A method for forming a stacking structure, including forming a ruthenium oxide layer over a substrate; forming a praseodymium oxide layer over the ruthenium oxide layer; and forming a titanium oxide layer over the praseodymium oxide layer; wherein the titanium oxide layer has a rutile phase with the existence of the praseodymium oxide layer underneath. The oxide layers are deposited by a plurality of atomic layer deposition cycles using ruthenium precursor, praseodymium precursor, titanium precursor, and ozone.