Direct Copper Plating Research Articles

Vacuum formed coils for MRI.

To describe a digital fabrication method used for custom MRI receive coils with vacuum forming and electroless copper plating. Our process produces intricate copper traces on curved surfaces. A three-dimensional scan of a desired anatomy is obtained and used to design coil elements. The layout is predistorted with a self built simulation of the vacuum forming process and the geometric overlaps are tested with electromagnetic simulation software. The desired coil geometry is patterned onto a polycarbonate sheet by sandblasting through a tape mask. The sandblasted areas are then catalyzed with a palladium-tin solution and vacuum formed. The catalyzed, three-dimensional part is placed into a custom built plating tank and copper plated. Electronic components are attached to the copper traces to form resonant receive coils. The methods described here are demonstrated and tested with an 8 channel visual cortex coil array. The prototype coils exhibit quality factor ratios higher than three, indicating body noise dominance. The coil array shows high signal-to-noise ratio (SNR) near the periphery of a head shaped phantom. In vivo images with up to spatial resolution were acquired on a human volunteer. This work presents the first example of vacuum formed coils with direct electroless copper plating. Our fabrication method results in coil arrays that are in close proximity to the body. This methods described here may enable the rapid development of a set of coils of different sizes for applications including longitudinal fMRI studies and MR-guided therapies.

Direct additive copper plating on polyimide surface with silver ammonia via plasma modification

In this paper, a facile method of fully additive process to manufacture copper lines on flexible polyimide (PI) substrates was developed. The selective modification on film, involving silver ammonia solution and plasma treatment, was performed to produce Ag particles that catalyze electroless copper plating. It was found that reductive aldehyde groups (R-CHO) were generated at the treated PI surface to reduce silver ammonia ion to Ag particles, which is supported by the of chemical and morphological characterizations. The obtained solid copper deposition demonstrates highly reliable features including limited oxidation, lower roughness and compact crystalline grain with low resistivity of 3.83 × 10-6 Ω·cm. The practical fabricated flexible circuits with designed pattern have passed the mechanical and electrical property tests, confirming the compatibility of the developed additive method with the flexible PI substrate.

Copper Plated Through-Holes for 3D Electro-Thermal Systems

NANO3D Systems has developed an electrochemical technique for direct copper plating on alumina & LTCC substrates and selective plating of screen-printed Ag & Ag/Pd features. When applied directly to the alumina substrate, electrodeposited copper outperformed the DBC substrates in thermal shock tests. When copper plated on thick screen patterned features, it reduces the line resistance and would not inevitably cause the features to delaminate under thermal stress.

Investigation of Cu/TaN and Co/TaN Barrier-Seed Oxidation by Acidic and Alkaline Copper Electroplating Chemistry for Damascene Applications

The effect of plating chemistry on standard damascene integration has been investigated to assess their effect on the interface quality of the final barrier/seed/fill integration. Dipping Co/TaN/SiO2 and Cu/TaN/SiO2 substrates wafers in acidic copper plating chemistry and ligand-based alkaline copper plating chemistry (aveni solution) shows that only the latter maintain the integrity of the substrate while the former degrades the seed (Co or Cu) and the barrier (TaN). We demonstrate that this degradation is extremely fast in the case of a cobalt seed thus only an alkaline ligand-based chemistry is compatible with a direct copper plating on cobalt seed approach. These results are critical because of the ever-going trend of decreasing semiconductors features size that requires the thinning down and removal of disposable metal layers while still maintaining the quality of the interfaces and the integrity of the whole integration.

Direct copper metallization on TGV (Thru-Glass-Via) for high performance glass substrate

Abstract IoT (Internet of things) society will be coming in the near future, and everything will be connected by the Internet. Consequently, data traffic will be increased, and so will the demand to improve the performance of communication devices. Currently, plastics and ceramics are commonly used as insulating materials for communication components, but they are getting close to the limit in terms of material properties, because the next generation high performance communication devices require signal frequency of 20GHz and beyond. Therefore, further improvements in the properties of the insulating materials as well as in the performance of electronic devices are being demanded. Copper conformal metallization on glass provides many opportunities for high frequency electronic devices. The most obvious advantage is given by the material properties. The glass substrate was chosen for low conductivity and low dielectric loss for high frequency application, and for its scalability to the larger area panels with low cost. While applications require strong interfacial adhesion between copper film and glass substrate, glass is often inferior as compared to metal-to metal adhesion. Direct copper metallization on glass is conventionally a difficult task, and it usually does not provide enough peeling strength either. Therefore, forming Ni and Ti seed layers by sputtering and precursors deposited by sol-gel method are being studied. However, these processes have been limitedly used or not been used in mass production, because creation of vias and simultaneous formation of seed layers on both sides by sputtering is difficult to undertake. The Sol-gel method does not provide stable peel strength and it takes a long process. This additional process requirement to add a layer to promote the adhesion of Cu to glass burdens the factories in a couple of ways: 1) enlarging the glass substrate is difficult due to the limitation in equipment size, 2) forming the film inside the through holes is also difficult due to high-aspect ratio via requirements, and 3) high cost due to slow processing speed. In an earlier reports, we presented evidence that we have successfully demonstrated direct copper plating on glass, showing the adhesion strength of 0.42kN/m between glass and copper seed layer. In the present work, we are reporting wet plating process which enables easy and uniform film formation on large glass substrates and inside through holes. This low cost wet plating process enables forming copper film directly on glass without adhesion layer and enhancing the adhesion strength without degrading glass properties and copper conductivity.

Growth-Inhibited Nucleation Enhancement: from High Density Nanoparticle Deposits to Nanometer Thin Continuous Films

In our group, we have been working on the electrochemical nucleation and growth of high island density deposits of copper, indium, nickel, cobalt and iron deposits for more than a decade. From simple electrolyte solutions, all metal systems seem to saturate at an island density of few times 1011 islands per cm2 at most or about 20-30nm spacing per particle. From direct copper plating for damascene processes, we know that the island density can be augmented by the introduction of growth inhibiting species such as the chloride-polyether suppressor additive combo. In this case, the Cl-suppressor adsorbs on the copper island as soon as it is formed. As the current-potential curve for the Cl-suppressor covered copper is polarized more negative with respect to the non-suppressed copper, the overpotential is driven more negative during galvanostatic deposition allowing higher island density [1]. As such the island density can be driven higher than 1013 cm-2 (spacing of about 3nm per particle) on oxide-poor noble metals such as Pt and up to 1012 cm-2(spacing of about 10nm per particle) for oxide-prone surfaces like RuTa alloys [2]. Note that these values are extrapolated as islands can no longer be distinguished from films at this point (coalescence thickness of 5nm and 2nm for hemispherical particles, respectively). The adsorbed suppressor typically also introduces flattened particle shapes helping to bring the effective coalescence thickness even lower. On platinum and cleaned RuTa surfaces, closed copper films with thicknesses down to 2-3nm could be obtained. From our study, it became apparent that the surface condition and overpotential were the two drivers.Based on the know-how from copper, several typical growth inhibiting additives (e.g. saccharine, 2-butyne-1,4-diol, PEG) were tried to increase the Ni and Co nanoparticle density. However, with no avail, as the adsorption and inhibition was typically too slow. In copper deposition, the additives already form complexes with the cuprous intermediate formed during copper deposition. As such the adsorption is very fast, whereas for Ni and Co, the additives need to adsorb via a physisorption which happens too late to affect the nucleation stage. Recently we found that the Ni particle density is strongly affected by the boric acid concentration [3]. The formation of growth inhibiting hydroxides gives the desired effect for growth-inhibited nucleation. However, the local pH cannot rise to fast as otherwise precipitation from solution already occurs in the depletion layer. Therefore a small concentration of boric acid was still needed at 5mM NiCl2 concentration to allow nickel growth to proceed long enough. At the best trade-off conditions a density of 4x1011 cm-2 Ni nanoparticles on TiN was obtained. By tuning the NiCl2 concentration, the growth-inhibited nucleation process could be extended to higher Ni island densities resulting in nanometer thin nickel films [4]; similar to what was achieved for copper. In this paper, we will go in on the mechanism of growth-inhibited growth for the fabrication of high density particles or (sub)nanometer thin films of Cu and Ni. “The Effect of Polyether Suppressors on the Nucleation and Growth of Copper on RuTa Seeded Substrate for Direct Copper Plating” M. Nagar, A. Radisic, K. Strubbe, P.M. Vereecken Electrochim. Acta, 127, 315-326 (2014).“Systematic studies of electrochemical nucleation and growth of copper on Ru-based substrates for damascene process”, Magi Margalit Nagar, PhD thesis, Universiteit Gent. “Enhanced nucleation of Ni nanoparticles on TiN through H3BO3-mediated growth inhibition” Johannes Vanpaemel, Marleen H. van der Veen, Stefan De Gendt, Stefan and Philippe Vereecken, Electrochimica Acta 109, 411-418 (2013).“Electrochemical deposition of sub-nanometer Ni films on TiN” Johannes Vanpaemel, Masahito Sugiura ,Daniel Cuypers, Marleen H. van der Veen, Stefan De Gendt, Stefan and Philippe M. Vereecken, Langmuir, 30 (8), 2047–2053 (2014).

Enhancement of Seeding and Electroless Cu Plating on TaN Barrier Layers: The Role of Plasma Functionalized Self-Assembled Monolayers

Self-assembled monolayers (SAMs) are extensively used in microelectronic copper metallization primarily as seed-trapping layers, diffusion barriers, or pore-sealants for porous dielectric materials. However, direct electroless copper plating of nitride barrier layers assisted by a seed-trapping SAM is rarely examined. Therefore, this work uses TaN, a standard barrier material for Cu metallization, as a model substrate to develop a new seeding (catalyst formation) process for electroless copper plating, involving substrate pretreatments from piranha etching (hydroxylation), octadecyltrichlorosilane SAM (OTS-SAM) deposition and subsequent functionalization. Catalytic particles upon adsorption onto piranha-treated (reference) TaN layers via Ta−OH linkages tend to agglomerate to give a limited density of 8 × 1013 m−2. In contrast, those adsorbed on piranha-treated TaN layers with a plasma-functionalized OTS-SAM over-coating are free from agglomeration and remain an average size of only 3 nm, along with an elevated density of 1 × 1015 m−2. X-ray photoelectron spectroscopy, together with transmission electron microscopy, clearly identifies the thin-film materials deposited and functional groups induced by each of the pretreatments, allowing the mechanism of seeding enhancement to be clarified. Finally, the enhancement of seeding to benefit electroless copper plating will be demonstrated.

Embedded Die Packages and Modules for Power Electronics Applications

Packages and modules with embedded semiconductor dies are of interest for various application fields and power classes. First packages in the lower power range are available in volume production since almost six years. Recent developments focus on medium and higher power applications raging over 500W into the kW range. Different approaches are available to realize such packages and modules. This paper will give an overview and detailed description of the latest approaches for such embedded die structures. In common of all of these approaches, is the use of laminate based die embedding, which uses standard PCB manufacturing technologies. Main differences are the used base substrate, which can still be a ceramic (DBC), Cu leadframe or high current substrate. Examples for the different methods will be given. As the main part, this paper will describe concepts, which enable significant smaller form-factor of power electronics modules, thereby allowing for lower price, high reliability, capability of direct mounting on e.g. a motor so as to form one unit with the motor housing, wide switching frequency range (for large application field) and high power efficiency. The innovative character of this packaging concept is the idea to embed the power drive components (IGBTs, MOSFETs, diode) as thinned chips into epoxy-resin layer built-up and to realize large-area interconnections on both sides by direct copper plating the dies to form a conductor structure with lowest possible electrical impedance and to achieve an optimum heat removal. In this way a thin core is formed on a large panel format which is called Embedded Power Core. The paper will specifically highlight the first results on manufacturing an embedded power discrete package as an example of an embedded power core containing a thin rectifier diode. For module realization, the power cores are interconnected to insulated metal substrates (IMS) by the use of Ag sintering interconnection technologies for the final manufacturing of Power modules. The paper will elaborate on the sintering process for Power Core/IMS interconnections, the microscopically features of the sintered interfaces, and the lateral filling of the sintering gap with epoxy prepregs. Firstly, 500W power modules were manufactured using this approach. Reliability testing results, solder reflow testing, temperature cycling test and active power cycling, will be discussed in detail.

Using Azo As a Conductive and Adhesive Liner for through Glass Vias Filling By Cu Electroplating

This study introduces a method using aluminum-doped zinc oxide (AZO) as a conductive and adhesive liner for through glass vias (TGVs) filling by Cu electroplating. AZO liner is formed on a glass surface by three steps: AZO sol-gel coating, sol-gel evaporation and annealing. AZO sol-gel evaporation was observed by thermogravimetry-differential thermal analysis (TG-DTA). Surface morphology was observed by OM and SEM, and crystallinity and grain size were measured by XRD. AZO sol-gel evaporation rate is key for forming a conformal AZO liner in TGVs. When AZO sol-gel coating was operated under the condition at lower evaporation rate, it would form thick and non-uniform liner and there was a risk of void formation after copper electrodeposition. On the contrary, when the AZO sol-gel coating was operated under the condition of ultrahigh evaporation rate, a thin and uniform AZO liner was formed on the sidewall of the TGVs. This phenomenon refers to the fast coffee ring effect in TGVs. Cu Electroplating was used after AZO liner was formed in the TGVs. This study combined an alkaline conformal copper plating bath with an acid button-up copper plating bath to fill the TGVs. AZO liner cannot only enhance the adhesive force between the deposited copper and the glass, but also play an important role for direct copper plating in TGVs.

From High Density Nanoparticle Deposits to Nanometer Thin Continuous Films By Growth-Inhibited Nucleation Enhancement

In our group, we have been working on the electrochemical nucleation and growth of high island density deposits of copper, indium, nickel, cobalt and iron deposits for about a decade. From simple electrolyte solutions, all metal systems seem to saturate at an island density of few times 1011 islands per cm2 at most or about 20-30nm spacing per particle. From direct copper plating for damascene processes, we know that the island density can be augmented by the introduction of growth inhibiting species such as the chloride-polyether suppressor additive combo. In this case, the Cl-suppressor adsorbs on the copper island as soon as it is formed. As the current-potential curve for the Cl-suppressor covered copper is polarized more negative with respect to the non-suppressed copper, the overpotential is driven more negative during galvanostatic deposition allowing higher island density [1]. As such the island density can be driven higher than 1013 cm-2 (spacing of about 3nm per particle) on oxide-poor noble metals such as Pt and up to 1012 cm-2(spacing of about 10nm per particle) for oxide-prone surfaces like RuTa alloys [2]. Note that these values are extrapolated as islands can no longer be distinguished from films at this point (coalescence thickness of 5nm and 2nm for hemispherical particles, respectively). The adsorbed suppressor typically also introduces flattened particle shapes helping to bring the effective coalescence thickness even lower. On platinum and cleaned RuTa surfaces, closed copper films with thicknesses down to 2-3nm could be obtained. From our study, it became apparent that the surface condition and overpotential were the two drivers.For the application of dense CNT forests, we were interested in fabrication of densely packed Ni, Co and Fe nanoparticles. We have shown that the density of the ECD catalyst particles is directly translated to the CNT density; the highest density of 2x1011cm-2 from an alkaline NiNO3-NH4Cl bath [3]. Based on the know-how from copper, several typical growth inhibiting additives (e.g. saccharine, 2-butyne-1,4-diol, PEG) were tried to increase the Ni and Co nanoparticle density. However, with no avail, as the adsorption and inhibition was typically too slow. In copper deposition, the additives already form complexes with the cuprous intermediate formed during copper deposition. As such the adsorption is very fast, whereas for Ni and Co, the additives need to adsorb via a physisorption which happens too late to affect the nucleation stage. Recently we found that the Ni particle density is strongly affected by the boric acid concentration [4]. The formation of growth inhibiting hydroxides gives the desired effect for growth-inhibited nucleation. However, the local pH cannot rise to fast as otherwise precipitation from solution already occurs in the depletion layer. Therefore a small concentration of boric acid was still needed at 5mM NiCl2 concentration to allow nickel growth to proceed long enough. At the best trade-off conditions a density of 4x1011 cm-2 Ni nanoparticles on TiN was obtained. By tuning the NiCl2concentration, the growth-inhibited nucleation process could be extended to higher Ni island densities resulting in nanometer thin nickel films [5]; similar to what was achieved for copper. In this paper, we will go in on the mechanism of growth-inhibited growth for the fabrication of high density magnetic metals such as Ni, Co and Fe.“The Effect of Polyether Suppressors on the Nucleation and Growth of Copper on RuTa Seeded Substrate for Direct Copper Plating” M. Nagar, A. Radisic, K. Strubbe, P.M. Vereecken Electrochim. Acta, 127, 315-326 (2014).“Systematic studies of electrochemical nucleation and growth of copper on Ru-based substrates for damascene process”, Magi Margalit Nagar, PhD thesis, Universiteit Gent."Electrochemical tailoring of catalyst nanoparticles for CNT spatial-dimension control" A. Romo-Negreira, D. J. Cott, K. Maex, M. M. Heyns and P. M. Vereecken, JES 157, K47 (2010).“Enhanced nucleation of Ni nanoparticles on TiN through H3BO3-mediated growth inhibition” Johannes Vanpaemel, Marleen H. van der Veen, Stefan De Gendt, Stefan and Philippe Vereecken, Electrochimica Acta 109, 411-418 (2013).“Electrochemical deposition of sub-nanometer Ni films on TiN” Johannes Vanpaemel, Masahito Sugiura ,Daniel Cuypers, Marleen H. van der Veen, Stefan De Gendt, Stefan and Philippe M. Vereecken, Langmuir, 30 (8), 2047–2053 (2014).

The Effect of Polyether Suppressors on the Nucleation and Growth of Copper on RuTa Seeded Substrate for Direct Copper Plating

The inhibition effect of different polyether suppressors on the nucleation and growth of copper during galvanostatic deposition was investigated as a function of deposition current density and suppression strength. An increase in the deposition current density resulted in higher island density, (Np). The copper island density increased significantly in the presence of suppressor additive while keeping the other parameters constant. Modification of the polyether molecular weight (Mw) and structure exhibited different inhibition behavior, which in turn affected the island density. Analysis of the potential-time transients shows that an exponential relationship exists between the island density, Np, and the actual deposition overpotential. Interestingly, the same exponential dependence between copper island density and overpotential as those in the additive free CuSO4 solutions was found. This relationship provides a universal equation for Np on RuTa surface and thus, the island density can be estimated from the actual deposition overpotential irrespective of the Cu2+ concentration, suppressor kind and current density. High Np can be achieved by controlling the overpotential which can be manipulated by increasing the current density, lowering the Cu2+ concentrations and adding a strong suppressor to the plating solution. These observations imply that a better solution composition can be tailored to fulfill the requirements for direct plating applications.

Atomic layer deposition for high aspect ratio through silicon vias

The paper presents atomic layer deposition (ALD) processes and process integration for the deposition of insulating liners, copper diffusion barriers, and seed layers for direct copper plating in high aspect ratio (>20:1) through silicon vias. A TaN-based copper diffusion barrier was deployed on an aluminum oxide insulating liner. The latter has the potential to act also as a dielectric barrier against copper diffusion according to BTS and TVS measurements. Furthermore, ruthenium ALD films applied as seed layers for direct copper plating were deposited with an intermediate annealing step to improve film adhesion and ensure the deposition of thick films without any delamination. The step coverage of the presented ALD processes was confirmed by SEM measurements on cross-sections of coated TSV structures. Finally a subsequent electrochemical deposition (ECD) of copper was conducted revealing the satisfying functionality of the Ru seed layer.

Direct Copper Plating on Ultra-Thin Sputtered Cobalt Film in an Alkaline Bath

We report on the electrochemical process and nucleation mechanism of the “direct-on-barrier” electroplating of copper on ultrathin cobalt adhesion layer from an alkaline CuSO4 and ethylenediamine (En) bath without additives. Results show that the corrosion current density was much lower in the alkaline bath than that in the commercial acidic bath due to formation of the CuEn22+ species in the aqueous CuSO4-En solution. The CuEn22+ species can well stop the reaction between the copper ions and Co by reducing the potential of copper ions. The current-time transients were not typical of a diffusion-limited nucleation and growth. Pure instantaneous or progressive nucleation of copper on Co layer was not observed. The impact of current density on the orientation, resistance and morphology was studied. Copper film in 250 nm thick was successfully deposited on the 10 nm Co film in the patterned wafers. And Cu was electroplated onto ultrathin Co layer with ∼5 nm thickness and TEM result shows that there is no obvious Co thickness loss.

Metallic Film Formation Using Direct Micropatterning with Photoreactive Metal Complexes

Palladium, cobalt, and nickel in complex with photoacid-generating ligands, 4-(2-nitrobenzyloxycarbonyl)catechol and 4-(6-nitroveratryloxycarbonyl)catechol, were prepared in solution. Films formed from the metal complex solutions perform as positive-tone, directly photopatternable palladium, cobalt, nickel oxide, or composite film precursors. After exposure, acid-bearing selectively soluble complexes could be removed to give patterned films upon developing in aqueous base, which were transformable to the corresponding pattern-preserving metal/metal oxide film. The photodynamics of photoinduced solubility and direct micropatterning of palladium, cobalt, nickel, and palladium/nickel oxide composite films were investigated. Employing palladium as the initiator for autocatalytic chemical plating, selective direct copper plating on palladium film on polyethylene naphthalate and palladium/nickel oxide composite film on glass was accomplished.

Multi-scale modeling of direct copper plating on resistive non-copper substrates

The direct copper plating on resistive non-copper substrates is studied using a multi-scale modeling approach. A micro-scale nucleation model is coupled with the macro-scale current distribution model to predict the coalescence thickness and the thickness profile on a wafer. Simulation results show that the coalescence thickness may vary significantly with the distance from the wafer edge. The simulation tool is applied to the study of different factors involved in the plating process, including the propensity to nucleate on a given substrate, suppressor additives, substrate conductivity and the input current. The collective effects of these factors on nucleation and front propagation are investigated. High nucleation density and low coalescence thickness are demonstrated on a resistive substrate by introducing suppressor additives and ramping current in the plating.

Multi-Scale Modeling of Direct Copper Plating on Resistive Non-Copper Substrates

not Available.

Direct Electroless Copper Plating on Polyimide for FPCB Applications

As electronic devices are getting smaller and lighter, the density of copper lines on flexible printed circuit board (FPCB) is getting higher. Conventionally, subtractive method was used for copper line on a flexible films, however, as the line pitch is getting smaller, the lateral etching of copper cause serious problem. To replace the subtractive method, semi-additive method was used for fine pitch copper line fabrication. In semi additive process, sputtered layer for the electroplating copper was required. The feasibility of electroless plating to replace high cost sputtered copper seed layer was investigated. Electroless depositions of copper were conducted on different substrate to find optimum conditions of electroless copper plating. To find optimum conditions, the effects and selectivity of activation method on several substrates were also investigated. The adhesion strength between polyimide and copper was improved by treating the polyimide surface with butylamines. Pretreatment prior to electroless plating is very sensitive and surface dependent. Surface morphologies were investigated with FESEM.

Direct Electroless Copper Plating on Glass

Direct Electroless Copper Plating on Glass

Direct Copper Plating on Highly Resistive Barrier Layers

not Available.

Process of direct copper plating on ABS plastics

The processes of direct copper plating on ABS plastics were investigated by atomic force microscopy (AFM), ultraviolet–visible absorption spectrometry (UV–vis) and X-ray fluorescence spectroscopy (XRF) techniques. The substrates were etched by CrO3/H2SO4 solution containing Pd2+ ions, catalyzed by Pd/Sn colloids solution and accelerated in an alkaline solution containing copper ions. The Pd2+ ions in etching solution can reduce the surface roughness and enhance the colloids adsorption. The good dispersivity colloids have excellent catalysis and its UV–vis peaks broaden. After acceleration, when the stability of Cu2+-complex is relatively low, Sn2+ was oxidized by Cu2+ in the alkaline solution meanwhile Cu2O can be formed. The disproportionation reaction of Cu2O will proceed and metallic copper forms between the Pd particles, so the conductivity of ABS surface increased. The copper particles play an important role in determining the uniformity of the propagation of copper plating. The particles of copper plating layer were uniformity and fine. The atomic concentration and the thickness of copper layer were analyzed by XRF.