Experimental and numerical investigations of heat transport and crystallization kinetics in laser-induced modification of barium strontium titanate thin films

Barium strontium titanate (BST) has a large application potential in microelectronics due to its implementation as a high-permittivity dielectric in thin-film capacitors. Technologies are therefore being investigated for the deposition of the ceramics as thin films onto semiconductor components. A two-step process will be presented in this paper: first, the deposition of an amorphous ceramic thin film on a platinum-coated silicon wafer and, secondly, the laser sintering of this film. A laser process with pulsed UV light of 248-nm and 193-nm wavelength and approximately 20-ns pulse length allows us to reduce the thermal load on the substrate during the sintering process by minimizing the interaction time between the heating source and the ceramic layer. The goal of this work is to investigate fundamental aspects of the solid-state physics and process technology during the laser sintering of amorphous, electroceramic thin films. Adjusting the film thicknesses prevents damage to the ceramic thin films by the laser treatment. Planar test structures are manufactured and characterized structurally and electrically. Characterization of the BST films reveals clearly improved dielectric properties in comparison to the amorphous films. The real part of the dielectric constant can be raised three- to fivefold at 10 kHz, while the imaginary part decreases by nearly an order of magnitude. Chemical analysis does not indicate any significant changes in the stoichiometry of the thin films due to the laser process. The laser-induced changes proceed similarly to the crystallization of the amorphous films in the furnace. Parallel to the experimental work, a numerical simulation model is developed, which, on the basis of thermal conduction, the Johnson-Mehl-Avrami crystallization kinetics, and thermoelasticity, models the temperature, crystallization, and mechanical load of the thin films. The simulation calculations are correlated with the results of the analysis of the laser-treated samples.