INVESTIGATION ON LEAKAGE CURRENT REDUCTION OF PHOTO-CVD TANTALUM OXIDE-FILMS ACCOMPLISHED BY ACTIVE OXYGEN ANNEALING

Previously, the authors demonstrated that photo-CVD Ta2O4 films formed on a Si substrate using TaCl5 and O2 acquire very low leakage current by active oxygen annealing. This paper investigates in detail the mechanism of the leakage current reduction. Low-leakage-current Ta2O5 films are produced provided there is a sufficient UV-activation of TaCl5 molecules during CVD, an abundant supply of electronically excited oxygen, O(1D) and O2(1-DELTA), during annealing, and Si migration from the substrate into the films during annealing, or CVD. A phenomenological model of the leakage current reduction is proposed. In the model, a certain Ta-O(x) void in the Ta-O network is compensated by chemically incorporating a Si atom and several excited oxygen species; O(1D) or O2(1-DELTA). This model can consistently interpret a series of phenomena on leakage current reduction reported in this paper and in our previous papers.