Transmission electron microscope investigation of SrBi2Ta2O9 memory capacitors on Si with silicon dioxide and silicon nitride as buffers

Abstract

Ferroelectric memory capacitors were made by deposition of SrBi2Ta2O9 (SBT) on Si with thin (∼40–90 Å) buffer layers of jet vapor deposition (JVD) silicon nitride and oxide. Transmission electron microscope analysis was carried out to compare the microscopic integrity of both films after subsequent processing steps. It was found that the thin SiO2 buffer layer failed to prevent further oxidation of the Si substrate and furthermore allowed the diffusion of the SBT towards the SiO2/Si interface. In contrast the silicon nitride layer deposited by the JVD process acted as a good barrier for the diffusion of SBT. It also stopped further oxidation of the Si substrate during subsequent annealing in oxygen. Electrical tests show that the capacitors have large memory windows and that the windows present only slight degradation after 1011 switching cycles. The use of JVD nitride as a buffer is encouraging for the further development of ferroelectric memory transistors.