In this study, the electroless deposition of copper and silver was investigated on epoxy and silicon dioxide-based substrates. A cost-efficient, Sn/Ag catalyst was investigated as a replacement for the Sn/Pd catalyst currently used in board technology. The surface of the epoxy based polyhedral oligomeric silsesquioxane (POSS) films was modified by plasma and chemical etching for electroless activation without the creation of a roughened surface. The electroless copper deposited on the modified POSS surface exhibited excellent adhesion when annealed at 180 • C in nitrogen for 90 min or at room temperature for 24 hr. Electroless copper deposition was also demonstrated on oxidized silicon wafers for through silicon via sidewall deposition.
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 Cu͑111͒ 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 Cu͑111͒ intensity and 30% reduction in resistivity compared to the constant potential deposition.
Superconformal Cu electroless deposition is demonstrated in a CuSO 4 -EDTA-HCHO ͑where EDTA is ethylenediaminetetraacetic acid͒ electrolyte containing 2-mercapto-5-benzimidazolesulfonic acid ͑MBIS͒. 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. Poly͑ethylene glycol͒ improved the surface roughness, maintaining the shape evolution of superconformal feature filling. © 2009 The Electrochemical Society. ͓DOI: 10.1149/1.3117343͔ All rights reserved.Manuscript submitted December 9, 2008; revised manuscript received February 3, 2009. Published April 21, 2009 Superconformal Cu electrodeposition has been successfully implemented in the metallization of electronic devices, thereby enabling the buildup of multilevel interconnects for ultralarge-scale integration ͑ULSI͒. 1Electroless Cu deposition has been mainly used in an area of printed circuit boards to form seed layers ͑conductive path͒ for Cu electrodeposition in high aspect ratio through-holes, taking advantage of its ability to metallize nonconductive epoxy glasses, polyimides, etc.2,3 Recent research on Cu electroless deposition has extended its application to seed layer deposition for Cu electrodeposition in ULSI interconnect fabrication, with increasing advantages over alternative methods as the feature size decreases to a submicrometer scale.4,5 Electroless deposition is a surface limited reaction that enables the deposition of considerably thin and uniform Cu seed layers with a superior step coverage compared to physical vapor deposition ͑PVD͒ or chemical vapor deposition seed layers. 6,7 Contrary to the conventional method that utilizes a conformal deposition property of electroless Cu, a superfilling of submicrometer features such as trenches or vias using only electroless deposition has also been attempted in several publications. [8][9][10][11][12] The most important factor that determines the feature-filling profiles is the effect of additives. In electrodeposition, a quantitative understanding of superconformal electrodeposition can be described by the curvature enhanced accelerator coverage ͑CEAC͒ mechanism that is derived from the competitive adsorption between additive species that accelerate and inhibit the deposition rate coupled with electrode area change. 13,14 The use of additives in Cu electroless deposition has been largely concerned with stabilizing the electrolyte or enhancing the physical properties of films, while the effect on feature filling has received less attention.In previous work, we have achieved superconformal Cu electroless deposition in the presence of bis-͑3-sulfopropyl͒-disulfide ͑SPS͒ 9,10 and 3-N,N-...
The role of each chemical component in Cu electroless deposition (ELD) solution was investigated in real-time by open-circuit potential (OCP) measurement assisted by quartz crystal microbalance. It was observed that Cu was continuously oxidized in alkaline bath. However, when ethylenediaminetetraacetic acid (EDTA), a well-known complexing agent, was in the solution together, EDTA was found to participate in the removal of Cu oxide formed on the surface as well as the complexation of Cu ions in the solution. Formaldehyde, a reducing agent, was adsorbed onto the Cu surface and inhibited further Cu oxidation in the alkaline media. Both components maintained low oxygen content on the Cu surface in the alkaline solution. Coulometric reduction method and X-ray photoelectron spectroscopy analysis revealed that the surface had a small amount of Cu 2 O. During Cu ELD process, the induction period was observed at the initial stage of the deposition and it was related with the time that methylene glycol anions were adsorbed and became activated on the surface. The OCP measurement during Cu ELD also indicated that the deposition followed the mixed potential theory to some extent.
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