WO2005033375A2 - Procedes de fabrication electrochimique a traitement post-depot ameliore - Google Patents

Procedes de fabrication electrochimique a traitement post-depot ameliore Download PDF

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Publication number
WO2005033375A2
WO2005033375A2 PCT/US2003/014660 US0314660W WO2005033375A2 WO 2005033375 A2 WO2005033375 A2 WO 2005033375A2 US 0314660 W US0314660 W US 0314660W WO 2005033375 A2 WO2005033375 A2 WO 2005033375A2
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Prior art keywords
substrate
mask
deposition
etching
layer
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PCT/US2003/014660
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English (en)
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Gang Zhang
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University Of Southern California
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Priority to AU2003304492A priority Critical patent/AU2003304492A1/en
Publication of WO2005033375A2 publication Critical patent/WO2005033375A2/fr

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    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D5/00—Electroplating characterised by the process; Pretreatment or after-treatment of workpieces
    • C25D5/02—Electroplating of selected surface areas
    • C25D5/022—Electroplating of selected surface areas using masking means
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D1/00—Electroforming
    • C25D1/003—3D structures, e.g. superposed patterned layers

Definitions

  • 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 to control deposition, such as for example in Electrochemical Fabrication (e.g. EFABTM) 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.
  • EFABTM Electrochemical Fabrication
  • the conformable portion of the mask 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.
  • 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 MEMGen ® Corporation of Burbank, California such masks have come to be known as INSTANT MASKSTM and the process known as INSTANT MASKINGTM or INSTANT MASKTM plating. Selective depositions using conformable contact mask plating may be used to form single layers of material or may be used to form multilayer structures.
  • the electrochemical deposition process may be carried out in a number of different ways as set forth in the above patent and publications.
  • this process involves the execution of three separate operations during the formation of each layer of the structure that is to be formed: 1. Selectively depositing at least one material by electrodeposition upon one or more desired regions of a substrate. 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. 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • CC masks 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.
  • the entire 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".
  • 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.
  • Figure 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.
  • Figure 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 26a and 26b in the insulator as shown in Figure 1 (b).
  • the CC mask is separated, preferably non- destructively, from the substrate 6 as shown in Figure 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.
  • 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.
  • Figure 1 (d) shows an anode 12' separated from a mask 8' that comprises a patterned conformable material 10' and a support structure 20.
  • Figure 1 (d) also depicts substrate 6 separated from the mask 8'.
  • Figure 1 (e) illustrates the mask 8' being brought into contact with the substrate 6.
  • Figure 1 (f) illustrates the deposit 22' that results from conducting a current from the anode 12' to the substrate 6.
  • Figure 1 (g) illustrates the deposit 22' on substrate 6 after separation from mask 8'.
  • 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 MASKTM (AIM) or as an anodeless conformable contact (ACC) mask.
  • AIM anodeless INSTANT MASKTM
  • ACC anodeless conformable contact
  • 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.
  • FIGS 2(a) - 2(f) An example of the electrochemical fabrication process discussed above is illustrated in Figures 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.
  • FIG. 1 illustrates that 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.
  • Figure 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.
  • the CC mask 8 is removed as shown in Figure 2(b).
  • Figure 2(c) depicts the second deposition material 4 as having been blanket-deposited (i.e.
  • 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 plana zed to achieve precise thickness and flatness as shown in Figure 2(d).
  • the multi-layer structure 20 formed of the second material 4 i.e. structural material
  • first material 2 i.e. sacrificial material
  • FIG. 3(a) - 3(c) Various components of an exemplary manual electrochemical fabrication system 32 are shown in Figures 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 Figures 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.
  • the CC mask subsystem 36 shown in the lower portion of Figure 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.
  • the blanket deposition subsystem 38 is shown in the lower portion of Figure 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.
  • the planarization subsystem 40 is shown in the lower portion of Figure 3(c) and includes a lapping plate 52 and associated motion and control systems (not shown) for planarizing the depositions. Another method for forming microstructures from electroplated metals (i.e. using electrochemical fabrication techniques) is taught in US Patent No.
  • 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.
  • the '630 patent as well as the other conformable contact mask plating (i.e. Instant Mask Plating) and electrochemical fabrication (i.e. EFAB) publications noted above describe copper as a sacrificial material and nickel as a structural material. The copper is the preferred material for selective deposition while the nickel is the preferred material for blanket deposition. In most applications after formation of the nickel structure it is desirable to reveal it by separating it from the copper sacrificial material.
  • the '630 patent proposes that this removal be performed by an etching operation and that useful etching compositions for selectively stripping copper from nickel structures include (1 ) solutions of ammonium hydroxide and copper sulfate or (2) solutions of ammonium hydroxide and sodium chlorite.
  • This prior art patent indicates that a preferred etchant is Enstrip C38 commercially available from Enthone OMI.
  • etching can also be performed in the presence of (1 ) vibrations, e.g., ultrasound applied to the etchant or the substrate that was plated, and (2) pressurized jets of etchant contacting the metal to be etched.
  • a first aspect of the invention provides an electrochemical fabrication process for producing a three-dimensional structure from a plurality of adhered layers, the process that includes: (A) supplying 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) selectively 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 wherein one of the first material or the second material is a structural material and the other is a sacrificial material; (C) forming a plurality of layers such that each successive layer is formed adjacent to and adhered to a previously deposited layer,
  • a second aspect of the invention provides a process for producing a structure, wherein the process includes: (A) supplying at least one preformed mask that 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 at the least one mask includes a support structure that supports the patterned conformable dielectric material; and (B) selectively depositing at least a first material onto the substrate, the depositing including (1 ) contacting the substrate and the conformable material of the preformed mask; (2) in presence of a plating solution, conducting an electric current through the at least one opening in the selected mask between an anode and the substrate, wherein the anode including 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) separating the selected preformed mask from the substrate; (C) depositing at least a second material onto the substrate after depositing the at least
  • a third aspect of the invention provides a process of etching a first material from a structure, including: (A) supplying a structure including at least a first material and a second material; and (B) placing the structure in an etching solution that includes ammonium hydroxide, a chlorite salt, and a nitrate salt.
  • etching solution that includes ammonium hydroxide, a chlorite salt, and a nitrate salt.
  • Figures 1 (a) - 1 (c) schematically depict side views of various stages of a CC mask plating process
  • Figures 1 (d) - (g) schematically depict a side views of various stages of a CC mask plating process using a different type of CC mask
  • Figures 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.
  • Figures 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 Figures 2(a) - 2(f).
  • Figures 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.
  • Figure 5 depicts a table of copper etchants and various properties associated with them.
  • Figure 6 depicts a plot of etching rate versus C-38 copper stripper concentration.
  • Figure 7 depicts a scanning electron microscope image of a nickel structure damaged by an etchant process that included excessive vibration.
  • Figure 8 depicts a nickel structure that was pitted by etching with C-38.
  • Figure 9 depicts a plot of etched length of a copper wire versus etching time.
  • 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.
  • Figures 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.
  • a side view of a substrate 82 is shown, onto which patternable photoresist 84 is cast as shown in Figure 4(b).
  • 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.
  • a metal 94 e.g. nickel
  • 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.
  • 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).
  • Figure 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.
  • Figure 4(h) the result of repeating the process steps shown in Figures 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 Figure 4(i) to yield a desired 3-D structure 98 (e.g.
  • a sacrificial material such as copper
  • the sacrificial material serves as a mechanical support of the structural material during structure formation.
  • additional material can be deposited over the entire layer without constraint.
  • the use of a sacrificial material eliminates virtually all geometrical restrictions, allowing the structural material on a layer to overhang and even be disconnected from that of the previous layer.
  • the use of a sacrificial material may allow a broader range of structural materials to be used in that the sacrificial material can be deposited in a selective process (e.g.
  • etching by a conformable contact mask process
  • the structural material may be deposited in some other manner (e.g. blanket deposition) where fewer deposition limitations may exist.
  • the basic rules governing etching are as follows: 1. Selectivity: Etchants should only remove sacrificial materials. No or little effect on main materials should occur. 2. Completion: A sacrificial material needs to be removed completely. 3. Speed: The less the etching time the higher the throughput. 4. Integration: An etching process should not damage delicate structures. Wet etching is a fast, cheap process and can also remove materials from blind geometries. Usually, to remove a metal, it must be of an oxidized form so as to transition from the metallic to an ionic state.
  • the active ingredient in a metal etchant needs to be an oxidizing agent.
  • electrochemical anodic etching provides the required oxidizing action by passing a current of cations from a work piece.
  • An acid or alkaline complexing agent may be included to increase the etching rate.
  • Other additives may also be included.
  • Common oxidizing agents used for stripping copper include chlorite, ferric chloride, cupric chloride, persulfate, organic nitro compounds, and peroxide.
  • electrochemical fabrication a fast reliable copper etching process without negative effect on structural material (e.g. nickel) and associated structures desired necessary to achieve the final structures (e.g. microstructures).
  • etching rates for the etchants were determined from either tests or from references, (2) Ni compatibility was determined, and (3) the etching processes for each etchant were examined. Copper foil samples were used for measuring etching rates and had dimensions of 2 cm x 4 cm x 60 ⁇ m and a purity of 99.5%. To hold the samples in the etchant solutions, a hole was drilled with a diameter of 0.48 cm in each sample. Etching time was variable depending on actual reaction rate of each etchant at room temperature ( ⁇ 20°C). The etching rate in each etchant was determined from the difference in measured weight of the copper foil before and after the test.
  • etchants with slow etching rate and bubble formation during the etching process were not considered further.
  • a slow etching rate means more process time while vigorous bubble formation could induce stress in free standing structures such as beams and cantilevers, could break delicate microstructures, or could inhibit etchant access into small passages.
  • the etchants were successful in removing thin sacrificial copper films, their slow etching rates and/or bubble formation make them impractical for removing relatively large amounts of copper in electrochemical fabrication or similar cases.
  • the ENSTRIP ® C-38 stripper had an etching rate of 460 ⁇ m/hr and appeared to be the most promising.
  • ENSTRIP ® C-38 stripper (Enthone-OMI Inc. of New Haven, CT) is a two- component, ammoniacal immersion stripper designed to quickly remove copper from steel and stainless steel substrates.
  • the recommended C-38 stripper is formed from two primary components, Enstrip C-38A at 75% by volume and Enstrip C-38B at 25% by volume. It is recommended that the Enstrip C-38 solution should only be operated within the pH range of 9.3 to 10.5 and within a temperature range from room temperature to a maximum of 38 °C. If the solution pH becomes too low, it is recommended that 27% ammonium hydroxide be added in small increments until the pH is brought into the right range.
  • the C-38 solution can dissolve up to 8 ounces of copper per gallon of solution.
  • the C-38 basic reaction mechanism is believed to be: On the etching surface: CIO 2 ⁇ + H 2 O + 2e ⁇ CIO " + 2OH " 2Cu - 2e ⁇ 2Cu + Cu + + 2NH 3 ⁇ [Cu(NH 3 ) 2 ] + In the bulk solution: CIO 2 ⁇ + H 2 O + 2e ⁇ CIO " + 2OH " 2[Cu(NH 3 ) 2 ] + + 4NH 3 - 2e ⁇ 2[Cu(NH 3 ) 4 ] 2+ C-38 does not attack nickel significantly.
  • Zinc is not suitable for use as an unprotected structural material but may be useful as a sacrificial material since it is quickly dissolved in C-38. All other metals and alloys that were tested were determined to be useful as structural materials when C- 38 is the etchant.
  • the etching rate of copper in C-38 can be adjusted downward by diluting the full strength C-38.
  • a plot of etching rates versus C-38 concentration is shown in Figure 6. For real microstructure release, the etching rate will be lower and will depend on actual geometric complexity since an etching rate is determined by rates of (1 ) fresh etchant delivery to etching surface and (2) reaction products delivery to the bulk solution.
  • etching rate of an epoxy embedded copper wire with a diameter of 0.64mm was only about 180 ⁇ m/hr for first two hours.
  • Stirring the etchant solution improved etching rate.
  • stirring or agitating can improve etching rates, if too violent such as by excess ultrasonic agitation damage to microstructures can result.
  • the preferred dilution is about one part C-38 by volume to about four to five parts H 2 O.
  • the level of dilution may range from as low as about one part C-38 to about ten parts waters and as high as undiluted C-38.
  • the etching endpoint is reached when a blue substance stops appearing from the structure and in particular from any cavity ports within the structure.
  • the structure is then dipped into a Dl water tank and is slowly moved through the water so as to displace the etchant with the water.
  • the structure is then transferred to an alcohol tank where the structure is slowly moved through the alcohol to displace the water with alcohol and it is thereafter removed from the tank and dried in an oven.
  • Ni is considered to be a slightly noble metal.
  • the diameter of pits is in the range of tens of micrometers and the depth of pits is equal to or more than their diameter.
  • C-38 works well in etching copper without attacking nickel.
  • pits have been observed to form on the nickel substrate and nickel deposits.
  • Figure 8 shows an SEM image of pits on a nickel deposit.
  • chlorite is not very stable and could decompose by light, temperature and catalysts to produce hypochlorite and/or chloride ions, especially for aged or used C-38 solutions.
  • hypochlorite is also produced during the etching process. Hypochlorite could attack nickel to form pits.
  • some preferred electrochemical fabrication etching processes involving C-38 include one or more of, and more preferably all of, (1 ) minimizing the C-38's contact with light, high temperature, or air during its storage period; (2) mixing the two components just before etching to ensure the freshness of the etchant; (3) checking the pH of the C-38 prior to each use to make sure it has a pH between 9.3 and 10.5. Additional preferred electrochemical fabrication etching processes add a corrosion inhibitor to the C-38 to help prevent pitting. The use of a corrosion inhibitor in combination with the etchant may be done in alone or in addition to the above noted handling and checking preferences.
  • the preferred inhibitor for use in etching electrochemical fabrication structures with a Chlorite based etchant like C-38 is sodium nitrate, NaNO 3 .
  • Corrosion inhibitors are chemical compounds which, when added in small concentration to a corrosion environment, can greatly increase the corrosion resistance of an exposed metal. It is known that nitrate can be used as a pitting inhibitor for steels, stainless steels, aluminum and its alloys, and for nickel it is believed that the anti-pitting mechanism of NaNO 3 is due to the preferential adsorption of NO 3 ⁇ on the nickel surface. In this way, NO 3 ⁇ ions prevent aggressive ions like CIO " from adsorbing on the surface to cause pitting.
  • the presence of the nitrate can shift a pitting potential (E p ⁇ t) to a more noble value.
  • E p ⁇ t pitting potential
  • Its efficiency can be evaluated by a pitting scan which is a potentiodynamic polarization curve measurement in which E pi t is determined from the anodic polarization curve as the potential where the current density sharply increases due to breakdown of the passive film and formation of pits. Pits initiate and grow above E P it, but not below. The more positive the E P j t , the better the efficiency of the inhibitor.
  • a test was performed to determine if the present of NaNO 3 could raise the E p ⁇ t value. The test was performed using polished nickel disks having diameters of 1.27 cm.
  • an effective quantity of an antipitting agent may be empirically determined by those of skill in the art in view of the teachings herein such that pitting is eliminated or brought down to a tolerable level. An experiment was performed to determine the effect of the presence of NaNO 3 on the copper etching rate.
  • the concentration of C-38 may be lowered to about 0.5g/100ml and still have obtain a benefit from the process and raised well above the 1 g/100ml concentration level without bringing harm to the etching process though a point may be reached where little additional benefit is added by the increased concentration.
  • Wet chemical sacrificial etching is dependent on the reacting species reaching the etching surface (e.g. by diffusion). If the etching area is relatively large and open to the etchant, and the etching length of the sacrificial layer is short (e.g. ⁇ 100 ⁇ m), the etchant can always be sufficiently supplied at the etching front. This etching mode is called reaction-limited etching.
  • FIG. 9 depicts a plot of etched copper length versus time in a one- dimensional etching test that was carried out in C-38 at 38°C aided by ultrasonic stirring for a 40 ⁇ m diameter copper wire (one end of an epoxy embedded copper wire is exposed to the etchant). With time, the etching rate dramatically decreased and after 5 hours, etching practically stopped.
  • electrochemical anodic etching may be used to assist in the removal of copper particularly from complex geometries such as narrow passages and blind cavities.
  • electrochemical anodic etching provides also for anodic dissolution by passing current through the etchant to the surface to be etched.
  • the applied electric field can drive copper ions through the etchant away from the structure being etched toward a cathode while simultaneously attracting anions to the surface of the structure, thus creating higher material transfer rate and helping to bring unreacted fluid closer to the copper front due to conservation of mass.
  • Some embodiments may use selective deposition processes on some layers that are not Instant Mask 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. In some embodiments the anode may be different from the CC mask support and the support may be a porous structure or other perforated structure. Some embodiments will use multiple CC 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.
  • the depth of deposition will be enhanced by pulling the CC 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.

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Abstract

L'invention concerne un processus de fabrication électrochimique servant à produire des structures tridimensionnelles à partir d'une pluralité de couches adhérées. Chaque couche comprend au moins une matière structurelle (par exemple, le nickel) et au moins une matière sacrificielle (par exemple, le cuivre) qui sera attaquée et éliminée de la matière structurelle, après formation de toutes les couches. Un agent d'attaque chimique contenant du chlorite (par exemple, enthone C 38) est mélangé à un inhibiteur de corrosion (par exemple, du nitrate de sodium) de façon à prévenir le piquage de la matière structurelle, pendant l'élimination de la matière sacrificielle. Un processus simple servant à sécher la structure attaquée sans que ce processus ne provoque le collage des surfaces entre elles, consiste à immerger la structure dans l'eau, après son attaque et, puis, dans l'alcool et à la disposer dans un four afin de la sécher.
PCT/US2003/014660 2002-05-07 2003-05-07 Procedes de fabrication electrochimique a traitement post-depot ameliore WO2005033375A2 (fr)

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