Thin films of BiOX, SrXTaYO, and SrXBiYTaZO (SBT) were deposited by liquid-delivery metalorganic chemical vapor deposition (MOCVD). The substrate temperature and the deposition pressure were varied from 300 to 600°C and from 0.35 to 7 mbar, respectively. Triallylbismuth (Bi-1), triphenylbismuth (Bi-2) or alkyl bismuth (Bi-3) and strontium bis-pentaethoxy-methoxyethoxy tantalate (Sr-Ta) were used as Bi precursors and as Sr-Ta precursor, respectively. X-ray photoelectron spectroscopy (XPS), ellipsometry, and scanning electron microscopy (SEM) were carried out to characterize the film properties.
The growth rates of the MOCVD of BiOX and SrXTaYO were compared to the growth rate of SBT to obtain information about mutual interaction between the precursors. The growth rate of bismuth oxide thin films deposited from Bi-1 and Bi-2 was low (∼10 nm/h at 0.35 mbar). The growth rate of strontium tantalate films was higher (up to 50 nm/h) and depended strongly on the temperature. Eight times higher (∼400 nm/h) growth rates of BiOX and SBT films were observed for the Bi-3 precursor. The deposition rate of the SBT films was quite similar to the rate of the bismuth oxide. However, the deposition rate of SBT was always lower than the deposition rate of the single Bi precursors. The growth rate significantly depended on the deposition pressure. A decrease of the deposition pressure in the reactor chamber reduced the deposition rate of BiOX, SrXTaYO, and SBT, but on the other hand, it improved the uniformity of the film thickness over the entire 150 mm wafer surface.
The XPS measurements showed a deficit of bismuth in the SBT films even though the concentration of the Bi-1 or Bi-2 precursor was several times higher compared to the Sr-Ta precursor. This problem disappeared when Bi-3 source was used.