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

A new capacitor technology, with extremely thin Ta
2
O
5
film deposition and weakspot oxidation, is developed to realize high capacitance and high reliability. The Ta
2
O
5
film was reactively sputtered and followed by the weakspot oxidation. The oxidation improves the breakdown voltage by selectively oxidizing Si surface at weakspots where Ta
2
O
5
is locally thin. Consequently it reduces the defect density of the Ta
2
O
5
capacitor with least reduction of capacitance. This technology is based on a newly discovered fact that Ta
2
O
5
film below 200 Å remains in amorphous state with high dielectric breakdown strength even after heat treatments up to 1000 °C. Application of the Ta
2
O
5
capacitor 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.