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ABSTRACT: Ag seed layers were pretreated with 1: 1,000 diluted nitric acid cleaning solution for 60 s to obtain a clean and oxide-free
Ag surface. When an applied potential was less than −800 mV in Ag electroplating, the deposition rate was over 2,000 Å/min
and the resistivity of Ag deposit was 1.80 μΩ·cm. But the deposit film became rougher with a negative increase in the potential,
and it was also observed through measuring the double layer capacitance. The resistivity of Ag film annealed at 350 °C for
30 min was decreased from 1.80 μΩ·cm to 1.67 μΩ·cm and the agglomeration of Ag grains was not observed on the surface of the
annealed Ag films. To reduce the surface roughness, thiourea was added in the electrolyte and it was decreased below 15 nm.
Korean Journal of Chemical Engineering 04/2012; 26(1):265-268. · 0.99 Impact Factor
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ABSTRACT: In this study, in-situ transmittance measurement was employed to study the stability and reactivity of the Cu electroless deposition (ELD) solution
as an alternative tool for chemical-sensitive electrochemical analysis and ex-situ studies of deposited films. Its advantages lie in both the simplicity of the analysis and the in-situ allowance in time-dependent characterization. To understand the basic behaviors of Cu ELD solution, the change of transmittance
with the size of Cu particles by the injection of SnPd colloids were observed. Based on the relationship between the transmittance
and the Cu particle growth, in-situ monitoring was applied to determine the effect of complexing agents, the important elements in determination of solution
performance, on stability and reactivity. In the stability test, it was observed that complexing agents with lower formation
constant (pKf) led to the decomposition of solution at 70°C, whereas complexing agents with higher pKf showed stable state. In reactivity test, the reaction time to Cu reduction with SnPd colloid was increased in the order of
pKf values. Also, the feasibility of this in-situ monitoring method was confirmed by comparison with the results from real deposition on Ta substrate.
Journal of The Electrochemical Society. 08/2011; 158(9):D541-D545.
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ABSTRACT: Electrodeposition of Ag was performed on Ru thin films following electrochemical reduction of native Ru oxide. Oxide reduction
in a tetramethylammonium hydroxide solution was critical for the formation of continuous Ag film, and a large overpotential
was important for high-density nucleation. From a kinetics viewpoint, the thermal stability of the Ag film was improved by
the application of a more negative potential, which suggested that better nucleation density at the initial stage of growth
induced better substrate adhesion. Suppression of growth by addition of an organic additive generated a larger and more uniformly
distributed initial population of Ag particles, and as a result a smooth film was obtained.
Journal of The Electrochemical Society. 04/2008; 155(5):D389-D394.
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ABSTRACT: In Ag electroless plating, Ag agglomeration has been the obstacle to obtain thin Ag films. The crystallographic misfit between
the substrate and Ag can accelerate Ag agglomeration. In this paper, Au, whose crystallographic characteristics are similar
with those of Ag, is used as the activation material. As a result, the Ag layer was deposited in the form of layer-by-layer
growth. Therefore, Ag film electrolessly deposited on a substrate activated by Au can be used to manufacture the interconnections
in microelectronic devices. In this experiment, the resistivity of the Ag film was measured to
, which was decreased to
by the annealing process.
Journal of The Electrochemical Society. 05/2005; 152(6):C388-C391.
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ABSTRACT: Co-alloy films with various solution compositions CoB, CoWB, and CoWBP were deposited with an electroless technique on Cu films without Pd activation, and their oxidation barrier performance was analyzed. The degrees of oxidation of all films were intensively studied. CoB showed excellent capping performance as an oxidation barrier, whereas CoWB and CoWBP exhibited even poorer oxidation resistance than the case of bare Cu at 400°C. The depth profile of the film compositions and chemical states of the CoB film before and after oxidation was investigated, the results of which suggested that the oxidation of the B component in the film had a clear role in the prevention of continuous Cu diffusion to the surface. The multilayer structure of CoB/ CoWBP/Cu for obtaining both electromigration and oxidation resistance was optimized, showing excellent oxidation resistance comparable to a single-composition CoB film. In the fabrication of Cu metal lines using the damascene process in ultralarge-scale integration technology, the upper Cu surface ex-posed after a chemical mechanical polishing CMP process must be shielded with a diffusion barrier. Dielectric materials such as SiN x and SiC x N y have been used for this purpose, and these are deposited on the whole substrate without a selective etching process. However, the dielectric constants of these materials are higher than those of the low-k materials used for the interlevel dielectric, which leads to an increase in the effective dielectric constant between the metal lines and the increment in resistor–capacitor delays. 1 Furthermore, a continuous increase in integrity has promoted an increase in the current density of the metal lines, which induces serious electromi-gration issues. 2 It has been reported that the high interfacial energy between metallic–dielectric interfaces Cu–dielectric capping layer is the region where the electromigration phenomenon occurs. 2,3 Electroless deposition of a thin Co-based alloy film on top of the exposed Cu metal line is the most promising solution to these problems. 4 Selective electroless deposition of Co-alloy layers, which act as diffusion barriers, also reduces the total volume of the capping layer and therefore decreases the effective dielectric constant of the entire metal line structure. 1 Furthermore, the interface of the Cu–Co alloy is metal–metal, which may have a lower interfacial energy than the previous metal–dielectric construction. This scheme signifi-cantly increases the lifetime of the metal line and also clearly in-creases the activation energy for the interfacial diffusion of Cu. 5 Capping layers based on Co or Ni with the addition of boron or phosphorus during electroless deposition have been widely re-searched for various applications, including wear-resistive coating and magnetic materials. These capping layers have also included further ternary refractory alloy metals such as tungsten or molybde-num. The incorporation of boron or phosphorus is known to result from the chemical reduction of reducing agents. 6 Boron, phos-phorus, and tungsten are considered to be elements capable of blocking the diffusion of Cu at the grain boundary of Co or Ni, thereby playing a vital role as a diffusion barrier. 7 Recent studies showed that the addition of a small amount of dimethylamine borane DMAB induces Pd-free electroless deposition on a Cu surface from a CoWP electrolyte, whereas using only hypophosphite re-quires Pd activation to deposit an alloy film. 8 Another property that is expected to improve with the electroless capping process is the oxidation resistance of the Cu line. Cu does not form a self-passivation layer like Al, and continuous oxidation occurs when it is exposed to an oxidizing environment. The forma-tion of an oxide layer between Cu and the diffusion barrier interface increases the effective resistivity of the metal line and is also a major cause of the electromigration phenomenon. In previous stud-ies, an improvement in the oxidation properties was mainly achieved by the injection of alloy elements during the deposition of Cu, which diffused to the surface to form a permanent passivation layer. 9,10 In previous research, our group showed that a thin Ag layer deposited by a displacement reaction with Cu enhanced the oxidation resis-tance of Cu. 11 Also, the insertion of Ag ions during the CMP process resulted in the deposition of a very thin and smooth Ag capping layer with good oxidation resistance. 12 In those studies, the growth mechanism of the Cu oxide was the continuous diffusion of Cu to the surface. Recently, it was reported that the CoB film had better oxidation resistance than other Co-based capping layers. 13 In this paper, capping layers, including CoWBP, CoWB, and CoB, deposited by electroless deposition without Pd activation on a Cu substrate were studied. Their performance as an oxidation barrier was tested, and their properties related to oxidation resistance are discussed.
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ABSTRACT: GaN on Al2O3 was drilled with a high power Nd:YAG laser. Micro-Raman spectroscopy showed that the induced damage was nominal at about 15 µm from the edge of the drilled through-wafer via-holes. Cu plating was accomplished using an electroless plating technique. FIB was employed to expose the interface between electrolessly plated Cu and GaN on the sidewall of the drilled holes, followed by SEM/EDX to confirm that the sidewall of the drilled holes was successfully covered with Cu. Cu electroless plating after laser drilling has the potential to simplify device layout and improve device integration.
Thin Solid Films 517(14):3841-3843. · 1.89 Impact Factor
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ABSTRACT: This paper describes electroless Cu filling of trenches with different widths ranging from 130 to 300 nm, using a concentration-dependent effect of 3-N,N-dimethylaminodithiocarbamoyl-1-propanesulfonic acid DPS. With a fixed DPS concentration, it is shown that these trenches with different dimensions cannot be superfilled simultaneously. This is presumably caused by different surface concentrations of the adsorbed additive, which depends on the feature size and surface area. A two-step filling method is employed to superfill those trenches, which is also effective in control of the deposited Cu amounts to obtain uniform growth front regardless of the trench dimensions. Superconformal electrodeposition of Cu using organic additives such as bis3-sulfopropyl-disulfide SPS-polyethyleneglycol PEG-chloride Cl − has been successfully implemented for the metallization of ultra-large-scale integrated circuits. 1,2 Such void-free filling of trenches and vias is quantitatively predicted by the curvature-enhanced adsorbate coverage model, which involves the competitive adsorption between accelerating species SPS-Cl and suppressing species PEG-Cl coupled with the effect of local area change. 3-6 However, Cu electroless deposition, for which reducing agents such as formaldehyde or glyoxylic acid are used to reduce Cu ions instead of an externally supplied current, has been applied only to the seed repair process for physical vapor deposition PVD seeds 7,8 or to the seed layer itself for Cu superconformal electrodeposition, because of its conformal deposition characteristics. 9,10 Recently, however, Cu electroless deposition has been explored as a possibil-ity for direct void-free filling of features covered with barrier layers because it is one approach to solving the pinch-off caused by poor step coverage of PVD seeds, as the feature size shrinks down and the aspect ratio increases. To date, Cu electroless gap filling has been achieved either in the presence of S and/or N bearing sulfonic acid series additives, 11-15 some of which are well known in Cu electrodeposition, or in the absence of deposition-rate-controlling additives. 16-19 When SPS, a well-known accelerator for superfilling in Cu elec-trodeposition, was applied to Cu electroless deposition, it was evi-dent that the deposition rate depended on the SPS concentration, namely, accelerating at low concentration and suppressing at higher concentration. The difference of surface concentration between the top and the bottom of 500 nm wide trenches led to bottom-up filling of Cu without seams or voids in electroless deposition, showing the typical overfill bumps. 12,13 Similarly, the use of 3-N,N-dimethyl-aminodithiocarbamoyl-1-propanesulfonic acid DPS, which has a molecular structure similar to 3-mercapto-1-propanesulfonic acid MPS, also showed the concentration-dependent effect on the depo-sition rate for the planar substrate and bottom-up filling profiles with smoother surface characteristics than SPS. 14 Although Cu electroless bottom-up filling was achieved in 500 nm wide trenches using the concentration-dependent bifunc-tional additives, different kinetics would be anticipated for electro-less Cu filling of differently sized features because the variation in the surface concentration of additives would be more strongly af-fected by the dimension of the trenches. Therefore, in this article, we investigate how the effect of the concentration-dependent bifunctional additive in Cu electroless fill-ing depends on the trench dimension, especially the widths being 320 nm, through the electron microscopic observation of Cu gap filling using a representative bifunctional additive, DPS. Further-more, we suggest an effective way to superfill the patterns of various dimensions with uniform growth fronts by modifying the conven-tional Cu electroless deposition.
