Composition control and ferroelectric properties of sidewalls in integrated three-dimensional SrBi_2Ta_2O_9-based ferroelectric capacitors

摘要

The difficult scaling of ferroelectric random access memories with the complementary metal-oxide semiconductor technology roadmap requires integration of three-dimensional (3D) ferroelectric capacitors (FeCAP's). In this work the unusual electrical behavior of 3D FeCAP sidewalls was studied by comparing the electrical properties of two-dimensional and 3D integrated FeCAP structures. We evidenced composition variations of the SrBi_2Ta_2O_9 (SBT) film in the sidewalls with marked bismuth segregation during metal-organic chemical-vapor deposition (MOCVD) of the SBT film. The segregation was reduced after decreasing the deposition temperature from 440℃, whereby the Bi-rich phase in the sidewalls does not contribute to polarization, down to 405℃, whereby sidewall SBT contributes to polarization. After further optimization of the MOCVD conditions at 405℃, the segregation is minimized and the ferroelectric contribution of the sidewall SBT is almost the same as the contribution of the planar SBT. As a result, 3D FeCAP's integrated up to metal interconnection exhibit a remnant polarization P_r～7.5 μC/cm~2.