By exposing a process control wafer having a porous low-k-dielectric layer thereon in an HF-based low-k dielectric etching solvent comprising a dilating additive and a passivating additive, the pores in the low-k dielectric layer are dilated some of which connect with one another to form one or more continuous channels extending through the thickness of the dielectric layer and allowing the HF-based solvent to reach down to the substrate. Then the passivating additive component of the HF-based etching solvent forms a passivation layer at the dielectric layer and the substrate interface that protects substrate from the HF-based etchant.