High capacitance ultra-thin Ta2O5dielectric film applied to a high-speed bipolar memory cell

A new capacitor technology, with extremely thin Ta2O5film deposition and weakspot oxidation, is developed to realize high capacitance and high reliability. The Ta2O5film was reactively sputtered and followed by the weakspot oxidation. The oxidation improves the breakdown voltage by selectively oxidizing Si surface at weakspots where Ta2O5is locally thin. Consequently it reduces the defect density of the Ta2O5capacitor with least reduction of capacitance. This technology is based on a newly discovered fact that Ta2O5film below 200 Å remains in amorphous state with high dielectric breakdown strength even after heat treatments up to 1000 °C. Application of the Ta2O5capacitor to a switched-load resistor memory makes it possible to reduce the memory cell area to one third that of a conventional one. The memory provides high speed operation, and has sufficient soft error immunity.