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Laser crystallisation during pulsed laser deposition of barium titanate thin films at low temperatures

: Gottmann, J.; Vosseler, B.; Kreutz, E.W.


Applied surface science 197-198 (2002), S.831-838
ISSN: 0169-4332
Fraunhofer ILT ()
pulsed laser deposition; laser crystallisation; Barium titanate; in situ laser annealing

Using a high dielectric material as substitute for SiOxNy in dielectric film capacitors of dynamic memories (DRAM) allows a significantly higher integration density and a reduction of the die size, even with planar capacitors. BaTiO3 is such a material. A dielectric constant of Epsilon r > 1000 has been achieved in thin films, made by pulsed laser deposition (PLD). For applications in microelectronic memories it is necessary to produce crystalline, defect-free and oriented BaTiO3 thin films at substrate temperatures, TS < 450 deg C.
Sintered targets of BaTiO3 are ablated by KrF excimer laser radiation. The processing gas atmosphere consists of O2 at pressures of 0.1-50 Pa. The substrate is resitively heated to 360-440 deg C and annealed after or during PLD on Pt/Ti/Si multilayer substrates using KrF excimer laser radiation with fluences up to 120 mJ/cm2.
The temperature distribution in the BaTiO3/Pt/Ti/Si multilayers during laser annealing is dynamically modelled and related to the resulting crystal quality and the dielectric properties of the films. With PLD a minimum substrate temperature of 500 deg C is necessary to deposit crystalline BaTiO3 films. Using in situ laser crystallisation crystalline BaTiO3 films can be deposited at substrate temperatures of TS = 360-440 deg C showing a dielectric constant of up to Epsilon r = 1200.
The ferroelectric and dielectric properties of the films are determined by C-V and P-V impedance measurements and correlated to the chemical and structural properties, as determined by X-ray photoemission spectroscopy, X-ray diffraction, micro Raman spectroscopy and scanning electron microscopy.