IN SITU MASS SPECTROSCOPY OF RECOILED ION STUDIES OF DEGRADATION PROCESSES IN SrBi_2Ta_2O_9 THIN FILMS DURING HYDROGEN GAS ANNEALING

摘要

It is known that the forming gas (N_2-H_2 mixture) annealing process required for microcircuit fabrication results in an unacceptable electrical degradation of SrBi_2Ta_2O_9 (SBT) ferroelectric capacitors due mainly to the interaction of H_2 with the ferroelectric layer of the capacitor. We have found a strong relationship between changes in the surface composition of the ferroelectric layer and the electrical properties of SBT capacitors as a result of hydrogen annealing. Mass spectroscopy of recoiled ions (MSRI) analysis revealed a strong reduction in the Bi signal as a function of exposure to hydrogen at high temperatures (～500 °C). The Bi signal reduction correlates with Bi depletion in the SBT surface region. Subsequent annealing in oxygen at temperatures in the range of 700-800 °C resulted in the recovery of the MSRI Bi signal, corresponding to the replenishment of Bi in the previously Bi-depleted surface region. XRD analysis (probing the whole SBT film thickness) showed little difference in the XRD spectra of the SBT films before and after hydrogen and oxygen-recovery annealing. The combined results of the MSRI and XRD analyses can be interpreted as an indication that the degradation of the electrical properties of the SBT capacitors, after hydrogen annealing, is mainly due to the degradation of the near surface region of the SBT layer.