Optimization of excimer laser modification of silicon-nanoparticle layers using one-dimensional temperature simulations

Computational fluid dynamics simulations of silicon μ-structure formation during excimer laser modification of silicon-nanoparticle layers

“…Time-dependent wetting of molten Si on sintered silicon nitride (SiN) was evaluated experimentally by Drevet et al [29]. They determined an initial contact angle of Θ 0 = 82 ± 3°, which decreases to its equilibrium value of Θ F = 49 ± 3°in about 150 s. For our case, dealing with ns-laser annealing of Si, the silicon is liquid for less than 130 ns after each laser pulse [8]. Hence, it can be assumed that the silicon solidifies with a non-equilibrium contact angle, independent of the substrate.…”

“…Within the software environment, it is easy to transfer simulation results to other simulations. In our case, we used the simulation results of a 1D temperature simulation of the same laser process, as described in a previous publication [8], as input to the CFD simulation. Furthermore, the contribution at hand is an extension of a model recently developed by us in COMSOL [2], which solves the Navier-Stokes equation for incompressible fluids (equations ( 1) and (2)), in order to simulate the flow of molten silicon in a nitrogen gas (N 2 ) environment.…”

“…For the present CFD model, the sequential melting of the Si-NP layer during pulsed laser modification is considered by implementing the time-dependent melting depth for each laser pulse. This melting characteristic is extracted from a corresponding temperature simulation of the same pulsed laser modification, which solves the heat diffusion equation in a 1D model, as recently described [8]. The temperature simulation considers multiple consecutive laser pulses at a specific substrate location with different intensities, which will result from a scanned Gaussian laser pulse profile.…”

“…The synthesis of the used Si-NPs, their dispersion in organic solvents, and the related sample preparation are described elsewhere [8,[25][26][27]. A pulsed KrF excimer laser (ATLEX-300SI, ATL Lasertechnik GmbH) emitting at a wavelength of 248 nm was used to laser modify the Si-NP layers.…”

“…As the duty cycle between two laser pulses (20 ms) is several orders of magnitude larger than the Si melting time (< 130 ns), the sample returns to thermodynamic equilibrium between the pulses. In consequence, there is no continuous sample heating and resolidified Si can be assumed between the pulses [8,33]. Therefore, to reduce the computational time, the time between melting intervals was Comparison of contact angles Θ of Si μ-cones on different substrates and corresponding literature surface energy values for the used substrates (silicon nitride (SiN), [36] glass, [37] aluminum (Al) [38] and tungsten (W) [39]).…”