An etching process for selectively etching exposed metal surfaces of a
substrate and forming a conductive capping layer over the metal surfaces
is described. In some embodiments, the etching process involves oxidation
of the exposed metal to form a metal oxide that is subsequently removed
from the surface of the substrate. The exposed metal may be oxidized by
using solutions containing oxidizing agents such as peroxides or by using
oxidizing gases such as those containing oxygen or ozone. The metal oxide
produced is then removed using suitable metal oxide etching agents such
as glycine. The oxidation and etching may occur in the same solution. In
other embodiments, the exposed metal is directly etched without forming a
metal oxide. Suitable direct metal etching agents include any number of
acidic solutions. The process allows for controlled oxidation and/or
etching with reduced pitting. After the metal regions are etched and
recessed in the substrate surface, a conductive capping layer is formed
using electroless deposition over the recessed exposed metal regions.