We report studies done on the heating of polysillcon thin films below the melting temperature with long-time (on the order of minutes) continuous-wave laser irradiations. It is shown that a well controlled steady-state temperature is locally established within the film. A thermal model is developed to correlate film temperature to beam intensity and a direct relationship is found. A correlation coefficient of 2.5 K/W/cm2 is empirically determined between film temperature and incident beam power density.

We have discovered that the β and γ brasses of Cu-Zn exhibit clearly resolved increases in reflectance upon melting with a 30 ns ruby laser, which allow their melt durations to be readily measured. This system thus offers potential for obtaining quantitative information about the solidification kinetics of metals. We have also found that a heteroepitaxial layer of β' brass is formed on the surface of (ordered) γ brass with 63 wt.% Zn following pulsed laser-induced melting. The β' layer is interpreted to mean that the metastable β phase (bcc) formed on the liquid-solid interface as the γ substrate attempted to regrow, and that β ordered to β' (B2) during cooling. The β formation implies that undercoolings > 16 K were attained during the attempted regrowth of the γ phase.

We have used excimer laser surface processing to melt and mix single Ti layers into the surface of polycrystalline SiC substrates. The mixing of Ti into the surface is very rapid and efficient. Examination of Rutherford backscattering (RBS) data for different mixing conditions shows the formation of a preferred composition at the Ti-substrate interface which propagates from the interface with further mixing. Reconstruction of the RBS spectrum indicates that the composition of the layer is Ti45C37Si18. X-ray diffraction demonstrates the formation of Ti suicides and carbides in the surface region. Profiling of C in both mixed and uncoated samples by 6 MeV He+ scattering demonstrates that laser processing of the SiC does not cause major changes in the stoichiometry of the substrate material.

We report a new non-invasive optical technique for the measurement of the absolute temperature of silicon wafers in a rapid thermal processing environment. The method is based on the temperature dependence of the infrared absorption of silicon. Unlike pyrometry, the method can be used with a quartz processing chamber, and it is well-suited to the temperature range of 400 °C to 800 °C. Temperature resolution on the order of one degree can be achieved, and the method can easily be applied to homoepitaxial and certain heteroepitaxial growth cycles.

Ge has a diamond cubic crystal structure (α) while Sn exists in both the diamond cubic (α) and body centred tetragonal (β) allotropic forms. The solid solubilities between Ge and Sn are very small according to the equilibrium phase diagram. This paper describes an investigation into the manufacture of metastable diamond cubic Ge-Sn alloy layers using pulsed laser melting of evaporated thin films . Cross-sectional and plan-view transmission electron microscopy have been used to characterise the microstructures of the Ge-Sn alloy layers, with alloy compositions determined by energy-dispersive X-ray microanalysis. The metastable diamond cubic Ge-Sn alloy microstructures are discussed in detail as a function of processing conditions.

The formation of pulsed laser processed AuTe/n—GaAs ohmic contacts was investigated using I—V measurements, Rutherford Backscattering, and Mössbauer spectroscopy. Ohmic contact resistances comparable to those of furnace processed AuTe and AuGe/GaAs contacts were measured; however, a much thinner intermixed layer was obtained by the laser processing. No evidence for the formation of a n++—GaAs layer could be derived from the experimental data. The results are more consistent with the model explaining the ohmic conduction mechanism by the formation of a graded heterojunction structure.

The difference in the melting temperature of ion implanted and relaxed amorphous silicon has been measured. Pulsed laser irradiation (λ=347 nm, τ=30 ns) has been used to induce surface melting in the amorphous layer and time resolved reflectivity to detect the melting onset. The threshold energy density for surface melting in the relaxed amorphous was found 15.9±.3% higher than that in the unrelaxed one. The estimate of the variation of the thermal parameters in amorphous silicon upon relaxation allowed a determination of ΔTM=45±10 K between relaxed and unrelaxed amorphous silicon.

Femtosecond time-resolved reflectivity measurements performed on highly oriented pyrolytic graphite (HOPG) and diamond elucidate the nature of the phase transition from solid to liquid carbon. In HOPG, we find that a high-reflectivity phase lasting as long as 10 ps appears when the surface is irradiated with pulse fluences in excess of 0.13 J/cm2, the critical fluence for melting. This transforms within 30 ps into an equilibrium low-reflectivity phase lasting hundreds of ps, similar to behavior observed in picosecond reflectivity experiments. The results suggest the occurrence of a two-step phase transition (graphite -> liquid metal -> liquid insulator) when HOPG is excited above the critical fluence. Similar results are obtained with diamond.

The migration of ion implanted 13C in tempered martensitic steel (nominal composition 1.05 wt. % C, 0.2 wt. % Si, and 0.3 wt. % Mn) during excimer laser melting was examined utilizing the resonance of the l3C(p,γ)14N reaction at Ep = 1747.6 keV. Depth concentration profiles after five and ten laser pulses of 1 J/cm2 revealed a deviation from random walk diffusion in a homogeneous media. This was modelled by using partitionless solidification and solubility controlled flow of carbon in the iron-carbon melt. A diffusion length of nm during the period to τ the melted phase was deduced. Ion implanted surfaces were initially crystalline but significant crystalline to amorphous transformation occurred following laser treatment.

A 100-ps-resolution electron pulse was used to study a 25-nm thick gold single crystal irradiated by a synchronized infrared optical pulse. The change in electron diffraction intensity following laser heating (the Debye-Waller effect) was measured as a function of delay time. The relaxation of a crystal lattice distortion in the surface region appears to explain an observed oscillation in time of the scattered electron intensity. This novel technique provides a sensitive structure probe for short-time dynamics and is, we believe, the fastest lattice temperature probe.

The different silica-phase morphologies formed in synthesizing silica-metal matrix composites layers have been studied, using a new evaporation technique, involving rapid condensation of silica from a laser beam induced-ceramic plume. This process occurs within a reactive gas environment (98.5% hydrogen, 1.5% methane), with a heated tungsten filament in proximity to the laser beam-material interaction zone. The silica phase in the composite layers deposited on a nickel substrate exhibited different metastable morphologies, namely, nanometer-size amorphous fibers or linear-chain shape aggregates. There appeared to be a correlation between the morphology of the deposits and the position of the heated tungsten filament. When the tungsten filament was absent, silica was deposited in the form of clusters. In this case, depending on the beam-ceramic target interaction times, there was a shift in the Si-O stretching vibration characteristics. The laser beam-ceramic target interaction and the formation of the laser-induced ceramic plume are briefly discussed. Characterization techniques involved FTTR, X-ray diffraction, Auger and microprobe analysis, EDX and WDX analysis, SEM and TEM.

The structure and morphologies of the thin amorphous a-Si and oc-Ge films crystallized “in situ” in an electronic microscope by pulsed YAG laser have been studied using conventional and high-resolution transmission electronic microscopy observations. It is found that the laser induced nucleation rate (I) is laser pulse length dependent. I is about 1021-1022 cm−3 s−1 (α-Si) and 1023-1025 cm−3 s−1 (α-Ge) near the melting point. Explosive dendritic formation is the result of competition between solid state light induced nucleation and melting mediated explosive growth.

We have developed a quantitative model, based on a two-dimensional finite difference enthalpy method, which accounts for the localized melting behavior of thin Si films on substrates. The model incorporates radiative and conductive heat flow components and takes account of the phase changes that occur during zone-melting recrystallization. Emphasis is placed on the effects resulting from the differences in reflectivity and emissivity between solid and liquid Si. The model provides quantitative information concerning the temperature profile of the Si film and the configuration of the solid-liquid interface. Results of the analysis indicate that there exist two distinct types of transition behavior: i) reflectivity-change dominated and ii) emissivity-change dominated. Partial melting and a nonplanar solid-liquid interface are characteristics of the reflectivity-change dominated behavior. The emissivity-change dominated behavior, on the other hand, can be characterized by explosive-like melting and a planar solid-liquid interface. The conditions and physical factors which give rise to these behaviors are discussed.

In zone melting recrystallization (ZMR) of thin silicon films different mechanisms can lead to thickness variations of the obtained silicon film. In this paper we will concentrate on some of these phenomena. One is the large scale mass transport, which typically leads to a thinned region at the start of the ZMR process. Another one, which is to a certain extent related to the first one, is the typical ripple formation that occurs especially under conditions that are commonly referred to as “low thermal gradient” regime.

Using a suitably homogenized excimer laser beam, we have shown that the threshold for crystallization of amorphous silicon is well defined and exhibits a square root dependence on the laser energy density above threshold. This sharp threshold behavior can be exploited in a number of ways.

The effects of four thermal parameters on the temperature distribution during Zone-Melting-Recrystalllzation processing of Slllcon-On-Insulator devices with graphite strip as the heat source were investigated numerically. Results indicate that the convective heat losses, the variability of the thermal conductivity of silicon as a function of temperature, and the multilayer nature of the structure do not affect the temperature distribution significantly. However, the velocity of the graphite strip can significantly affect the temperature distribution. The temperature profile remains the same for graphite strip velocities below 0.03 cm/sec. The relationship between required graphite strip temperature and velocity of the strip for film melting to occur is presented in graphical form.

Non-alloyed refractory ohmic contacts to P+-ln0.53 Ga0.47 As layer have been fabricated using sputtered W and rapid thermal processing. These contacts showed excellent thermal stability over the temperature range of 300 to 750°C, with an abrupt and almost unreacted metal-semiconductor interface. The W film biaxial stresses were found to be strongly depended on the Ar pressure during the sputter deposition. At low Ar pressures the film were deposited with compressive stress, and became tensile at pressures higher than 7mTorr with a maximum value of about 8×l09 dyne cm2 as a result of Ar deposition pressure of 28mTorr. The W contacts to Zn doped 1×1019 cm−3 In0.53GA0.47 As film was found to be ohmic already as deposited with a minimum specific resistance of about 7.5×10−6 Ωcm−2, achieved as a result of heating at 600°C for about 30 sec.

In this work the effects of laser melting on the micro-morphology, structures and solid particle erosion behaviors of plasma spray alumina, alumina-titania and zirconia coatings have been studied. The results have indicated that laser melting has modified the micro-mophologies and structures of coatings, eliminated the porosity of sprayed coatings and increased the erosion resistance of ceramic coatings. The erosion mechanisms of ceramic coatings have been investigated.

Ion irradiation and implantation experiments of high temperature superconductors (HTSC) thin films resulted in many interesting effects. Among those are: (i) the superlinear increase of the resistivity, p, with ion fluence, φ, leading to a metal to insulator transformation, (ii) the large recovery above 150 K of the radiation induced changes of ρ and Tc observed in low temperature irradiation experiments, and (iii) the large structural changes such as the increase of the c-axis lattice parameter with φ, the radiation induced orthorhombic to tetragonal phase transition, and the amorphization. Displaced oxygen atoms play an important role for the observed property changes.

The amorphous state can be produced in α-Al2O3 by ion beam induced displacements at 77 K or by displacements combined with chemical effects at room temperature. Progress toward understanding the amorphization process has been made from studies of the short-range order, electronic charge on implanted species, and the critical composition for amorphization. Results are presented for implantation of Al + O in the stoichiometric ratio, zirconium, iron, and tin.