4. Conclusions
In thiswork, the activation of dielectric surface by the colloidal solution
of cobalt compounds was examined as a Pd-free process. It has
been shown that the usual catalyst Pd(0)was replaced by Co(0) species
which are able to initiate electroless copper deposition. The method
consists of three main steps: deposition of an ultra-thin film of cobaltbased
precursor using the colloidal solution of cobalt compounds, decomposition
of the precursor film simultaneously with the reduction
of cobalt compounds to seed the surface with Co(0) species and the
copper metallization itself. It has been determined that for successful
reduction of adsorbed cobalt oxy/hydroxy compounds elevated temperatures
are required.Moreover, it has been determined that the presence
of a small amount of Cu2+ ions in the colloidal Co-based solution
catalyzes the reduction of adsorbed Co-based precursor on the dielectric
surface producing Co(0) seeds which initiate electroless copper deposition.
A continuous copper film was deposited on a glass sheet after
its activation in the colloidal solution of cobalt compounds containing
Cu2+ ions.
It has also been determined that the reduced Co(0) seeds are further
oxidized by oxygen dissolved in rinsing water. To prevent the oxidation
of reduced Co(0) seeds on the substrate surface it is necessary
to add 0.2–0.4 g/l of sodium borohydride to the rinsing water.