Search

We have studied the influence of the dilution of silane and disilane in nitrogen during the laser photodissociation at 193 nm, in a sealed reaction chamber. The experimental results prove the existence of two phenomena: the presence of thermalization reactions and the influence of the total pressure on the mean free path of the radical. At high pressure, these two phenomena are compensated and the deposition yield remains constant with total pressure.

The crystallization of amorphous silicon films with an Ar-F excimer laser pulse (λ = 193 nm, τ = 20 ns) was studied by grazing X-ray diffraction and optical reflectivity measurements performed with a Beckman spectrophotometer. The influence of the Si deposition technique on the crystallization process has been investigated: the initial amorphous Si films were deposited by sputtering or by chemical vapour deposition on amorphous substrates. The laser energy threshold Etfor the crystallization is deduced from these experiments. For the films deposited by CVD, the found value of 85 mJ/cm2is in good agreement with the calculated threshold energy for melting of amorphous silicon. Additional information was deduced from X-ray diffraction: a preferential 〈111〉 growth direction of the grains in the crystallized layer and differences between the dynamics of crystallization in relation with the deposition process were noted.

This paper presents some aspects of the crystallization by ArF excimer laser pulses (λ = 193 nm, τ = 20 ns) of various energy densities (in the range 90–400 mJ cm-2) of a-Si: H films deposited by chemical vapour deposition on amorphous SiO2substrates. The classical division of the crystallized material into a large grain layer and a fine grain layer is found with these experimental conditions but also we show that a layer with bubbles appears between the two crystallized zones. A comparison with the calculation of temperature leads us to think that crystallization cannot occur if the temperature reached at a given depth is below a temperature Tmin. This temperature may be related to the nucleation rate in a-Si.

The redistribution of arsenic into molten silicon after multiple ArF excimer laser irradiation, which is much deeper than expected from the thermal simulations, results mainly from the strong reduction, at 193 nm, both of the solid and liquid reflectivity of heavily doped crystalline Si against virgin Si (up to 40% reduction for an As concentration of ≈ 2 × 1021cm-3). The decrease of the melting temperature of highly doped Si (up to 150 K) has also to be included in th e thermal melting calculations in order to properly simulate the final dopant redistribution profiles which control the junction depth.

Formation of epitaxial Si1−yCyalloy 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.