It has recently been shown that the front surface region of the silicon lattice is severely strained during pulsed laser irradiation. This uniaxial strain reduces the symmetry of the front surface region, resulting in additional shifts and splittings of the phonon frequency and changes in the Raman scattering tensor. It is shown that, for the case of pulsed laser irradiation, the phonon frequency is increased, and the 3-fold degenerate optical phonon is split into a singlet and a doublet. The changes in the Raman scattering tensor make it non-symmetric, and generally invalidate the technique used by Compaan et al. to determine the cross section experimentally. The complications introduced by the presence of stress during pulsed laser annealing, coupled with the temperature dependence of the optical and Raman tensors, make a simple interpretation of the Stokes to anti-Stokes ratio in terms of lattice temperature extremely unreliable.

The goal of this paper is to investigate optical properties of heavily doped silicon, performed by laser annealing of implanted layers.

The optical properties were investigated by using U.V. and visible light (between 200 and 500 nm)reflectance and Raman spectrometry measurements. The experimental observations have been correlated with the contribution of the supersaturated solid solution of arsenic in the silicon lattice. Furthermore,the absorption coefficent of these layers has been deduced from ellipsometry measurements.

Time-resolved Si lattice-temperature measurement has been developed on wide time scale from 10−9 to 100 sec during laser annealing, by utilizing the time-dependent optical interference in Si on sappire. This interference is due to small changes in Si refractive index induced by temporal changes in Si lattice-temperature. For ns–pulsed laser annealing, part of the absorbed photon energy is found to be transferred into lattice (phonons) in a time much shorter than 40-ns pulse duration. A new method using a microscope is demonstrated for time- and space-resolved Si latticetemperature measurements during cw laser annealing.

Using a visible probe laser (632.8 nm) we have directly observed motion of the melt front in silicon-on-sapphire during pulsed laser annealing. The average penetration and regrowth velocities have been determined to be 13 and 6.5 m/sec. respectively. These values are in agreement with recent conductivity measurements and heat flow calculations. In addition, the data demonstrate that the high-reflectivity phase can penetrate at least .5 um (Si thickness) and requires a significant amount of the time to do so. These results are further evidence that the high–reflectivity phase is molten silicon.

we have investigated microstructural changes and phase transformations in 30Si+, 75As+, 63Cu+, and 115In+ implanted amorphous silicon layers as a function of pulse energy density. Cross-section electron microscopy studies have revealed the formation of two distinct regions, large and fine polycrystalline regions below the threshold for “defect-free” annealing. The fine polycrystalline region is formed primarily by explosive recrystallization, and occasionally by bulk nucleation and growth. The impurity redistribution in the large and fine polycrystalline regions were determined by Rutherford backscatterinq measurements. Large redistributions of impurities in the large poly region are consistent with velocity of solidifications of 3–5 ms−1. The nature of impurity redistributions in the fine poly region as a function of distribution coefficient provides information on the details of liquid phase crystallization phenomena.

The formation of amorphous Si by the quench of a thin surface layer melted by fast UV laser irradiation has been investigated. The starting (111) surface layers were either pure or doped with As, Bi, In and Te by implantation. The asimplanted samples were recrystallized by ruby laser irradiation resulting in surface accumulation of Bi,In and Te. For the same UV irradiation condition, the amorphous layer formed in As, Bi, In or Te doped Si is about twice the thickness of the amorphous layer formed on pure Si. In the presence of the surface accumulation of Bi, In or Te, the amorphization results in an inward segregation of the dopant. For In, a very thin metal layer ˜15Å thick, is formed 150Å beneath the amorphous surface. These results show that the amorphous-liquid interfacial segregation coefficients for Bi, In or Te are less than unity and that the amorphous solidification proceeds from the surface and bottom of the liquid layer.

Atomic processes at the interface in regrowth following laser induced melting were investigated by observing behavior of impurity segregation. The interfacial segregation coefficient k* was obtained from depth profiles of solute atoms redistributed by laser irradiation of uniformly doped Si, Ge, and GayAl1−yAs crystals. It was found that k*=k0 for B in Si, Ga in Ge ih the growth rate range of 1 m/s. It is concluded that rapid growth freezes a state of liquid monolayer adjacent to the interface which has the character of ideal solution from dilute to eutectic composition for dopant-silicon systems and in the entire range of composition for the mixed crystal.

The increase of reflectivity associated with a strong decrease of the laser penetration depth at the melting threshold of laser irradiated silicon induces a symmetry breaking with formation of a mixture of solid and liquid regions. We present a steady state solution in the case of solid and liquid stripes and we show that the liquid regions are slightly hotter than solid ones in contradiction with the previous idea of an undercooled liquid. The pattern size has to be smaller than a critical value of the order of the laser penetration depth, and can be selected by additional interference and diffraction effects.

We describe our preliminary observations of the interaction of short pulse 1 µm radiation with crystalline silicon. In particular we find that for 7 ps pulses, but not for 46 ps pulses, the crystal-amorphous transition can be induced on the Si surface. Additionally, we have measured the single shot melting threshold for c-Si to be 0.6 ± 0.2 J cm-2 for 7 ps pulses. The formation of ripple patterns and other surface structures with pulses as short as 4 ps is also reported.

A unified approach is presented which reconciles contradictory results obtained in earlier studies of optical spectra of inhomogeneous electronic systems in semiconductors: A consistent analysis of the optical data implies strong deviations from quasi-equilibrium in the carrier distributions. The non-equilibrium nature of the plasma is confirmed by a Mott-transition based study of the plasma transport.

The present level of development of excimer lasers, as it relates to semiconductor processing, and the advantages of these lasers for such processing, are reviewed. Extensive comparisons of the quality of annealing of ion-implanted Si obtained with XeCl and ruby lasers are presented. Major applications in the area of solar cell fabrication, siliconon-sapphire technology, laser photochemical processing, and submicron optical lithography are outlined and discussed.

Small geometry NMOS transistors were fabricated using junctions implanted with 1016; Asplus;/cm2; @ 180 keV and annealed through 1067 Å of SiO 2; with a cw argon laser. Phosphosilicate glass densification was the only other high temperature step. Channel lengths were varied from 1.3 to 50 μ. and channel widths from 1 to 50,μ. Physical characterization of these devices revealed a junction depth of 3000 Å with negligible lateral diffusion. The smallest transistor had approximately a square channel with WxL = 1×l.3μ2;. IDS;−VDS; characteristics of this device were similar to those of large geometry devices due to counteracting short and narrow channel effects. The threshold voltage was 0.61±0.013 V across an entire wafer, while there was no punch-through for VDS;<13 V and no avalanche breakdown for VDS; < 14 V. The junctions showed a forward-biased ideality factor of 1.17, and the contact resistance in an 8 × 8 μ2; area was 1.5Ω to the source/drain regions and 0.5Ω to laser-recrystallized polysilicon interconnects. It is concluded that cw laser annealing can be used to fabricate small-geometry devices with excellent performance and without any deleterious effects.

Metastable solid solutions of arsenic and phosphorus atoms were created by high-dose ion implantation in silicon, followed by annealing either with pulsed (Nd:YAG) or CW (CO2;) laser irradiation. The relaxation of these supersaturated layers was investigated by thermal post-treatment at temperatures between 600 and 1000°C. By measuring the time dependence of the sheet carrier concentration, the time constant and the activation energies for the relaxation of the electrically-active As and P atoms were investigated. In addition, the equilibrium carrier concentrations at different temperatures were obtained by Halleffect measurements in connection with a layer-removal technique.

The formation of single crystal multiple layers on silicon substrates with thicknesses in excess of 1 μm has been demonstrated to be a viable process. Film build-up is via repetitions of the steps (1) pre-deposition chemical cleaning of wafer, (2) magnetron sputter deposition of 0.3 pm thick amorphous Si, (3) interfacial mixing via 190 keV implantation of Si, and (4) film epitaxial crystallization via pulsed laser annealing. Doping has been demonstrated by both (1) P ion implantation and (2) P incorporation from PH3; included in the sputter gas ambient.

4 He backscattering and channeling and 4-point probe resistivity measurements are used to characterize the doping of 〈100〉 Si directly from the gas phase by using a laser induced melt/recrystallization process. Impurity concentrations from 3×1019 to 5×1020 cm−3 and sheet resistivities as low as 20 Ω/╒ are obtained by variation of the laser energy density or number of passes. Diodes fabricated by this process exhibit near ideal I-V characteristics with sharp reverse breakdowns determined by junction edge effects. Annealing at 850° C further reduces the generation-recombination centers to values that result in an ideality factor of 1.0.

Silicon implanted with arsenic or boron has been annealed with a 100kW argon arc lamp turned on for a few seconds until the wafer temperature was in the 850–1250°C temperature range. The differences in defect behavior between such rapid annealing and furnace annealing is pointed out, and the dopant diffusion is measured. Aside from an initial movement of the boron atoms left in interstitial positions after the implant, diffusion of the boron and arsenic is consistent with standard diffusion models.

Residual stress introduced in middle carbon steels by a solid-solid transformation following a laser heating are studied by two methods : a destructive one which consists in taking away layers of material, the other one, a non destructive method, based on the ferromagnetic noise analysis. The first method gives an average value of the stresses existing in the machined layers, the second one gives informations on localized variations.

Single crystals of GaAs (100) and Si (110) were laser annealed with a 20 ns ruby laser pulse. Both the velocity distribution and the density variation of evaporated Ga or As and Si atoms were determined by a time-of-flight measurement. In addition time-resolved measurements were made of the reflectivity of the surface during the laser annealing. The data consistently show that the molten phase occurs at energy densities of ≳ 0.35 J cm–2 for GaAs and ≳O.8 J cm for Si.

We have achieved wide area (38 cm2) electron beam heating of semiconductor materials using a glow discharge electron beam with electron energies between 3 and 7 keV. A continuous beam 7 cm in diameter with a power density up to 90 W/cm2 was used to anneal both boron-implanted (30 keV, 5 × 1015 atoms/cm2) n-type <100> silicon wafers as well as two types of Ti-Si composite films to form this titanium disilicide Annealing of the implanted samples was obtained without redistribution of the original dopant profile using a 15-sec. electron beam exposure. Formation of TiSi2 was found to decrease the sheet resistivity of these samples a factor of ten for both 400 Å films of Ti on Si and codeposited Ti-Si mixtures of overall stoichiometry TiSi2. Due to the high electron beam power density achieved over a large area, one can uniformly anneal an entire wafer in a single exposure without sample or beam scanning.

Shallow-junction semiconductor devices have been fabricated using ion implantation and transient annealing with a Varian IA-200 isothermal annealer. Boron implanted diodes, npn bipolar transistors and CMOS ring oscillators have been fabricated and are compared to furnace annealed devices. Boron implanted diodes have been annealed with the RIA and yield acceptably low leakage currents, comparable to furnace annealed devices. The RIA devices have recombination lifetimes of ∼10 μsec. The bipolar transistors subjected to a transient anneal have good base-collector and emitterbase junctions as well as gains of ∼100 in good agreement with the design of the device. MOSFETs and CMOS ring oscillators were fabricated using self-aligned polysilicon gates. The transient annealed devices were equal or superior to devices which were furnace annealed at 800°C for 10 min. The low temperature furnace anneal was necessary to minimize short channel effects. The transient anneal resulted in ring oscillators which were a factor of two faster than furnace samples that were annealed.