In spite of development of other competitive technologies, it is obvious that applications of electroless deposition of metals and alloys will continue to grow in the future. Applications of electroless deposition of metals and alloys are related to developments in the electronics industries, battery technologies, medical devices, and protective and decorative coatings. According to literature review, more work is required to understand fundamental issues related to the reaction mechanisms of electroless deposition, the influence of processing parameters on properties of deposited coatings, etc. This knowledge is needed to ensure the successful operation of the process.

Electroless Deposition of Metals and Alloys

The preparation of nanoscaled palladium (Pd) particles for catalyzation of electroless copper (Cu) plating has been investigated in this research. Nanosized Pd catalysts were electrochemically deposited on Si/SiO 2 /Ta x N substrates using displacement activation and sensitization activation, and their formation and microstructures were characterized. By displacement activation, large Pd particles with nonuniform size distribution from 20 to 200 nm are observed, resulting in subsequent rough and discontinuous Cu films electrolessly deposited on these Pd catalysts. In comparison, tremendous, small, and uniform Pd nanoparticles of about 10 nm are obtained by sensitization activation as fine nucleation sites for following electroless deposition of smooth and conformal Cu films. Nucleation, growth, coalescence, and then connection and film growth steps are observed in the formation process of Cu films. No preferred orientation of both electrolessly deposited Cu films is found. Well-controlled, electrochemically deposited nanoscaled Pd catalysts and uniform Cu films can be used as 65 nm Cu interconnect metallization.

Electrochemical Deposition of Nanoscaled Palladium Catalysts for 65 nm Copper Metallization

An electrochemical deposition process for copper (Cu) metallization has been developed and investigated by the integration of nanoscaled palladium (Pd) catalyzation, electroless plating of Cu seed layers, and electroplating of Cu films in this study. Following surface cleaning and etching, sensitization and activation of Si/SiO 2 /TaN substrates were performed to obtain uniformly distributed Pd catalysts of only about 10 nm. Smooth and continuous 30 nm thick Cu seed layers with low electrical resistivity were electrolessly deposited using the nanosized Pd catalysts as nucleation sites. Copper metallization with high purity small surface roughness, low electrical resistivity of 1.77 μΩ cm, low residual stresses, and good adhesion to substrates was achieved using the subsequent electroplating on the electroless seed layers and postannealing. Good gap-filling capability on finely patterned structures was performed and exhibited the great application potential of low-temperature integrated electrochemical deposition process for next-generation Cu metallization of ultralarge-scale integrated circuits.

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Integrated Electrochemical Deposition of Copper Metallization for Ultralarge-Scale Integrated Circuits

Activation of Ta/SiO 2 /Si substrates using a PdCl 2 buffered oxide etch (BOE)/HNO 3 displacement solution and electroless Cu deposition have been investigated in this paper. Surface morphologies and distribution of Pd nuclei on the Ta layer were strongly dependent on the ratio of BOE/HNO 3 during activation as confirmed by scanning electron microscopy and atomic force microscopy surface observation. Using an activation solution with a ratio of BOE/HNO 3 of 3:2, electrolessly deposited Cu films with good surface coverage and low electrical resistivity were obtained. The surface coverage of electroless Cu grains on the Ta layer degraded with longer activation time and other activation solutions due to the Pd removal resulting from lateral under-substrate cut during activation, No preferred orientation of the electrolessly deposited Cu films was found from X-ray diffraction analysis. Good selectivity of electroless Cu deposition contributed to the preferred nucleation of Cu on Pd nuclei which deposited only on the Ta layer rather than on SiO 2 during activation.

Displacement activation of tantalum diffusion barrier layer for electroless copper deposition

Recent advances in electroless nickel‑boron coatings

An improved activation process using a PdCl 2 -HF-NH 4 F system for the activator solution is reported. The process is applicable for autocatalytic electroless deposition of metals on rough as well as smooth/polished, n- and p-type silicon substrates of all doping levels. Using the improved activation process, adhesion of more than 8.33 x 10 6 N/m 2 for palladium deposits and 7.25 x l0 6 N/m 2 for nickel deposits has been obtained. The etch rate of SiO 2 in the activator so ution is low enough for it to be compatible with planar integrated-circuit technology. The activator avoids the use of tin, which is undesirable in device fabrication.

D. Sridhar

Papers

A Novel Activation Process for Autocatalytic Electroless Deposition on Silicon Substrates

A Novel Activation Process for Autocatalytic Electroless Deposition on Silicon Substrates.