In accordance with some embodiments, a method for forming via holes is provided. The method includes providing a substrate with an etch stop layer and a dielectric layer sequentially formed thereon. The method also includes etching the dielectric layer to form a first via hole of a first size and a second via hole of a second size within the dielectric layer by a plasma generated from an etch gas, until both the first via hole and the second via hole are reaching the etch stop layer. The etch gas includes CH2F2 and an auxiliary gas of N2 or O2.