A capacitor includes: a lower electrode including a metal nitride represented by MM′N, wherein M is a metal element, M′ is an element different from M, and N is nitrogen; a dielectric layer on the lower electrode; an interfacial layer between the lower electrode and the dielectric layer and including a metal nitrate represented by MM′ON, wherein M is a metal element, M′ is an element different from M, N is nitrogen, and O is oxygen; and an upper electrode on the dielectric layer.