MOCVD kinetics of strontium bismuth tantalate thin film growth

Abstract

The thin films of BiOx, SrxTayOz , and strontium bismuth tantalate (SBT) were deposited by metalorganic chemical vapour deposition (MOCVD) on 150 mm silicon (100) wafers. Some of the wafers were pre-deposited with Pt electrodes. The substrate temperature and the deposition pressure were varied from 300 to 600 ◦C and from 0.35 to 7 mbar, respectively. Bi(/\//)3 (triallyl bismuth) and Sr[Ta(OEt)5(OC2H4OMe)]2 (strontium bis[tantalum(pentaethoxy)(2-methoxyethoxide)] were used as a Bi precursor and as a Sr–Ta precursor, respectively. A liquid delivery system was used to supply and to evaporate the precursor into the reactor. X-ray photoelectron spectroscopy (XPS) and ellipsometry were carried out to characterize the film properties. The growth rate of the MOCVD of BiOx and SrxTayOz was compared to the growth rate of SBT to obtain information about mutual interaction between precursors. The deposition rate of bismuth oxide thin films was low (∼10 nm/h at 0.35 mbar) and did virtually not depend on the temperature. On the contrary, the growth rate of strontium tantalate films depended strongly on the temperature. The deposition rate of the SBT films was similar to the bismuth oxide film deposition, which slightly increased with increasing substrate temperature. However, the deposition rate of SBT was always lower than the deposition rate of the single precursors. The growth rate significantly depends on pressure. The decrease of the deposition pressure in the reactor chamber reduces the deposition rate of BiOx, SrxTayOz, and SBT, but on the other hand, it improves the uniformity of the film thickness. The XPS measurements showed a deficit of bismuth in the SBT films even though the concentration of the Bi precursor was several times higher. The XPS depth-profiling by Ar ion sputtering indicated different bond characteristics of Ti, Sr, and Bi before and after ion beam bombardment.