| High dielectric constant materials such as Barium Strontium Titanate (BST) will be necessary for future (>1 gigabit) high-density memories. The integration of a new material into well-established silicon processing facilities is a complex task. Through this work, we hope to take a step towards that end.; Special electrode materials are necessary to withstand the severe conditions required for BST processing. Platinum (Pt) has been the material of choice for this purpose. However, the poor diffusion barrier properties and alpha particle emission problem with Pt prompted the search for alternate electrode materials. We propose using Ir electrodes to overcome the difficulties associated with platinum.; High quality Ir (ρ = 7μΩ-cm) and IrO2 (75μΩ-cm) films were deposited using DC magnetron sputtering. The thermal stability of these films under oxidizing, reducing and neutral conditions was studied. While IrO2 may not be a suitable electrode material due to its instability in forming gas (N2/H2), Ir appears to be a promising candidate. Hence, we studied the effect of processing parameters on the electrical characteristics of RF sputtered BST thin films on Ir electrodes. Three different film compositions Ba0.5Sr0.5TiO 3, Ba0.4Sr0.6TiO3 and SrTiO3 were studied. Dielectric films (400Å–500Å thick) with high dielectric constant (ϵr = 350) and low leakage currents (J = 5 × 10−8 A/cm2) were obtained. However, the dielectric dispersion (frequency dependent loss in capacitance) for BST films with Ir electrodes was high (2.65% loss per decade of frequency).; The dielectric dispersion in BST films was studied in detail. A model was developed to separate the electrode-dielectric interface effects from that of the film itself. Based on the results, a new multi-layer capacitor structure was proposed and successfully fabricated to yield a combination of high dielectric constant and low dielectric dispersion. We also studied the effect of external mechanical stress on the electrical characteristics of BST thin films. We find that unlike in the case of materials with a large piezoelectric coefficient e.g. Pb(Zr,Ti)O3, BST thin films respond differently to external mechanical stress. The mechanism may be related to the electrode-dielectric interface rather than piezoelectricity. |
