We review recent work on the kinetics of laser-induced solid phase epitaxial crystallization of silicon as determined from time-resolved reflectivity measurements. Specific topics which are addressed include: the intrinsic kinetics of solid phase epitaxy (SPE) in ion-implanted and UHV-deposited films; SPE rate enhancement by implanted dopant atoms and the effects of electrical compensation on the SPE rate; and the temperature dependence of SPE and competing processes in samples containing impurity atoms at concentrations exceeding the solid solubility limit. The high temperature kinetics results are compared with predictions from transition state theory and are discussed with respect to a proposed depression in the amorphous Si melting temperature.

The nature of residual damage in As+, Sb+, and In+ implanted silicon after CW laser and e− beam annealing has been studied using plan-view and cross-section electron microscopy. Lattice location of implanted atoms and their concentrations were determined by Rutherford backscattering and channeling techniques. Maximum substitutional concentrations achieved by furnace annealing in a temperature range of 500–600°C have been previously reported [1] and greatly exceeded the retrograde solubility limits for all dopants studied. Higher temperatures and SPE growth rates characteristic of electron or cw laser annealing did not lead to greater incorporation of dopant within the lattice and often resulted in dopant precipitation. Dopant segregation at the surface was sometimes observed at higher temperatures.

Self-sustained or explosive crystallization results on a-Si and a-Ge are reviewed and compared. cw laser experiments on a-Si allow to follow all the phenomena encountered, and to experimentally measure the crystallization front velocity. The published theories agree well with the experimental results on a-Si. Moreover, a-Ge presents the same behaviour as a-Si, but for a-Si, the high nucleation rate can induce a specific explosive growth.

Explosive recrystallization of amorphous layers, induced by scanned electron or CW Ar+ laser beams, has been investigated in arsenic implanted (100) specimens. We have studied the microstructural changes using plan-view and crosssection electron microscopy to obtain the mechanism of explosive recrystallization phenomenon. The confinement of heat in the amorphous layers during laser irradiation and the nature of amorphous silicon determine the modes of explosive recrystallization. We indicate that, depending upon the degree of undercooling, two distinct modes of liquid-phase recrystallization are observed: one occurring at a velocity of, ∼2 ms−1 and the other at ∼10ms−1. Explosively recrystallized grains contain <110> and <110> as surface normal and growth direction respectively. We present a model for unseeded crystallization to explain the <110> texture observed in diamond cubic lattices.

We present an experimental method, based on the isothermal nature of the boundaries of explosively crystallized silicon, to display instantaneous isotherms produced by fast scanning laser beams. This method is especially useful for the case of multilayer structures or complex geometries, where thermal profiles simulation is a difficult problem. We can also obtain directly a measure of the spatial intensity distribution in the laser beam.

Transient ripple formation in pulsed laser annealing of semiconductor materials is shown to arise from amplified surface polariton scattering. The permanent ripple patterns are frozen in after transverse thermal and material diffusion during the laser-annealing process. The model is in good agreement with time-resolved measurements of the ripple formation in 1.06−µm laser annealing of Ge. Dispersion of the ripple wavevector in the UV spectral region is discussed.

Laser induced periodic surface structure can be understood as a universal phenomenon which occurs when high intensity pulses are absorbed near the surface of solids or liquids. The phenomenon occurs on metals, semiconductors and insulators because of the interference between the incident pulse and an induced “radiation remnant”. This scattered field may be enhanced by the existence of true surface modes such as surface plasmons or phonon-polaritons but this is not essential. The universality characteristics include beam polarization, since we show that circularly polarized light can induce surface ripples, with the damage structure showing a dependence on the sense of rotation. We also present time resolved results of the formation of the ripples to illustrate the essential dynamical processes that occur.

We report the results of a study of surface transformations in semiconductors (Si, GaAs) and metals (Cu) produced by 100 ps long pulses from a Nd:YAG laser system. We present and outline the conclusions of our model for growth of spontaneous periodic surface structures or ripples often associated with laser damage and annealing. The effect of repetitive subthreshold illumination is also examined. Theoretical analysis is presented to support time-resolved experiments performed with two excitation pulses at different wavelengths.

Aligned, coexisting liquid and solid regions are observed in cw laser annealing of polycrystalline Si films on quartz substrates. These stripe patterns are the precursors of surface topography that exists after cooling. It is proposed that a similar situation exists in the pulse annealing process. A calculation of the temperature evolution which assumes stripe symmetry and kinetic restraints of the crystallization process has been carried out. These calculations indicate a lattice temperature of between 1100 and 1300 K, 10 nsec after the sample has fully solidified.

A simple interferometric method is presented which allows measurement of small vertical displacement of a surface heated by a laser beam. Calculations applied to a silicon crystal in the case of a c.w. laser show reasonable agreement with experiment. The method can be applied to assess surface temperature and thermal constants.

The diffusion of an impurity into a solid which is irradiated by laser pulses of some milliseconds duration has been analysed in terms of effective diffusion time and temperature. In the case of Fe in Si, the diffusion coefficient is found to be similar to that measured by COLLINS and CARLSON, and independent of boron doping. In the case of Al in Si, a value of 2.10–10 cm2/ at 1400°C has been found both for single crystals and for fine-grained polycrystals.

In an effort to enhance vacancy trapping and detection in laser-annealed Si, float zone Si was implanted with oxygen to achieve concentrations between one and two orders of magnitude greater than the equilibrium saturation limit. Oxygen, which is known to be an effective trap for vacancies, was found to incorporate efficiently into Si regrown with Q-switched laser annealing Interstitial oxygen, oxygen-vacancy defects and divacancies were observed after implantation. The laser-regrown layers, however, were free of detectable vacancy-associated defects.

Picosecond laser annealing has been performed on implantationamorphised silicon. A multiannular (up to five rings) recrystallization pattern has been generated by a single~30 psec pulse at 1.06 μM and 0.53 μm wavelength and energy density just below the damage threshold. The different patterns have been investigated by scanning the surface with a Raman microprobe with a 1pm spacial resolution. Information are thus given on the different phases (amorphous or crystalline) and on lateral as well as in depth dimensions of the different rings.

Evaluation of thermal profiles along the scan direction of a line shaped e-beam as well as the topographic distribution of the thermally induced stresses have been performed by solving the heat diffusion equation for several incident power values. The resulting stresses have been computed in the “nearly isotropic” approximation but taking into account that the slip planes, in <100> oriented silicon crystals, are{lll} and the slip directions in the plane are <110>.The threshold of damage introduction has been evaluated by comparing the computed stresses with the yield stress of the material at any annealing temperature. Experimental observations based on X-Ray topography have been performed in order to study the damage introduction on <100> silicon samples annealed in the same conditions used for stress computation. A very good agreement between computed and experimental results was found.

Laser annealing experiments on silicon have shown that rapid solidification can trap large amounts of certain impurities in the crystal lattice. Concentrations that exceed the equilibrium solubility limits by several orders of magnitude have been obtained. In this paper we discuss the impurity trapping process using Monte Carlo simulation data from the kinetic Ising model. The dependence of the impurity concentration in the crystalon the solidification rate is calculated. The simulation data are compared with recent laser annealing results for bismuth and indium. Excellent agreement between the model and the bismuth experiments is obtained. The larger trapping rate on the (111) relative to the (100) orientation is found to be caused by the slower crystallization kinetics on the (111) face. Similar results are obtained for indium, although the difference in trapping on the (111) and (100) faces is somewhat smaller in the model than in the experiment.

Recent experiments dealing with the thermodynamics of crystallization and melting of amorphous Si are reviewed. differential scanning calorimetry measurements give the heat of crystallization of implanted, amorphous Si to be 11.3±t.8 kJ/mole. Gibbs free energy calculation based on these measurements indicate that amorphous Si melts at a temperature of 1460°K compared to the crystalline value of 1685°K. Evidence for this reduced melting temperature also comes from rapid heating measurements using a) structural information after solidification and b) dynamic conductance measurements during the melt. Solid phase epitaxial regrowth experiments which apparently do not show such a depression in amorphous melting temperature will be discussed.

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.

It Will be shown that under suitable conditions ion implanted impurities in Si can precipitate and grow coherently within the single crystal lattice during recrystallization induced by pulsed laser or thermal annealing. Ion channeling and transmission electron microscopy (Tem) were used to characterize such precipitates in Si implanted with Sb and B and thermally annealed, and in Si implanted with Tl and annealed with a pulsed ruby laser.The orientations of these precipitates were determined from TEM and detailed angular scans using ion scattering channeling.The nucleation and precipitation processes will be discussed in terms of differences in the liquid and solid phase regrowth mechanisms.

Incorporation of Group III, IV, V dopants in silicon occurs as a result of solute trapping during laser annealing. Distribution coefficients and substitutional solubilities are far greater than equilibrium values, and can be functions of growth velocity and crystal orientation. Mechanisms limiting dopant incorporation at high concentrations are identified and discussed.

Ion backscattering/channeling and transmission electron microscopy (TEM) were used to investigate the annealing behavior of ion implanted Ge single crystals using a Q-switched ruby laser. The impurities studied were Bi, In, Sb and Pb, which were implanted at liquid nitrogen temperature into both (100) and (111) crystal orientations. A rather unique damage structure which can form during room temperature implantation of Ge is discussed. Maximum substitutional concentrations, which far exceed the retrograde maxima, are reported for all the dopants studied in (100)Ge. The maximum concentrations were limited by an interfacial instability during epitaxial growth following laser irradiation which led to the formation of a well-defined cellular structure.