Elke Fritsch

Ferroelectric strontium bismuth tantalate thin films deposited by metalorganic chemical vapour deposition (MOCVD)

Thin films of Sr 1-x Bi 2+x Ta 2 O 9 (SBT) have been deposited by metalorganic chemical vapor deposition (MOCVD) on 150 mm Si wafers with Pt/Ti electrodes. The choice of Bi precursor significantly affects the process; film homogeneity is significantly improved when using a β-diketonate Bi precursor in combination with compatible Sr and Ta precursors. A highly repeatable process has been developed, with good run-to-run composition and thickness control. Effects of Bi volatility have been investigated in annealing experiments that show the onset of Bi loss at ∼570°C at reduced pressure (1-10 Torr). Film properties relevant to integrated ferroelectric random access (Fe RAMS) memories have also been characterized. Remenant polarizations (2P r ) up to 24 μC cm -2 have been obtained at 5 V, with 90% saturation of 2P r at 1.5 V and a coercive voltage of 0.52 V for a 140 mn film. Electrical leakage current density values were < 2×10 -8 A cm -2 at 1.5 V. Fatigue endurance has been measured to 10 11 cycles with < 10% degradation in switched charge.

MOCVD of SrBi 2 Ta 2 O 9 for Integrated Ferroelectric Capacitors

SrBi 2 Ta 2 O 9 (SBT) is a promising material for ferroelectric random access memories (FERAMs) because it has high resistance to fatigue and imprint combined with low coercive field. Metalorganic chemical vapor deposition (MOCVD) offers the ability to produce high quality, conformai SBT films for both high and low density memory applications. An MOCVD process based on liquid delivery and flash vaporization has been developed which allows precise delivery of low vapor pressure precursors to the process. Precursor decomposition has been examined over a wide temperature range and the effects of process pressure have been examined. It is shown that Bi(thdb is superior to Bi(Ph) 3 as a source of Bi, offering a wide decomposition window with compatible Sr and Ta precursors so that a simple, well-controlled, and repeatable process is achieved at low temperatures. Films with 90% conformallity have been grown on 0.6 μm structures with a 1:1 aspect ratio. The MOCVD process yields the fluorite phase, which is transformed to the ferroelectric layered perovskite phase upon annealing in oxygen. Dielectric constants (e) of 200 and remanent polarization (2P r )up to 16 μC/cm 2 have been achieved on 150 mm wafers.

Properties of SrBi/sub 2/Ta/sub 2/O/sub 9/ thin films grown by MOCVD for high density FeRAM applications

Summary form only given. A new, low temperature SrBi/sub 2/Ta/sub 2/O/sub 9/ (SBT) MOCVD process exhibiting excellent run-to-run repeatability has been developed for high density FeRAM applications. 90% step coverage and good adhesion were achieved on feature sizes down to 0.5 /spl mu/m on both Pt or SiO/sub 2/ surfaces. Postanneal process optimization resulted in an increase of remanent polarization of about 30%. Electrical characterization showed dielectric constants (/spl epsiv/) of /spl ges/200 and remanent polarization values (2Pr) of up to 23 /spl mu/C/cm/sup 2/. Endurance has been demonstrated up to 10/sup 11/ cycles.