Competitive anion/anion interactions on copper surfaces relevant for Damascene electroplating

Interaction of Bis-(sodium-sulfopropyl)-Disulfide and Polyethylene Glycol on the Copper Electrodeposited Layer by Time-of-Flight Secondary-Ion Mass Spectrometry

The interactions of the functional additives SPS (bis-(sodium-sulfopropyl)-disulfide) and polyethylene glycol (PEG) in the presence of chloride ions were studied by time-of-flight secondary-ion mass spectrometry (TOF-SIMS) in combination with cyclic voltammetry measurements (CV). The PEG, thiolate, and chloride surface coverages were estimated and discussed in terms of their electrochemical suppressing/accelerating abilities. The conformational influence of both the gauche/trans thiolate molecules, as well as around C-C and C-O of PEG, on the electrochemical properties were discussed. The contribution of the hydrophobic interaction of -CH₂-CH₂- of PEG with chloride ions was only slightly reduced after the addition of SPS, while the contribution of Cu-PEG adducts diminished strongly. SPS and PEG demonstrated significant synergy by significant co-adsorption. It was shown that the suppressing abilities of PEG that rely on forming stable Cu-PEG adducts, identified in the form C₂H₄O₂Cu⁺ and C₃H₆OCu⁺, were significantly reduced after the addition of SPS. The major role of thiolate molecules adsorbed on a copper surface in reducing the suppressing abilities of PEG rely on the efficient capture of Cu²⁺ ions, diminishing the available copper ions for the ethereal oxygen of PEG.

Studies of Bis-(Sodium-Sulfopropyl)-Disulfide and 3-Mercapto-1-Propanesulfonate on/into the Copper Electrodeposited Layer by Time-of-Flight Secondary-Ion Mass Spectrometry

Interactions of functional additives SPS (bis-(sodium-sulfopropyl)-disulfide), MPS (3-Mercapto-1-Propanesulfonate), and Cl accumulated and incorporated on/into a copper electrodeposited layer were studied using time-of-flight secondary-ion mass spectrometry (TOF-SIMS) in combination with cyclic voltammetry measurements (CV). It was shown that the Cl and MPS surface coverage is dependent on the applied overpotential and concentration of Cl, SPS, or MPS in the solution. Detailed discussion on the mechanism of yielding CH₂SO₃^-, C₃H₅SO₃^-, CuSC₃H₆SO₃^-, and CuS^- fragments and their assignment to the gauche or trans conformation was proposed. The mechanism of the process of incorporation and re-adsorption of MPS on/into a copper surface under electrochemical conditions without and with chloride ions and its impact on electrochemical properties was proposed. Moreover, it was shown that the presence of chloride ions, the ratio gauche/trans of MPS molecules, as well as the ratio chloride/thiols demonstrate a high impact on the accelerating abilities. Comparative studies conducted under open circuit potential conditions on the nitinol and copper substrate allowed for the identification of specific reactions/interactions of MPS, or SPS and Cl ions on the nitinol and copper surface.

In Situ Wide-Frequency Surface-Enhanced Infrared Absorption Spectroscopy Enables One to Decipher the Interfacial Structure of a Cu Plating Additive

In situ spectroscopic characterization of the interfacial structure of an organic additive at a Cu electrode is essential for a mechanistic understanding of Cu superfilling at the molecular level. In this work, we demonstrate wide-frequency attenuated total reflection surface-enhanced infrared absorption spectroscopy (wf-ATR-SEIRAS) to elucidate the dissociative adsorption of bis(sodium sulfopropyl)-disulfide (a typical accelerator) on a Cu electrode in conjunction with the electrochemical quartz crystal microbalance measurement and modeling calculations. The wf-ATR-SEIRAS clearly identifies the peaks featuring the sulfonate and methylene groups as well as the C-S_sulfonate and C-S_thiol vibrations of the adsorbate. Analysis of relative peak intensities from 1100 to 650 cm^-1 reveals a more tilted alkyl chain axis for the thiolate on Cu than that on Au, which is supported by comparative density functional theory calculations. This work opens a new avenue for the wf-ATR-SEIRAS to study interfacial structures of electroplating additives related to advanced microelectronics manufacture.

Recent Progress in the Preparation Technologies for Micro Metal Coils

The recent development of micro-fabrication technologies has provided new methods for researchers to design and fabricate micro metal coils, which will allow the coils to be smaller, lighter, and have higher performance than traditional coils. As functional components of electromagnetic equipment, micro metal coils are widely used in micro-transformers, solenoid valves, relays, electromagnetic energy collection systems, and flexible wearable devices. Due to the high integration of components and the requirements of miniaturization, the preparation of micro metal coils has received increasing levels of attention. This paper discusses the typical structural types of micro metal coils, which are mainly divided into planar coils and three-dimensional coils, and the characteristics of the different structures of coils. The specific preparation materials are also summarized, which provides a reference for the preparation process of micro metal coils, including the macro-fabrication method, MEMS (Micro-Electro-Mechanical System) processing technology, the printing process, and other manufacturing technologies. Finally, perspectives on the remaining challenges and open opportunities are provided to help with future research, the development of the Internet of Things (IoTs), and engineering applications.

1-(4-Hydroxyphenyl)-2H-tetrazole-5-thione as a leveler for acid copper electroplating of microvia

Microvia filling by copper electroplating was performed using plating solution with 1-(4-hydroxyphenyl)-2H-tetrazole-5-thione (HPTT) as the leveler. Galvanostatic Measurements (GMs), Linear Sweep Voltammetry (LSV) and Electrochemical Impedance Spectroscopy (EIS) tests were carried out to investigate the electrochemical behaviors of HPTT and its synergistic effect with other additives, in comparison with 1-phenyltetrazole-5-thione (PMT). GMs showed a convection-dependent interaction between PEP and HPTT. LSV and EIS tests indicated both HPTT and PMT enhanced the inhibition effect of PEP, and the synergistic effect of HPTT and PEP was stronger than that of PMT. Cross-section images illustrated the filling rate of the microvia with a 150 μm diameter and a 75 μm depth was 95.6% in 60 minutes with HPTT as the leveler. Frontier Molecular Orbitals (FMO) and Electrostatic Potential (ESP) of HPTT and PMT using quantum chemical calculations predicted the reaction sites for electrophilic and nucleophilic attack. Quantum chemical calculations suggested that HPTT is easier than PMT to bond to a copper surface and PEP.

Microvia filling by copper electroplating was performed using plating solution with 1-(4-hydroxyphenyl)-2H-tetrazole-5-thione (HPTT) as the leveler.

Experiment and simulation of single inhibitor SH110 for void-free TSV copper filling

Three-dimensional integration with through-silicon vias (TSVs) is a promising microelectronic interconnection technology. Three-component additives are commonly used for void-free TSV filling. However, optimising the additive concentrations is an expensive process. To avoid this, a single-component additive was developed: 3-(2-(4,5-dihydrothiazol-2-yl) disulfanyl) propane-1-sulfonic acid/sulfonate (SH110). Sodium 3,3'-dithiodipropane sulfonate (SPS) and SH110 were used as additives for TSV electroplating copper filling. SH110 resulted in void-free filling, whereas large keyhole voids were found for SPS. To understand how the additives affect the filling mechanism, linear sweep voltammetry of the plating solutions was carried out. The interactions between the Cu surface and additives were simulated by molecular dynamics (MD) analysis using Materials Studio software, and quantum chemistry calculations were conducted using GAUSSIAN 09W. SH110 adsorbs to the Cu surface by both 4,5-dihydrothiazole (DHT) and 3-mercaptopropane sulfonate (MPS) moieties, while SPS is adsorbed only by MPS moieties. MD simulations indicated that the adsorption of the coplanar MPS moiety is the main factor governing acceleration. Quantum chemistry calculations showed that DHT provides an inhibitory effect for TSV filling, while MPS acts as an accelerator for SH110. SH110 is an excellent additive exhibiting both the acceleration and the suppression necessary for achieving void-free TSV filling.

Chain length variation to probe the mechanism of accelerator additives in copper electrodeposition

We evaluate the effect of chain length for a series of alkyl sulfonic acid additives on Cu electrodeposition by using a combination of electrochemical and Raman spectroscopic methods. Rotating disk linear sweep voltammetry revealed the influence of these additives on the bulk concentration of Cu+ and on the exchange current densities of the reduction of Cu2+/Cu+ and Cu+/Cu. We then used in situ shell-isolated, nanoparticle-enhanced Raman spectroscopy to correlate the additives' effects on deposition kinetics with their chemical structures at the electrode surface. The combination of these methods suggests that effective Cu electrodeposition acceleration processes require: (1) direct tethering of mercaptoalkylsulfonate species to the electrode, (2) partial desolvation of Cu2+ by the sulfonate group to minimize its solvent reorganization energy, and (3) stabilization of Cu+ adjacent to the electrode surface by addition of halide. The model provides support for recently proposed theories for the electrodeposition of metals where charge is carried across the electrode interface by the cation, rather than the electron.

Study of underpotential deposited Cu layers on Pt(111) and their stability against CO and CO2 in perchloric acid

The underpotential deposition (UPD) of copper on a Pt(111) electrode and the influence of gas coadsorbates, i.e. CO and CO2, on the thus deposited copper layer were studied in a 0.1 M HClO4 electrolyte by means of EC-STM. By UPD, an atomically flat Cu layer is formed, which exhibits a pseudomorphic (1 × 1) structure. However, it contains several point defects due to which its total coverage is less than a monolayer, in agreement with the measured charge density in the CV curves. Upon exposure to a CO-saturated solution the pseudomorphic structure collapses to a coalescent structure with many vacancy islands. This phase transition is induced by the preferential binding of CO to the Pt(111) surface. In contrast, CO2, which binds stronger to copper, does not affect the pseudomorphic structure of the Cu layer.

In situ video-STM studies of methyl thiolate surface dynamics and self-assembly on Cu(100) electrodes

The atomic-scale surface dynamic behavior of adsorbed methyl thiolate on Cu(100) electrodes, prepared via the dissociative adsorption of dimethyl disulfide, was studied in 0.01 M HCl solution over a wide regime of coverages. Using video-rate in situ STM, we directly observed the motion of the adsorbates within the c(2 × 2) lattice of the chloride coadsorbates with high spatial and temporal resolution, revealing complex mutual interactions of the organic adsorbates as well as pronounced interactions with Cu adatoms, which significantly affect the thiolate self-assembly. Quantitative measurements of the tracer diffusion of isolated thiolates reveal a 35 meV lower diffusion barrier as compared to that of sulfide adsorbates with a linear potential dependence of 0.5 eV/V. The effective intermolecular interactions between the thiolates resemble those between adsorbed sulfide and are repulsive at the nearest-neighbor distance of a(0) within the c(2 × 2) lattice, attractive at the next-nearest-neighbor distance of √2a(0) and again repulsive at a distance of 2a(0). Thiolates at these small spacings are found to exhibit characteristic collective properties, which are significant for the self-assembly of these species: First, their mobility is greatly enhanced relative to that of isolated thiolates. Second, Cu adatoms can be transiently trapped in between the two thiolates of a metastable dimer with an intermolecular spacing of √2a(0). With increasing coverage, small, highly mobile molecular clusters and subsequently the formation of ordered adlayer domains with a c(2 × 6) structure are observed. Common structural elements of the clusters and c(2 × 6) domains are stripes of thiolate dimers, which are oriented in the [011] direction, spaced at distances of √2a(0) and of which a large fraction is occupied by Cu adatoms. The c(2 × 6) phase can be rationalized as a close-packed arrangement of these dimer stripes. Because of the self-acceleration of the thiolate mobility, the ordering and reorganization of the ordered c(2 × 6) adlayers occur orders of magnitude faster than the surface diffusion of isolated thiolates, illustrating the importance of collective effects in organic self-organization.

Adsorption and desorption of bis-(3-sulfopropyl) disulfide during Cu electrodeposition and stripping at Au electrodes

The adsorption and desorption of bis-(3-sulfopropyl) disulfide (SPS) on Cu and Au electrodes and its electrochemical effect on Cu deposition and dissolution were examined using cyclic voltammetry stripping (CVS), field-emission scanning electron microscopy (FESEM), and X-ray photoelectron spectroscopy (XPS). SPS dissociates into 3-mercapto-1-propanesulfonate when it is contacted with Au and Cu electrodes, producing Cu(I)- and Au(I)-thiolate species. These thiolates couple with chloride ions and promote not only the reduction of Cu(2+) in Cu deposition but also the oxidation of Cu(0) to Cu(+) in Cu stripping. During Cu electrodeposition on the SPS-modified Au electrode, thiolates transfer from Au onto the Cu underpotential deposition (UPD) layer. The Cu UPD layer stabilizes a large part of the transferred thiolates which subsequently is buried by the Cu overpotential deposition (OPD) layer. The buried thiolates reappear on the Au electrode after the copper deposit is electrochemically stripped off. A much smaller part of thiolates transfers to the top of the Cu OPD layer. In contrast, when SPS preadsorbs on a Cu-coated Au electrode, almost all of the adsorbed SPS leaves the Cu surface during Cu electrochemical stripping and does not return to the uncovered Au surface. A reaction mechanism is proposed to explain these results.