A previously presented computer model was used to calculate melt thresholds and carrier temperatures in crystalline silicon and gallium arsenide subjected to picosecond laser pulses at 532 nm. The energy relaxation time of hot carriers was a variable parameter. For Si, a thermalization time of 1 ps yields results which are in very satisfactory agreement with published experimental data: the melt threshold is 0.19 J/cm2, and the maximum carrier temperature for the threshold pulse is 5500 K. The melt threshold in GaAs is substantially less, 0.03 J/cm2 for a thermalization time of 1 ps.

The kinetics of amorphous-to-polycrystalline conversion and solid phase epitaxy (SPE) in UHV-deposited Si films have been determined over a wide temperature range by the use of optical reflectivity measurements made during rapid heating by a cw Ar laser. Crystallization rates measured in UHV following film deposition are reported and compared to rates measured in air in order to elucidate the effects of contaminants on the processes. The effects of boron doping on nucleation and growth kinetics are also reported. The crystallization rates determined in these studies can be used to predict the volume fraction of polycrystalline material formed during laserinduced SPE growth of thick epitaxial layers.

We have used cross-section TEM and Nomarski optical microscopy to examine the origin of halo patterns previously observed following picosecond irradiation of ion implantation amorphized Si. The importance of melt depth, quench rate and the incomplete nature of the initial amorphization step are emphasized. A search for a post annealing morphological or microstructural signature related to a plasma activated process proved negative.

Time-resolved-reflectivity measurements have been combined with transmission electron microscopy (cross-section and plan-view), Rutherford backscattering and ion channeling techniques to study the details of laser induced solid phase epitaxial growth in In+ and Sb+ implanted silicon in the temperature range from 725 to 1500 °K. The details of microstructures including the formation of polycrystals, precipitates, and dislocations have been correlated with the dynamics of crystallization. There were limits to the dopant concentrations which could be incorporated into substitutional lattice sites; these concentrations exceeded retrograde solubility limits by factors up to 70 in the case of the Si-In system. The coarsening of dislocation loops and the formation of a/2<110>, 90° dislocations in the underlying dislocation-loop bands are described as a function of laser power.

EBIC and voltage contrast SEM microscopy, combined with optical microscopy. chemical etching and Talystep profiling have been used to investigate cw laser annealing of a-Si in the slip-free SPE regime. Special attention is devoted to the edges and extremities of the line scans, i.e. to the c-to a-Si boundary. At very low power, evidence is given for an initial reordering and thus electrical activation stage of the a-Si. For the higher power range regrowth occurs through two different processes. The EBIC yield is interpreted in terms of a balance between annealing of the ion implantation damage and defect generation in the si substrate during the laser annealing. These results are extended to the case of a scanned electron beam annealing.

Experimental results are presented which indicate that amorphous silicon does not melt at a temperature significantly lower than the melting point of crystalline silicon (1693°K), contrary to recent reports which suggest a 300 to 500°K melting point depression. Time-resolved optical reflectivity measurements are used to determine the temperature and to investigate phase changes which occur in silicon during cw laser heating. It is shown that amorphous silicon films produced by arsenic implantation into Si(100) do not melt when heated to temperatures in excess of 1600°K. An alternate interpretation of previous work that is consistent with the present findings is proposed.

The regrowing features of disordered germanium under low power multi-pulse irradiation are discussed. It is shown that implanted amorphous germanium starts the regrowth from the specimen surface while glow-discharge amorphous material starts from the amorphous-single crystal interface. Evidence against a melting mechanism in the case of multi-pulse irradiation are also presented.

Measurements were made of the conductance of single crystal Au-doped Si and silicon-on-sapphire (SOS) during irradiation with 30 nsec ruby laser pulses. After the decay of the photoconductive response, the sample conductance is determined primarily by the thickness and conductivity of the molten layer. For the single crystal Au-doped Si, the solid-liquid interface velocity during recrystallization was determined from the current transient to be 2.5 m/sec for energy densities between 1.9 and 2.6 J/cm2, in close agreement with numerical simulations based on a thermal model of heat flow. SOS samples showed a strongly reduced photoconductive response, allowing the melt front to be observed also. For complete melting of a 0.4 μm Si layer, the regrowth velocity was 2.4 m/sec.

We have grown epitaxial silicon films on silicon (100), (110) and (111) oriented substrates, using pulsed ruby laser irradiation as a means to obtain clean, ordered substrate surfaces. On these surfaces epitaxial layers were grown in two ways: I. Rȯom temperature deposition and pulsed laser induced epitaxy of 100–300 nm films was carried out repeatedly, yielding ∼1 μm thick epitaxial layers. II. Low temperature molecular beam epitaxy (M.B.E.), even at 250°C on Si(100),of layers up to 1 μm.

Applying the second technique to implanted substrates, we annealed and cleaned arsenic implanted silicon (100) samples in situ, and produced epitaxial overlayers of 100–1000 nm, thus creating a buried n-type channel in silicon.

Polycrystalline silicon films were deposited on singlecrystal silicon substrates from a SiH4 –H2 mixture at 660°C and epitaxially recrystallized with ruby laser pulses during the deposition. The surface morphology was found to depend critically on the surface conditions of the substrate. Using appropriate cleaning procedures, 0.5 and 1.0 micron thick layers were deposited and laser recrystallized during the deposition. Ion scattering/channeling analysis showed that the layers were single crystalline with a high degree of perfection. Using TEM, dislocation densities of 103–104 cm−2 were found, but some areas were dislocation free.

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.

The Fourier transforms of the grating-like damage patterns formed on the surface of Ge by single 1.06μm YAG laser pulses reveal a great deal of information about the damage structure. A theory is presented based on scattering from surface roughness which accurately accounts for both the spacing and orientation of the fringes produced at various angles of incidence by beams of different polarizations.

A large number of impurities which do not form covalent bonds with silicon cannot be incorporated into the lattice at measurable (by RBS) concentrations by pulsed laser annealing. At low concentrations the impurities can be zone refined to the surface, while at high concentrations the interface becomes unstable during regrowth leading to a cell structure. For each impurity there is a critical concentration required for interfacial instability to develop. The results are in qualitative agreement with a simple model for solute trapping and zone refining which assumes that the impurity diffusivity in the interfacial region is intermediate between that of the liquid and the solid.

Rapid oxidation in silicon induced by nanosecond UV laser pulses has been recently reported [1]. A significant amount of oxygen was observed to be incorporated in theregrown silicon layer when irradiation took place in air or in oxygen ambient. The fundamental interaction and transport kinetics involved include: incorporation of impurity during surface melting, trapping of solute during resolidification, and rapid reaction to form chemical bonds. The present study has investigated the mechanism of oxygen incorporation and trapping under various regrowth conditions. Oxygen depth-concentration distributions were analyzed using secondary-ion-mass spectroscopy (SIMS). The oxide formed was studied using differential Fourier-Transformed IR (FT-IR) spectroscopy.

Oxygen indiffusion during pulsed laser annealing of silicon has been studied using the 186 O(α,α) 186 O resonance at 3.045 MeV. Anneals were carried out with a Q–switched ruby laser, energy density of the pulses 1.5 J/cm2 , pulse width 20 ns. No evidence for oxygen indiffusion was found, neither for ion–implanted single pulse air–annealed silicon nor for a silicon wafer, cleaned with 8 laser shots in a UHV environment. In the latter case, the upper limit of the oxygen concentration was found to be 3.1 * 1018 at/cm3 , which is lower than the solid solubility limit of oxygen in silicon. The non–occurrence of indiffusion is consistent with the dissolution time of SiO2 in Si, which is orders of magnitude longer than the melt duration of the Si–substrate.

Highly-degenerate As-doped n-type and B-doped p-type Si(l11)−(1×1) surfaces have been prepared via ion implantation and laser annealing and studied using photoemission. For As concentrations of ∼4–7%, surface states become very different from those for intrinsic Si(l11)−(1×1) and the Fermi level EF at the surface moves to the conduction band minima resulting in a zero height n-type Schottky barrier. Emission from the conduction band minima has been directly viewed in momentum space.

We have studied the valence band and surface-core-level states for laser-annealed, thermally-annealed, and cleaved Ge(111) and Si(l11) surfaces with high resolution photoelectronspectroscopy using synchrotron radiation. For the annealed surfaces we find two surface states near the top of the valence band as well as characteristic surface core level spectra. These indicate the existence of a common local bonding geometry for all these surfaces. We observe that the (1 × 1) and cleaved (2 × 1) surfaces are not related as recently reported for Si.

A high efficiency technique for incorporating As or other high volatility elements into Si and other semiconductors by laser pulse processing is described. By this method more than 80% of the As atoms painted onto a Si surface were made to relocate onto substitutional sites in the 73Si crystal. Mossbauer analysis of laser diffused As atoms in a Ge crystal indicates that although the final As sites are >97% substitutional, the majority are associated with one or more defects not seen in conventionally diffused material.

In this paper we report experiments on annealing of arsenic-implanted silicon using a pulsed imploding-plasma X-ray source. Silicon wafers of <100> orientation were implanted with arsenic ions at 50 keV to a dose of 3.5 ∼ 1015 cm−2 and exposed to a single 50 ns pulse of X-rays in the energy density range of 0.15 to 0.55 J/cm2 The characteristic X-ray absorptiog coeificient in silicon for these experiments was 1.6 ∼ 10 cm−1, resulting in most of the energy being absorbed in the first 100 nm of the wafer surface.

For wafers annealed in the energy density range of 0.3 to 0.4 J/cm2 backscattering and channeling measurements show recovery of the crystallinity of the damaged layer with incorporation of about 86% of the implanted arsenic onto substitutional lattice positions. Evidence of redistribution and flattening of the arsenic profile in the annealed wafer was observed in the backscattering data and confirmed by SIMS profiling. Detailed results on the electrical and structural properties of these annealed layers will be presented. High energy pulsed X-ray sources offer the unique capability of simultaneously exposing large numbers of wafers to an extremely uniform energy flux at much higher efficiencies than conventional lasers.

Electrical measurements and Rutherford backscattering have been used to evaluate the thermal stability of single crystal and polycrystalline Si films that were ion implanted and laser annealed. The films were implanted with 75As or 31p and annealed with either a pulsed ruby, a pulsed Nd:YAG or a CW­Ar+ laser. The samples were then thermally annealed at temperatures between 450 and 900°C. The single crystal samples implanted with arsenic below 1 × 10-15 cm−2 were thermally stable. For higher doses the electrical concentration reaches a minimum at 800°C. The same trends are observed in the polysilicon films for sufficiently high doping levels. RBS shows that As is precipitating at 700°C in single crystal material and has begun to go back into solution at 900°C for concentrations of ∼7 × 1020 cm−3. Similar trends are observed for 31P implanted samples.