Correlation between oxidation resistance and crystallinity of Ti-Al as a barrier layer for high-density memories

The Ti-Al intermetallic material system has been investigated for application as a conducting diffusion barrier in a three-dimensional stacked capacitor-transistor geometry. La-Sr-Co-O (LSCO)/Pb-Zr-Ti-Nb-O/La-Sr-Co-O ferroelectric capacitors were fabricated on Ti-Al/polycrystalline-Si/Si substrates. The electrical and ferroelectric properties are found to correlate strongly with the crystallinity of the Ti-Al layer. The crystalline Ti-Al layer shows a distinct chemical reaction with the bottom LSCO electrode thus preventing ohmic electrical contact between the ferroelectric capacitor and transistor. In contrast, the amorphous Ti-Al layer does not react and forms an ohmic contact to LSCO. For crystalline Ti-Al, X-ray photoelectron spectroscopy (XPS) shows the formation of Al2O3 induced by the segregation of Al to the LSCO/Ti-Al interface. For amorphous Ti-Al, XPS reveals that no Al2O3 layer is formed. In addition, Rutherford backscattering analysis shows almost no difference in the Ti-peak spectrum before and after deposition of LSCO.