Abstract

Ferro-electric thin film materials have been used for nonvolatile random access memories(FRAM*). PZT(Pb(Ti,Zr)O3) is one of several promising materials for use as a FRAM capacitor in combination with a platinum film as an electrode. However the ferroelectric properties of this capacitor are degraded by commonly used LSI processes, such as a passivation/ insulator(CVD-SiO2) process. Recently, mechanisms of process degradation are being investigated**,***, but are not clearly understood yet. For example, to our knowledge the existence of hydrogen in the capacitor after an annealing in hydrogenous atmosphere has not yet been measured by analytical methods. As a result in this study, we measured electrical properties of Pt/PZT/Pt capacitors after a 7.6 torr N2-H2 annealing at various hydrogen partial pressures and temperatures. Then we measured composition profiles of these capacitors by Secondary Ion Mass Spectrometry(SIMS). We found that after the N2-H2 annealing, the non-volatile polarization(Pnv)(uC/cm2) of the capacitors rapidly decreased under the presence of hydrogen at lower temperatures. At the same time, SIMS profiles showed that hydrogen concentration increased in the PZT film, and oxygen concentration decreased in the upper Pt film. We considered that the increase of hydrogen in the PZT film causes the degradation of electric properties, and the decrease of oxygen in the Pt film makes the adhesion force between the upper platinum electrode and the PZT film weaker. Moreover we found that the degradation can be eliminated by annealing in oxygen at temperatures as high as 400 °C.

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