposition of a second material which may be different from or the same as the first material.
35. The process of claim 34 wherein the deposition anode comprises the activation anode.
36. The process of claim 34 wherein the deposition anode and the activation anode are different.
37. The process of claim 34 wherein the deposition that occurs after activation comprises a deposition of nickel.
38. The process of claim 37 wherein the at least portion of the substrate surface that is activated comprises nickel.
Description
    RELATED APPLICATIONS
  • [0001]
    This application claims benefit of U.S. Provisional Patent Application No. 60/379,129, filed on May 7, 2002 which is hereby incorporated herein by reference as if set forth in full.
  • GOVERNMENT SUPPORT
  • [0002] This invention was made with Government support under Grant Number DABT63-97-C-0051 awarded by DARPA. The Government has certain rights.
  • FIELD OF THE INVENTION
  • [0003]
    This invention relates to the field of electrochemical deposition and more particularly to the field of electrochemical deposition using conformable contact masks that are formed separate from a substrate (e.g. INSTANT MASKS™)to control deposition, such as for example in Electrochemical Fabrication (e.g. EFAB™) where such masks are used to control the selective electrochemical deposition of one or more materials according to desired cross-sectional configurations so as to build up three-dimensional structures from a plurality of at least partially adhered layers of deposited material.
  • BACKGROUND
  • [0004]
    A technique for forming three-dimensional structures (e.g. parts, components, devices, and the like) from a plurality of adhered layers was invented by Adam L. Cohen and is known as Electrochemical Fabrication. It is being commercially pursued by MEMGenŽ Corporation of Burbank, Calif. under the name EFAB™. This technique was described in U.S. Pat. No. 6,027,630, issued on Feb. 22, 2000. This electrochemical deposition technique allows the selective deposition of a material using a unique masking technique that involves the use of a mask that includes patterned conformable material on a support structure that is independent of the substrate onto which plating will occur. When desiring to perform an electrodeposition using the mask, the conformable portion of the mask is brought into contact with a substrate while in the presence of a plating solution such that the contact of the conformable portion of the mask to the substrate inhibits deposition at selected locations. For convenience, these masks might be generically called conformable contact masks; the masking technique may be generically called a conformable contact mask plating process. More specifically, in the terminology of MEMGenŽ Corporation of Burbank, Calif. such masks have come to be known as INSTANT MASKS™ and the process known as INSTANT MASKING™ or INSTANT MASK™ plating. Selective depositions using conformable contact mask plating may be used to form single layers of material or may be used to form multi-layer structures. The teachings of the '630 patent are hereby incorporated herein by reference as if set forth in full herein. Since the filing of the patent application that led to the above noted patent, various papers about conformable contact mask plating (i.e. INSTANT MASKING) and electrochemical fabrication have been published:
  • [0005]
    1. A. Cohen, G. Zhang, F. Tseng, F. Mansfeld, U. Frodis and P. Will, “EFAB: Batch production of functional, fully-dense metal parts with micro-scale features”, Proc. 9th Solid Freeform Fabrication, The University of Texas at Austin, p161, August 1998.
  • [0006]
    2. A. Cohen, G. Zhang, F. Tseng, F. Mansfeld, U. Frodis and P. Will, “EFAB: Rapid, Low-Cost Desktop Micromachining of High Aspect Ratio True 3-D MEMS”, Proc. 12th IEEE Micro Electro Mechanical Systems Workshop, IEEE, p244, January 1999.
  • [0007]
    3. A. Cohen, “3-D Micromachining by Electrochemical Fabrication”, Micromachine Devices, March 1999.
  • [0008]
    4. G. Zhang, A. Cohen, U. Frodis, F. Tseng, F. Mansfeld, and P. Will, “EFAB: Rapid Desktop Manufacturing of True 3-D Microstructures”, Proc. 2nd International Conference on Integrated MicroNanotechnology for Space Applications, The Aerospace Co., April 1999.
  • [0009]
    5. F. Tseng, U. Frodis, G. Zhang, A. Cohen, F. Mansfeld, and P. Will, “EFAB: High Aspect Ratio, Arbitrary 3-D Metal Microstructures using a Low-Cost Automated Batch Process”, 3rd International Workshop on High Aspect Ratio MicroStructure Technology (HARMST'99), June 1999.
  • [0010]
    6. A. Cohen, U. Frodis, F. Tseng, G. Zhang, F. Mansfeld, and P. Will, “EFAB: Low-Cost, Automated Electrochemical Batch Fabrication of Arbitrary 3-D Microstructures”, Micromachining and Microfabrication Process Technology, SPIE 1999 Symposium on Micromachining and Microfabrication, September 1999.
  • [0011]
    7. F. Tseng, G. Zhang, U. Frodis, A. Cohen, F. Mansfeld, and P. Will, “EFAB: High Aspect Ratio, Arbitrary 3-D Metal Microstructures using a Low-Cost Automated Batch Process”, MEMS Symposium, ASME 1999 International Mechanical Engineering Congress and Exposition, November, 1999.
  • [0012]
    8. A. Cohen, “Electrochemical Fabrication (EFABTM)”, Chapter 19 of The MEMS Handbook, edited by Mohamed Gad-EI-Hak, CRC Press, 2002.
  • [0013]
    9. “Microfabrication—Rapid Prototyping's Killer Application”, pages 1-5 of the Rapid Prototyping Report, CAD/CAM Publishing, Inc., June 1999.
  • [0014]
    The disclosures of these nine publications are hereby incorporated herein by reference as if set forth in full herein.
  • [0015]
    The electrochemical deposition process may be carried out in a number of different ways as set forth in the above patent and publications. In one form, this process involves the execution of three separate operations during the formation of each layer of the structure that is to be formed:
  • [0016]
    1. Selectively depositing at least one material by electrodeposition upon one or more desired regions of a substrate.
  • [0017]
    2. Then, blanket depositing at least one additional material by electrodeposition so that the additional deposit covers both the regions that were previously selectively deposited onto, and the regions of the substrate that did not receive any previously applied selective depositions.
  • [0018]
    3. Finally, planarizing the materials deposited during the first and second operations to produce a smoothed surface of a first layer of desired thickness having at least one region containing the at least one material and at least one region containing at least the one additional material.
  • [0019]
    After formation of the first layer, one or more additional layers may be formed adjacent to the immediately preceding layer and adhered to the smoothed surface of that preceding layer. These additional layers are formed by repeating the first through third operations one or more times wherein the formation of each subsequent layer treats the previously formed layers and the initial substrate as a new and thickening substrate.
  • [0020]
    Once the formation of all layers has been completed, at least a portion of at least one of the materials deposited is generally removed by an etching process to expose or release the three-dimensional structure that was intended to be formed.
  • [0021]
    The preferred method of performing the selective electrodeposition involved in the first operation is by conformable contact mask plating. In this type of plating, one or more conformable contact (CC) masks are first formed. The CC masks include a support structure onto which a patterned conformable dielectric material is adhered or formed. The conformable material for each mask is shaped in accordance with a particular cross-section of material to be plated. At least one CC mask is needed for each unique cross-sectional pattern that is to be plated.
  • [0022]
    The support for a CC mask is typically a plate-like structure formed of a metal that is to be selectively electroplated and from which material to be plated will be dissolved. In this typical approach, the support will act as an anode in an electroplating process. In an alternative approach, the support may instead be a porous or otherwise perforated material through which deposition material will pass during an electroplating operation on its way from a distal anode to a deposition surface. In either approach, it is possible for CC masks to share a common support, i.e. the patterns of conformable dielectric material for plating multiple layers of material may be located in different areas of a single support structure. When a single support structure contains multiple plating patterns, the entire structure is referred to as the CC mask while the individual plating masks may be referred to as “submasks”. In the present application such a distinction will be made only when relevant to a specific point being made.
  • [0023]
    In preparation for performing the selective deposition of the first operation, the conformable portion of the CC mask is placed in registration with and pressed against a selected portion of the substrate (or onto a previously formed layer or onto a previously deposited portion of a layer) on which deposition is to occur. The pressing together of the CC mask and substrate occur in such a way that all openings, in the conformable portions of the CC mask contain plating solution. The conformable material of the CC mask that contacts the substrate acts as a barrier to electrodeposition while the openings in the CC mask that are filled with electroplating solution act as pathways for transferring material from an anode (e.g. the CC mask support) to the non-contacted portions of the substrate (which act as a cathode during the plating operation) when an appropriate potential and/or current are supplied.
  • [0024]
    An example of a CC mask and CC mask plating are shown in FIGS. 1(a)-1(c). FIG. 1(a) shows a side view of a CC mask 8 consisting of a conformable or deformable (e.g. elastomeric) insulator 10 patterned on an anode 12. The anode has two functions. FIG. 1(a) also depicts a substrate 6 separated from mask 8. One is as a supporting material for the patterned insulator 10 to maintain its integrity and alignment since the pattern may be topologically complex (e.g., involving isolated “islands” of insulator material). The other function is as an anode for the electroplating operation. CC mask plating selectively deposits material 22 onto a substrate 6 by simply pressing the insulator against the substrate then electrodepositing material through apertures 26 a and 26 b in the insulator as shown in FIG. 1(b). After deposition, the CC mask is separated, preferably non-destructively, from the substrate 6 as shown in FIG. 1(c). The CC mask plating process is distinct from a “through-mask” plating process in that in a through-mask plating process the separation of the masking material from the substrate would occur destructively. As with through-mask plating, CC mask plating deposits material selectively and simultaneously over the entire layer. The plated region may consist of one or more isolated plating regions where these isolated plating regions may belong to a single structure that is being formed or may belong to multiple structures that are being formed simultaneously. In CC mask plating as individual masks are not intentionally destroyed in the removal process, they may be usable in multiple plating operations.
  • [0025]
    Another example of a CC mask and CC mask plating is shown in FIGS. 1(d)-1(f). FIG. 1(d) shows an anode 12′ separated from a mask 8′ that comprises a patterned conformable material 10′ and a support structure 20. FIG. 1(d) also depicts substrate 6 separated from the mask 8′. FIG. 1(e) illustrates the mask 8′ being brought into contact with the substrate 6. FIG. 1(f) illustrates the deposit 22′ that results from conducting a current from the anode 12′ to the substrate 6. FIG. 1(g) illustrates the deposit 22′ on substrate 6 after separation from mask 8′. In this example, an appropriate electrolyte is located between the substrate 6 and the anode 12′ and a current of ions coming from one or both of the solution and the anode are conducted through the opening in the mask to the substrate where material is deposited. This type of mask may be referred to as an anodeless INSTANT MASK™ (AIM) or as an anodeless conformable contact (ACC) mask.
  • [0026]
    Unlike through-mask plating, CC mask plating allows CC masks to be formed completely separate from the fabrication of the substrate on which plating is to occur (e.g. separate from a three-dimensional (3D) structure that is being formed). CC masks may be formed in a variety of ways, for example, a photolithographic process may be used. All masks can be generated simultaneously, prior to structure fabrication rather than during it. This separation makes possible a simple, low-cost, automated, self-contained, and internally-clean “desktop factory” that can be installed almost anywhere to fabricate 3D structures, leaving any required clean room processes, such as photolithography to be performed by service bureaus or the like.
  • [0027]
    An example of the electrochemical fabrication process discussed above is illustrated in FIGS. 2(a)-2(f). These figures show that the process involves deposition of a first material 2 which is a sacrificial material and a second material 4 which is a structural material. The CC mask 8, in this example, includes a patterned conformable material (e.g. an elastomeric dielectric material) 10 and a support 12 which is made from deposition material 2. The conformal portion of the CC mask is pressed against substrate 6 with a plating solution 14 located within the openings 16 in the conformable material 10. An electric current, from power supply 18, is then passed through the plating solution 14 via (a) support 12 which doubles as an anode and (b) substrate 6 which doubles as a cathode. FIG. 2(a), illustrates that the passing of current causes material 2 within the plating solution and material 2 from the anode 12 to be selectively transferred to and plated on the cathode 6. After electroplating the first deposition material 2 onto the substrate 6 using CC mask 8, the CC mask 8 is removed as shown in FIG. 2(b). FIG. 2(c) depicts the second deposition material 4 as having been blanket-deposited (i.e. non-selectively deposited) over the previously deposited first deposition material 2 as well as over the other portions of the substrate 6. The blanket deposition occurs by electroplating from an anode (not shown), composed of the second material, through an appropriate plating solution (not shown), and to the cathode/substrate 6. The entire two-material layer is then planarized to achieve precise thickness and flatness as shown in FIG. 2(d). After repetition of this process for all layers, the multi-layer structure 20 formed of the second material 4 (i.e. structural material) is embedded in first material 2 (i.e. sacrificial material) as shown in FIG. 2(e). The embedded structure is etched to yield the desired device, i.e. structure 20, as shown in FIG. 2(f).
  • [0028]
    Various components of an exemplary manual electrochemical fabrication system 32 are shown in FIGS. 3(a)-3(c). The system 32 consists of several subsystems 34, 36, 38, and 40. The substrate holding subsystem 34 is depicted in the upper portions of each of FIGS. 3(a) to 3(c) and includes several components: (1) a carrier 48, (2) a metal substrate 6 onto which the layers are deposited, and (3) a linear slide 42 capable of moving the substrate 6 up and down relative to the carrier 48 in response to drive force from actuator 44. Subsystem 34 also includes an indicator 46 for measuring differences in vertical position of the substrate which may be used in setting or determining layer thicknesses and/or deposition thicknesses. The subsystem 34 further includes feet 68 for carrier 48 which can be precisely mounted on subsystem 36.
  • [0029]
    The CC mask subsystem 36 shown in the lower portion of FIG. 3(a) includes several components: (1) a CC mask 8 that is actually made up of a number of CC masks (i.e. submasks) that share a common support/anode 12, (2) precision X-stage 54, (3) precision Y-stage 56, (4) frame 72 on which the feet 68 of subsystem 34 can mount, and (5) a tank 58 for containing the electrolyte 16. Subsystems 34 and 36 also include appropriate electrical connections (not shown) for connecting to an appropriate power source for driving the CC masking process.
  • [0030]
    The blanket deposition subsystem 38 is shown in the lower portion of FIG. 3(b) and includes several components: (1) an anode 62, (2) an electrolyte tank 64 for holding plating solution 66, and (3) frame 74 on which the feet 68 of subsystem 34 may sit. Subsystem 38 also includes appropriate electrical connections (not shown) for connecting the anode to an appropriate power supply for driving the blanket deposition process.
  • [0031]
    The planarization subsystem 40 is shown in the lower portion of FIG. 3(c) and includes a lapping plate 52 and associated motion and control systems (not shown) for planarizing the depositions.
  • [0032]
    Another method for forming microstructures from electroplated metals (i.e. using electrochemical fabrication techniques) is taught in U.S. Pat. No. 5,190,637 to Henry Guckel, entitled “Formation of Microstructures by Multiple Level Deep X-ray Lithography with Sacrificial Metal layers. This patent teaches the formation of metal structure utilizing mask exposures. A first layer of a primary metal is electroplated onto an exposed plating base to fill a void in a photoresist, the photoresist is then removed and a secondary metal is electroplated over the first layer and over the plating base. The exposed surface of the secondary metal is then machined down to a height which exposes the first metal to produce a flat uniform surface extending across the both the primary and secondary metals. Formation of a second layer may then begin by applying a photoresist layer over the first layer and then repeating the process used to produce the first layer. The process is then repeated until the entire structure is formed and the secondary metal is removed by etching. The photoresist is formed over the plating base or previous layer by casting and the voids in the photoresist are formed by exposure of the photoresist through a patterned mask via X-rays or UV radiation.
  • [0033]
    To form successful depositions it is of importance that adequate adhesion occur between the deposited material and a substrate. If it is desired to exploit the electrical properties of the deposited material it may be desired that any resistivity associated with the bonding between the substrate and the deposited layer be as small as possible or at least of a similar order of magnitude compared to the resistivity of the bulk deposit of material. These requirements become even more important when forming structures where a layer comprises a plurality of separately deposited materials. These requirements become of even further importance when forming structures from a plurality of adhered layers. As adhesion failure or other failure on a single layer may destroy the usefulness of the entire structure, even a small chance of failure of achieving desired properties between successive depositions within a given layer or of achieving desired properties between depositions on successive layers may result in an unacceptable failure rate when the total number of depositions is considered. In electrochemical fabrication processes where multiple materials may be deposited on any given layer and multiple materials may be deposited in non-overlaying positions on subsequent layers, it may be insufficient to consider a technique that results in good adhesion between successive depositions of like materials, or even depositions of a first material onto a second material, but also depositions of the second material onto the first material, and the like when more than two materials are used. The loss associated with the formation of a multilayer structure may not be the just the wasted time, wasted material, and cost associated with a single layer but instead may be the wasted time, wasted material, and cost associated with the formation of the entire structure.
  • [0034]
    For successful plating to occur, a pretreatment process may be applied, which includes three general steps: (1) cleaning to remove all superficial substances such as grease and soil, (2) descaling to remove scale and rust, and (3) immediately prior to plating, activation to remove remaining oxides from metal surfaces. The surface is made active by complete removal of all surface contamination and oxides. After it is rendered active it must be kept in this state until it is covered by the metal being deposited.
  • [0035]
    Except for noble metals such as gold and platinum, most metals exposed to air or water oxidize in a very short time to form a thin oxide or passive film on their surfaces. Both copper and nickel, two materials used in some preferred embodiments of conformable contact mask plating and electrochemical fabrication, are subject to this rapid oxidation. The oxide or passive film usually acts as a barrier to bonding of electrodeposits. In addition, a metal oxide usually has lower strength than the deposit and the substrate. Thus, adhesion failure can occur due to the presence of the oxide at a lower external force that would otherwise be required. In addition, the presence of the oxide can increase the electrical resistance between the two depositions. The purpose of activation is to remove these oxide layers or to at least render them as thin as possible. If the activation is inadequate, a satisfactory bond of the deposit to the base metal may not be obtained and electrical properties between the deposit and the base metal may be different than that desired.
  • [0036]
    Various processes are known for activating copper and nickel surfaces.
  • [0037]
    Though the need for surface activation is generally known in the electroplating arts, the need for and optimization for surface activation in conformable contact mask plating and electrochemical fabrication processes have not been addressed in the field. Each of the above noted publications that is explicitly directed to the use of conformable contact masks (i.e. Instant Masks) and electrochemical fabrication (i.e. EFAB), whether taken alone or in combination, are silent concerning modifications that can be made to the conformable contact mask plating and electrochemical fabrication processes to enhance layer-to-layer bonding and other inter-layer properties. A need exists in the electrodeposition arts, and more particularly in the field of conformable contact mask plating and electrochemical fabrication for production methods that result in structures having intra-layer and inter-layer properties that meet certain requirements.
  • SUMMARY OF THE INVENTION
  • [0038]
    It is an object of certain aspects of the invention to provide an electrodeposition process is capable of producing structures having a desired intra-layer or inter-layer property that meets or exceeds a minimum requirement.
  • [0039]
    It is an object of certain aspects of the invention to provide an electrodeposition process that produces enhanced properties between depositions of material and existing material.
  • [0040]
    It is an object of certain aspects of the invention to provide a conformable contact mask plating process is capable of producing structures having a desired intra-layer or inter-layer property that meets or exceeds a minimum requirement.
  • [0041]
    It is an object of certain aspects of the invention to provide a conformable contact mask plating that produces enhanced properties between depositions of material and existing material.
  • [0042]
    It is an object of certain aspects of the invention to provide an electrochemical fabrication process is capable of producing structures having a desired intra-layer or inter-layer property that meets or exceeds a minimum requirement.
  • [0043]
    It is an object of certain aspects of the invention to provide an electrochemical fabrication process that produces enhanced properties between depositions of material and existing material.
  • [0044]
    Other objects and advantages of various aspects of the invention will be apparent to those of skill in the art upon review of the teachings herein. The various aspects of the invention, set forth explicitly herein or otherwise ascertained from the teachings herein, may address any one of the above objects alone or in combination, or alternatively may not address any of the objects set forth above but instead address some other object ascertained from the teachings herein. It is not intended that all of these objects be addressed by any single aspect of the invention even though that may be the case with regard to some aspects.
  • [0045]
    A first aspect of the invention provides a method for activating a surface of a substrate onto which a metal will be deposited by electrodeposition, including: (A) supplying a substrate onto which one or more depositions may have occurred, wherein the substrate has a surface to be activated prior to occurrence of a deposition of at least one additional material; (B) contacting a plating solution and the substrate; (C) contacting the plating solution and an activation anode; and (D) applying a voltage or current between the activation anode and the substrate at a level and for a time such that at least partial activation of at least a portion of the substrate surface occurs without significant deposition of the at least one additional material occurring onto the surface, and thereafter without separating the substrate from the plating solution, applying a voltage or current between a deposition anode and the substrate at a level and for a time so as to cause deposition of the at least one additional material.
  • [0046]
    A second aspect of the invention provides an electrochemical fabrication process for producing a three-dimensional structure from a plurality of adhered layers, the process including: (A) depositing a first material onto the substrate to form a portion of a layer and depositing at least a second material to form another portion of the layer, wherein the substrate may include previously deposited material; and (B) forming a plurality of layers such that each successive layer is formed adjacent to and adhered to a previously deposited layer, wherein said forming includes repeating operation 1(A) a plurality of times; wherein at least a plurality of the selective depositing operations include: (1) contacting the substrate and a patterned mask having at least one opening; (2) in presence of a plating solution, conducting an electric current between an anode and the substrate, which functions as a cathode, through the at least one opening in the mask, such that the selected one of the first or second deposition materials is deposited onto the substrate to form at least a portion of a layer; and (3) separating the mask from the substrate; wherein for a plurality of layers, in the presence of a plating solution, applying a current between an activation anode and the substrate, which functions as a cathode, at such a level and for such a time that at least partial activation of at least a portion of a surface of the substrate occurs without significant deposition of material occurring, and then without separating the substrate and the plating solution, applying a current between a deposition anode and the substrate which functions as a cathode, at such a level so as to cause deposition of a desired one of the first or second materials.
  • [0047]
    A third aspect of the invention provides an electrochemical fabrication process for producing a three-dimensional structure from a plurality of adhered layers, the process including: (A) supplying at least one material to be deposited, wherein the at least one material has an effective deposition voltage that is higher than an open circuit voltage, and wherein a deposition control parameter is capable of being set to such a value that a voltage can be controlled to a value between the effective deposition voltage and the open circuit voltage such that no significant deposition occurs but such that surface activation of at least a portion of the substrate can occur; (B) forming a plurality of layers by depositing one or more materials which include the at least one material, wherein each successive layer is formed adjacent to and adhered to a previously deposited layer, wherein after making electrical contact between an anode and the substrate via a plating solution, setting the deposition control parameter to at least one value and for a time such that at least a portion of the surface of the substrate is activated without any significant deposition occurring, and thereafter without breaking the electrical contact, applying a current between the anode and the substrate such that deposition of the at least one material occurs, wherein the deposition of the at least one material or a deposition of at least one other material includes: (1) contacting or placing in proximity a patterned mask having at least one opening and a substrate; (2) in presence of a plating solution, conducting an electric current between an anode and the substrate, which functions as a cathode, through the at least one opening in the mask, such that one of the at least one deposition material or the other deposition material is deposited onto the substrate to form at least a portion of a layer, after which the mask is removed from the substrate.
  • [0048]
    A fourth aspect of the invention provides an electrochemical fabrication process for producing a three-dimensional structure from a plurality of adhered layers, the process including: forming a plurality of layers, wherein each layer is formed from the deposition of one or more materials, and wherein each successive layer is formed adjacent to and adhered to a previously deposited layer, wherein said forming includes: (A) contacting the substrate and a patterned mask having at least one opening; (B) in presence of a plating solution, conducting an electric current between an anode and the substrate, which functions as a cathode, through the at least one opening in the mask, such that the first deposition material is deposited onto the substrate to form at least a portion of a layer; and (C) separating the mask from the substrate; and wherein for a plurality of layers, in the presence of a plating solution, applying a current between an activation anode and the substrate, which functions as a cathode, at such a level and for such a time that at least partial activation of at least a portion of the substrate surface occurs without significant deposition of material occurring, and then without separating the substrate and the plating solution, applying a current between a deposition anode and the substrate, which functions as a cathode, at such a level so as to cause deposition of a second material which may be different from or the same as the first material.
  • [0049]
    A fifth aspect of the invention provides a method for activating a surface of a substrate in preparation for deposition of a first material, including: (A) supplying a substrate onto which one or more depositions may have occurred, wherein the substrate has a surface to be activated prior to occurrence of a deposition of the first material; (B) contacting a patterned mask to the substrate, wherein the patterned mask has at least one opening; (C) in the presence of a plating solution, conducting an electric current through the at least one opening in the patterned mask between a deposition anode and the substrate, wherein the substrate functions as a cathode, such that a second deposition material is deposited onto the substrate, to form at least a portion of a layer; and (D) applying a current between an activation anode and the substrate through a plating solution at a level and for a time such that at least partial activation of at least a portion of a surface of the substrate occurs without significant deposition of the first material occurring onto the surface, and then without separating the substrate and the plating solution, applying a current between a deposition anode and the substrate at a level and for a time so as to cause deposition of the first material, and wherein the substrate functions as a cathode.
  • [0050]
    A sixth aspect of the invention provides an electrochemical fabrication apparatus for producing a three-dimensional structure from a plurality of adhered layers, the process including: (A) a plurality of preformed masks, wherein each mask includes a patterned conformable dielectric material that includes at least one opening through which deposition can take place during the formation of at least a portion of a layer, and wherein each mask includes a support structure that supports the patterned conformable dielectric material; (B) means for selectively depositing at least a portion of a layer onto the substrate, wherein the substrate may include previously deposited material; and (C) means for forming a plurality of layers such that each successive layer is formed adjacent to and adhered to a previously deposited layer, wherein the means of (B) is used a plurality of times; wherein means of (B) includes: (1) means for contacting the substrate and the conformable material of a selected preformed mask; (2) means for applying an electric current through a plating solution within at least one opening in the selected mask between an anode and the substrate, wherein the anode includes a selected deposition material, and wherein the substrate functions as a cathode, such that the selected deposition material is deposited onto the substrate to form at least a portion of a layer; and (3) means for separating the selected preformed mask from the substrate; and (D) means for applying a current between an activation anode and the substrate through a plating solution, which substrate functions as a cathode, at such a level and for such a time that at least partial activation of at least a portion of the substrate surface occurs without significant deposition of material occurring, and then without separating the substrate and the plating solution, applying a current between a deposition anode and the substrate, which substrate functions as a cathode, at such a level so as to cause deposition onto the substrate to occur; and (E) means for operating the means of (D) during the formation of a plurality of layers.
  • [0051]
    Further aspects of the invention will be understood by those of skill in the art upon reviewing the teachings herein. Other aspects of the invention may involve combinations of the above noted aspects of the invention and/or addition of various features of one or more embodiments. Other aspects of the invention may involve apparatus that can be used in implementing one or more of the above method aspects of the invention. These other aspects of the invention may provide various combinations of the aspects presented above as well as provide other configurations, structures, functional relationships, and processes that have not been specifically set forth above.
  • BRIEF DESCRIPTION OF THE DRAWINGS
  • [0052]
    FIGS. 1(a)-1(c) schematically depict side views of various stages of a CC mask plating process, while FIGS. 1(d)-(g) schematically depict a side views of various stages of a CC mask plating process using a different type of CC mask.
  • [0053]
    FIGS. 2(a)-2(f) schematically depict side views of various stages of an electrochemical fabrication process as applied to the formation of a particular structure where a sacrificial material is selectively deposited while a structural material is blanket deposited.
  • [0054]
    FIGS. 3(a)-3(c) schematically depict side views of various example subassemblies that may be used in manually implementing the electrochemical fabrication method depicted in FIGS. 2(a)-2(f).
  • [0055]
    FIGS. 4(a)-4(i) schematically depict the formation of a first layer of a structure using adhered mask plating where the blanket deposition of a second material overlays both the openings between deposition locations of a first material and the first material itself.
  • [0056]
    [0056]FIG. 5 provides an example of a failed structure due to failed adhesion between two layers.
  • [0057]
    FIGS. 6(a) and 6(b) depict cathodic polarization curves for a nickel substrate in a nickel sulfamate plating bath.
  • [0058]
    [0058]FIG. 7(a)-7(c) depict Ni cathode potentials before and after various forms of activation.
  • [0059]
    [0059]FIG. 8 depicts a perspective view of a 5 layer structure that was used in performing a contact resistance analysis for in situ cathodically activated nickel depositions.
  • [0060]
    [0060]FIG. 9(a)-9(c) respectively illustrate the set up for (1) an adhesive based adhesion test, (2) a solder based adhesion test, and (3) the Ollard method of testing adhesion.
  • DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
  • [0061]
    FIGS. 1(a)-1(g), 2(a)-2(f), and 3(a)-3(c) illustrate various features of one form of electrochemical fabrication that are known. Other electrochemical fabrication techniques are set forth in the '630 patent referenced above, in the various previously incorporated publications, in various other patents and patent applications incorporated herein by reference, still others may be derived from combinations of various approaches described in these publications, patents, and applications, or are otherwise known or ascertainable by those of skill in the art from the teachings set forth herein. All of these techniques may be combined with those of the various embodiments of various aspects of the invention to yield enhanced embodiments. Still other embodiments be may derived from combinations of the various embodiments explicitly set forth herein.
  • [0062]
    FIGS. 4(a)-4(i) illustrate various stages in the formation of a single layer of a multi-layer fabrication process where a second metal is deposited on a first metal as well as in openings in the first metal where its deposition forms part of the layer. In FIG. 4(a), a side view of a substrate 82 is shown, onto which patternable photoresist 84 is cast as shown in FIG. 4(b). In FIG. 4(c), a pattern of resist is shown that results from the curing, exposing, and developing of the resist. The patterning of the photoresist 84 results in openings or apertures 92(a)-92(c) extending from a surface 86 of the photoresist through the thickness of the photoresist to surface 88 of the substrate 82. In FIG. 4(d), a metal 94 (e.g. nickel) is shown as having been electroplated into the openings 92(a)-92(c). In FIG. 4(e), the photoresist has been removed (i.e. chemically stripped) from the substrate to expose regions of the substrate 82 which are not covered with the first metal 94. In FIG. 4(f), a second metal 96 (e.g., silver) is shown as having been blanket electroplated over the entire exposed portions of the substrate 82 (which is conductive) and over the first metal 94 (which is also conductive). FIG. 4(g) depicts the completed first layer of the structure which has resulted from the planarization of the first and second metals down to a height that exposes the first metal and sets a thickness for the first layer. In FIG. 4(h) the result of repeating the process steps shown in FIGS. 4(b)-4(g) several times to form a multi-layer structure are shown where each layer consists of two materials. For most applications, one of these materials is removed as shown in FIG. 4(i) to yield a desired 3-D structure 98 (e.g. component or device).
  • [0063]
    A basic standard plating configuration (i.e. non-CC mask plating configuration) includes an anode and a cathode which are immersed in a plating bath. The distance between the anode and cathode is at least 1 mm. A power source provides a pre-set current passing through the plating cell so that the anode metal usually dissolves into the plating bath and the metal ions in the plating bath are reduced at the cathode to become a metallic deposit. Depending on various parameters, including the composition of the plating bath, the plating bath is usually operated at a constant temperature some wherein the range of between 20-60° C. The plating bath is agitated mechanically or by compressed air to ensure that fresh plating solution is delivered to the cathode and that the products of the electrochemical reactions are removed from the electrodes into the bulk solution.
  • [0064]
    Through-mask plating is a selective plating process since the substrate (cathode) is patterned by a thin non-conductive material (e.g. a patterned photoresist). Otherwise, its plating configuration is the same as that of standard plating process as outlined above. As such, through-mask plating, for the purposes herein, may be considered a selective form of standard plating.
  • [0065]
    CC mask plating is different from normal and through-mask plating in several aspects. In one form of CC mask plating, the plating bath is trapped in a closed volume defined by the substrate, the side walls of the conformable material, and the anode. Examples of such closed volumes 26 a and 26 b are depicted in FIG. 1(b). Another form of CC mask plating may involve the use of a porous support and a distal anode. In this alternative form of CC mask plating, the barrier presented by the support portion of the CC mask, though allowing at least some ion exchange, may present a sufficient hindrance to the exchange of some components of the plating solution that the solution in the deposition region may still be considered to be substantially isolated from the bulk solution. This trapping results in little or no mass exchange between the volume of solution in the plating region and the bulk solution and as such no or little fresh solution with proper additives can be supplied into the microspace and no or little reaction products can be removed.
  • [0066]
    A preferred form of CC mask plating involves closed volumes where at least one of the dimensions of at least one of the plating volumes is on the order of tens of microns (e.g. 20 to 100 μm) or less. As such, this form of CC mask plating may be considered to be a microbath plating process (i.e. micro-CC mask plating).
  • [0067]
    In micro-CC mask plating, the preferred separation between the anode and cathode is presently between about 20 μand about 100 μm, and more preferably between about 40 and 80 μm. As such, regardless of the size of the area being deposited, these preferred embodiments may be considered to be micro-CC mask plating processes. Of course thinner separation distances (e.g. 10 μm or less) and thicker separation distances (300 μm or more) are possible. Due to this close spacing between anode and cathode, deposition processes at the cathode and dissolution processes at the anode, unlike standard plating, are highly interacting.
  • [0068]
    Agitating the plating bath, as is common with standard plating processes, though possible, is not necessarily desirable in electrochemical fabrication due potentially to the high interaction between anode and cathode processes and due to the believed enhanced risk of shorting when agitation is used. Shorting refers to a portion of the deposition height bridging the space between the cathode and the anode prior to the lapse of the desired deposition time, in which case the current is directed almost solely through deposited conductive material as opposed to flowing primarily through the plating bath as intended such that the continuing of deposition is inhibited.
  • [0069]
    Using a pyrophosphate bath at high temperature (i.e. above around 43° C. to 45° C.), though recommended in the standard plating processes, is not desirable in the current form of micro-CC mask plating due to the higher rate of attack at the interface between the CC mask support and the conformable material and the associated shortening of CC mask life.
  • [0070]
    CC mask plating has its own characteristics and the conventional wisdom associated with standard plating processes may be more of a hindrance than a help in developing commercially viable CC mask plating processes and systems.
  • [0071]
    Successful deposits in most electrodeposition processes must not only have desired thicknesses of appropriate uniformity, they must also demonstrate reasonable adhesion to the substrate on which they were deposited. In some forms of CC mask plating (e.g. electrochemical fabrication) these deposits must also show reasonable bulk properties (i.e. intra-deposit characteristics), and reasonable inter-deposit characteristics (e.g. reasonable adhesion between successive deposits, and reasonably small contact resistance between deposits). These reasonable inter-deposit characteristics in electrochemical fabrication where a single structural material and a single sacrificial material are being used may involve four unique situations: (1) characteristics between structural material being deposited and previously deposited structural material, (2) characteristics between sacrificial material being deposited and previously deposited sacrificial material (3) characteristics between structural material being deposited and previously deposited sacrificial material, and (4) characteristics between sacrificial material being deposited and previously deposited structural material. In other forms of conformable mask plating or electrochemical fabrication where no sacrificial material is used, the possible situations may be reduced to the first one listed above. On the other hand, in other forms of CC mask plating or electrochemical fabrication, if more than one structural material is used or more than one sacrificial material is used, the classification of potential situations may be more complex.
  • [0072]
    Of the possible situations that may arise, characteristics involving structural material to structural material contact is the most critical in that the characteristics must not only be appropriate to allow production of the structure but they must also meet any use requirements to which the structure will be placed. Of course if the structure will remain adhered to the original substrate when the structure is put to use, the contact characteristics between the structure and the original substrate may also be of elevated importance.
  • [0073]
    As noted above, in some preferred embodiments of electrochemical fabrication, the materials to be plated are nickel and copper. In some preferred embodiments of CC mask plating and electrochemical fabrication, before performing the first plating operation in association with a given layer the deposits from the previous layer are planarized by lapping. Ultrasonic cleaning may also be used.
  • [0074]
    A copper surface usually contains a layer of oxide film after being lapped, rinsed and exposed to air before plating. For example, when a clean copper surface is exposed to air or water, a thin layer of Cu2O film quickly forms. With time, the oxide thickness may reach up to 40-50 Å in thickness in air at room temperature but it can be readily removed by dipping in 5% H2SO4 for a few seconds. After acid dipping and a quick, thorough rinse, the copper containing substrate can be immediately put into the plating tank. In this way, oxide formation can be minimized. The active state of a copper surface can be maintained in a nickel sulfamate bath (i.e. a preferred bath for plating nickel in the electrochemical fabrication process) and a copper pyrophosphate bath (i.e. a preferred bath for plating copper in the electrochemical fabrication process) since the nickel bath is a weak acid solution (pH ˜4.0) and the copper bath contains the copper complexing agent pyrophosphate.
  • [0075]
    Nickel normally passivates in air, water, and plating baths to form a passive oxide film on its surface. Nickel coatings can not be successfully plated with good adhesion on to passive nickel surfaces. An activated surface can readily become passive again if it is allowed to dry or is exposed to oxygen-containing solutions. The problem with nickel is to activate its surface and to keep it active until plating has started. In electrochemical fabrication, good adhesion between nickel layers is very important since layered microstructures can fall apart even if poor adhesion occurs only at one layer. FIG. 5 shows a failed chain that was produced by electrochemical fabrication (i.e. EFAB) in which two layers separated in region 82 at one horizontal link due to improper activation.
  • [0076]
    Various nickel activation processes are known. A simple mild activation method is chemical acid dipping in a 20-25% by volume HCl solution or a 15% by volume H2SO4 where nickel oxide (NiO) can be dissolved into nickel ions and water. Despite its instability in acids, NiO may still break down at a very low rate. By these simple methods, adequate activation may be obtained on some nickel surfaces but not on all.
  • [0077]
    For faster treatment, concentrated acids such as HNO3 or HF can be used, e.g., HNO3:H2O or HF:H2O with 1:1 ratios by volume. Unfortunately, these acids also dissolve the nickel metal at a faster rate as well.
  • [0078]
    Electrochemical activation is more successful for ensuring good adhesion between the deposit (e.g. nickel) and the substrate (e.g. nickel). There are three basic types: (1) anodic treatment, (2) cathodic treatment, and (3) a combination of anodic and cathodic treatment. Well-known and generally practiced methods for producing adherent nickel electrodeposits on nickel and nickel alloys are described in detail in ASTM Standards B558 and B343. In the anodic treatment, nickel is used as an anode immersed in an acid solution, e.g., H2SO4. The oxide film and a small amount of nickel are dissolved by an external anodic current. In the cathodic treatment, nickel is used as a cathode immersed in HCl or H2SO4. An applied cathodic current reduces the oxide to the metal. No base metal is etched using this method. Usually this method is recommended when the nickel surface has not been severely passivated. The combined anodic and cathodic treatment, which generally employs an anodic treatment followed by a cathodic treatment, has two variations. In one variation the process is carried out in an acid solution, while in the other the process is performed in a combined nickel activation-plating bath. Furthermore, the second process involves deposition of a nickel deposit on the nickel surface after the anodic treatment.
  • [0079]
    In certain preferred embodiments of electrochemical fabrication, each layer is actually a composite of copper and nickel. A preferred treatment should generally not cause significantly different etching rates for copper and for nickel. Otherwise, the flatness of a layer may suffer or even the dimensions of a deposited layer within the plane of deposition if a selective deposit were performed in association with a given layer prior to performing the activation process.
  • [0080]
    A combined anodic and cathodic treatment recommended by ASTM B343 was evaluated for electrochemical fabrication. In the treatment procedure the surface is first etched at a current density of 20 mA/cm2 for 10 minutes (i.e. the substrate on which further deposition will occur is treated as the anode) then passivated (e.g. an oxide film is formed) by use of a high anodic current density of 200 mA/cm2 for 2 minutes (this high current density results in passivation as opposed to significant dissolution), and finally made cathodic for 2 or 3 seconds at 200 mA/cm2. The recommended treatment solution was 16.6% H2SO4 by volume. Unfortunately, after this treatment, a significant differential in etching rate was noticed between the copper and nickel composite layer. Although it produced excellent adhesion, this treatment does not appear to be suitable for a multilayer electrochemical fabrication process that uses both nickel and copper.
  • [0081]
    To minimize differential etching, a cathodic treatment has an advantage since it reduces the oxide, but does not attack the base metal. Cathodic treatments alone have not been previously proposed for use in electrochemical fabrication and standard cathodic activation treatments are not carried out in the same bath as is used for plating. In these standard processes, after cathodic activation, the substrate needs to be rinsed and is then transferred into the plating bath. During this period, a thin oxide film forms. If handled efficiently, the oxide may not have sufficient thickness to interfere significantly with adhesion but this handling and the extent of oxide formation may still remain an uncontrolled variable. Additionally, depending on the time between immersion into the plating bath and the beginning of plating, further thickening of the oxide may occur. However, an ideal cathodic treatment, and the treatment proposed herein, would be one which could be carried out within the plating bath. Furthermore in the most preferred approach, plating can be carried out immediately after activation (i.e. in-situ cathodic activation) by switching the cathodic current to the desired plating value, thereby avoiding the formation of an oxide between the cathodic activation treatment and the plating.
  • [0082]
    Many deposits can be obtained at a potential of the cathode that is slightly lower than its stable open-circuit potential because the deposition process has a fairly small activation overvoltage which can usually be neglected. In these metal plating baths, in-situ cathodic activation is impossible since deposits form even when only small currents pass through the cathode.
  • [0083]
    However, for nickel the activation overvoltage is large. The nickel deposit can not be obtained unless the potential of the cathode is at least −200 mV beyond its stable open-circuit potential. This feature is useful since either the oxide or H+ is reduced in this no-deposit region by the applied cathodic current. Also, the H2 formed as the result of the reduction of H+ can reduce the oxide since H2 is a reducing agent.
  • [0084]
    Experiments were performed to determine the deposition overvoltage of nickel on copper and of nickel on nickel (the same result was obtained for both substrates) in the sulfamate bath. A complete cathodic polarization curve is shown in FIG. 6(a) while the portion 112 of FIG. 6(a) is shown in FIG. 6(b). The test samples were copper or nickel disks with an exposed area of 1.27 cm2. The polarization curve has a distinct change 84 at about −0.68 V (vs. SCE). No nickel deposit could be seen before this potential by visually checking the copper disk, however at more negative potentials the nickel deposition occurred. This no-deposition region is about 420 mV wide which also means that nickel deposition does not occur if the cathodic current density is less than 90 μA/cm2.
  • [0085]
    If we use a current density of 50 μA/cm2 for the reduction of nickel oxide in the sulfamate bath and assume that the NiO reduction efficiency is 100%, we arrive at a reduction rate of NiO of about 1030 Å/hr or 17 Å/min. Theoretically, if the oxide thickness is of the order of ˜50 Å, application of a cathodic current density of 50 μA/cm2 for several minutes should reduce the NiO completely.
  • [0086]
    Experiments were performed to evaluate the effect of such cathodic treatment, open circuit plating bath potentials of nickel samples before and after the in-situ cathodic treatment were measured in a 5% Na2SO3 solution at room temperature. During these tests, in-situ cathodic treatment was performed in the 5% Na2SO3 solution as it was believed that the actual solution used would have little impact on the treatment process (i.e. the results obtained are believed to be similar to those that would be obtained by activating in the plating solution. If the oxide is at least partially removed (i.e. the surface is at least partially activated), the potentials before and after the treatment should be different. Since an activated nickel surface is easily repassivated in oxygen-containing solutions, in order to obtain a true nickel potential after the in-situ cathodic treatment, the Na2SO3 (a reducing agent) solution was employed to minimize the oxygen content in the solution to form an almost-oxygen-free environment (since Na2SO3 consumes oxygen). Currents were applied and potentials were measured using an EG&G 273 Potentiostat/Galvanostat. A saturated calomel electrode (SCE) was used as a reference electrode. The applied activation current density was 50 μA/cm2. Nickel disks (purity: 99.9+% from Goodfellow) with an exposed area of 1.27 cm2 were polished with SiC sandpaper (grit 600), degreased in acetone, dipped in 5% H2SO4 for 1 min, washed with DI water in between, and finally dried with compressed air. The specimens were then placed in air for at least 1 hour to form an oxide film on the nickel surface at room temperature. The oxide films formed rapidly (i.e. within a few seconds) in air at room temperature, however the initial rapid oxidation of nickel quickly decreased after several minutes as the oxide films formed. The experimental oxidation time assured that there were oxide films of similar thickness on each specimen.
  • [0087]
    The results of the potential measurements are shown in FIG. 7(a). The stable potential of the untreated nickel sample was −560 mV (vs. SCE), which was more positive than that of the samples with in-situ cathodic treatment. This means that the surface was activated by the in situ cathodic treatment since the more negative the potential, the more active the surface. Preferably the treatment time should be enough to finish nickel surface activation, which depends on the oxide thickness. The experimental results confirmed that the more treatment time, the more negative the stable nickel potential after the treatment, which indicates that the degree of the cathodic reduction of the oxide became greater with treatment time. The stable potential (˜−0.710 V vs. SCE) of the sample after the 2 min treatment was very close to that (˜−0.730 V vs. SCE) of the sample after the 4 min treatment. As such an activation time of 2 minutes may be sufficient for some purposes but increased activation time may still provide some enhancement though with significantly diminishing returns versus the time spent.
  • [0088]
    The contact resistance between layers was measured for a 5-layer microstructure produced by the electrochemical fabrication process using a four-point probe method. The structure measured is depicted in FIG. 8. Before plating each nickel layer, the base surface was activated by an in-situ cathodic activation at 50 μA/cm2 for 5 min. The measured total resistance for this microstructure was 201 μΩ. Neglecting any contribution to total resistance from the interfaces between layers, the resistance for this bulk microstructure can be calculated. For the pure nickel a resistivity of 7.2 μΩ-cm is known, which in turn yields a total anticipated resistance for the nickel structure (of the configuration tested) to be 195.3 μΩ. Comparing this to the measured resistance and assuming any difference is the result of the summed contact resistance for each layer, then the contact resistance for each layer is only 1.14 μΩ. Since the contact resistance represents the resistance of the oxide film at the interface, this small contact resistance means that only very little oxide was present. Since the actual resistivity of the interlayer portions of the nickel deposit from the sulfamate bath could be greater than that of the pure nickel, the actual contact resistance could be even less.
  • [0089]
    Experiments were run using other activation processes with the results being shown in FIGS. 7(b) and 7(c). The other activation processes included acid dipping, and use of two commercial activation products known as Original C-12 (from Puma Chemical of Warne, N.C.) and Multiprep 506 (from MacDermid, Inc. of Waterbury, Conn.). The potentials of the nickel samples after acid dipping (acid activation) in 20% HCl and in 20% H2SO4 by volume were measured in a 5% Na2SO3 solution at room temperature. The results are shown in FIG. 7(b). In the Original C-12 activator solution, the nickel surface can be activated either by simple immersion or by applying a voltage of 2V between the cathode (which is the nickel sample) and an anode for 30 to 60 seconds. The measured stable potentials in a 5% Na2SO3 solution at room temperature for a selected time for each treatment method are shown in FIG. 7(c). The Multiprep 506 solution was used to activate a nickel surface by dipping the surface into the solution at 55.5° C. for 2.5 minutes. The measured stable potential after the treatment in a 5% Na2SO3 solution at room temperature is shown in FIG. 7(c).
  • [0090]
    As can be seen from these figures the in situ cathodic activation process yielded larger negative voltages and thus higher levels of activation. The stable nickel potentials in the Na2SO3 solution after the acid treatment, the Original C-12 treatment, and the Multiprep 506 treatment were more negative than that of the untreated sample, but more positive than that of the in-situ cathodically treated sample. Although the measured potentials do not reveal the extent of adhesion of the deposit resulting from the different treatment methods, the most active nickel surface was obtained by the in-situ cathodic treatment since the treated samples had the most negative potential undergoing both the 2 minute and 4 minute treatments among all tested activation methods.
  • [0091]
    Adhesion tests were performed with measurements being obtained from three different methods: an adhesion method which is schematically depicted in FIG. 9(a), a soldering method which is schematically depicted in FIG. 9(b), and the Ollard method which is schematically depicted in FIG. 9(c) where measurements were made using an Instron Model 4204 universal testing instrument (lnstron Corporation of Canton, Mass.) using a crosshead speed of 5 mm/minute. Adhesion tests showed that samples that under went in situ. cathodic activation resulted in improved adhesion strength compared to samples where deposition occurred without any activation process. In a total of seven tests, under specific conditions, using in situ cathodic activation, five strengths were measured to be between about 32-40 MPa with one measurement at about 23 MPa and a final measurement at about 47 MPa. Four tests where no activation process was used yielded three strengths between about 14-20 MPa and one strength at about 2 MPa.
  • [0092]
    It is clear from these results that the in situ cathodic activation process provides a very active surface with enhanced adhesion between the substrate and the deposit. It is anticipated that the in situ cathodic activation process can be combined with other standard or commercial methods so that even better coating adhesion may be realized. Furthermore it is believed that post formation heat treatment may be used to greatly improving the adhesion strength of metallic deposits.
  • [0093]
    Various other embodiments of the present invention exist. Some of these embodiments may be based on a combination of the teachings herein with various teachings incorporated herein by reference. Some embodiments may not use any blanket deposition process and/or they may not use a planarization process. Some embodiments may involve the selective deposition of a plurality of different materials on a single layer or on different layers. Some embodiments may use blanket depositions processes that are not electrodeposition processes. Some embodiments may use selective deposition processes on some layers that are not conformable contact masking processes and are not even electrodeposition processes. Some embodiments may use nickel as a structural material while other embodiments may use different materials such as gold, silver, or any other electrodepositable materials that can be separated from the copper and/or some other sacrificial material. Some embodiments may use copper as the structural material with or without a sacrificial material. Some embodiments may remove a sacrificial material while other embodiments may not. In some embodiments the anode may be different from the conformable contact mask support and the support may be a porous structure or other perforated structure. Some embodiments may use multiple conformable contact masks with different patterns so as to deposit different selective patterns of material on different layers and/or on different portions of a single layer. In some embodiments, the depth of deposition will be enhanced by pulling the conformable contact mask away from the substrate as deposition is occurring in a manner that allows the seal between the conformable portion of the CC mask and the substrate to shift from the face of the conformal material to the inside edges of the conformable material.
  • [0094]
    In view of the teachings herein, many further embodiments, alternatives in design and uses of the instant invention will be apparent to those of skill in the art. As such it is not intended that the invention be limited to the particular illustrative embodiments, alternatives, and uses described above but instead that it be solely limited by the claims presented hereafter.
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Classifications
U.S. Classification205/123, 205/183, 205/159
International ClassificationH01L21/288, C25D5/12, H05K3/24, H01L21/768, C25D5/02, C25D5/18, C25D5/34, C25D1/00, C25D5/10, C25D5/40, C25D5/50, C25D5/14, C25D5/48
Cooperative ClassificationC25D5/48, C25D5/40, H05K3/243, C25D5/50, C25D5/10, C25D5/022, H01L21/2885, C25D5/34, C25D5/18, C25D5/14, C25D5/12, H05K3/241, H01L21/76879
European ClassificationH01L21/768C4B, H01L21/288E, C25D1/00, C25D5/48, C25D5/14, C25D5/10, C25D5/18, C25D5/40, C25D5/50, C25D5/02B, C25D5/34
Legal Events
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Sep 8, 2003ASAssignment
Owner name: UNIVERSITY OF SOUTHERN CALIFORNIA, CALIFORNIA
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:ZHANG, GANG;REEL/FRAME:014467/0630
Effective date: 20030820