We demonstrate that after a fine-tuned ashing process the damage behavior of extra low-k material (ELK, k=2.5) is continued at the surface and the thickness of the damaged layer can be kept under control. Therefore, damaged-free treatment can be achieved by process optimization. Finally, we prove the effectiveness of this treatment by using a novel near-field scanned microwave probe to perform microwave capacitance measurements on a well-designed test vehicle. It is the first implementation of this methodology to monitor low-k damage in patterned low-k structures