Method of copper hillock detecting

A method of copper hillock detecting, comprising:

• disposing a testkey structure on a substrate, wherein the testkey structure comprises:
• a lower metallization layer, an upper metallization layer, and a dielectric layer between the lower metallization layer and the upper metallization layer, wherein the lower metallization layer comprises a plurality of first metal lines parallel to each other, and the upper metallization layer comprises a plurality of second metal lines parallel to each other;
• applying a force voltage difference to the lower metallization layer and the upper metallization layer under a test temperature and stress time, wherein a part of the second metal lines are connected to a first voltage, the other part of the second metal lines are connected to a second voltage, and the first metal lines are connected to ground;
• and
• detecting a changed sensing voltage difference to the lower metallization layer and the upper metallization layer for detecting copper hillock.