Optical properties of semi-insulating polycrystalline silicon (SIPOS) thin films containing 30 at. % oxygen atoms are investigated in the near ultraviolet, visible and infrared region to improve knowledge on the structure and chemical bonding of these mixtures. An effective medium approximation model is used for a microscopic investigation of the oxide species involved as a function of the annealing temperature (600–1200 °C). The results are compared with other optical spectroscopies (infrared and Raman) and with transmission electron microscopy to give a selected picture of the pure and oxide components.

We present new results on the ion-assisted amorphous to polycrystal transition in silicon. The grain growth velocity vg and the nucleation rate r exhibit quite different behaviours: i) ion irradiation enhances r by a factor which is several orders of magnitude larger than that observed for vg; ii) irradiation with lighter ions produces a decrease of vg and a strong increase of r; iii) the increase of dose rate produces a decrease of both vg and r, but is particulary severe for r. These results have been explained by assuming that ion irradiation produces three fundamental effects: i) generation of long living defects which increase the free energy of the amorphous phase to the value of the fully unrelaxed amorphous silicon, causing the decrease of the thermodynamic barrier to nucleation; ii) generation of defects promoting the transition kinetics at concentrations well above the thermal equilibrium value; iii) prompt amorphization of a small volume at the surface of each crystalline grain.

The layer-by-layer amorphization process is explored in a temperature range in which the kinetics of crystallization can be neglected. It has been found that the pure amorphization rate increases exponentially as the substrate temperature is decreased with an apparent activation energy of 0.48 eV. Moreover the rate increases with both the ion flux and the energy deposited into elastic collisions. A phenomenological model is proposed to explain the experimental results.

The damage produced by high current density ∿l0µA/cm2 implants of 120 keV P+ into <111> and <100> silicon wafers, 500 °m thick, has been investigated in the fluence range 1×l01 5/cm2-l×l016 /cm2 by ion channeling and by transmission electron microscopy. For both orientations the thickness of the damage layers increases with the fluence up to 2×1015 /cm2 and then decreases. The rate of regrowth is a factor two faster for the <100> with respect to the <111> oriented Si crystals. Similar ratios have been found in pre-amorphized samples and irradiated with Kr+ ions in the temperature range 350°C-430°C. The TEM analysis reveals the presence of hexagonal silicon and of twins in small amounts for both orientations. The beam induced epitaxial growth depends also on the species present in the amorphous layer. A comparison between self-annealing and beam annealing in Si <100> preamorphized with Ar+ or P+ shows a noticeable retardation of the growth rate in the presence of Ar+.

The kineticsof phase formation and growth in Au-Al and Cu-Al thin film bilayers under ion beam bombardment was investigated in detail for the dependence on the beam energy. The experimental data can be interpreted within the radiation enhanced diffusion description, taking into proper account the target configuration, the growth of a new phase and the deposited energy density distribution.

Impurity redistribution in Bi-implanted Si and in As-implanted Si has been investigated after irradiation with 25 ps Nd(λ=l.06 μm) laser pulse in the energy range 0.1–1.5 J/cm2 . Channeling effect in combination with 2.0 MeV He+ backscattering in glancing detection has been used to characterize the epitaxial crystallization, the impurity location and its depth distribution. The amorphous to single crystal transition occurs at an energy density of about 0.4 J/cm 2 . Bi atoms are located after crystallization in substitutional lattice sites for the in depth part of the distribution. Part of the Bi atoms accumulated at the sample surface and the amount of segregation increases with the pulse energy density and depends on the substrate orientation. A computer model has been also developed to calculate several parameters of interest, as the melt threshold,the melt duration, the carrier temperature etc including a detailed description of the absorption and of the energy relaxation processes. The calculations indicate that the simple thermal description accounts quantitatively for the experimental data on melt duration and impurity segregation.

The crystallization onset and the annealing thresholds have been nmeasured as a function of the absorbed energy density in ion implanted amorphous silicon irradiated with nanosecond Nd pulse. Thin amorphous layers (∼500 Å) require higher thresholds ccapared with thick (∼4000 Å) amorphous layers. This result can be explained in terms of balance between absorbed energy and heat flow. For a given thickness of the amorphous layer the thresholds depend on the absorption coefficient of the amorphous material. This last parameter has been varied frcm 104 to 102 CM−1 by low temperature (T<400°C) pre-treatment of the ion implanted sample. The observed drastic variations of both crystallizazion and annealing thresholds agree well with nunerical evaluation of heat flow.