3-Mercapto-1-propanesulfonic acid and Bis(3-sulfopropyl) Disulfide Adsorbed on Au(111): In Situ Scanning Tunneling Microscopy and Electrochemical Studies

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A cyclic voltammetry (CV) screening method is proposed in this work to identify an effective accelerator for the copper superfilling of microvias of a printed circuit board (PCB). Five typical organosulfides are used as model additives to evaluate the performance of the screening method. The five organosulfides are 3-mercapto-1-propanesulfonate (MPS), bis(3-sulfopropyl) disulfide (SPS), 3-mercaptopropionic acid (MPA), 3-mercapto-1-propanol (MPO), and 3,3-thiobis(1-propanesulfonate) (TBPS), where MPS, MPA, and MPO contain a thiol head-group, SPS contains a disulfide group, and TBPS contains a thioether group. MPS, SPS, and TBPS have one or two terminal groups of sulfonates, whereas MPA has a terminal group of carboxylic acid, and MPO has a terminal group of alcohol. The CV screening method revealed that MPS, SPS, and TBPS are accelerators for copper electrodeposition and that MPA and MPO are not. A specific copper deposition peak, specifically, the α peak, that appears in the CV patterns is an indicator for accelerator screening. This study is the first to indicate that TBPS with a thioether group rather than a thiol group can accelerate copper electrodeposition and can be used for the copper superfilling of the microvias of a PCB.

Section: Resultsmentioning

confidence: 99%

mentioning

confidence: 99%

Accelerator Screening by Cyclic Voltammetry for Microvia Filling by Copper Electroplating

Chiu

Dow

2013

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“…Therefore, the lifetime of the SPS adlayer is transient, leading to a transient accelerating effect on copper nucleation and growth. The rapid copper nucleation and growth occurred at specific sites because of various orientations of the polycrystalline Au surface and different conformations of the adsorbed SPS, 5,36 such that the rice-shaped copper crystals were isolated and independently grew. These rice-shaped copper crystals became micro-WEs, leading to an increase in surface area of the WE and a local hemispherical mass transfer around the rice-shaped copper crystals.…”

Section: Resultsmentioning

confidence: 99%

“…A general ERD of thiol molecules from Au(111) is as follows 5,36,[38][39][40] R À S À Au þ e À ! R À S À þ Au [10] The coulomb value of ERD can be regarded as the adsorptive amount of the thiol molecule and correlated with the surface coverage of the thiol molecule.…”

Section: Resultsmentioning

confidence: 99%

Sensitivity Enhancement for Quantitative Electrochemical Determination of a Trace Amount of Accelerator in Copper Plating Solutions

Chiu

Dow

Huang

et al. 2011

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An accelerator is an indispensable organic additive for the bottom-up filling of copper electroplating in nano- or micro-scale features. However, its effective concentration is too low to be easily determined and controlled. Herein, a new electrochemical analysis method based on self-assembly monolayers of thiol molecules on a gold electrode was developed to accurately determine a trace amount of accelerator. The accelerator employed in copper plating solutions is bis-(3-sulfopropyl) disulfide (SPS), which is the most common accelerator for the filling of vias and trenches of interconnects. The SPS concentration in copper plating solutions ranged from 0.3 to 9.0 ppm. Following selective chemisorption of SPS onto the gold electrode, the SPS-modified gold electrode was transferred into a specific electrolyte composed of CuSO4, H2SO4, polyethylene glycol and chloride ions to run cyclic voltammetry (CV) for copper deposition and stripping. A specific peak current of copper reduction formed in the CV, and its peak area depended on the SPS concentration in the copper plating solution. A good linear calibration line was obtained by using this electrochemical analysis method, which can determine a trace amount of SPS in a concentration range of 0.3-1.0 ppm, which is a significant challenge for traditional instruments

“…10 The devise of scanning tunneling microscopy (STM) greatly helps our understanding of these OSCs involved in Cu electroplating. STM has revealed MPA, 10 and a number of OSCs, [11][12][13][14] adsorbed on copper and gold electrodes. Furthermore, in situ STM has shed insights into electrodeposition of Cu on bare and modified metallic electrodes of gold, platinum, rhodium, etc.…”

mentioning

confidence: 99%

In Situ Scanning Tunneling Microscopy Imaging Self-Assembled Monolayers of Mercaptoacetic Acid and Cupric Ion on Au(111) Electrode

Lai¹,

Chen²,

Yau³

et al. 2014

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We employed voltammetry and scanning tunneling microscopy (STM) to study the coadsorption of mercaptoacetic acid (MAA) and cupric ions (Cu 2+ ) on Au(111) electrode from 0.5 M sulfuric acid + 0.8 M CuSO 4 + 0.03 mM MAA. Irreversibly adsorbed Cu 2+ ions were reduced at 0.27 V first then at −0.2 V (vs. Ag/AgCl), ascribed to the underpotential and overpotential deposition processes, respectively. Counting the amount of charge involved in the stripping peak of the Cu deposit rendered quantification of Cu 2+ ions codeposited with MAA on the Au(111) electrode, which yielded roughly 7.7 × 10 14 Cu 2+ ions/cm 2 . MAA alone and MAA + Cu 2+ were adsorbed in Au(111) -(3 × √ 13) and (p × √ 3) structures, respectively. Cu 2+ could be imaged by the STM, but their high mobility made it difficult to obtain high -quality STM results needed to quantify the amount of adsorbed Cu 2+ . Spatial structures of MAA molecules segregated onto the Cu deposit were found to vary with potential. They returned to the Au(111) electrode once the Cu deposit was oxidized at E > 0.4 V, yielding MAA + Cu 2+ structures different from those seen at the pristine sample.Organosulfur compounds (OSCs) have found wide applications in electroanalysis and electrodeposition. 1-4 In developing glucose biosensor, for example, gold electrode modified with mercaptopropanic acid (MPA) is able to trap protein molecules in the presence of cationic polymeric molecules, which enables charge transfer and detection of biomolecules using current as the gauge to quantify analyte. 1 In addition, gold electrodes coated with MPA and MAA (mercaptoacetic acid) are used to pre-concentrate copper ions, making it possible to quantify Cu 2+ by cathodic stripping analysis. 5 Of close relevance to this study is the role of OSCs in electrodeposition, as many of them are essential ingredients in electroplating baths. For example, bis-3-sodiumsulfopropyl-disulfide (SPS) and mercaptopropanic sulfonic acid (MPS), are used as accelerators to implement Cu superfilling in recess on silicon chips. [6][7][8][9] In addition, OSCs with carboxylic acid end groups such as MPA can yield bright Cu deposit. 10 The devise of scanning tunneling microscopy (STM) greatly helps our understanding of these OSCs involved in Cu electroplating. STM has revealed MPA, 10 and a number of OSCs, 11-14 adsorbed on copper and gold electrodes. Furthermore, in situ STM has shed insights into electrodeposition of Cu on bare and modified metallic electrodes of gold, platinum, rhodium, etc. [15][16][17] In this study we employed in situ STM to examine spatial structures of MAA and MAA + Cu 2+ adlayers deposited on Au(111) from acidic aqueous dosing solutions. Not only strongly adsorbed MAA molecules but also Cu 2+ ions were imaged by molecular -resolution STM. Results obtained show that MAA molecules rearranged to accommodate coadsorbed Cu 2+ ions. We substantiated this study by looking at the reduction processes of surface bound Cu 2+ on Au(111). STM revealed organized MAA molecules segregated from the gold substrate ont...