Laser annealing of BST thin films with reduced cracking at an elevated temperature

An excimer laser (KrF, 248 nm) was used to crystallize barium strontium titanate thin films of thickness 95 nm. Numerical simulation was first performed to get an idea about the laser energy suitable for crystallization. Amorphous films deposited by chemical solution deposition were irradiated at different energies with different frequencies (40–l50 Hz), laser fluences (100–150 mJ/cm2) and pulses (400–1000) while maintaining the substrate at 25 and 250 °C. Films were found to crystallize above 100 mJ/cm2 in both cases. Films crystallized with substrate temperatures of 250 °C were noticed to have less cracks. The microstructure of these films were analyzed with a scanning electron microscope. From the XPS analysis, it is inferred that the top few nanometers have a different structure compared to normal furnace annealed thin films. This top surface layer was found to be dependent on the laser energy used for crystallization. The dielectric constant was found to increase from 60 to 180 for the 95 nm thin films on increasing the laser fluence. Films crystallized with 120 mJ/cm2 while maintaining a substrate temperature of 250 °C have leakage current densities of 1 × 10 −7 A/cm2 at 1.5 V and a dielectric constant of 200.