COMPARISON OF TA2O5 CAPACITORS ON SI WITH AND WITHOUT RAPID THERMAL NITRIDATION

Abstract

The tantalum pentoxide (Ta2O5) film attracts great interest because of its potential application as the dielectric film for the storage capacitor and the gate insulator in ULSIs. However, its high leakage current limits its application. In this project, the Rapid Thermal Nitridation (RTN) pre-treatment of the substrate and the post Rapid Thermal Annealing (RTA) treatment of the Low Pressure Chemical Vapour Deposited (LPMOCVD) Ta2O5 films of 8.4 nm or 15 nm thickness in O2 or N2O are used to increase the capacitance and reduce the leakage current. The comparison of the electrical properties of the two kinds of films with and without RTN after RTA in O2 or N2O by using capacitors is provided. The XTEM analysis shows that after RTA the Ta2O5 layer becomes thinner and the interfacial layer becomes thicker in both the capacitors with and without RTN. The thinner Ta2O5 layer will increase the capacitance and reduce the leakage current. The thicker interfacial layer will reduce the capacitance and the leakage current. RTN treatment increases the capacitance of the Ta2O5 capacitor and reduces the leakage current if proper RTA is conducted. The interfacial layer is oxidized when RTA is conducted. There is an optimum condition of RTA for the samples with RTN to have good electrical properties. When the duration time is reduced from 30s to 10s, fewer O atoms will diffuse into the Ta2O5 layer, and the effect of the thinning Ta2O5 layer will be weakened. When the Ta2O5 layer thickness increases from 8.4 nm to 15 nm, fewer O atoms will diffuse through the Ta2O5 layer, reach and oxidise the interfacial layer. Therefore the effect of the thickening interfacial layer will be reduced. The leakage current is related to the defect states in the Ta2O5 films. The trap status in the films with and without RTN detected by the ZBTSC (Zero-Bias Thermally Stimulated Current) technique provides explanation to their different I-V characteristics. The lower leakage current in our samples is due to the reduction in the concentration of shallow defect states. SIMS analysis provides the comparison of impurity depth profiles in the two kinds of samples after RTA in O2 or N2O at different temperature. The electrode material effects are discussed in the project. The superiority of Au/Cr/TiN over to Al is shown in terms of the low leakage current.