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

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.