Three fundamental types of suppressor additives for copper electroplating could be identified by ... more Three fundamental types of suppressor additives for copper electroplating could be identified by means of potential transient measurements. These suppressor additives differ in their synergistic and antagonistic interplay with anions that are chemisorbed on the metallic copper surface during electrodeposition. In addition these suppressor chemistries reveal different barrier properties with respect to cupric ions and plating additives (Cl, SPS). While the type-I suppressor selectively forms efficient barriers for copper inter-diffusion on chloride-terminated electrode surfaces we identified a type-II suppressor that interacts non-selectively with any kind of anions chemisorbed on copper (chloride, sulfate, sulfonate). Type-I suppressors are vital for the superconformal copper growth mode in Damascene processing and show an antagonistic interaction with SPS (Bis-Sodium-Sulfopropyl-Disulfide) which involves the deactivation of this suppressor chemistry. This suppressor deactivation is rationalized in terms of compositional changes in the layer of the chemisorbed anions due to the competition of chloride and MPS (Mercaptopropane Sulfonic Acid) for adsorption sites on the metallic copper surface. MPS is the product of the dissociative SPS adsorption within the preexisting chloride matrix on the copper surface. The non-selectivity in the adsorption behavior of the type-II suppressor is rationalized in terms of anion/cation pairing effects of the poly-cationic suppressor and the anion-modified copper substrate. Atomic-scale insights into the competitive Cl/MPS adsorption are gained from in situ STM (Scanning Tunneling Microscopy) using single crystalline copper surfaces as model substrates. Type-III suppressors are a third class of suppressors. In case of type-I and type-II suppressor chemistries the resulting steady-state deposition conditions are completely independent on the particular succession of additive adsorption. In contrast to that a strong dependence of the suppressing capabilities on the sequence of additive adsorption ("first comes, first serves" principle) is observed for the type-III suppressor. This behavior is explained by a suppressor barrier that impedes not only the copper inter-diffusion but also the transport of other additives (e.g. SPS) to the copper surface.
ABSTRACT The temporal instability of different types of suppressor additives relevant for Damasce... more ABSTRACT The temporal instability of different types of suppressor additives relevant for Damascene and 3D-TSV copper electroplating is studied by means of potential transient experiments in combination with structure sensitive methods such as in-situ scanning tunneling microscopy and in-situ synchrotron x-ray diffraction. The molecular interplay of various types of suppressor additives with their specific antagonists at the copper/electrolyte interface is discussed in the light of the successful fill of sub-50nm Damascene features and μm-sized 3D-TSVs.
Copper pillar is a transformative technology for next generation 2.5D/3D packaging. Fine-pitch c... more Copper pillar is a transformative technology for next generation 2.5D/3D packaging. Fine-pitch copper pillar bumps have replaced conventional flip chip solder bumps when the need for extremely low profile, high connectivity interconnect is required. Cu pillar Flip-Chip is expected to grow at a 35% CAGR between 2010 - 2018 in terms of wafer count. It will be a key interconnect technology in future semiconductor packages. However, it is not just copper deposition into vias, but also needs high speed trough-mask wafer plating, high uniform bump height, flat bump shape, good surface morphology and electric reliability. Copper deposition in microvias is effected by electric field which is photoresist shielding causing “current distribution”. A bump center has higher current density than peripheries, so the shape will become convex. The inner microvia flow field is another factor which causes higher copper ion concentration at center and forms a domed bump. Although, these two fac...
Cell interactions with adhesive surfaces play a vital role in the regulation of cell proliferatio... more Cell interactions with adhesive surfaces play a vital role in the regulation of cell proliferation, viability and differentiation, and affect multiple biological processes. Since cell adhesion depends mainly on the nature and density of the adhesive ligand molecules, spatial molecular patterning, which enables the modulation of adhesion receptor clustering, might affect both the structural and signalling activities of the adhesive interaction. We herein show that cells plated on surfaces that present a molecularly defined spacing gradient of an integrin RGD ligand, can sense small but consistent differences in adhesive ligand spacing of about 1 nm across the cell diameter, which is approximately 61 m when the spacing includes 70 nm. Consequently, these positional cues induce cell polarization, and initiate cell migration and signalling. We propose that differential positional clustering of the integrin transmembrane receptors is used by cells for exploring and interpreting their environment, at high spatial sensitivity. Adhesion of tissue cells to the extracellular matrix depends on the activation of specific transmembrane receptors; e.g. integrins, which leads to the assembly of specialized adhesion sites known as focal adhesions (FA). 1 Activation and spatial organization of integrins are mainly controlled by epitopes containing a RGD (R = arginine, G = glycine, D = aspartate) sequence, that are present on a variety of adhesive extracellular matrix (ECM) proteins. Recent studies indicated that beyond the chemical specificity of the adhesive epitope, 2 many physical features of the adhesive surface, including its topography, 3 rigidity, 4 and precise epitope spacing, 5 are critical for guiding receptor-mediated adhesion formation and signalling. Specifically, it was demonstrated that cyclic RGDfK peptides linked to nanogold particles 6 which were arranged in pattern on substrates and interspaced by 58 or 73 nm, influence cell adhesion, 5 spreading, focal adhesion assembly, and migration 7, 8 in very different ways. In these studies, control experiments demonstrated that only the specific functionalization of nanogold particles with cyclic RGD induced integrin clustering and such focal adhesion formation upon interaction with cells such as 3T3-fibroblasts or
The cover picture shows the first demonstration of cell adhesion activation through a nanoadhesiv... more The cover picture shows the first demonstration of cell adhesion activation through a nanoadhesive pattern with single integrin resolution. Scanning electron microscopy images nanoscopic 6‐nm large Au particles as white dots, which are functionalized with cell ligands and organized in a square pattern. The free glass substrate area between the Au is covered with a biologically inert polymer, thereby avoiding protein or cell interactions with the glass. A few cell lamellipodia experience this environment and adhere entirely to the Au–nanoparticle pattern squares. The substrate forms a well‐defined, rigid adhesion pattern where Au particles control integrin–integrin interactions in focal adhesions by their separation distance. A separation between single intergrins of ≥73 nm results in limited cell attachment and spreading, and dramatically reduces the formation of focal adhesion and actin stress fibers. The range of 58–73 nm is found to be a universal length scale for integrin cluste...
A combination of soluble and extracellular matrix (ECM)-immobilised molecular gradients steer cel... more A combination of soluble and extracellular matrix (ECM)-immobilised molecular gradients steer cell migration and location in vivo. Here, gradients of ECM molecules are formed in vitro by the combination of a surface nanopatterning technique called block copolymer nanolithography (BCN) and a biofunctionalisation technique. A modified substrate dip coating process of BCN allows for the formation of precise molecular gradients of cyclic RGDfK peptide patches at interfaces which are presented to cells for testing cell adhesion and polarisation. Surfaces formed by BCN consist of hexagonally ordered gold dot patterns with a gradient in particle spacing. Each dot serves as a chemical anchor for the binding of cyclic RGDfK peptides which are specifically recognised by α v β 3 integrins. Due to steric hindrance only up to one integrin binds to one functionalised gold dot. Applying particle spacing gradients we demonstrate how cell morphology, adhesion area, actin and vinculin distribution as well as polarisation are influenced by the peptide patch spacing gradient. As a consequence, these gradients of adhesive ligands induce cell orientation towards smaller particle spacing when the gradient strength is 15 nm/mm at least. Eventually, this measures a minimal value of ligand patch spacing sensitivity of adhesive cells which is approximately 1 nm across the cell body.
Cell motility consists of repeating cycles of protrusion of a leading edge in the direction of mi... more Cell motility consists of repeating cycles of protrusion of a leading edge in the direction of migration, attachment of the advancing membrane to the matrix, and pulling of the trailing edge forward. In this dynamic process there is a major role for the cytoskeleton, which drives the protrusive events via polymerisation of actin in the lamellipodium, followed by actomyosin contractility. To study the transition of the actin cytoskeleton from a 'protrusive' to 'retractive' form, we have monitored the formation of focal adhesions and stress fibres during cell migration on a micro-patterned surface. This surface consisted of parallel arrays of 2 mm-wide, fibronectincoated gold stripes, separated by non-adhesive (poly(ethylene glycol)-coated) glass areas with variable width, ranging from 4-12 mm. Monitoring the spreading of motile cells indicated that cell spreading was equally effective along and across the adhesive stripes, as long as the non-adhesive spaces between them did not exceed 6 mm. When the width of the PEG region was 8 mm or more, cells became highly polarised upon spreading, and failed to reach the neighboring adhesive stripes. It was also noted that as soon as the protruding lamella successfully crossed the PEG-coated area and reached an adhesive region, the organisation of actin in that area was transformed from a diffuse meshwork into a bundle, oriented perpendicularly to the stripes and anchored at its ends in focal adhesions. This transition depends on actomyosin-based contractility and is apparently triggered by the adhesion to the rigid fibronectin surface.
Three fundamental types of suppressor additives for copper electroplating could be identified by ... more Three fundamental types of suppressor additives for copper electroplating could be identified by means of potential transient measurements. These suppressor additives differ in their synergistic and antagonistic interplay with anions that are chemisorbed on the metallic copper surface during electrodeposition. In addition these suppressor chemistries reveal different barrier properties with respect to cupric ions and plating additives (Cl, SPS). While the type-I suppressor selectively forms efficient barriers for copper inter-diffusion on chloride-terminated electrode surfaces we identified a type-II suppressor that interacts non-selectively with any kind of anions chemisorbed on copper (chloride, sulfate, sulfonate). Type-I suppressors are vital for the superconformal copper growth mode in Damascene processing and show an antagonistic interaction with SPS (Bis-Sodium-Sulfopropyl-Disulfide) which involves the deactivation of this suppressor chemistry. This suppressor deactivation is rationalized in terms of compositional changes in the layer of the chemisorbed anions due to the competition of chloride and MPS (Mercaptopropane Sulfonic Acid) for adsorption sites on the metallic copper surface. MPS is the product of the dissociative SPS adsorption within the preexisting chloride matrix on the copper surface. The non-selectivity in the adsorption behavior of the type-II suppressor is rationalized in terms of anion/cation pairing effects of the poly-cationic suppressor and the anion-modified copper substrate. Atomic-scale insights into the competitive Cl/MPS adsorption are gained from in situ STM (Scanning Tunneling Microscopy) using single crystalline copper surfaces as model substrates. Type-III suppressors are a third class of suppressors. In case of type-I and type-II suppressor chemistries the resulting steady-state deposition conditions are completely independent on the particular succession of additive adsorption. In contrast to that a strong dependence of the suppressing capabilities on the sequence of additive adsorption ("first comes, first serves" principle) is observed for the type-III suppressor. This behavior is explained by a suppressor barrier that impedes not only the copper inter-diffusion but also the transport of other additives (e.g. SPS) to the copper surface.
A multistep procedure for creating nanohole‐patterned gold films (see Figure) is presented. The s... more A multistep procedure for creating nanohole‐patterned gold films (see Figure) is presented. The steps include the self‐assembly of metal‐loaded polystyrene‐block‐poly(2‐vinylpyridine) micelles on GaAs substrates, hydrogen gas plasma treatment, directional reactive ion etching, and gold sputtering. The size and separation of holes resemble that of the gold cluster pattern.
The use of eutectic Sn-Cu alloys in packaging applications in microelectronics industry is not so... more The use of eutectic Sn-Cu alloys in packaging applications in microelectronics industry is not something entirely new. However, this alloy was mostly used in large features and fabricated using metal powders and metallurgical deposition techniques. The diameter of an individual grain of the eutectic Sn-Cu powder is typically similar in size to the diameter of pillars or bumps currently used in 3D stacking, and if we were to check its usefulness as a solder on this scale, an alternative manufacturing technique had to be used. We have electrochemically deposited Sn-Cu alloys having up to 10 wt.% Cu and explored its possible benefits when used as a solder in combination with different Under bump metallization (UBM) materials. Sn-Cu alloys were deposited on blanket and patterned coupons, and promising experiments then transferred to a wafer-scale, i.e. Sn-Cu alloys were deposited on 300 mm wafers in an industrial-type plating tool. A typical sample/wafer had a Cu seed with a diffusion barrier (e.g. TiW) underneath and patterned features defined with a photoresist mask. Characteristic dimensions of the patterned features were on the order of mm and cm (lines), (diameter)D50µm × (height)H60 µm (pillars), and D8µm × H15 µm (bumps). Cu, Ni, or Co were used as UBM layers. Chemical composition of deposited alloys has been examined by using X-ray fluorescence (XRF), Micro X-ray fluorescence (Micro-XRF), Inductively coupled plasma mass spectrometry (ICP-MS), and Electron probe microanalysis (EPMA). Surface morphology and the shape of deposited features have been examined using Scanning electron microscopy (SEM) and Laser scanning microscopy (LSM), while thermodynamic properties have been studied using Differential scanning calorimetry (DSC). Within-wafer (WIW) and within-die (WID) height uniformity of the pillars has been analyzed using Falcon 630 Plus tool (Camtek Ltd), capable of capturing heights of all the structures on the wafer simultaneously. The kinetics of Intermetallic compound (IMC) formation have been studied in the number of selected samples by combining ex-situ Focused ion beam (FIB) and in-situ measurements of resistance change of the features during anneal/thermal ageing [1]. We will discuss possible benefits and drawbacks for use of electrochemically deposited Sn-Cu alloy solders in combination with different UBM layers based on these results. References: [1] Lin Hou, Jaber Derakhshandeh, Eric Beyne, and Ingrid De Wolf, “A Novel Resistance Measurement Methodology for in-situ UBM/Solder Interfacial Reaction Monitoring”, DOI 10.1109/TCPMT.2019.2950448, IEEE Transactions on Components, Packaging and Manufacturing Technology. Figure 1
This paper introduces an approach where the match of two different length scales, i.e., pattern f... more This paper introduces an approach where the match of two different length scales, i.e., pattern from self-assembly of block copolymer micelles (< 100 nm) and electron-beam (e-beam) writing (> 50 nm), allow the grouping of nanometer-sized gold clusters in very small numbers in even aperiodic pattern and separation of these groups at length scales that are not accessible by pure self-assembly. Thus, we could demonstrate the grouping of Au nanoclusters in different geometries such as squares, rings, or spheres.
The competitive interaction of chloride and SPS (bis-(sodium-sulfopropyl)-disulfide) at Cu(1 0 0)... more The competitive interaction of chloride and SPS (bis-(sodium-sulfopropyl)-disulfide) at Cu(1 0 0)/electrolyte model interfaces was studied by means of cyclic voltammetry in combination with in situ STM and DFT. This specific anion/anion interaction is of paramount importance for the suppressor ensemble deactivation in the context of the industrial Cu Damascene process used for the state-of-the-art on-chip metallization. It is the interplay between chemisorbed chloride and SPS which regulates the dissociative SPS adsorption on copper as the key step in the course of the surface-confined MPS (mercaptopropane sulfonic acid) production. The latter species is considered as the actual anti-suppressor (depolarizer) in context of the Cu Damascene process. Under competitive conditions the chloride adsorbs and orders much faster on Cu(1 0 0) than the SPS. The resulting c(2 × 2)-Cl adlayer acts as an effective barrier for the dissociative SPS adsorption, at least under non-reactive conditions. Defect sites within the chloride matrix are identified as crucial prerequisites for the dissociative SPS adsorption. Defects are generated under reactive conditions during copper dissolution or copper deposition due to rapid anion adsorption/desorption dynamics. As consequence of the SPS dissociation a mixed, defect-rich c(2 × 2)-Cl-MPS co-adsorption phase forms on Cu(1 0 0) where every second chloride species of the pristine c(2 × 2)-Cl adlayer is displaced by MPS units. This co-adsorption phase reveals an apparent p(2 × 2) symmetry in the STM experiment since only the sulfonic head groups of the MPS units are imaged while the S and the Cl species chemisorbed on the copper surface remain invisible at the "buried" interface. The relevance of this surface reaction for the Cu Damascene process is discussed in detail.
This study reinvestigates the electrochemical characteristics of three different suppressor addit... more This study reinvestigates the electrochemical characteristics of three different suppressor additives that are used in context of industrial copper plating (Damascene, Through-Silicon-Via). It is the particular aim of this contribution to further substantiate our recently introduced classification scheme of suppressor chemistries that relies on their antagonistic and synergistic interplay with MPS (mercaptopropane sulfonic acid/sulfonate). The latter appears as intermediate species in the course of copper electrodeposition in the presence of SPS (bis-(sodium-sulfopropyl)-disulfide). Both the linear sweep voltammetry and potential transient experiments reveal a purely antagonistic interaction between PAG (polyalkylene glycol) based suppressor ensembles and the SPS (MPS precursor) which is rationalized in terms of the coordinative dissolution of a hyper-branched PAG-Cu(I)-Cl coordination network by the MPS. Such purely antagonistic suppressor/MPS interplay is our criterion for a so-called type-I suppressor. A purely synergistic suppressor/MPS interaction is observed for the PEI (polyethylene-imine) which can be considered as a prototypical type-II suppressor. Beyond classical interfacial anion/cation pairing the partly protonated, poly-cationic PEI is capable to form MPS-stabilized Cu(I) adducts. Their suppressing effect relies on an in situ hyper-branching achieved by a combination of Cu(I) coordination and an inner salt formation. Polymerizates of imidazole and epichlorohydrin (Imep) actually show both an antagonistic and a synergistic MPS/suppressor interaction. While free MPS acts as antagonist with respect to the formed Imep-Cu(I)-MPS suppressor adduct it is the MPS coordinated to Cu(I) which serves as crucial co-additive for the Imep suppressor ensemble. It is this interplay of antagonistic and synergistic MPS/suppressor interactions which introduces an extra feedback loop into the reaction cycle of those plating additives thus giving rise to the appearance of non-linear temporal instabilities into the plating characteristics under galvanostatic control.
Three fundamental types of suppressor additives for copper electroplating could be identified by ... more Three fundamental types of suppressor additives for copper electroplating could be identified by means of potential transient measurements. These suppressor additives differ in their synergistic and antagonistic interplay with anions that are chemisorbed on the metallic copper surface during electrodeposition. In addition these suppressor chemistries reveal different barrier properties with respect to cupric ions and plating additives (Cl, SPS). While the type-I suppressor selectively forms efficient barriers for copper inter-diffusion on chloride-terminated electrode surfaces we identified a type-II suppressor that interacts non-selectively with any kind of anions chemisorbed on copper (chloride, sulfate, sulfonate). Type-I suppressors are vital for the superconformal copper growth mode in Damascene processing and show an antagonistic interaction with SPS (Bis-Sodium-Sulfopropyl-Disulfide) which involves the deactivation of this suppressor chemistry. This suppressor deactivation is rationalized in terms of compositional changes in the layer of the chemisorbed anions due to the competition of chloride and MPS (Mercaptopropane Sulfonic Acid) for adsorption sites on the metallic copper surface. MPS is the product of the dissociative SPS adsorption within the preexisting chloride matrix on the copper surface. The non-selectivity in the adsorption behavior of the type-II suppressor is rationalized in terms of anion/cation pairing effects of the poly-cationic suppressor and the anion-modified copper substrate. Atomic-scale insights into the competitive Cl/MPS adsorption are gained from in situ STM (Scanning Tunneling Microscopy) using single crystalline copper surfaces as model substrates. Type-III suppressors are a third class of suppressors. In case of type-I and type-II suppressor chemistries the resulting steady-state deposition conditions are completely independent on the particular succession of additive adsorption. In contrast to that a strong dependence of the suppressing capabilities on the sequence of additive adsorption ("first comes, first serves" principle) is observed for the type-III suppressor. This behavior is explained by a suppressor barrier that impedes not only the copper inter-diffusion but also the transport of other additives (e.g. SPS) to the copper surface.
ABSTRACT The temporal instability of different types of suppressor additives relevant for Damasce... more ABSTRACT The temporal instability of different types of suppressor additives relevant for Damascene and 3D-TSV copper electroplating is studied by means of potential transient experiments in combination with structure sensitive methods such as in-situ scanning tunneling microscopy and in-situ synchrotron x-ray diffraction. The molecular interplay of various types of suppressor additives with their specific antagonists at the copper/electrolyte interface is discussed in the light of the successful fill of sub-50nm Damascene features and μm-sized 3D-TSVs.
Copper pillar is a transformative technology for next generation 2.5D/3D packaging. Fine-pitch c... more Copper pillar is a transformative technology for next generation 2.5D/3D packaging. Fine-pitch copper pillar bumps have replaced conventional flip chip solder bumps when the need for extremely low profile, high connectivity interconnect is required. Cu pillar Flip-Chip is expected to grow at a 35% CAGR between 2010 - 2018 in terms of wafer count. It will be a key interconnect technology in future semiconductor packages. However, it is not just copper deposition into vias, but also needs high speed trough-mask wafer plating, high uniform bump height, flat bump shape, good surface morphology and electric reliability. Copper deposition in microvias is effected by electric field which is photoresist shielding causing “current distribution”. A bump center has higher current density than peripheries, so the shape will become convex. The inner microvia flow field is another factor which causes higher copper ion concentration at center and forms a domed bump. Although, these two fac...
Cell interactions with adhesive surfaces play a vital role in the regulation of cell proliferatio... more Cell interactions with adhesive surfaces play a vital role in the regulation of cell proliferation, viability and differentiation, and affect multiple biological processes. Since cell adhesion depends mainly on the nature and density of the adhesive ligand molecules, spatial molecular patterning, which enables the modulation of adhesion receptor clustering, might affect both the structural and signalling activities of the adhesive interaction. We herein show that cells plated on surfaces that present a molecularly defined spacing gradient of an integrin RGD ligand, can sense small but consistent differences in adhesive ligand spacing of about 1 nm across the cell diameter, which is approximately 61 m when the spacing includes 70 nm. Consequently, these positional cues induce cell polarization, and initiate cell migration and signalling. We propose that differential positional clustering of the integrin transmembrane receptors is used by cells for exploring and interpreting their environment, at high spatial sensitivity. Adhesion of tissue cells to the extracellular matrix depends on the activation of specific transmembrane receptors; e.g. integrins, which leads to the assembly of specialized adhesion sites known as focal adhesions (FA). 1 Activation and spatial organization of integrins are mainly controlled by epitopes containing a RGD (R = arginine, G = glycine, D = aspartate) sequence, that are present on a variety of adhesive extracellular matrix (ECM) proteins. Recent studies indicated that beyond the chemical specificity of the adhesive epitope, 2 many physical features of the adhesive surface, including its topography, 3 rigidity, 4 and precise epitope spacing, 5 are critical for guiding receptor-mediated adhesion formation and signalling. Specifically, it was demonstrated that cyclic RGDfK peptides linked to nanogold particles 6 which were arranged in pattern on substrates and interspaced by 58 or 73 nm, influence cell adhesion, 5 spreading, focal adhesion assembly, and migration 7, 8 in very different ways. In these studies, control experiments demonstrated that only the specific functionalization of nanogold particles with cyclic RGD induced integrin clustering and such focal adhesion formation upon interaction with cells such as 3T3-fibroblasts or
The cover picture shows the first demonstration of cell adhesion activation through a nanoadhesiv... more The cover picture shows the first demonstration of cell adhesion activation through a nanoadhesive pattern with single integrin resolution. Scanning electron microscopy images nanoscopic 6‐nm large Au particles as white dots, which are functionalized with cell ligands and organized in a square pattern. The free glass substrate area between the Au is covered with a biologically inert polymer, thereby avoiding protein or cell interactions with the glass. A few cell lamellipodia experience this environment and adhere entirely to the Au–nanoparticle pattern squares. The substrate forms a well‐defined, rigid adhesion pattern where Au particles control integrin–integrin interactions in focal adhesions by their separation distance. A separation between single intergrins of ≥73 nm results in limited cell attachment and spreading, and dramatically reduces the formation of focal adhesion and actin stress fibers. The range of 58–73 nm is found to be a universal length scale for integrin cluste...
A combination of soluble and extracellular matrix (ECM)-immobilised molecular gradients steer cel... more A combination of soluble and extracellular matrix (ECM)-immobilised molecular gradients steer cell migration and location in vivo. Here, gradients of ECM molecules are formed in vitro by the combination of a surface nanopatterning technique called block copolymer nanolithography (BCN) and a biofunctionalisation technique. A modified substrate dip coating process of BCN allows for the formation of precise molecular gradients of cyclic RGDfK peptide patches at interfaces which are presented to cells for testing cell adhesion and polarisation. Surfaces formed by BCN consist of hexagonally ordered gold dot patterns with a gradient in particle spacing. Each dot serves as a chemical anchor for the binding of cyclic RGDfK peptides which are specifically recognised by α v β 3 integrins. Due to steric hindrance only up to one integrin binds to one functionalised gold dot. Applying particle spacing gradients we demonstrate how cell morphology, adhesion area, actin and vinculin distribution as well as polarisation are influenced by the peptide patch spacing gradient. As a consequence, these gradients of adhesive ligands induce cell orientation towards smaller particle spacing when the gradient strength is 15 nm/mm at least. Eventually, this measures a minimal value of ligand patch spacing sensitivity of adhesive cells which is approximately 1 nm across the cell body.
Cell motility consists of repeating cycles of protrusion of a leading edge in the direction of mi... more Cell motility consists of repeating cycles of protrusion of a leading edge in the direction of migration, attachment of the advancing membrane to the matrix, and pulling of the trailing edge forward. In this dynamic process there is a major role for the cytoskeleton, which drives the protrusive events via polymerisation of actin in the lamellipodium, followed by actomyosin contractility. To study the transition of the actin cytoskeleton from a 'protrusive' to 'retractive' form, we have monitored the formation of focal adhesions and stress fibres during cell migration on a micro-patterned surface. This surface consisted of parallel arrays of 2 mm-wide, fibronectincoated gold stripes, separated by non-adhesive (poly(ethylene glycol)-coated) glass areas with variable width, ranging from 4-12 mm. Monitoring the spreading of motile cells indicated that cell spreading was equally effective along and across the adhesive stripes, as long as the non-adhesive spaces between them did not exceed 6 mm. When the width of the PEG region was 8 mm or more, cells became highly polarised upon spreading, and failed to reach the neighboring adhesive stripes. It was also noted that as soon as the protruding lamella successfully crossed the PEG-coated area and reached an adhesive region, the organisation of actin in that area was transformed from a diffuse meshwork into a bundle, oriented perpendicularly to the stripes and anchored at its ends in focal adhesions. This transition depends on actomyosin-based contractility and is apparently triggered by the adhesion to the rigid fibronectin surface.
Three fundamental types of suppressor additives for copper electroplating could be identified by ... more Three fundamental types of suppressor additives for copper electroplating could be identified by means of potential transient measurements. These suppressor additives differ in their synergistic and antagonistic interplay with anions that are chemisorbed on the metallic copper surface during electrodeposition. In addition these suppressor chemistries reveal different barrier properties with respect to cupric ions and plating additives (Cl, SPS). While the type-I suppressor selectively forms efficient barriers for copper inter-diffusion on chloride-terminated electrode surfaces we identified a type-II suppressor that interacts non-selectively with any kind of anions chemisorbed on copper (chloride, sulfate, sulfonate). Type-I suppressors are vital for the superconformal copper growth mode in Damascene processing and show an antagonistic interaction with SPS (Bis-Sodium-Sulfopropyl-Disulfide) which involves the deactivation of this suppressor chemistry. This suppressor deactivation is rationalized in terms of compositional changes in the layer of the chemisorbed anions due to the competition of chloride and MPS (Mercaptopropane Sulfonic Acid) for adsorption sites on the metallic copper surface. MPS is the product of the dissociative SPS adsorption within the preexisting chloride matrix on the copper surface. The non-selectivity in the adsorption behavior of the type-II suppressor is rationalized in terms of anion/cation pairing effects of the poly-cationic suppressor and the anion-modified copper substrate. Atomic-scale insights into the competitive Cl/MPS adsorption are gained from in situ STM (Scanning Tunneling Microscopy) using single crystalline copper surfaces as model substrates. Type-III suppressors are a third class of suppressors. In case of type-I and type-II suppressor chemistries the resulting steady-state deposition conditions are completely independent on the particular succession of additive adsorption. In contrast to that a strong dependence of the suppressing capabilities on the sequence of additive adsorption ("first comes, first serves" principle) is observed for the type-III suppressor. This behavior is explained by a suppressor barrier that impedes not only the copper inter-diffusion but also the transport of other additives (e.g. SPS) to the copper surface.
A multistep procedure for creating nanohole‐patterned gold films (see Figure) is presented. The s... more A multistep procedure for creating nanohole‐patterned gold films (see Figure) is presented. The steps include the self‐assembly of metal‐loaded polystyrene‐block‐poly(2‐vinylpyridine) micelles on GaAs substrates, hydrogen gas plasma treatment, directional reactive ion etching, and gold sputtering. The size and separation of holes resemble that of the gold cluster pattern.
The use of eutectic Sn-Cu alloys in packaging applications in microelectronics industry is not so... more The use of eutectic Sn-Cu alloys in packaging applications in microelectronics industry is not something entirely new. However, this alloy was mostly used in large features and fabricated using metal powders and metallurgical deposition techniques. The diameter of an individual grain of the eutectic Sn-Cu powder is typically similar in size to the diameter of pillars or bumps currently used in 3D stacking, and if we were to check its usefulness as a solder on this scale, an alternative manufacturing technique had to be used. We have electrochemically deposited Sn-Cu alloys having up to 10 wt.% Cu and explored its possible benefits when used as a solder in combination with different Under bump metallization (UBM) materials. Sn-Cu alloys were deposited on blanket and patterned coupons, and promising experiments then transferred to a wafer-scale, i.e. Sn-Cu alloys were deposited on 300 mm wafers in an industrial-type plating tool. A typical sample/wafer had a Cu seed with a diffusion barrier (e.g. TiW) underneath and patterned features defined with a photoresist mask. Characteristic dimensions of the patterned features were on the order of mm and cm (lines), (diameter)D50µm × (height)H60 µm (pillars), and D8µm × H15 µm (bumps). Cu, Ni, or Co were used as UBM layers. Chemical composition of deposited alloys has been examined by using X-ray fluorescence (XRF), Micro X-ray fluorescence (Micro-XRF), Inductively coupled plasma mass spectrometry (ICP-MS), and Electron probe microanalysis (EPMA). Surface morphology and the shape of deposited features have been examined using Scanning electron microscopy (SEM) and Laser scanning microscopy (LSM), while thermodynamic properties have been studied using Differential scanning calorimetry (DSC). Within-wafer (WIW) and within-die (WID) height uniformity of the pillars has been analyzed using Falcon 630 Plus tool (Camtek Ltd), capable of capturing heights of all the structures on the wafer simultaneously. The kinetics of Intermetallic compound (IMC) formation have been studied in the number of selected samples by combining ex-situ Focused ion beam (FIB) and in-situ measurements of resistance change of the features during anneal/thermal ageing [1]. We will discuss possible benefits and drawbacks for use of electrochemically deposited Sn-Cu alloy solders in combination with different UBM layers based on these results. References: [1] Lin Hou, Jaber Derakhshandeh, Eric Beyne, and Ingrid De Wolf, “A Novel Resistance Measurement Methodology for in-situ UBM/Solder Interfacial Reaction Monitoring”, DOI 10.1109/TCPMT.2019.2950448, IEEE Transactions on Components, Packaging and Manufacturing Technology. Figure 1
This paper introduces an approach where the match of two different length scales, i.e., pattern f... more This paper introduces an approach where the match of two different length scales, i.e., pattern from self-assembly of block copolymer micelles (< 100 nm) and electron-beam (e-beam) writing (> 50 nm), allow the grouping of nanometer-sized gold clusters in very small numbers in even aperiodic pattern and separation of these groups at length scales that are not accessible by pure self-assembly. Thus, we could demonstrate the grouping of Au nanoclusters in different geometries such as squares, rings, or spheres.
The competitive interaction of chloride and SPS (bis-(sodium-sulfopropyl)-disulfide) at Cu(1 0 0)... more The competitive interaction of chloride and SPS (bis-(sodium-sulfopropyl)-disulfide) at Cu(1 0 0)/electrolyte model interfaces was studied by means of cyclic voltammetry in combination with in situ STM and DFT. This specific anion/anion interaction is of paramount importance for the suppressor ensemble deactivation in the context of the industrial Cu Damascene process used for the state-of-the-art on-chip metallization. It is the interplay between chemisorbed chloride and SPS which regulates the dissociative SPS adsorption on copper as the key step in the course of the surface-confined MPS (mercaptopropane sulfonic acid) production. The latter species is considered as the actual anti-suppressor (depolarizer) in context of the Cu Damascene process. Under competitive conditions the chloride adsorbs and orders much faster on Cu(1 0 0) than the SPS. The resulting c(2 × 2)-Cl adlayer acts as an effective barrier for the dissociative SPS adsorption, at least under non-reactive conditions. Defect sites within the chloride matrix are identified as crucial prerequisites for the dissociative SPS adsorption. Defects are generated under reactive conditions during copper dissolution or copper deposition due to rapid anion adsorption/desorption dynamics. As consequence of the SPS dissociation a mixed, defect-rich c(2 × 2)-Cl-MPS co-adsorption phase forms on Cu(1 0 0) where every second chloride species of the pristine c(2 × 2)-Cl adlayer is displaced by MPS units. This co-adsorption phase reveals an apparent p(2 × 2) symmetry in the STM experiment since only the sulfonic head groups of the MPS units are imaged while the S and the Cl species chemisorbed on the copper surface remain invisible at the "buried" interface. The relevance of this surface reaction for the Cu Damascene process is discussed in detail.
This study reinvestigates the electrochemical characteristics of three different suppressor addit... more This study reinvestigates the electrochemical characteristics of three different suppressor additives that are used in context of industrial copper plating (Damascene, Through-Silicon-Via). It is the particular aim of this contribution to further substantiate our recently introduced classification scheme of suppressor chemistries that relies on their antagonistic and synergistic interplay with MPS (mercaptopropane sulfonic acid/sulfonate). The latter appears as intermediate species in the course of copper electrodeposition in the presence of SPS (bis-(sodium-sulfopropyl)-disulfide). Both the linear sweep voltammetry and potential transient experiments reveal a purely antagonistic interaction between PAG (polyalkylene glycol) based suppressor ensembles and the SPS (MPS precursor) which is rationalized in terms of the coordinative dissolution of a hyper-branched PAG-Cu(I)-Cl coordination network by the MPS. Such purely antagonistic suppressor/MPS interplay is our criterion for a so-called type-I suppressor. A purely synergistic suppressor/MPS interaction is observed for the PEI (polyethylene-imine) which can be considered as a prototypical type-II suppressor. Beyond classical interfacial anion/cation pairing the partly protonated, poly-cationic PEI is capable to form MPS-stabilized Cu(I) adducts. Their suppressing effect relies on an in situ hyper-branching achieved by a combination of Cu(I) coordination and an inner salt formation. Polymerizates of imidazole and epichlorohydrin (Imep) actually show both an antagonistic and a synergistic MPS/suppressor interaction. While free MPS acts as antagonist with respect to the formed Imep-Cu(I)-MPS suppressor adduct it is the MPS coordinated to Cu(I) which serves as crucial co-additive for the Imep suppressor ensemble. It is this interplay of antagonistic and synergistic MPS/suppressor interactions which introduces an extra feedback loop into the reaction cycle of those plating additives thus giving rise to the appearance of non-linear temporal instabilities into the plating characteristics under galvanostatic control.
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Papers by Marco Arnold