This paper provides a brief overview of the application of transient annealing to the removal of ion implantation damage and dopant activation in GaAs. It is shown that both the liquid phase and solid phase annealing processes are more complex in GaAs than those observed in Si. Particular attention is given to observations of damage removal, surface dissociation, dopant redistribution, solubility and the electrical properties of GaAs. The various annealing mechanisms are discussed and areas in need of further investigation are identified.

Significant dissociation is normally detected under non-optimised transient annealing of GaAs. We have utilised neutron activation to measure As and Ga loss from virgin and implanted material annealed under various transient conditions. Complementary RBS data are reported. In particular, surface dissociation has been measured as a function of pulsed ruby laser power and for several combinations of time and surface temperature using an incoherent light source and a vitreous carbon strip heater.

The results indicate that neutron activation analysis offers a powerful tool to identify the conditions required to minimise GaAs dissociation during annealing. For examplq ruby laser pulses of energy 0.29–1.38 J cm−2 caused As loss of 4 – 90 × 10 cm−2.

Experimental results obtained by rapid isothermal annealing of Si implanted semi-insulating GaAs are presented and compared with results obtained by electron-beam and conventional furnace annealing. We shall show that for high Cr-doped material the problem of redistribution cannot be avoided and that for undoped material, this technique yields very good activation (near 100%) and high mobility (approximately 4400 cm2 /V.sec).

Current-voltage, capacitance-voltage and defect spectroscopy techniques are used to characterize the electrical properties of GaAs crystals after pulsed laser irradiation with either a Nd-YAG or a Ruby laser. I(V) and C(V) measurements performed in conjunction on Au/GaAs Schottky structures after laser irradiation at low energy density show an important barrier lowering, of the order of 300mV. Carrier compensation up to 6×lO16/cm3 is observed in a subsurface layer whose thickness increases with deposited laser energy density. D.L.T.S. is used to study the tail of laser induced defects behind the heavily compensated layer. Finally the results are compared to those obtained following conventional thermal treatment.

Electron beams can transfer energy very efficiently to semiconductors. Systems have been developed for rapid heating to temperature around 1000°C under a variety of conditions from adiabatic to isothermal. Pulsed, focused, line and synthesized shaped beams are used to obtain a wide range of thermal cycles. The following applications are described: the annealing of ion-implanted Si, particularly the activation of As implants and shallow implants (Rp<150Å), the annealing of Si and Se in GaAs, the e-beam processing of implanted silicon devices and the improvement of SOS substrate quality. Localized annealing by a computer controlled e-beam and the recrystallization of deposited films on insulators are also considered.

Optical and electrical characterization of CdTe synthetized by laser irradiationofamultilayer film of alternately Cd and Te is achieved. Optical absorption measurements evidence the good quality of these films and show that they have behaviour comparable to the single crystal. The influence of the irradiation conditions on the electrical properties of such CdTe films is discussed; they are compared to single crystal from the point of view of resistivity. It is shown that it is possible to prepare by this means samples devoid of impurity states in the middle of the forbidden gap. Finally, the ohmicity of Au, Al, Cr, ITO and non irradiated Cd/Te sandwich contacts is tested.

Thermal pulse annealing has been used to modify the near surface of Hg1−xCdxTe. Using anneals of approximately 260°C for seven seconds, the crystal quality of epitaxial HgCdTe surfaces can be improved as observed by MeV He+ ion channeling. Similar anneals have also been used to repair the damage resulting from a 250 keV, 101511 B/cm2 implant into HgCdTe held at LN2. For higher temperatures and/or longer anneals, surface Hg loss is observed. Rutherford Backscattering measurements are used to measure this loss. The resulting loss rate data is described by No= A exp (−ΔE/kT) where A and ΔE depend on the material composition with A = 1029, ΔE = 1.8 eV and A = 1036, ΔE = 2.6 eV for x = 0.23 and 0.4, respectively.

Pulsed XeCl (308 nm) and XeF (351 nm) laser annealing of undoped and Mn-implanted single crystal and polycrystalline ZnS films deposited upon either Si or GaAs substrates is described. Annealing energy densities in the range ~0 .6–2.5 J cm−2 have been employed, with the specimens held under an Ar environment at ~ 100–200 psig pressure. Film thicknesses in the range ~0.2–1.0 μm have been investigated, with the substrates cleaned in various ways prior to deposition. In all the cases investigated, laser annealing results in polycrystalline regrowth of the films as shown by RHEED analysis. Furthermore the RHEED patterns obtained are consistent with the presence of both the cubic and the hexagonal phases of ZnS, except for thin (~0.2 μm thick) films annealed above ~ 2 J cm−2. These show a purely cubic structure on both Si and GaAs, possibly due to regrowth from the underlying cubic substrates.

InP layers implanted with Si+ ions are successfully activated through the use of a focused incoherent energy source. High mobility values and excellent carrier concentrations, both directly comparable to values attained using conventional furnace annealing, are achieved with this technique. Under optimized anneal conditions, electrical evaluation also indicates no surface anomalies such as those encountered with pulsed laser or electron beam annealed InP.

The annealing technique described here makes use of the output from two broad spectrum 1000 watt incandescent sources. Through the use of elliptical mirrors, a combined thermal image of these sources is formed as the output at a common focus. The sample is placed at this focus during the anneal cycle. Anneal time is controlled electronically and for these experiments is varied for 1 to 15 sec. Substrate temperature is measured with a low-mass thermocouple recorder readout system placed at the focus in contact with the sample. Annealing temperatures range from 750°C to 950°C. To prevent phosphorus loss and other surface anomalies, dielectric encapsulation and a solid phosphorus proximity source technique are examined. While the proximity technique has proven useful, PSG/Si02 double layered dielectric encapsulants appear to provide the most consistent results.

Short laser pulses have recently been discovered to be powerful means for glass formation in binary alloys as well as in some pure elements Due to relevant cooling rates in excess of 1010°K/s, glass formation is achieved in binary systems over most of the phase diagram, even in systems not previously known as glass formers. We first give a review of recent progress in laser melt quenching, and then discuss the kinetic conditions of glass formation by laser irradiation.

We have studied pulsed ruby laser melting of metallic glasses – Fe40Ni40P14B6 and Fe40Ni40B20. Both amorphous and crystallised samples were used, and some of them were implanted with Ru to serve as a marker species. SEM measurements on surface topography and RBS (1.8 MeV He+) depth profiling of Ru marker redistribution were used to establish melting above about 1 J/cm2. Heat flow calculations and liquid phase diffusion analysis of the Ru marker species under a moving melt front have been performed. The observed redistribution of Ru upto 2.5 J/cm2 is consistent with an effective D ∼ 5 × 10−5 cm2 s−1. The flat Ru depth profiles at higher energy densities are shown to arise from convection effects. Results on crystallised and amorphous samples are similar. Preliminary TEM measurements of quenched regions on a crystallised sample show an unexpected absence of amorphous phase.

Cobalt (∼300Å) and CoSi2 (∼1000Å) thin films on Si have been annealed by intense proton beams. RBS and TEM were performed to study ion beam annealing effects.

For ion beam energy densities above about 1 J/cm2, epitaxial CoSi2 layers were formed for both Co and polycrystalline CoSi2 on Si. At low energy densities, Co2Si was found to coexist with Co. The results are discussed in terms of eutectic melting processes.

Composition profiles of thermal and pulsed ion beam annealed PtCr/Si and CrTa/Si have been determined using Rutherford backscattering analysis. Thermal annealing resulted in layered phase separation with Pt-silicide in the PtCr/Si case, and CrSi 2 in the CrTa/Si case, forming at the Si surface. Pulsed ion beam annealing, 300–380 keV protons at energy densities ~0.75–1.6 J/cm2 , produced interface melting with no layered phase separation.

4He+ Backscattering and SIMS were used to study impurity redistribution during laser formation of refractory silicides. Thin films of Mo and W were evaporated on to <100> p-type silicon substrates, which were As or B implanted to doses of 1 ×1015 to 1 ×1016cm−2 . These samples were laser reacted with multiple or single laser scans at various powers. Analysis of these films indicate impurity movement into the forming silicide layer. Impurity concentrations in the films were observed to be as high as 7.8×1020 cm−3−> for As in WSi2 , however a reduction in this concentration occurred with subsequent thermal annealing.

A submicron conductor array was fabricated without using lithography by selectively etching a recrystallized A1-A12Cu eutectic alloy thin film. The 2 micron thick eutectic films were deposited on glass substrates and directionally solidified with both a quartz-iodine lamp and a scanning laser at rates between .0016 and .14 cm/sec. The resulting structure consisted of alternate parallel stripes of the two eutectic phases with a spacing between .5 and 4 microns that was controlled by the solidification rate. An array of submicron Al- rich conductors was fabricated by selectively etching away the Al2 Cu phase. At solidification rates greater than .004 cm/sec using the lamp heater the solid-liquid interface became non-planar while with the laser the structure was well alligned at the highest rates used, .14 cm/sec. At the maximum theoretical solidification rate that produces a two phase aligned eutectic structure the width of the Al wires would be 100A.

The development of predictive models for rapid surface melting and resolidification requires coupling of realistic heat flow models to emerging theories of rapid solidification processing. Attainment of unique microstructures and phases,for example through plane-front solidification and solute trapping, can be correlated to solid/liquid interface velocity,temperature and temperature gradients, and to theories of morphological stability. However, there are important limitations on achievable solid/liquid interface velocity depending upon the heating mode and heat flux distribution,melt thickness and location of the interface within the molten zone.

An overview is given of the emerging guidelines for prediction and control of rapid solidification conditions and microstructures. Homogenization of the liquid by convection and diffusion is also discussed. Electron beam surface melting of alloy substrates is used as an example of these processes.

Fe(Pd) surface alloys formed by either ion implanting Pd into Fe or by vapor depositing Pd on Fe have been examined after pulsed (∼70 nsec) electron beam melting. TEM and ion backscattering/channeling showed that the implanted alloys with up to 9.6 at.% Pd were bcc and epitaxial with the substrate, inspite of predictions of initial solidification to the fcc phase by the Fe-Pd phase diagram. The resolidified Pd films, however, were fcc as predicted by the diagram. The defect structures observed in these alloys are discussed.

The Microstructural Transition From The Epitaxial Crystalline To Amorphous State As A Function Of Ni Concentration Is Examined In Al(Ni) Alloys Formed By Ion Implantation And E-Beam Melt Quenching. The Evolution From Epitaxial Crystalline Al At ≲ 3.5 At.% Ni To Amorphous Phase Formation At 15–30 At.%Ni Is Characterized In Detail For 8, 10 And 12% Ni Uniform Concentration Samples By Ion Channeling And Transmission Electron Microscopy. The Transition Occurs Via Complete Loss Of Epitaxial Regrowth At 9 At.% And The Formation Of A Finegrained Polycrystalline Al, With Grain Size Decreasing With Increasing Ni From 20–100 Å At 10% Ni Concentration To ≲ 10–50 Å At 12% Ni.