Electroless deposition of copper for metallization in ULSI

Abstract

Electroless Cu film properties were studied as a function of bath composition (HCHO concentration) and deposition conditions (pH and temperature). The effects of 2,2’-bipyridyl on the formation of electroless Cu thin film was also studied in this work. Cu thin film was investigated by monitoring surface microstructure and electrical resistivity. To prevent contamination from alkali metal, alkali-free formaldehyde-based solution was used with cupric acid as a copper source and EDTA (Ethylenediamine-tetraacetic acid) as a complexing agent. Also no metal catalyst was used in this work to prevent metal contamination during electroless deposition process. The characteristics of electroless Operating temperature of electroless Cu deposition affected the grain structure of electroless Cu film. The optimum solution temperature was found as 73-75℃. Solution pH was found to determine the size of electroless Cu grains. As solution pH increased the grain size of electroless Cu film increased. The concentration of reducing agent, HCHO had an influence on deposition rate. As the concentration of formaldehyde increased the thickness of electroless Cu film increased. The concentration of 2,2’-bipyridyl affected size and shape of electroless Cu grains, and the density of nucleation centers. As the amount of 2,2’-bipyridyl increased the grain size became smaller, the shape of grain became more spherical, and the density of nucleation center increased.