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

Abstract

Using a high dielectric material as substitute for SiO x N y 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. BaTiO 3 is such a material. A dielectric constant of ε 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 BaTiO 3 thin films at substrate temperatures, T S<450 °C. Sintered targets of BaTiO 3 are ablated by KrF excimer laser radiation. The processing gas atmosphere consists of O 2 at pressures of 0.1–50 Pa. The substrate is resitively heated to 360–440 °C and annealed after or during PLD on Pt/Ti/Si multilayer substrates using KrF excimer laser radiation with fluences up to 120 mJ/cm 2. The temperature distribution in the BaTiO 3/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 °C is necessary to deposit crystalline BaTiO 3 films. Using in situ laser crystallisation crystalline BaTiO 3 films can be deposited at substrate temperatures of T S=360–440 °C showing a dielectric constant of up to ε 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.