High resolution Rutherford backscattering and channelling TEM and electrical measurements have been employed to investigate pulsed-ruby laser annealing effects in high dose rate ion implanted silicon wafers. The laterally non-uniform, part amorphous, part crystalline disordered structure which can result from high dose rate implants has been utilized to investigate the selective removal of amorphous or crystalline damage at near-threshold laser powers. Evidence is found for preferrential recrystallisation of amorphous damage regions over a broad laser power window which is below the threshold power required to melt adjacent crystalline silicon. At laser power levels above the crystalline-to-melt threshold, excellent uniformity in damage removal and electrical properties were obtained over the entire wafer.

Several types of periodic ripple structures have been observed on the surface of solids that have been laser irradiated with beam intensities near their melting thresholds.1-7 We restrict our attention here to the coherent, onedimensional (RD) gratings induced by linearly polarized beams.3-7 These gratings have a period close to the free space laser wavelength (λ0) for normally incident beams and are normally found in the beam spot near the melt boundary (Fig. 1). The grating lines are always perpendicular to the optical electric field Ei independent of the crystallographic orientation of the sample.

Low temperature photoluminescence is used to study damage centers in ion implanted, pulsed laser annealed Si. A number of intense, damage related photoluminescence lines W, G and 13 are observed. It is shown that most of the W (and 13) centers are created by solid phase annealing of implant damage beyond the laser melted region. Peak G, on the other hand, is present in the tail of the implant damage before laser annealing.

Optical, X-ray and transmission electron microscopy plus preferential chemical etching have been used to examine the dislocations and lattice strain introduced during cw laser annealing of silicon. In addition to a substrate scanning mode we operate our cw Ar-ion laser in a “pulse” mode by using an electronically activated shutter located within the laser cavity. This permits accurate measurements to be made on isolated spots or large area scans with a dislocation density that can be deliberately varied. In particular we discuss surface slip traces, their component dislocations and resulting lattice strains, as well as submicron extrinsic dislocation loops which result from the condensation of ion-implantation produced interstitial silicon. Recommendations are presented for producing defect and strain-free material, as well as samples with specific densities of dislocations.

This paper describes the conditions for activating ion implants in a range of semiconductor materials in the solid state. This includes phosphorus and arsenic implants into silicon, boron and phosphorus implants into SOS, gallium into germanium and silicon into gallium arsenide. For each material the restoration of electrical activity correlates with structural data from RBS analysis. Negligible implant diffusion occurs for the typical annealing treatments which result in full activation of dopants.

This review examines the annealing behaviour of ion implanted gallium arsenide during furance, laser and e-beam processing.The two annealing regimes, namely solid phase regrowth via furnace or CW laser/e-beam annealing and liquid phase epitaxy produced by pulsed lasers/e-beam, are examined in some detail.Emphasis is placed upon an understanding of the physical processes which are important during the various annealing modes.Comparison with the annealing behaviour of ion implantedelemental semiconductors(notably silicon) is made throughout the review to highlight relevant similarities and differences between compound and elemental semiconductors.The electrical properties of annealed gallium arsenide layers are not treatedin any detail, although particular observations which are relevant to the annealing processes are briefly discussed.

The properties of p+ and n+ layers formed by pulsed ruby laser annealing (PRLA) of shallow (Rp ~ 320–680 Å) implantations of Mg, Zn, Si and Se ions in both n- and p-type semiconducting GaAs have been evaluated using a combination of SIMS and electrical properties measurements. High activation (> 80%) was obtained for high dose (5 × 1015 ions/cm2 ) implants of both Mg and Zn, within a pulsed laser energy density “window” 0.5 ≤ Eλ ≤ 0.8 J/cm2 (FWHM pulse duration = 20–25 ns). SIMS measurements following PRLA show a wellbehaved increasing penetration of dopant ions into the GaAs substrate, with dopant ion concentrations well in excess of 1020 ions/cm3 in the near-surface region. Measured hole mobilities are consistent with the values anticipated for these high concentrations of ionized impurity scattering centers.

It is shown that, in the pulsed-laser irradiation of crystalline or lightly damaged GaAs, good agreement is obtained between measured and calculated thresholds for melting, for catastrophic damage due to vaporization, and for the duration of surface melting at various energy densities. Good agreement between theory and experiment is also obtained for dopant profile spreading during pulsed-laser annealing.

The thermal behavior of Te implanted, laser annealed GaAs was investigated by helium backscattering spectroscopy and transmission electron microscopy in order to correlate structural changes with the two stage reduction in the carrier concentration due to post laser anneal heating above 200°C. The activation energy for stage one which occurs in the range 200–400°C was determined to be approximately 1.3 eV. Post laser anneal heating at 450°C caused no observable structural changes. On the other hand, 850°C post laser anneal heating induced the formation of precipitates and dislocation loops as well as narrowing the channeling half-angle of Te by about 11%.

Pulse diffusion has been used for doping GaAs n-type to over 1019 cm−3. Surface arsenic loss is avoided through using As2Se3 as the diffusion source. A reduction in electrical activity similar to that reported for pulse annealed implanted layers occurs with any subsequent heat treatment. A resistive region, found at the surface of the profile, can be circumvented through additionally heating the GaAs thermally during the pulse diffusion and reducing the rapidity of the quench.

Gallium arsenide crystals, both VPE and Cz grown, were annealed with a pulsed Nd:YAG laser. Gold Schottky diodes were fabricated and defects were studied using the DLTS technique. The native defect E(0.83eV) was found to anneal while other electron traps, E(0.39eV) in both materials and E(0.30eV)in Cz material, remained after irradiation. A new trap, E(0.70eV), was observed after laser irradiation in both materials.

Cz GaAs samples implanted with both Ga and As were also laser annealed. The E(0.83eV) level was not observed after implantation. The E(0.30eV) trap and new levels, E(0.44eV) and E(0.6leV) were observed. C-V measurements and defect profiles indicate that the recrystallized layer is far from defect free.

A scanned cw Nd: YAG laser was used to anneal ion-implanted GaAs and InP wafers. Measurements show that electrical activation is greater for p-type than for n-type dopants in GaAs, while in InP, the opposite is observed. A simple Fermi-level pinning model is presented to explain not only the electrical properties we have measured, but also those observed by other workers. We have fabricated GaAs and InP solar cells with junctions formed by ion implantation followed by laser annealing. The GaAs cells have much better conversion efficiencies than the InP cells, and this difference can be explained in terms of the model.

The possibility of annealing low dose implants (≃ 1013cm-2) in GaAs using a cw scanning laser has been investigated. We have observed that above the threshold of laser-induced damage, a gallium oxide (3-Ga2O3) can be grown at laser scan speeds of 0.5mm/sec. The heat transferred to the substrate during the growth of the oxide is utilized to anneal low dose Si implanted layers. As suggested by sheet electrical measurements, close to complete activation of the implanted species is obtained.

Indium antimonide can be recrystallized epitaxially in the liquid phase by a scanning cw argon ion laser beam for improvements in crystal quality, surface morphology and oxide interface properties. Selected area diffraction measurements, Auger sputter depth profiling and dispersive x-ray analysis indicate that crystallization occurs epitaxially, and stoichiometry is preserved in the laser processed regions. Complete elimination of all asperities present in the original polished surface was observed subsequent to laser irradiation. Scanning electron microscopy and mechanical stylus measurements of the lateral profile of the laser irradiated region revealed the presence of a slight surface contour (convex meniscus) with a maximum change in height of 700 Å across a 64 μm recrystallized strip. In contrast to previous work with other compound semiconductors (e.g., GaAs), these results with InSb indicate that cw laser-induced melting and subsequent liquid phase epitaxial recrystallization can be used to provide improved materials properties of particular compound semiconductors.

The results of successful Nd:YAG laser annealed ohmic contacts on n-type GaP are reported. Comparisons on identical laser and thermal annealed contacts on the same substrates are performed. In addition aging investigations are also studied. The results indicate that laser annealed contacts have far superior electrical characteristics, much better surface morphology and are substantially more stable with aging than the same but thermally alloyed ones.

We have laser annealed double heterostructure GaAlAs material with homogeneous ruby laser pulses such that maximum laser light absorption occurs in the active layer. With laser anneal intensities sufficient to melt the active layer, the radiative efficiency of the double heterostructures was reduced by a factor of two. Performance of electroluminescent devices fabricated from annealed material was much worse than performance of devices fabricated from unannealed material.

Ohmic contacts on GaAs were realized by pulse annealing AuGe and AuGe-Ni layers deposited on top of n-type GaAs conducting layers. We used focused and largediameter YAG laser beam pulses (λ =1.06 µm), a large diameter Ruby laser beam pulse (λ = 0.69 µm) and a largediameter electron beam pulse. We tested the electrical quality of the contacts obtained. We also examined the compatibility of the alloying techniques used with theself-alignment technology for IC fabrication. In particular, we tested the quality of Al Schottky diodes and of the boron implanted insulating regions which coexist on the same IC with the ohmic contacts and are subject to the same pulse annealing treatment. The relative merit of the different pulse treatments are discussed.

Some of the basic requirements currently envisioned for advanced microelectronic devices and circuits are outlined and discussed in terms of fabrication techniques. Phenomenological aspects of laser processing of semiconductor materials are presented and related to the potential application of this technology for overcoming some of the fundamental limitations of conventional fabrication methods. Laser processing results obtained from a variety of siliconbased materials and test structures are presented and used to illustrate the unique features of the laser technique and the novel approach it brings to semiconductor device and circuit fabrication.

Pulsed electron beams [1] were used to anneal ion-implanted diodes, transistors, and resistors. Devices were fabricated by patterning a thermal oxide on a silicon wafer, ion-implanting and pulse processing with the oxide in place, and then applying contacts. Oxide films over 0.3 micron thick were not damaged, and the silicon below these films was not melted by the pulsed electron beam. Low-dose (101311B+/cm2), implanted, pulse-annealed resistors showed no change in sheet resistance for oxide windows 2.5 to 50.0 microns wide. Diodes were fashioned with good forward and reverse I-V characteristics, with m=1.09 and IO=2.7×10−10 A/cm2 for I=IO exp(qV.mkT)−1 , when a low-temperature (550˚C, 1 hr), postpulse anneal was included in the process sequence. Both bipolar and FET types of transistors were fabricated. Results compare favorably with thermal annealing cycles.

In this work the capability of pulsed ruby laser and multiscan electron beam techniques in the formation of Al-Si ohmic contacts on shallow (0.3 μm) junctions has been investigated. To measure the contact resistivity, properly designed test patterns have been employed, whereas to evaluate the junction leakage induced by the Al-Si interaction during sintering, the diode reverse current has been tested.

Laser beam annealing gives rise to scattered values of contact resistivity, ranging from 10-4 to 5 × 10-3 ohm-cm2 without any clear dependence on the energy used. The corresponding diode reverse currents were higher than those of the unannealed specimens by about three orders of magnitude.

E-beam annealing achieves contact resistivities on the order of 10-5 ohm-cm2 typical of conventional thermal treatment, with a parallel increase in the reverse current by only one order of magnitude.

These results indicate electron-beam annealing as a promising technique in the realization of Al-Si ohmic contacts for VLSI technology.