ULTRATHIN TANTALUM OXIDE CAPACITOR DIELECTRIC LAYERS FABRICATED USING RAPID THERMAL NITRIDATION PRIOR TO LOW-PRESSURE CHEMICAL-VAPOR-DEPOSITION

We describe the formation of ultrathin tantalum oxide capacitors, using rapid thermal nitridation of the storage-node polycrystalline-silicon surface prior to low pressure chemical vapor deposition of tantalum oxide. The amorphous tantalum oxide film is deposited on the nitride polysilicon surface using penta-ethoxy-tantalum [Ta(OC2H5)5] and oxygen (O2) gas mixture at 470-degrees-C. The films are annealed ai 600-900-degrees-C in dry O2. Densification of the as-deposited film by annealing in dry O2 is indispensable to the formation of highly reliable ultrathin tantalum oxide capacitors. During this densification, CH4 and H2O desorb from the as-deposited film, and the film crystallizes into an orthorhombic structure. The RTN treatment allows a reduction of the SiO2 equivalent thickness (t(eq)) of the capacitor dielectric layer and results in superior leakage and reliability characteristics.