Hyo-Chol Koo

Effect of 2-Mercapto-5-benzimidazolesulfonic Acid in Superconformal Cu Electroless Deposition

Superconformal Cu electroless deposition is demonstrated in a CuSO 4 -EDTA-HCHO (where EDTA is ethylenediaminetetraacetic acid) electrolyte containing 2-mercapto-5-benzimidazolesulfonic acid (MBIS). MBIS reveals a concentration-dependent effect in the deposition rate on planar substrates, whereby acceleration at low concentration and suppression at high concentration are evident. The half-cell reaction experiments show that the acceleration effect of MBIS is mainly associated with the cathodic reaction, while MBIS inhibits the oxidation of HCHO in the anodic reaction. The addition of MBIS offers preferential Cu electroless deposition at the bottom of 500 nm wide trenches. Poly(ethylene glycol) improved the surface roughness, maintaining the shape evolution of superconformal feature filling.

Pulse Electrodeposition for Improving Electrical Properties of Cu Thin Film

Pulse deposition, which has an advantage to apply relatively high current density by supplement of Cu ions during off-time, was applied to deposit 250 nm Cu film. The microstructural change during off-time was to be investigated. The differences between constant potential and pulse deposition were due to the change during off-time. The application of pulse deposition led to the increase in the Cu(111) intensity and the reduction in the film resistivity compared to constant potential deposition. The film characteristics were further improved as the duty cycle decreased. The change during the off-time was verified to be grain growth in contact with the electrolyte. Additionally, it was clarified that the grain growth completed in a second, unlike self-annealing process, which proceeded for tens of hours, and affected within about 2.0 nm of Cu film from the surface. Under optimum conditions, pulse deposition led to 50% enhancement in Cu(111) intensity and 30% reduction in resistivity compared to the constant potential deposition.

The Inhibition of Silver Agglomeration by Gold Activation in Silver Electroless Plating

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 2.5 μΩ cm, which was decreased to 1.95 μΩ cm by the annealing process.

Ag Seed-Layer Formation by Electroless Plating for Ultra-Large-Scale Integration Interconnection

A high density of Pd catalytic particles is an important factor for obtaining a uniform and continuous Ag seed layer in electroless plating. Adequate surface pretreatment is critical for the formation of such a Pd catalytic particle population. In this study, electroless plating of Ag thin films on TiN substrates was performed using Sn sensitization and Pd activation as pretreatment methods. Sn surface sensitization improves surface wetting and aids in the formation of a Pd catalytic layer in surface-oxidative Pd activation. The Pd activation supported by Sn sensitization also accelerated the formation of a continuous thin Ag film. Furthermore, a thin Ag seed layer deposited on a patterned structure showed excellent conformality.

Effects of Stabilizing Agents on Film Properties in Ag Electroless Plating

The material properties of Ag electroless deposited films with the addition of stabilizing agents were analyzed. The resistivity of Ag film was significantly increased by the addition of benzotriazole to the electroless plating solution. The high resistivity of the Ag film dramatically decreased after annealing at relatively low temperatures. Auger electron spectroscopy and X-ray diffraction analysis showed that a contribution to the high resistivity of the Ag film with benzotriazole might be from the high reflection of the electron transfer at the grain boundary. In contrast, the addition of 5-aminotetrazole did not significantly increase the resistivity, and a smooth and continuous film was obtained. In this research, a model of the film-structure formation on the Pd-activated substrate in Ag electroless plating is proposed, and a reason for the formation of a highly resistive Ag film is suggested.

Improvement in the Oxidation Resistance of Cu Films by an Electroless Co-Alloy Capping Process

c KC Tech Company, Limited, Kyonggi 456-843, Korea 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 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 SiNx and SiCxNy 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.

Silver Direct Electrodeposition on Ru Thin Films

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.

Two-Step Filling in Cu Electroless Deposition Using a Concentration-Dependent Effect of 3-N,N-dimethylaminodithiocarbamoyl-1-propanesulfonic Acid

This paper describes electroless Cu filling of trenches with different widths ranging from 130 to 300 nm, using a concentrationdependent 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.

Local Corrosion of the Oxide Passivation Layer during Cu Chemical Mechanical Polishing

In this article, we analyze the effect of complexing agents in Cu chemical mechanical polishing slurry on the formation of oxide and the evolution of stress. The passivation property and surface morphology of the oxide on the surface showed significant differences depending on the kind of complexing agent. Oxalic acid showed fast oxide formation with poor passivation performance, and this caused large tensile stress evolution over 250 MPa in the Cu film. The synergetic effect of stress evolution and temperature increase due to the friction during the polishing caused severe pitting of the Cu surface after polishing in oxalic-acid-based slurry.

Direct-Electroplating of Ag on Pretreated TiN Surfaces

The electroplating of Ag without a seed layer on a highly resistive TiN substrate was investigated. The Ag particles deposited by a displacement reaction were used to increase the initial nucleation density. The electroplated Ag film on a Pd-Ag-activated TiN surface showed a continuous morphology with good adhesion and high conductivity, while a continuous film was not obtained on the nonactivated surface. Consecutive Ag activation following Pd activation resulted in higher density Ag clusters with good uniformity, in addition to better film adhesion than in the cases of either Pd or Ag activation. The high-density Ag particles generated played a part in enlarging the centers and provided an electron-transfer path. After annealing in a N 2 ambient, a pure Ag film with a thickness of 160 nm was present which had a resistivity of 2.16 μΩ cm. This is comparable to the value of an Ag film electroplated on a sputtered seed layer.