Solid-phase Epitaxy Of Silicon Research Articles

Molecular-dynamics simulations of solid phase epitaxy in silicon: Effects of system size, simulation time, and ensemble

Solid phase epitaxial (SPE) recrystallization of amorphous Si on a Si(001) substrate was examined by large-scale (6144–129024 Si atoms), long-time (up to 2000 ns) molecular-dynamics (MD) simulations using the empirical Tersoff interatomic potential. We particularly focused on the effects of the MD cell size, simulation time, and ensemble on the SPE growth rate. We found that the simulations under the isothermal–isochoric conditions (NVT ensemble) show a higher crystallization rate than those under the isothermal–isobaric conditions (NPT ensemble). The system size dealt with in the present MD simulation, i.e., >6144 Si atoms, was enough to estimate the SPE growth rate. The Arrhenius plot of the growth rate between 1300 and 1600 K exhibited a single activation energy, ∼2.4 eV, which is in agreement with the experimental value (∼2.7 eV). However, the growth rate at temperatures below 1300 K deviated from the extrapolated ones from 1300 to 1600 K, which is because recrystallization does not reach a steady state: long-time MD simulations are required to estimate the growth rate at low temperature. The structure analysis of amorphous/crystalline interfaces suggested that the braking of atomic bonds parallel to the interface becomes a rate-limiting step of the SPE growth.

Dopant effects on solid phase epitaxy in silicon and germanium

The kinetics of dopant-enhanced solid phase epitaxy (SPE) are studied in amorphous silicon (a-Si) and germanium (a-Ge) layers formed by ion implantation. Implanted Sb dopants into a-Ge up to a concentration of 1 × 1020 cm−3 are considered and compared to As implanted layers at similar concentrations. Although an active Sb concentration above the solubility limit is achieved, a significant portion of the implanted atoms are not. P, As, and B enhanced SPE rates in Si from the literature are also considered. The relative velocities of P and As in Si is similar to that of As and Sb in Ge. Theoretical predictions using a simple form of the generalized Fermi level shifting model, which incorporates both dopant and dopant-induced stress effects, is shown to agree well with the data. A single set of two parameters are determined, which describe the dopant enhanced SPE data well independent of dopant species and concentration.

Recent Insights In Solid Phase Epitaxy of Silicon and Germanium

The crystallization of amorphous layers via solid phase epitaxy (SPE) is commonly used in semiconductor device fabrication to activate dopants. The kinetics of SPE depend on temperature, dopant and impurity concentration, hydrostatic pressure and crystallographic orientation. The effect of H on SPE in both Si and Ge is discussed. Numerical simulations are performed to model the H diffusion, the moving amorphous/crystalline interfaces and the refinement of the H profile at these interfaces. Despite the high H concentration involved, a simple Fickian diffusion model results in good agreement with the SIMS data. A significant fraction of the H escapes from the a-Si layer during SPE and becomes trapped at end of range defects. The light-emitting properties of these defects are investigated. Finally, the formation of germanides via SPE is discussed.

Recent Insights into Solid Phase Epitaxy of Silicon and Germanium

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Fabrication of single-crystalline insulator∕Si∕insulator nanostructures

We study the growth of double-barrier insulator∕Si∕insulator nanostructures on Si(111) using molecular beam epitaxy. Based on different investigations, we develop an approach for the fabrication of nanostructures with continuous ultrathin single-crystalline silicon buried in a single-crystalline insulator matrix with sharp interfaces. The approach is based on an epitaxial encapsulated solid-phase epitaxy, in which the solid-phase epitaxy of silicon is accompanied by a vapor-phase epitaxy of the second insulator layer. As an example, we demonstrate the growth of epitaxial silicon buried in epitaxial Gd2O3. The incorporation of epitaxial Si islands into single-crystalline Gd2O3 is also demonstrated.

Cooperative solid-vapor-phase epitaxy: An approach for fabrication of single-crystalline insulator/Si/insulator nanostructures

We study the growth of insulator/Si/insulator nanostructures on Si(111) using molecular beam epitaxy. Based on different investigations, we develop an approach for the fabrication of a nanostructure with a continuous ultrathin single-crystalline silicon buried in a single-crystalline insulator matrix with sharp interfaces. This approach is based on an epitaxial encapsulated solid-phase epitaxy, in which the solid-phase epitaxy of silicon is accompanied by a vapor-phase epitaxy of the second insulator layer. We call this approach as cooperative solid-vapor-phase epitaxy. As an example we demonstrate the growth of buried epitaxial silicon in epitaxial Gd2O3.

Modeling the effect of hydrogen infiltration on the asymmetry in arsenic-enhanced solid phase epitaxy in silicon

The kinetics of solid phase epitaxy (SPE) in surface amorphous silicon layers doped with a single arsenic profile have been examined in relation to the generalized Fermi level shifting model of the SPE growth process. The model has been extended to include passivation by hydrogen of the defects responsible for SPE and∕or passivation of dopant atoms. A previous study has suggested that the asymmetry between the dopant-enhanced SPE rate and the arsenic concentration profile is due to the infiltration of hydrogen from the surface oxide. Theoretical calculations of the dopant-enhanced SPE rate compare well with experiment if it is assumed that the indiffusing hydrogen passivates some of the SPE defects and∕or some of the dopant atoms.

Kinetics of arsenic-enhanced solid phase epitaxy in silicon

The kinetics of intrinsic and arsenic-enhanced solid phase epitaxy (SPE) have been measured in buried amorphous Si (a-Si) layers in which crystallization occurs free from the rate retarding effects of hydrogen. Surface a-Si layers, where H infiltration can occur during crystallization, have also been studied. A single 1.45×1016 As/cm2 implant at 1200 keV was used to form an As concentration profile with a peak concentration of 3×1020 As/cm3 centered at 8000 Å beneath the crystal surface, allowing many different enhanced SPE rates to be examined simultaneously. The SPE rate through this profile and its intrinsic counterpart were measured using time-resolved reflectivity. The effects of hydrogen on the SPE rate can be determined by a comparison between the buried and surface a-Si layers. For the surface a-Si layers, it was found that the As-enhanced SPE rate versus depth curve is offset with respect to the concentration profile. We attribute this offset to the H infiltration in the case of the surface a-Si layer.

The effect of potassium on the rate of solid phase epitaxy in silicon

Rutherford backscattering spectroscopy and ion channeling and secondary ion mass spectroscopy have been used to study the evolution of a potassium profile in amorphous silicon during solid phase epitaxial crystallisation. The potassium profile exhibits some propensity for refinement in front of the crystallising interface for the concentrations used in this experiment. Also, the potassium is partially substitutional in the crystallised layer. Preliminary studies on the influence of potassium on the rate of solid phase epitaxy (SPE) in silicon are presented. Surface amorphous films doped with potassium were crystallised and the rate of epitaxy was monitored using time resolved reflectivity. The inclusion of potassium was found to retard the rate of SPE. These results indicate that potassium doped amorphous films may be helpful in efforts to further refine present models of SPE in silicon.

Impurity and concentration dependence of growth rate during solid epitaxy of implanted Si

The increase of the growth rate during solid-phase epitaxy in silicon implanted with B, P, As, and Sb is explained in terms of strain in the host lattice due to the addition of the dopant. The growth rate increases proportionally to the strain thus taking into account both species and concentration dependence below the solid solubility limit. The strain itself is in a simple way related to the difference between the tetrahedral covalent radii of Si and of the dopant.

Laser-Induced Solid Phase Epitaxy of Silicon Deposited Films

ABSTRACTA comparative study of solid phase epitaxy (SPE) of deposited and ion-implanted amorphous Si films was conducted with the use of a newly developed laser technique. The effects of interface contaminants and contaminants distributed within a deposited film on the rate of SPE and final crystal quality are reported. In the absence of impurities, deposited Si films crystallize at the same rate as ion-implanted layers and yield epitaxial films with comparable crystal quality. The presence of impurities in deposited films at the interface or distributed within the film can severely retard the SPE growth, causing several deleterious effects which ultimately degrade the film quality. These effects are more severe at high temperatures.

Effects of temperature on the solid phase epitaxy of silicon

We studied the thin film system consisting of a palladium silicide layer on a 〈100〉Si single-crystal substrate covered by an overlying film of amorphous Si. After annealing at temperatures between 440 and 520°C, we observed the nucleation of Si islands on the 〈100〉Si surface, with a corresponding erosion of the amorphous Si film. At constant temperature the islands grow in size but not in number. For various temperatures the observed density of islands varies as a thermally activated quantity with an activation energy of 1.8 eV. The islands finally develop into a uniform layer of epitaxial Si. Some residual palladium silicide in the grown Si layers was detected by Rutherford backscattering. The temperature dependence of the amount of residual palladium silicide also has an activation energy of 1.8 eV. We propose a simple model in which the residual palladium silicide is a consequence of the island growth.

Repetitive growth stages in the solid phase epitaxy of silicon

We have studied the solid phase epitaxial growth of Si in the thin film system with a layer structure of Si(〈100〉 substrate)/Pd silicide/Si(amorphous). At approximately 500°C the 〈100〉Si single-crystal substrate grows with a corresponding consumption of the Si(amorphous) layer. Growth starts with nucleation of islands on the substrate. These islands then grow laterally to form a uniform layer. A second stage of island growth then develops and the process goes on repetitively. However, differences between the first and subsequent stages are observed.