Giovanni Mannino

Depth profiles of vacancy- and interstitial-type defects in MeV implanted Si

We demonstrate that the depth distribution of defects in MeV implanted n-type and p-type crystalline Si is severely affected by the impurity content of the material. Silicon samples with different concentrations of dopants (P or B) and intrinsic contaminants (i.e., C and O) were implanted with 1 or 2 MeV He ions to fluences in the range 2.5×108–1×1013/cm2. Using deep-level transient spectroscopy and spreading resistance measurements, we have identified the defects and determined their concentration and depth distribution. It is found that less than 4% of the defects generated by the beam escape recombination and are stored in electrically active, room temperature stable defect clusters, such as divacancies and carbon–oxygen pairs. When the concentration of these defects is much smaller than the doping level, their profile mirrors the initial defect distribution, as calculated by transport of ions in matter (TRIM), a Monte Carlo code. In particular, the profile presents a maximum at the same depth predicte...

Ultra-shallow junction formation by excimer laser annealing and low energy (<1 keV) B implantation: A two-dimensional analysis

Formation of shallow junctions has been investigated by using excimer laser annealing in combination with two implantation schemes: BF2-ions at 20 keV and B-ions at low energies (<1 keV). The latter approach was shown to produce best results, with ultra-shallow profiles extending to a depth as low as 35 nm. The lateral distribution of the implanted B following laser annealing has been studied with two-dimensional measurements using selective etching and cross-section transmission electron microscopy (TEM) on samples where the implanted dopant was confined within an oxide mask. The results show that there is substantial lateral diffusion of B under the oxide mask when melting occurs in this region while, if melting under the oxide mask is prevented, the implanted B close to the oxide mask edge was not activated by laser annealing. The results have been explained by numerical heat-flow calculations and it is concluded that the melting of the Si under the masked region and, therefore, the lateral diffusion, can be controlled by the oxide mask thickness.

Similar Structural Dynamics for the Degradation of CH3 NH3 PbI3 in Air and in Vacuum.

We investigate the degradation path of MAPbI3 (MA=methylammonium) films over flat TiO2 substrates at room temperature by means of X-ray diffraction, spectroscopic ellipsometry, X-ray photoelectron spectroscopy, and high-resolution transmission electron microscopy. The degradation dynamics is found to be similar in air and under vacuum conditions, which leads to the conclusion that the occurrence of intrinsic thermodynamic mechanisms is not necessarily linked to humidity. The process has an early stage, which drives the starting tetragonal lattice in the direction of a cubic atomic arrangement. This early stage is followed by a phase change towards PbI2 . We describe how this degradation product is structurally coupled with the original MAPbI3 lattice through the orientation of its constituent PbI6 octahedra. Our results suggest a slight octahedral rearrangement after volatilization of HI+CH3 NH2 or MAI, with a relatively low energy cost. Our experiments also clarify why reducing the interfaces and internal defects in the perovskite lattice enhances the stability of the material.

ROOM-TEMPERATURE MIGRATION AND INTERACTION OF ION BEAM GENERATED DEFECTS IN CRYSTALLINE SILICON

We have investigated the room‐temperature migration properties of ion generated defects in crystalline Si. The defects were injected into the bulk of a pure epitaxial Si layer by a low energy (40 keV) Si implant and monitored using a preexisting defect distribution, produced by a high energy He implant, as a marker. The depth of this defective marker layer was changed by varying the He implant energy in the range 1–3 MeV. Spreading resistance measurements show that the injected defects produce a partial annihilation of the pre‐existing damage. The magnitude of the annihilation process is strongly dependent on the depth of the defective marker, being very large when this marker is confined within 5 μm from the surface and negligible when it lies beyond a depth of ∼10 μm. From these results, detailed information on the nature of ion‐generated defects which are injected and on their migration properties is obtained. It is found that the observed phenomena are due to the annihilation of divacancies and phosphorus‐vacancy defect complexes, generated by the He implant, by Si self‐interstitials injected by the shallow Si implant.

Atomic transport properties and electrical activation of ultra-low energy implanted boron in crystalline silicon

Abstract The growing importance of ultra-low energy implantation in Si processing imposes extensive characterization and understanding of such a novel energy regime. In this paper we investigate the evolution of ultra-low energy B implants (0.25–1 keV) after post-implantation annealing, both in terms of atomic diffusion and electrical activation of the doping atoms. Transient enhanced diffusion (TED) of boron after annealing at 900°C is observed even for boron implanted at 250 eV, and also when the implant dose is below the amorphization threshold. At higher temperatures for long anneal times, the TED is overwhelmed by the equilibrium diffusion and it is not visible. However, provided the correct combination of temperatures and times is chosen, the TED can always be observed in samples implanted with a dose at least of 1×10 14 cm 2 . We suggest a possible microscopic mechanism to justify the dependence of the enhanced diffusion of ultra-low energy implanted boron on the implant dose, energy and annealing temperature. An excess of interstitials occurs giving rise to the formation of interstitials-like complexes containing B, probably due to enhanced annihilation of vacancies at the surface. Such an excess of interstitials is able to promote enhanced diffusion of implanted boron, provided the implant dose is high enough to generate a significant total number of point defects. The electrical activation of the ultra-low energy implanted B is shown to be strictly connected to its diffusion. With increasing the dose, the motion of B is supported by the increased amount of ion beam generated interstitials. We have also observed, at the same time, that the electrical activation is favored. The electrical activation, which can be achieved by the ultra-low energy implants we have investigated, is between 10 and 40% after annealing at 1100°C, depending on the implanted dose. For the highest dose we have studied, i.e. 1×10 15 cm 2 , the sheet resistance measured after annealing at 1100°C in a range between 250 eV and 1 keV, is below 1000 Ω. Ultra-low energy implantation is therefore extremely appealing for the future generations of semiconductor devices.

Depth distribution of B implanted in Si after excimer laser irradiation

Liquid phase epitaxial regrowth following laser melting significantly modifies the concentration of point defects in Si, such that peculiar depth distribution of subsequently implanted B arises. At room temperature, a large fraction of B atoms, ∼15%, implanted in laser preirradiated Si, migrate up to the original melt depth. During high temperature annealing, the nonequilibrium diffusion of B is reduced to ∼25% of that measured in unirradiated Si. Both these phenomena are conclusively attributed to an excess of vacancies, induced in the lattice during solidification and to their interaction with impurities and dopant.

Pseudoepitaxial transrotational structures in 14 nm-thick NiSi layers on (001) silicon

In a system consisting of two different lattices, structural stability is ensured when an epitaxial relationship occurs between them and allows the system to retain the stress whilst avoiding the formation of a polycrystalline film. The phenomenon occurs if the film thickness does not exceed a critical value. Here we show that in spite of its orthorhombic structure, a 14 nm-thick NiSi layer can three-dimensionally adapt to the cubic Si lattice by forming transrotational domains. Each domain arises by the continuous bending of the NiSi lattice, maintaining a close relationship with the substrate structure. The presence of transrotational domains does not cause a roughening of the layer, but instead it improves the structural and electrical stability of the silicide in comparison with a 24 nm-thick layer formed using the same annealing process. These results have relevant implications for the thickness scaling of NiSi layers which are currently used as metallizations of electronic devices.

An investigation on the modeling of transient enhanced diffusion of ultralow energy implanted boron in silicon

We have investigated and modeled the B diffusion in Si following ultralow energy implantation. Secondary ion mass spectrometry measurements revealed that B diffusion is transient enhanced. For the simulation we have used a kick-out model which requires only two uncorrelated parameters able to describe the microscopical processes involved. By optimizing the parameters, an excellent agreement between the simulated and the experimental profile broadening is achieved. Moreover, an extension of the previous model that accounts for interstitial cluster formation and dissolution was implemented in order to achieve a better description of B diffusion. The extracted parameters are discussed and compared with published values.

Diffusion and electrical activation of indium in silicon

In this work we investigate the diffusion and the electrical activation of In atoms implanted into silicon with energies ranging from 40 to 360 keV and doses of 5×1012 and 5×1013 In/cm2 during rapid thermal processing. Our investigation shows a clear dependence of In outdiffusion and electrical activation on the implant depth. For a fixed dose, the electrical activation was found to increase with the implant energy. We propose that the data can be explained by considering the balance between the local In concentration and the C background. The occurrence of coupling between the C present in the substrate and the implanted In, depending on the C/In ratio, may in fact give rise to significant formation of C–In complexes. Such complexes play a role in the enhanced electrical activation due to the shallower level they introduce into the Si band gap (Ev+0.111 eV), with respect to the rather deep level (Ev +0.156 eV) of In alone [R. Baron et al., Appl. Phys. Lett. 30, 594 (1977); R. Baron et al., ibid. 34, 257 ...

Effects of boron-interstitial silicon clusters on interstitial supersaturation during postimplantation annealing

Boron marker-layer structures have been used to investigate the effects of B doping on the evolution of the implantation damage and of the associated transient enhanced diffusion. The samples were damaged by Si implants at different doses in the range 2×1013–1×1014 cm−2 and annealed at 740 °C for times between 2 s and 4 h. The values of interstitial supersaturation, from the beginning of the annealing up to the complete damage recovery, have been determined for the different Si doses for a given B doping level. Damage removal has been followed by double crystal x-ray diffraction. Our results confirm that the formation of boron-interstitial silicon clusters traps a relevant fraction of the interstitials produced by the implantation. This trapping action gives rise to a strong reduction of the interstitial supersaturation, prevents the interstitial clusters from being transformed in {113} defects and modifies the time evolution of the transient enhanced diffusion. X-ray analyses indicate also that the size ...