INTERFACIAL REACTION IN THE POLY-SI TA2O5/TIN CAPACITOR SYSTEM/

For tantalum pentoxide capacitors in 1 Gbit dynamic random access memo ry, titanium nitride is adopted as the top electrode. After postanneal ing at temperatures higher than 750 degrees C, the capacitance of Ta2O 5, reduces due to an interfacial reaction between TN and Ta2O5. This w as studied by high resolution electron microscopy and energy dispersiv e spectroscopy with a 1 nm electron probe. It is found that voids form along the interface between TN and Ta2O5 and a large proportion of Ta dissolves into the TiN film. The origin of the reaction is concluded to be a large solid solubility of Ta in TiN. After Ta outdiffusion int o TIN, vacancies agglomerate and form voids in Ta2O5 and thereby reduc e its capacitance. Since the driving force of the reaction is the soli d solubility of Ta in TiN, the amount of the reaction is affected by t he thickness of the TiN films. (C) 1998 American Institute of Physics.