A. Grob

Damage created in silicon by BFn+ (1≤ n ≤ 3) and PFn+ (1⪯ n:≤ 5) implantations

The number of host atoms displaced in monocrystalline silicon at 77 K by molecular projectiles was measured using in situ backscattering channeling experiments. Boron and phosphorous fluorides were chosen not only for their interest in microelectronic technology but also for their composition of light atoms for which the cascade damage density is generally assumed to be too low to induce any spike effects. The results, compared to the simple addition of the amount of damage created by the corresponding atomic species are discussed in terms of cascade overlap probabilities. An excess damage for molecular ions which increases with the number of atoms in the molecule and with decreasing energy is demonstrated. This leads for example to an 80% increase in induced damage for PF5+ projectiles around 1 keV/amu and 30% for BF2+ at 0.7 keV/amu. This excess damage is explained by the overlap of two or three subcascades. The contribution of higher order effects is negligible.

Laser‐beam annealing of heavily damaged implanted layers on silicon

The behavior during annealing of heavily doped silicon layers obtained by a high‐current‐density ion implantation, realized by discharge in BF3 atmosphere, is investigated. The annealing is performed by a laser pulse and the surface layers are studied by Rutherford backscattering, SIMS, and conductivity measurements. Comparisons with thermal annealing show the advantage of using laser pulses to restore the original crystallinity.

Evolution of implanted carbon in silicon upon pulsed excimer laser annealing

Formation of epitaxial Si1−yCy substitutional alloy layers on monocrystalline silicon surfaces with y≊1 at. % is reported. The preparation method was carbon ion implantation, followed by KrF excimer laser annealing. Results of Rutherford backscattering (RBS), secondary ion mass spectrometry (SIMS) and infrared absorption analyses are compared. The authors concluded that, up to ∼1 at. % carbon content, the dominant process is nonequilibrium trapping of carbon in substitutional lattice sites upon fast resolidification. Above this concentration the complex carbon redistribution processes are influenced by silicon carbide precipitation in the melt and segregation effects in the near‐surface region.

Preparation of Si1−xGex thin crystalline films by pulsed excimer laser annealing of heavily Ge implanted Si

Abstract Thin crystalline Si 1−x Ge x layers were obtained by irradiating heavily Ge implanted (10 17 atoms cm −2 ) 〈100〉 oriented Si substrates with a pulsed excimer (ArF) laser. The respective influences of the implantation conditions, laser energy density or number of successive laser pulses were investigated using Rutherford backscattering channeling analysis and Raman spectroscopy. In particular, it is shown that layers of good crystalline quality can be readily obtained, the width almost constant Ge concentration being controlled by the irradiation conditions. Optimizing these conditions leads to 200 nm thick alloy layers with a constant Ge content x = 0.14. These results were interpreted using a computer simulation based on the melting-resolidification process which occur during the pulsed laser irradiations.

Transverse straggling of MeV oxygen ions implanted in silicon

Abstract The 16O(d, α)14 N nuclear reaction was used to evaluate the lateral dispersion of oxygen ions implanted in silicon with energy ranging from 0.6 to 2 MeV. The projected range and longitudinal straggling, also measured in this experiment, are in close agreement with computer programs like TRIM or PRAL. However, the lateral spread is significantly lower than predicted, saturating towards 0.3 μm for high energies.

A dechanneling investigation of MeV oxygen implanted silicon

Axial channeling of H+ and He+ particles was used to study the residual damage in silicon after MeV oxygen ion implantation, prior to annealing. The comparison between the energy dependence of dechanneling and direct backscattering at defects confirms the presence of a mixing of point defects and partial dislocations observed by electron microscopy. The absolute concentrations of point defects and Frank dipoles are followed as a function of beam power density.

A silicon-on-insulator structure formed by implantation of megaelectronvolt oxygen☆

Abstract 3 MeV backscattering-channelling analysis, the 16O(d, α)14N nuclear reaction and cross-sectional transmission electron microscopy were used to characterize silicon samples implanted with 2 MeV oxygen ions. The distribution parameters, projected range, longitudinal and transverse stragglings and skewness were determined experimentally for a dose of 1017 O+ cm−2. The lateral straggling was obtained by deconvolution of the oxygen concentration profiles corresponding to oblique incidence implantation. The subcritical dose of 1.5 × 10 18 cm −2 of 2 MeV O+ ions was implanted without external heating during oxygen implantation. It is shown that a temperature of about 200°C resulting from beam heating is sufficient to avoid amorphization. However, in the as-implanted state, the crystal is strongly damaged beyond 1 μm. The implanted samples were subsequently annealed at 1350°C for 4 h in an argon ambient. The annealing process results in the creation of a silicon surface layer 2 μm thick free of SiO2 precipitates. Furthermore, no dislocations were observed within the top silicon layer using cross-sectional transmission electron microscopy. The average residual dislocation density was estimated to be lower than 107 cm−2. Beneath the silicon overlay the implanted and annealed sample contains a discontinuous buried layer of large SiO2 precipitates.

Evolution of implanted carbon in silicon upon pulsed excimer laser annealing: epitaxial Si1−yCy alloy formation and SiC precipitation

Abstract Formation of epitaxial Si1−yCy alloy layers on monocrystalline silicon surfaces with y≈1 at% is reported. The preparation method was carbon ion implantation, followed by KrF excimer laser annealing in air. Results of Rutherford backscattering (RBS) measurements, secondary ion mass spectrometry (SIMS), Raman spectroscopy, infrared (IR) absorption analysis, and transmission electron microscopy (TEM) are compared. The evolution of the implanted carbon was affected by the implantation conditions, i.e., implantation energies, ion current, and implanted ion distribution (single-energy versus flat profile implantation), as well as by the laser annealing parameters. Up to approximately 1 at% carbon content, the dominant process was nonequilibrium trapping of carbon atoms in substitutional lattice sites upon fast resolidification, allowing perfect epitaxial recovery of the crystal lattice by laser annealing. Above this concentration, silicon carbide precipitates were formed, embedded into an otherwise well-ordered substitutional Si–C alloy matrix. Upon multipulse processing, the complex carbon redistribution processes were influenced by trapping of carbon in SiC precipitates, dissolution of SiC in the melt and segregation effects in the near-surface region.

Damage created in silicon by 1 MeV O+ ions as a function of beam power

Abstract Rutherford backscattering (RBS) and channeling of H+ and He+ particles were used to study the damage accumulation during 1 MeV O+ implantation in silicon. The beam current was varied between 0.2 and 3 μA, leading, in our experimental conditions, to a temperature rise up to about 400°C. The contributions of point and extended defects were separated using the energy dependence of the dechanneled fraction of particles passing through the disordered regions. Transmission electron microscopy observations have been performed in order to determine the dominant type of defect in a few cases. Mixing of points defects and partial dislocations was revealed for temperatures higher than 200°C. Their respective concentrations have been followed as a function of beam power and dose. Self-annealing and trapping are the dominant mechanisms pointed out. In the first microns, the residual amount of point defects per incident ion is shown to obey to an Arrhenius relation, with an activation energy of about 0.4 eV. Beam assisted regrowth of amorphous islands formed in the early stage of implantation is thought to occur. Unlike point defects, the formation of partials seems to be independent of temperature but only an effect of dose.

Activation and diffusion during rapid thermal annealing of arsenic and boron implanted silicon

The redistribution of arsenic and boron implanted respectively in single crystal and in preamorphized silicon wafers is investigated after rapid thermal annealing (RTA) at temperatures ranging from 1000 up to 1150°C. SIMS dopant profiles are compared to calculated distributions for which the diffusion equation is solved with a diffusivity depending on temperature, on impurity concentration and, eventually, on time. For both ions, an additional diffusion has to be considered. This excess diffusivity is shown to be dependent on RTA duration. Using channeling-backscattering measurements, this behaviour is clearly related to the coarsening or to the annealing of residual extended defects. Thus, the enhanced diffusion is explained by an excess point defects surviving SPE regrowth, which can be trapped or released on dislocation arrays. The electrical characteristics of junctions prepared by implantation and RTA are presented.