G. Fisicaro

N-type doping of Ge by As implantation and excimer laser annealing

The diffusion and activation of arsenic implanted into germanium at 40 keV with maximum concentrations below and above the solid solubility (8 × 1019 cm−3) have been studied, both experimentally and theoretically, after excimer laser annealing (λ = 308 nm) in the melting regime with different laser energy densities and single or multiple pulses. Arsenic is observed to diffuse similarly for different fluences with no out-diffusion and no formation of pile-up at the maximum melt depth. The diffusion profiles have been satisfactorily simulated by assuming two diffusivity states of As in the molten Ge and a non-equilibrium segregation at the maximum melt depth. The electrical activation is partial and decreases with increasing the chemical concentration with a saturation of the active concentration at 1 × 1020 cm−3, which represents a new record for the As-doped Ge system.

B-doping in Ge by excimer laser annealing

An experimental and theoretical study of the effect of excimer laser annealing (ELA) on B redistribution and electrical activation in Ge is reported. We performed detailed structural, chemical, and electrical characterizations of Ge samples implanted with B (20 keV, 1 × 1015, or 1 × 1016 B/cm2) and processed by ELA (λ = 308 nm) with multiple pulses (1, 3, or 10). We also developed a diffusion model, in order to simulate the B redistribution induced by the ELA process. We found an anomalous impurity redistribution in the molten phase, which causes a dopant incorporation during the melt-growth at the maximum melt depth. The investigated samples showed a partial electrical activation of the B dopant. The inactivation of B in the samples implanted with 1 × 1015 B/cm2 was correlated to an oxygen contamination, while the poor electrical activation of B in the samples implanted with 1 × 1016 B/cm2 was related to the precipitation of the dopant, in good agreement with the experimental and theoretical results.

Defect kinetics and dopant activation in submicrosecond laser thermal processes

Defect evolution in ion implanted c-Si at the submicrosecond time scales during a laser thermal annealing process is investigated by means of kinetic simulations. Nonmelting, melting, and partial melting regimes are simulated. Our modeling considers irradiation, heat diffusion, and phase transition together with defect diffusion, annihilation, and clustering. The reduction in the implantation damage and its reorganization in defect aggregates are studied as a function of the process conditions. The approach is applied to double implanted Si and compared to experimental data, indicating a relationship between damage reduction and dopant activation.

Coupled Monte Carlo-Poisson method for the simulation of particle-particle effects in dielectrophoretic devices

Simulations can aid to bridge the gap between the proof-of-concept stage and the engineering of dielectrophoretic devices. We present a simulation method overcoming the limits of fluid-flow based approaches. In our Monte-Carlo-Poisson simulator, the colloidal system is described at the particle resolution. This characteristic allows for taking into account volume forces and particle-particle interactions usually neglected in the continuum approximation. In turn, large number of particles and large systems can be simulated to meet the device design needs. In an experimentally verifiable case study, we discuss the role of the multi-particle interaction in high and moderate density regimes.

Crystallization of implanted amorphous silicon during millisecond annealing by infrared laser irradiation

We investigated the homogenous nucleation of crystalline grains in amorphous Si during transient temperature pulse of few milliseconds IR laser irradiation. The crystallized volume fraction is ∼80%. Significant crystallization occurs in nonsteady regime because of the rapid temperature variation (106 °C/s). Our model combines the time evolution of the crystal grain population with the consumption of the amorphous volume due to the growth of grains. Thanks to the experimental approach based on a laser source to heat α-Si and the theoretical model we extended the description of the spontaneous crystallization up to 1323 K or 250 K above the temperature investigated by conventional annealing.

Extended Defects Formation in Nanosecond Laser-Annealed Ion Implanted Silicon

Damage evolution and dopant distribution during nanosecond laser thermal annealing of ion implanted silicon have been investigated by means of transmission electron microscopy, secondary ion mass spectrometry, and atom probe tomography. Different melting front positions were realized and studied: nonmelt, partial melt, and full melt with respect to the as-implanted dopant profile. In both boron and silicon implanted silicon samples, the most stable form among the observed defects is that of dislocation loops lying close to (001) and with Burgers vector parallel to the [001] direction, instead of conventional {111} dislocation loops or {311} rod-like defects, which are known to be more energetically favorable and are typically observed in ion implanted silicon. The observed results are explained in terms of a possible modification of the defect formation energy induced by the compressive stress developed in the nonmelted regions during laser annealing.

Theoretical and experimental study of the role of cell-cell dipole interaction in dielectrophoretic devices: application to polynomial electrodes.

BackgroundWe aimed to investigate the effect of cell-cell dipole interactions in the equilibrium distributions in dielectrophoretic devices.MethodsWe used a three dimensional coupled Monte Carlo-Poisson method to theoretically study the final distribution of a system of uncharged polarizable particles suspended in a static liquid medium under the action of an oscillating non-uniform electric field generated by polynomial electrodes. The simulated distributions have been compared with experimental ones observed in the case of MDA-MB-231 cells in the same operating conditions.ResultsThe real and simulated distributions are consistent. In both cases the cells distribution near the electrodes is dominated by cell-cell dipole interactions which generate long chains.ConclusionsThe agreement between real and simulated cells’ distributions demonstrate the method’s reliability. The distribution are dominated by cell-cell dipole interactions even at low density regimes (105 cell/ml). An improved estimate for the density threshold governing the interaction free regime is suggested.

Kinetic Monte Carlo simulations of boron activation in implanted Si under laser thermal annealing

We investigate the correlation between dopant activation and damage evolution in boron-implanted silicon under excimer laser irradiation. The dopant activation efficiency in the solid phase was measured under a wide range of irradiation conditions and simulated using coupled phase-field and kinetic Monte Carlo models. With the inclusion of dopant atoms, the presented code extends the capabilities of a previous version, allowing its definitive validation by means of detailed comparisons with experimental data. The stochastic method predicts the post-implant kinetics of the defect-dopant system in the far-from-equilibrium conditions caused by laser irradiation. The simulations explain the dopant activation dynamics and demonstrate that the competitive dopant-defect kinetics during the first laser annealing treatment dominates the activation phenomenon, stabilizing the system against additional laser irradiation steps.

Solid phase phosphorous activation in implanted silicon by excimer laser irradiation

The activation mechanism in phosphorous implanted silicon under excimer laser irradiation is investigated. The activation efficiency in the solid phase has been measured in a wide range of irradiation conditions, tuning the laser fluence in the sub-, partial, and total melting regime. Moreover, fixing the fluence, the activation as a function of the shot number has been analyzed. The total active fraction varies by several orders of magnitude and shows a complex trend depending on the process conditions. Our model, based on the interaction between defects and the active/inactive impurities, explains this scenario. In particular, it predicts experimental P active profiles, thus demonstrating that the status of the defect system rules the activation phenomenon, where the coupling between dopant and defect clusters at the early irradiation stage plays a crucial role.

Modeling boron profiles in silicon after pulsed excimer laser annealing

In this work, we investigated four possible mechanisms which were candidates to explain the shape of boron profiles after ion implantation and melting excimer laser annealing in silicon. A laser with a wavelength of 308 nm and a pulse duration of ∼180 ns was used. To simulate this process, an existing model for the temperature and phase evolution was complemented with equations for the migration of dopants. Outdiffusion, thermodiffusion, segregation, and adsorption were investigated as possible mechanisms. As a result, we found that outdiffusion and segregation can be excluded as major mechanisms. Thermodiffusion as well as adsorption could both reproduce the build-up at low melt depths, but only adsorption the one at deeper melt depths. In both cases, ion beam mixing during SIMS measurement had to be taken into account to reproduce the measured profiles.