Composition control and ferroelectric properties of sidewalls in integrated three-dimensional SrBi_(2)Ta_(2)O_(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_(2)Ta_(2)O_(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 deg C, whereby the Bi-rich phase in the sidewalls does not contribute to polarization, down to 405 deg C, whereby sidewall SBT contributes to polarization. After further optimization of the MOCVD conditions at 405 deg C, 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) approx 7.5 (mu)C/cm~(2).