Synergic effect of benzotriazole and chloride ion on Cu passivation in a phosphate electrochemical mechanical planarization electrolyte

In this study, the effect of chloride ion (Cl⁻) in phosphate electrolytes of pH 2 containing benzotriazole (BTAH) developed for use in electrochemical mechanical planarization (ECMP) was investigated at various anodic potentials. According to D.C. and A.C. electrochemical analyses, the inhibition effect of the BTAH passive film formed in phosphate electrolyte containing both BTAH and Cl⁻ was superior to that formed in phosphate electrolytes containing BTAH alone, even at high anodic potential. The effective window for BTAH passivation reached ∼1.3 V vs. Ag/AgCl nearly three times that of the ∼0.5 V vs. Ag/AgCl recorded for electrolyte containing BTAH alone. According to analyses conducted by atomic force microscopy (AFM) and secondary ion mass spectrometer (SIMS), the thickness of the passive film grown from the BTAH-only electrolyte at 0.3 V vs. Ag/AgCl was ∼52 ± 7 nm and ∼55 nm, respectively. As for the passive film grown from the BTAH and Cl⁻ electrolyte, the thickness increased to ∼104 ± 18 nm and ∼106 nm, respectively. The mechanism for the enhanced inhibition capability was that the passive film grown from the BTAH and Cl⁻ electrolyte was thicker compared to that formed from the BTAH-only electrolyte due to the incorporation of Cl⁻ into the BTAH passive film. The ECMP polishing results also demonstrated an obvious step height reduction of ∼1000 nm in a patterned structure for only 60 s polishing at a high potential of 1.0 V vs. Ag/AgCl under a low downward pressure (∼0.5 psi). Subsequently, this study proposes that the control of Cl⁻ in a phosphate ECMP electrolyte of pH 2 may be useful in enhancing the passivation capability of BTAH passive film, thus expanding the operating potential window.     

Characterization of phosphate electrolytes for use in Cu electrochemical mechanical planarization

Electrochemical mechanical planarization (ECMP) is a potential replacement or complement to conventional chemical mechanical planarization (CMP) techniques. ECMP can operate at very low downforces (<1.0 psi), potentially without slurry particles or oxidizers, and can also be tailored to achieve specific dissolution rates via applied potential. Through the modification of a phosphate-based electrolyte by the use of benzotriazole (BTA), a possible ECMP electrolyte was developed. Utilizing a rotating disk electrode (RDE), a broad range of electrolyte characteristics were screened. The most important parameters investigated were pH, salt concentration, and BTA concentration. The optimal electrolyte composition was found to be around 1 M potassium phosphate with a pH value of 2. Removal rates varied from 750 to 2500 nm min⁻¹ within an operating potential window from 0.5 to 1.0 V vs. Ag/AgCl reference electrode.     

An investigation of phosphate based ECMP electrolyte performance on feature scale planarization

Conventional copper chemical mechanical planarization (CMP) techniques are being pushed to their limits by increasing industrial standards caused by device miniaturization and the use of new materials. There is a need to investigate alternative methods of polishing to maintain and/or improve planarization standards while operating at low downforce. In this study, electrochemical mechanical planarization (ECMP) is considered as an alternative and/or an extension to current CMP processes. ECMP is unique due to the combination of an applied voltage to oxidize Cu and an abrasion from a polishing pad, which potentially allows the system to achieve high levels of planarization through the use of an appropriately tailored electrolyte. An electrolyte containing 1.0 M potassium phosphate salt concentration with a pH value of 2 and a benzotriazole (BTA) concentration of 0.001 M was tested for its planarization capability on patterned Cu structures using a custom built ECMP tool. Feature sizes of the Cu structures were varied from 1 to 6 μm. Similar planarization results were achieved using three pad types. All experiments were performed at 0.5 V versus Ag/AgCl reference. The average step height reduction (SHR) was ~840 nm while the decrease in the average metal thickness removed (λ_avg) was on the order of ~430 nm. Because features were approximately 50% of the substrate area, the total average metal thickness removed was approximately half of the SHR for all three pad types.     

The influence of chloride ions and benzotriazole on the corrosion behavior of Cu37Zn brass in alkaline medium

This paper describes an investigation of the corrosion behavior of Cu37Zn brass in a solution of sodium tetraborate, at pH 10.0, with the addition of chloride ions and benzotriazole (BTA) inhibitor. The application of cyclic voltammetry has led to the conclusion that the anodic current densities increase with increase in immersion time in sodium tetraborate solution as well as in solutions of sodium tetraborate containing chloride ions of various concentrations. The values of anodic current density are considerably smaller in sodium tetraborate solutions with the addition of BTA compared with those in the inhibitor-free solution.The study also analyses the electrochemical behavior of Cu37Zn brass after various times of alloy exposure to BTA solution, as well as its behavior in BTA solutions of various concentrations. Also, the study describes the electrochemical behavior of Cu37Zn brass after the effect of Cl⁻ ions, but subsequent to the formation of a polymeric protective film on the electrode surface.     

Investigation of dissolution inhibitors for electrochemical mechanical planarization of copper using beta-alanine as a complexing agent

Dissolution inhibition capabilities of benzotriazole (BTAH) and ammonium dodecyl sulfate (ADS) are investigated, in combination with β-alanine, as a complexing agent for applications in electrochemical mechanical planarization (ECMP) of copper. Cu electrodissolution is induced by linear sweep voltammetry (LSV), and Fourier transform electrochemical impedance spectroscopy (FT-EIS) is combined with LSV to examine the relative roles of the electrolyte additives in governing the surface reactions of Cu under voltage activated conditions of ECMP. The experiments focus on the electrochemical rather than mechanical component of ECMP, and are designed to probe both the individual and combined effects of BTAH and ADS on Cu electro-dissolution in the absence of abrasion.     

Electrochemically induced nanocluster migration

In the presented study the influence of electrochemical treatments on size-selected Pt nanoclusters (NCs) supported on amorphous carbon is investigated by means of transmission electron microscopy (TEM). Well-defined Pt NCs are prepared by an ultra-high vacuum (UHV) laser vaporization source and deposited with low kinetic energy (≤10 eV/cluster) onto TEM gold grids covered by a thin (2 nm) carbon film. After transfer out of UHV Pt NCs are verified to be uniform in size and randomly distributed on the support. Subsequently, the TEM grids are employed as working electrodes in a standard electrochemical three electrode setup and the Pt nanoclusters are subjected to different electrochemical treatments. It is found that the NC arrangement is not influenced by potential hold conditions (at 0.40 V vs. RHE) or by potential cycling in a limited potential window (V_max = 0.55 V vs. RHE). Upon potential cycling to 1.05 V vs. RHE, however, the NCs migrate on the carbon support. Interestingly, migration in oxygen or argon saturated electrolyte leads to NC coalescence, a mechanism discussed for being responsible for performance degradation of low temperature fuel cells, whereas in carbon monoxide saturated electrolyte the Pt NC agglomerate, but remain separated from each other and thus form distinctive structures.     

Effect of Ni content on the corrosion behavior of Cu-Ni alloys in neutral chloride solutions

The effect of systematic increase of Ni content on the electrochemical behavior of the Cu-Ni alloys in neutral chloride solutions was investigated. The pitting corrosion behavior of Cu-Ni alloys with different Ni contents, namely, 5, 10, 30 and 65 mass% Ni, in a stagnant 0.6 mol dm⁻³ NaCl solution of pH 7.0 was studied. The effect of chloride ion concentration on the electrochemical behavior of these alloys was also investigated. The results show that the increase in nickel content decreases the corrosion rate of the alloys in the neutral chloride solution. The increase of chloride concentration up to 0.3 mol dm⁻³ increases the corrosion rate. At higher concentrations ([Cl⁻] > 0.3 mol dm⁻³) the corrosion rate decreases due to the hydrolysis of Cu(I) chloride to form the passive Cu(I) oxide film. The breakdown potential depends on the chloride ion concentration and the nickel content of the alloy. For these investigations conventional electrochemical techniques and electrochemical impedance spectroscopy (EIS) were used. The impedance measurements have shown that the increase of the Ni content and the immersion time of the alloys in the chloride solution increase the corrosion resistance of the alloys. The experimental impedance data were fitted to theoretical values according to a proposed equivalent circuit model.     

The effect of Cu addition on the electrochemical corrosion and passivation behavior of stainless steels

The effect of Cu addition on the electrochemical corrosion behavior of austenitic, ferritic and martensitic stainless steels in both the active and passive state was investigated by potentiodynamic polarization and electrochemical impedance spectroscopy in 0.1 M H₂SO₄. The semiconducting properties of the passive films were investigated by capacitance measurements by using the Mott-Schottky approach. Cu addition generally improved corrosion resistance and facilitated passivation but did not notably affect the resistance of the passive films. Capacitance results revealed that the passive films behave as n-type and p-type semiconductors at potentials below and above the flatband potential, respectively. Cu addition caused an increase in the donor and acceptor densities, which we have attempted to correlate with the passive film stability.     

Electrochemical stability of Cu-10Al-5Ni alloy in chloride-sulfate electrolytes

The electrochemical behavior of the Cu-10Al-5Ni alloy in simulated electrolytes like those used in the industrial processes under normal working conditions was investigated. Conventional electrochemical techniques including open circuit potential measurements, polarization techniques, and electrochemical impedance spectroscopy were used. The alloy was found to be more stable against corrosion when the chloride-sulfate solution had a pH of 7-9. A sulfate concentration of ≅0.1 M in the chloride-sulfate electrolyte leads to the passivation of the alloy surface. The activation energy of the corrosion process was found to be 8 kJ mol⁻¹ assigning a diffusion controlled reaction. The impedance measurements and impedance data fitting to equivalent circuit models have shown that the passive film posses a duplex nature.     

AC impedance studies of anodically treated polycrystalline and homoepitaxial boron-doped diamond electrodes

The electrochemical properties of several types of diamond electrodes, including polycrystalline and homoepitaxial films, that underwent anodic treatment were examined with the electrochemical impedance spectroscopic (EIS) technique, as well as with capacitance-potential measurements. From an analysis of the impedance behavior, it was found that an additional capacitance element, which is apparent in the relatively high-frequency range (100-1000 Hz), was generated on the polycrystalline and (1 0 0) homoepitaxial diamond electrodes after anodic treatment. This capacitive element can be characterized as being non-Faradaic, because it has negligible dependence on the applied potential. Acceptor densities and depth profiles were calculated from the Mott-Schottky plots, and the acceptor densities in the near-surface region of the anodically treated surfaces were found to be extremely low. These results indicate that passive layers were generated on the diamond surfaces by the anodic treatment. The capacitance-potential behavior was also consistent with a model consisting of a semiconductor with a passive surface film. The passive film is proposed to arise as a result of the removal of hydrogen acting as an acceptor in the subsurface region, leaving hydrogen that is paired essentially quantitatively with the boron dopant, effectively neutralizing it.     

Thin films of amorphous nitrogenated carbon a-CNx: Electron transfer and surface reactivity

The electrochemical behaviour of thin films of nitrogenated amorphous carbon a-CN_x is similar to that of boron-doped diamond, with a wide potential window in aqueous media. They are elaborated by cathodic sputtering of a graphite target in an Ar-N₂ active plasma for varying nitrogen contents, determined by XPS (0.06 ≤ x ≤ 0.39). Their electrochemical reactivity is sensitive to the surface state. The present study reports on the influence of electrochemical pre treatment on the electronic transfer rate of a fast redox system ferri-ferrocyanide, by focusing on the direction of the potential excursion. On the other hand, the role of both the pH and the potential on the interfacial capacitance in the presence of Na₂SO₄ without redox species is documented. The results show up the sensitivity of the film surface to the electrochemical conditions.     

Effect of benzotriazole (BTA) addition on Polypyrrole film formation on copper and its corrosion protection

Benzotriazole (BTA) was added in a conducting Polypyrrole (PPy) film prepared on copper in oxalic acid aqueous solution containing pyrrole monomer to improve corrosion protection by the PPy film and reduce copper corrosion. When BTA was added in the preparation solution, the copper surface was covered by a BTA–Cu complex layer before the anodic polymerization of PPy was started. On the copper surface with the BTA layer, the initial dissolution of copper was inhibited and the PPy polymerization-deposition was started immediately after the anodic current was imposed. The PPy film thus formed was doped with oxalic ions and ionized BTA and was homogeneous in thickness and strongly adhesive. The PPy film containing BTA protected the copper from corrosion in 3.5 wt.% NaCl solution. In 400 h of immersion, copper dissolution was inhibited with 80% protection efficiency relative to that of bare copper.     

Investigation of the inherent electrical potential of PEO electrolyte films

Measurement of the through-plane potential of PEO-lithium triflate electrolyte films has demonstrated that they possess an inherent potential as cast from an acetonitrile solution onto a Teflon substrate. These films have an inherent potential of around 0.2 V and the cast films display a discharge behavior similar to a double layer capacitor system with a small discharge capacitance of 80 nF cm⁻². It is postulated that electrochemical properties of the films can be attributed to different salt concentration at the two surfaces. This difference in concentration may result from a matching of the surface-free energy of the Teflon substrate side of the film and the side of the film where evaporation occurs with the lithium triflate species in the polymer. Different spherulite morphologies were also observed for each surface. These morphologies can be assigned to spherulites having much different ion concentrations. Attenuated total reflection (ATR) IR spectroscopy was used to investigate the surface concentrations of free ions, ion pairs and ion multiples of both surfaces of the films. AC impedance spectroscopy of the surfaces of the film was also conducted. These data indicated that there is a difference in the surface concentration of each side. The ability of electrolyte films to exhibit a potential as fabricated may have potential applications as an easily manufactured power source for micro and nanodevices.     

Electrochemical preparation and kinetic study of poly(o-tolidine) in aqueous medium

Poly(o-tolidine), PoT, film was prepared by electrochemical oxidation of the monomer, oT, in 0.1 M HCl + 0.1 M KClO₄. The presence of KClO₄ in the formation medium was found to be essential for the electropolymerization process to proceed. Increasing the upper potential limit up to +1.5 V, instead of +1.0 V, leads to appearance of a new anodic peak at +1.36 V and enhancement of the polymer formation of PoT without changing the film structure. The electrochemical behavior of the formed polymer films was investigated in 1.0 M HClO₄. The kinetic parameters were calculated from the values of the charge consumed during the electropolymerization process. The rate of the polymerization reaction was found to depend on the concentration of the monomer rather than the electrolyte. The polymerization rate is first order with respect to the monomer concentration and zero order with respect to the electrolyte. The electrolyte plays no active role in the kinetics of the electropolymerization process and its role is most likely limited to polymer doping.     

Influence of micro-structure on corrosion behavior of a Ni-based superalloy in 3.5% NaCl

The electrochemical corrosion behavior of a Ni-based superalloy with polycrystalline (cast alloy), single-crystalline (SC (2 0 0)) and nanocrystalline (NC) micro-structures has been studied in 3.5% NaCl solution. The results indicated that among the three materials, the corrosion resistance increased in the order cast alloy < SC (2 0 0) alloy < NC coating. XPS analyses revealed that the composition of passive film on the three materials was different. In addition to Cr₂O₃ and TiO₂, some NiO was detected in the passive film on the cast alloy, little in that of the SC (2 0 0) alloy and none in that of the NC coating. The double-log plots showed the compact property of the passive film formed on the samples also varied in the order cast alloy < SC (2 0 0) alloy < NC coating, with the cast alloy displaying the worst compact property and the NC coating the best. The micro-structure influenced both the composition of passive film as well as the initial growth of passive film, which determined the compact property of the film and resulted in the observed differences in the corrosion behavior of the three materials.     

Effect of surface defects by RF oxygen plasma on the electrical properties of thin boron-doped diamond layers in electrolyte

The effect of surface defects induced by RF oxygen plasma treatment on the electrical properties of thin boron-doped epitaxial diamond layers was investigated by electrochemical analysis in the modes of electrochemical electrode and ion sensitive field-effect transistor (ISFET). The doping profile employed allowed almost full depletion in the electrolyte used within the potential window of water electrolysis. The high near surface defect density leads to an extremely high free carrier sheet charge density (approximately 3 × 10¹⁴ cm⁻²) concentrated within the first nm below the surface accompanied by a high channel sheet resistance in the 10 MΩ range. The analysis, also taking into account earlier measurements, points thus towards a channel carrier mobility of 10⁻³ cm²/Vs, comparable to what is seen in highly disordered thin film transistors.     

Local electrochemical impedance measurements on inclusion-containing stainless steels using microcapillary-based techniques

MnS inclusions are good precursor sites for pitting corrosion of stainless steel. The objective of this paper was to quantify the passive properties of resulfurized stainless steel after immersion in chloride media. This was done by combining microcapillary techniques with electrochemical impedance spectroscopy and numerical analysis (specific equivalent circuit). It was shown that sulfur species produced in the electrolyte during the dissolution of inclusions react with the native passive film to CrS and FeSO₄. Local electrochemical impedance spectroscopy measurements provided data describing the behaviour of the affected matrix at the microscale. For example, the value of the charge transfer and migration of point defects resistance decreases from 51,700 Ω cm², in sites free of any metallurgical heterogeneity down to 12,200 Ω cm², in sites containing a high density of inclusions. It was also shown that the integrity of the microcapillary can be altered by the presence of high quantity of sulfur in the electrolyte. Local impedance data allowed the detection of such problems.     

Electrodeposited Ni-B alloy coatings: Structure, corrosion resistance and mechanical properties

Ni-B alloy coatings with different boron content ranging from 4 to approximately 28 at.% were prepared by electrodeposition in a nickel-plating bath containing sodium decahydroclovodecaborate as a boron source. The influence of the boron concentration in the coatings on their structure, morphology, electrochemical and corrosion behavior, physico-mechanical and electrical properties was investigated using X-ray diffractometry (XRD), scanning electron microscopy (SEM), potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and other methods. It was found that the electrodeposited Ni-B coatings with relatively low boron content (≤8 at.%) are nanocrystalline and comprise a solid solution of boron in f.c.c. Ni lattice having a mixed substituted-interstitial type. Further increase in the boron content (up to 10-15 at.%) leads to the appearance of heterogeneous amorphous-nanocrystalline structure, and the coatings with a high boron content (20 at.% and above) are X-ray amorphous. Polarization measurements in neutral NaCl solutions showed that the Ni-B coatings with relatively low boron content demonstrate a potential region of low anodic currents associated with the passive film formation at the alloy surface. The anodic current in this potential region increases significantly with increasing the boron content above 10 at.%, suggesting the non-protective nature of the anodic film formed on the amorphous Ni-B alloys. Immersion tests monitored by EIS measurements revealed a significantly better corrosion performance of the Ni-B coatings with low boron content (4 at.%) in comparison with that of the amorphous coatings. The microhardness and wear resistance of the Ni-B coatings essentially increases with increasing the boron content. Maximum microhardness and wear resistance were found for the coatings containing 8 at.% B.     

A quartz crystal microbalance study of the kinetics of interaction of benzotriazole with copper

The kinetics of interaction of benzotriazole (C₆H₅N₃, BTAH) with the surface of copper in salt water were studied using an electrochemical quartz crystal microbalance and X-ray photoelectron spectroscopy (XPS). Upon injecting BTAH into the electrolyte, three regions appear in the time response of the microbalance. Region I (at short time of few minutes), exhibits rapid linear growth of mass with time, which is attributed to the formation of a protective Cu(I)BTA complex. Region II reveals attachment of BTAH at a slower rate onto the inner Cu(I)BTA complex. Region III is a plateau indicating that the BTAH film attains an equilibrium mass and thickness, which increase with the concentration of BTAH. The intensity of the N1s peak in the XPS spectra increases with the time of immersion, indicating more BTAH on the surface. The results suggest a duplex inhibitor film composed of an inner thin layer of Cu(I)BTA and an outer layer of physically adsorbed BTAH which increases in thickness with time and BTAH concentration. They also offer an explanation for the much documented findings of simultaneous increase of the polarization resistance and decrease of double layer capacity with inhibitor concentration and time of immersion.     

Material removal mechanisms in electrochemical-mechanical polishing of tantalum

Material removal mechanisms in tantalum chemical-mechanical polishing (CMP) and electrochemical-mechanical polishing (ECMP) were investigated using the single frequency electrochemical impedance spectroscopy (EIS). Through measuring the impedance of the tantalum surface, the single frequency EIS scan made it possible to observe the CMP and ECMP processes in situ. The impedance results presented competing mechanisms of removal and formation of a surface oxide layer of tantalum. Analysis indicated that the thickness of the oxide layer formed during polishing was related to the mechanical power correlated to the friction force and the rotating speed. Furthermore, the rate of growth and removal of the oxide film was a function of the mechanical power. This understanding is beneficial for optimization of CMP and ECMP processes.