Abstract: The present invention provides a method of forming a barrier layer over a via or a trench. The method includes generating a high density plasma in a chamber and depositing a barrier material over the via or the trench by using the high density plasma. The depositing of the barrier material comprises at least a first deposition step, a second deposition step and a third deposition step in sequence. The first, second and third deposition steps is respectively performed under a first bias power, a second bias power and a third bias power. The third bias power is greater than the second bias power, and the second bias power is greater than the first bias power. The present invention also provides a via structure formed by the method.