A low-k dielectric layer stack is provided including a silicon based dielectric
material with a low permittivity, wherein an intermediate silicon oxide based etch
indicator layer is arranged at a depth that represents the depth of a trench to
be formed in the dielectric layer stack. A thickness of the etch indicator layer
is sufficiently small to not unduly compromise the overall permittivity of the
dielectric layer stack. On the other hand, the etch indicator layer provides a
prominent optical emission spectrum to reliably determine the time point when the
etch process has reached the etch indicator layer. Thus, the depth of trenches
in highly sophisticated low-k dielectric layer stacks may reliably be adjusted
to minimize resistance variations of the metal lines.
