Many attempts have been made to apply ferroelectric thin films to a variety of devices as dielectric thin films for DRAMs, ferroelectric RAMs, infrared sensors and optical waveguides. Dielectric thin films with low leakage current and high dielectric permitivity are necessary for capacitors in ULSI DRAMs.
In this study, Electron cyclotron resonance plasma enhanced chemical vapor deposition (ECR PECVD) method is used to prepare ferroelectric $PbTiO_3$ and $(Pb,La)TiO_3$ films. Single-phase perovskite $PbTiO_3$ and PLT films with smooth surface were successfully fabricated on $Pt/Ti/SiO_2/Si$ substrates at low temperatures of 400~500℃ using metal-organic(MO) sources. Used MO sources are $Pb(DPM)_2$, Ti-iso-propoxide and $La(DPM)_3$. The effects of the deposition parameters, such as deposition temperature, $O_2$ flow rate, microwave power and MO source flow rates, on the crystalline structure, composition, surface morphology and electrical properties, like polarization-electric field (P-E), capacitance-voltage (C-V), capacitance-frequency (C-f), leakage current-voltage (I-V) and current-time (I-t), were investigated. The films had the composition and structure of the stoichiometric perovskite $PbTiO_3$ and PLT even if the MO source input ratios were not perfectly controlled at the process temperature above 450℃ if the oxygen supply is sufficient. When $Pb(DPM)_2$ was introduced into the ($Ar+O_2$) plasma prior to the PLT deposition, the crystallinity and the composition uniformity of the films were improved. La content in the PLT films could be easily controlled by varying the $La(DPM)_3$ and TiIP flow rates at a fixed temperature. Excellent electrical properties were obtained from the as-deposited PLT films containing of La. The $SiO_2$ equivalent thickness of the 1250Å thick PLT (La11%) film decreased from 7.8Å to 6.9Å after the post RTA process at 700℃ for 1 min. The leakage current density of PLT(La11%) film was less than $10^{-7}A/㎠ at 3V. The leakage current mechanism in high voltage region was proved to be Schottky conduction and the zero-bias barrier height of PLT(La11%) film was 0.76eV. The Shottky barrier height can be lowered by the positive charges at the interface between the films and the electrodes. C-V measurement of the films showed that the positive fixed charges and/or the surface state density was higher at the upper electrode. Consequently, the films were more leaky with negatiely biased upper electrode. The distribution of the fixed charges became more symmetric after RTA treatment and higher dielectric constant was obtained.
From the above results, I would conclude that the PLT film is one of the very attractive dielectric thin films for ULSI DRAM capacitors.
