There are a number of viable approaches to silicon-on-insulator (SOI) technologies, and the panel session has assembled a number of leaders in the SOI community for their views of “SOI Technologies for Integrated Circuits.” Their viewpoints, shown in tabulated form, were presented for general discussion in the session which was attended by about 150 people. Although SOI technologies are useful for many applications, most of the panelists agreed that the most appropriate near-term applications are for high-speed, high-density integrated circuits. Various SOI technologies, including silicon-on-sapphire (SOS), are currently in the running, but the majority of the panelists felt that for SOI technologies to be widely adopted, SOI must be available as a proven manufactured product within two to three years.

High intensity pulsed beams of photons, electrons and ions provide extremely efficient means for electronically exciting solids near their surfaces. Among these three, laser beams with ever-increasing time resolution have also served as diagnostic probes to clarify the picosecond time scale on which interchange of energy between the electronic and the vibrational states of solids takes place at very high excitation energy densities. Because of this rapid transfer of electronic excitation to heat, pulsed beams provide versatile tools to investigate transient thermodynamic phenomena in solids, particularly those associated with metastable phases such as amorphous silicon.

Energetic ion beams used outside the traditional role of ion implantation are considered for semiconductor applications involving interface modification for self-aligned silicide contacts, composition modification for formation of buried oxide layers in Si on insulator structures and reduced disorder in high energy ion beam annealing for buried collectors in transistor fabrication. In metals, aside from their use in modification of the composition of near surface regions, energetic ion beams are being investigated for structural modification in crystalline to amorphous transitions. Pulsed beams of photons and electrons are used as directed energy sources in rapid solidification. Here, we consider the role of temperature gradients and impurities in epitaxial growth of silicon.

The potential of rapid thermal processing for applications in silicon integrated circuit technology, silicon microwave bipolar technology and GaAs FET technology is explored.In addition, two novel applications for GaAs processing are described.

Laser processing of materials has raised a number of interesting issues relating to phase transitions and the structure of optically excited semiconductors. In this paper we describe the dynamics of structural changes that take place on a silicon surface following excitation with an intense optical pulse. Second harmonic generation from the silicon surface is used as a tool to measure crystalline order with 90 femtosecond resolution. The three-fold rotational symmetry of the silicon <111> surface is observed to become rotationally isotropic within a picosecond after excitation consistent with a transition from the crystalline to the liquid molten state.

Time-resolved studies of reflectivity and transmission at 0.532 μm, 1.064 vm and 2.8 μm of thin silicon films following irradiation with ps pulses at 0.532 μm have been performed. The formation of the electron-hole plasma and the evolution of lattice temperature is investigated as a function of pump fluence and time delay. Quantitative determination of the plasma densities and lattice temperature up to the melting temperature shows that the maximum plasma density is limited to ∼ 1 × 1021 cm−3 by Auger recombination even on a time scale of picoseconds at fluences sufficient to cause the phase transition. The thermal nature of the phase transition is confirmed.

We demonstrate a novel technique to study in detail the picosecond dynamics of semiconductors close to the melting phase transition. A variable-energy IR pulse (1.06 μm) is used to melt Si or GaAs samples via free carrierabsorption (FCA) in the dense and hot electron-hole plasma (EHP) produced by a preceding visible (532 nm) pulse. By varying the delay between the pulses and their relative intensities, we are able to verify the Lietoila-Gibbons model for pulsed laser heating, and to measure in detail important parameters of the EHP over a wide range of experimental conditions.

We have performed infrared reflectivity measurements using 5.3 and 10.6μm probes to determine the plasma density, lattice temperature and melting kinetics of silicon and germanium following excitation by 25 nanosecond, 0.53 and 1. 06μm pulses. Below the threshold of melting, the maximum plasma densities are approximately 1020 cm−3; for both materials; these values and the spatial and temporal evolution of the plasma are consistent with well known generaticn, diffusion and recombination processes. Above the threshold for melting we have taken advantage of the large skin depth at infrared wavelengths to determine the melt front kinetics for depths up to 1000 Å using a contactless technique.

The emission spectra of the electron-hole plasma created at the surface of a Si sample by intense laser pulses (65 ns or 400 ps) are investigated. It is shown that the plasma drift is necessary for a consistent interpretation of the luminescence line shape and the energetic position of the line. We determine average densities up to 2.1019 cm−3 for 300K and typical drift velocities up to 4.106 cm/s.

Mechanisms are discussed by which sufficient momentum and energy may be localized on individual atoms, ions or molecules to account for photoablation in different regimes. In order of increasing excitation intensity, these include the roles of: “recoilless emission” (as in Bragg scattering and the Mössbauer effect) during Auger recombination of a core exciton, particularly in the Knotek-Feibelman effect; the metastable binding of multiple holes earlier proposed by Feibelman, particularly in the data of Itoh and coworkers; the change in the equilibrium interatomic spacing concomitant with excitation of a Frenkel exciton (localized broken bond), particularly in the ablative photodecomposition reported by Srinivasan and co-workers; the interaction of virtual excitons with real excitons in a strongly polarized solid, e.g. one subject to laser annealing pulses; and the interaction of ions with surface plasmons, particularly in the laser sputtering data of Hanabusa et al. A connection is made to rapid annealing and to sub-threshold defect formation. Further support is noted for the bose condensation model of pulsed laser annealing.

Direct measurements of the liquid/solid interface veiocity have been made during both melt-in and regrowth for puised (20 psec) ultraviolet lasei irradiation or crystailine silicon. The regrowth velocity was 25 m/sec, independent or laser fluence. Regrowtn velocities of 50 to 100 m/sec are expected from heat diffusion calculations which neglect undercooling, whereas the inclusion of an appropriate undercooling curve brings the calculation into good agreement with the data. Tne liquid films produced were up to 40 nm thick and were fully amorphized on resoliaificaion.

Measurements of the time of the onset of melting of self-implantation amorphized (a) Si, during an incident laser pulse, have been combined with modified melting model calculations and measurements of surface melt duration to demonstrate that the thermal conductivity, Ka, of a-Si is very low (≃0.02 W/cm-K). Ka is also shown to be the dominant parameter determining the dynamical response of ionimplanted Si to pulsed laser radiation; the latent heat and melting temperature of a-Si are relatively unimportant. Cross-sectional transmission electron micrographs on implantation-amorphized Si layers of several different thicknesses show that for energy densities less than the threshold value for complete annealing there are usually two distinct regions in the re-solidified a-Si, consisting of fine-grained and large-grained polycrystalline Si, respectively. The presence of the fine-grained poly-Si suggests that bulk nucleation occurs directly from the highly undercooled liquid phase. Thermal melting model calculations suggest that the nucleation temperature, Tn is ≃1200°C.

Subnanosecond ultra-violet radiation pulses are used to produce relatively thick, large area amorphous layers onSi crystals by transient melting and solidification. The different behaviours of (001) and (111) Si orientations are highlighted. Observations of crystal growth phenomena during solidification at velocities lower than required for amorphization are correlated with theoretical predictions. Computer modelling of heat flow in amorphous silicon is refined.

Transient electrical conductance has been used to measure the resolidification velocity in silicon containing implanted solutes. Nonequilibrium segregation of the solutes occurs during the rapid resolidification following pulsed laser melting. The velocity of the liquid-solid interface is observed to depend on the type and concentration of the solute. A 25% reduction in solidification velocity is observed for an implanted indium concentration of three atomic percent. Implanted oxygen is also shown to reduce the solidification velocity. The dependence of the velocity on solute concentration impacts a variety of segregation, trapping and supersaturated solution studies.

We present the results of a systematic study of phonon softening due to free electrons and holes in extremely heavily doped Si and Ge. Metastable concentrations of Bi, Sb, As, P, Al and B were implanted and pulsed laser annealed (ruby or XeCl) to produce substitutional concentrations up to 4×1021 cm−3 . We find softening of the zone center optic phonon of as much as ˜5% in p-type Ge, ˜5.4% in p-type Si, and 2% in n-type Si. The shifts are explained by phonon coupling to single particle electronic excitations. In addition we discuss the density dependence of the Raman-active vibrational local modes of P and Al in Ge and of B in Si which we demonstrate can provide a convenient measure of substitutional concentrations of these low mass dopants.

Laser heating of crystalline silicon is investigated with 10 ns laser pulses at 532 nm Raman spectra below the transition threshold show distinct shifts to low frequencies. The absence of line shifts at higher energy is due to a time resolution artifact. Temperatures evaluated from frequency resolved anti-Stokes/Stokes ratios are in agreement with the temperature estimated from line shifts, and provide clear evidence that the surface reaches the melting point. These conclusions are confirmed by independent measurements of the thermal emission. Time-resolved pyrometry also provides the temperature evolution of the liquid phase.

Nanosecond structural changes in a crystal lattice during pulsed laser annealing have been measured using time-resolved Low Energy Electron Diffraction (LEED). LEED is both structure and surface (∼ 10Å) sensitive. Lattice temperatures can be extracted from Debye-Waller like extinction coefficients. Combining these with nanosecond time resolution provides a surface probe for short-time dynamical processes. The technique is used to observe the time evolution of a Ge(l11) surface during pulsed laser annealing. The results demonstrate rapid formation of a liquid layer and subsequent surface recrystallization and cooling.

Three different photoelectric regimes are observed in the interaction of 15 ps, 266 nm laser pulses with crystalline silicon samples versus light fluence. A superposition of linear and quadratic photoionization is followed by a space charge limited regime up to the critical fluence F4ωth for the surface amorphization where highly nonlinear ion emission is observed. Ion and electron emissions become equal in magnitude at a fluence - ∼ 2F4ωth The absence of observable thermionic effects indicates that thermal equilibrium of the electronhole plasma and the lattice is reached during the laser pulse duration.

Recent experimental and theoretical work suggests that bulk nucleation occurs in highly undercooled liquid silicon formed by the pulsed laser melting of amorphous layers. In this paper we discuss the dynamics of solidification of undercooled liquid silicon in terms of results from melting model calculations and from the theory of homogeneous bulk nucleation. The relationship between the occurrence of bulk nucleation and the ability to induce a liquid-to-amorphous phase transition by large undercoolings of the liquid is considered. It is concluded that the observed liquid-toamorphous transition in silicon cannot be explained by an equilibrium thermodynamic approach.

It has been shown previously that dopant concentrations far above the equilibrium solubility limit can be obtained in semiconductors by pulsed laser annealing of heavily ion implanted material. We exploit this fact to study the photoluminescence of germanium with dopant concentrations up to 1021 cm−3. From this study we obtain information on the filling of higher lying band minima and the shift of the optical band gap as a function of carrier concentration over a much wider range than accessible with bulk doped material. In addition it is shown that photoluminescence provides a diagnostic tool to characterize implanted layers.